Anatomy Ch 22: The Respiratory System

generation of the respiratory rhythm

-there is little question that breathing is rhythmic, but we still cannot fully explain the origin of its rhythm -one hypothesis is that there are pacemaker neurons, which have intrinsic (automatic) rhythmicity like the pacemaker cells found in the heart -pace-maker-like activity has been demonstrated in certain VRG neurons, but suppressing their activity does not abolish breathing -this leads us to the second (and more widely accepted) hypothesis: normal respiratory rhythm results from reciprocal inhibition of interconnected neuronal networks in the medulla -rather than a single set of pacemaker neurons, there are two (or possibly three) sets that inhibit each other and cycle their activity to generate rhythm

arytenoid and corniculate cartilages

-three pairs of small cartilage form part of the lateral and posterior walls of the larynx -the most important of these are the pyramid-shaped arytenoid cartilages, which anchor the vocal folds

heimlich maneuver

-tracheal obstruction is life threatening -a procedure in which air in the victim's lung is used to "pop out" or expel, an obstructing pice of food, has saved many people from becoming victims of "cafe coronaries" -it is best learned by demonstration because crack ribs are a distinct possibility when it is done incorrectly

external respiration

-during ________ _______ (pulmonary gas exchange), dark red blood flowing from the pulmonary circuit is transformed into the scarlet river that is returned to the heart for distribution by systemic arteries to all body tissues -this color change is due to O2 uptake and binding to hemoglobin in red blood cells (RBCs), but CO2 exchange (unloading) is occurring equally fast the following three factors influence this type of respiration: -partial pressure gradients and gas solubilities -thickness and surface area of the respiratory membrane -ventilation-perfusion coupling (matching alveolar ventilation with pulmonary blood perfusion)

inspiration

-during normal quiet (resting) inspiration, the inspiratory muscles-- the diaphragm and external intercostal muscles-- are activated -action of the diaphragm. when the dome-shaped diaphragm contracts, it moves inferiorly and flattens out. as a result, the superior-inferior dimension (height) of the thoracic cavity increases -action of the the intercostal muscles. when the external intercostal muscles contract, they lift the rib cage and pull the sternum superiorly -because the ribs curve downward as well as forward around the chest wall, the broadest lateral and anteroposterior dimensions of the rib cage are normally directed obliquely downward -but when the ribs are raised and drawn together, they swing outward, expanding the diameter of the thorax both laterally and in the anteroposterior plane -although these actions expand the thoracic dimensions by only a few millimeters along each plane, this is enough to increase thoracic volume by almost 500 ml-- the usual volume of air that enters the lungs during a normal quiet inspiration -of the two types of inspiratory muscles, the diaphragm is far more important in producing these volume changes that lead to normal quiet inspiration -as the thoracic dimensions increase during inspiration, the lungs are stretched and the intrapulmonary volume increases -as a result Ppul drops about 1 mm Hg relative to Patm -anytime the intrapulmonary pressure is less than the atmospheric pressure, air rushes into the lungs along the pressure gradient. during the same period, Pip declines to about -6 mm Hg relative to Patm -during the deep or forced inspirations that occur during vigorous exercise and in some chronic obstructive pulmonary diseases, accessory muscles further increase thoracic volume -several muscles, including the scalene and sternocleidomastoid muscles of the neck and the pectoralis minor of the chest, raise the ribs even more than during quiet inspiration -additionally, the back extends as the erector spine muscles straighten the thoracic curvature

tidal volume (TV)

-during normal quiet breathing, about 500 ml of air moves into and out of the lungs with each breath -this respiratory volume is the _______ ______

gross anatomy of the lungs (continued)

-each lobe contains a number of pyramid-shaped bronchopulmonar segments separated from one another by connective tissue septa -the right lung has 10 bronchopulmonary segments, but the left lung is more variable and consists of 8 to 10 segments -each segment is served by its own artery and vein and receives air from an individual segmental (tertiary) bronchus -the bronchopulmonary segments are clinically important because pulmonary disease is often confined to one or a few segments -their connective tissue partitions allow diseased segments to be surgically removed without damaging neighboring segments or impairing their blood supply -the smallest subdivisions of the lung visible with the naked eye are the lobules, which appear at the lung surface as hexagons ranging from the size of a pencil eraser to the size of a penny -a large bronchiole and its branches serve each lobule. in most city dwellers and in smokers, the connective tissue that separates the individual lobules is blackened with carbon -the balance of lung tissue, or its stroma, is mostly elastic connective tissue. as a result, the lungs are soft, spongy, elastic organs that together weigh just over 1 kg

residual volume (RV)

-even after the most strenuous expiration, about 1200 ml of air remains in the lungs -this is the ________ _____, which helps to keep the alveoli open and prevent lung collapse

chronic obstructive pulmonary diseases (COPD)

-exemplified best by emphysema and chronic bronchitis, are a major cause of disability and death in North America -the key physiological feature of these diseases is an irreversible decrease in the ability to force air out of the lungs other features they share in common are: -more than 80% of patients have a history of smoking -dyspnea, difficult or labored breathing often referred to as "air hunger" gets progressively worse -coughing and frequent pulmonary infections are common -most COPD patients develop respiratory failure manifested as hypoventilation (insufficient ventilation in relation to metabolic needs, causing them to retain CO2), respiratory acidosis, and hypoxemia

ventilation-perfusion coupling

-for optimal gas exchange, there must be a close match, or coupling between ventilation (the amount of gas reaching the alveoli) and perfusion (the blood flow in pulmonary capillaries) -both are controlled by local autoregulatory mechanisms that continuously respond to local conditions for the most part: -PO2 controls perfusion by changing arteriolar diameter -PCO2 controls ventilation by changing bronchiolar diameter

oxygen transport

-molecular oxygen is carried in blood in two ways: bound to hemoglobin within RBCs and dissolved in plasma -oxygen is poorly soluble in water, so only about 1.5% of the oxygen transported is carried in the dissolved form -if this were the only means of oxygen transport, a PO2 of 3 atm or a cardiac output of 15 times normal would be required to provide the oxygen levels needed by body tissues -hemoglobin solves this problem-- 98.5% of the oxygen is carried from lungs to tissues in a loose chemical combination with hemoglobin

high altitude

-most people live between sea level and an altitude of approximately 2400 m (8000 feet) -in this range, differences in atmospheric pressure are not great enough to cause healthy people any problems when they spend brief periods in higher-altitude areas -however, if you travel quickly from se level to elevations above 8000 ft, where atmospheric pressure and PO2 are lower, your body responds with symptoms of acute mountain sickness (AMS)-- headaches, shortness of breath, nausea, and dizziness -AMS is sometimes seen in travelers to ski resorts such as Vail, CO -in severe cases of AMS, lethal pulmonary and cerebral edema may occur -high-altitude conditions result in lower-than-normal hemoglobin saturation levels because less O2 is available to be loaded -for example, at about 19,000 ft above sea level, O2 saturation of arterial blood is only 67% (compared to nearly 98% at sea level) -but Hb unloads only 20-25% of its oxygen at sea level, which means that even at the reduced saturations at high altitudes, the O2 needs of the tissues are still met under resting conditions -additionally, at high altitudes hemoglobin's affinity for O2 is reduced because BPG concentrations increase. this releases more O2 to the tissues during each circulatory round -when blood O2 levels decline, the kidneys produce more erythropoietin, which stimulates bone marrow production of RBCs. this phase of acclimatization, which occurs slowly, provides long-term compensation for living at high altitudes

carbon dioxide transport

-normally active body cells produce about 200 ml of CO2 each minute--exactly the amount excreted by the lungs blood transports CO2 from the tissue cells to the lungs in three forms: 1) dissolved in plasma (7-10%). the smallest amount of CO2 is transported simply dissolved in plasma 2) chemically bound to hemoglobin (just over 20%). dissolved CO2 is bound and carried in the RBCs as carbamionhemoglobin CO2 + Hb --> HBCO2 -this reaction is rapid and does not require a catalyst -carbon dioxide transport in RBCs does not compete with oxyhemoglobin transport because carbon dioxide binds directly to the amino acids of globin -CO2 loading and unloading are directly influenced by the PCO2 and the degree of Hb oxygenation -carbon dioxide rapidly dissociates from the hemoglobin in the lungs, where the PCO2 of alveolar air is lower than that in blood -carbon dioxide readily binds with hemoglobin in the tissues, where PCO2 is higher than that in blood -deoxygenated hemoglobin combines more readily with carbon dioxide than does oxygenated hemoglobin 3) as bicarbonate ions in plasma (about 70%). most carbon dioxide molecules entering the plasma quickly enter RBCs -the reactions that convert carbon dioxide to bicarbonate ions (HCO3-) for transport mostly occur inside RBCs -when dissolved CO2 diffuse into RBCs, it combines with water, forming carbonic acid (H2CO3). H2CO3 is unstable and dissociates into hydrogen ions and bicarbonate ions -although this reaction also occurs in plasma, it is thousands of times faster in RBC because they (and not plasma) contain carbonic anhydrase, an enzyme that reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid -hydrogen ions released during the reaction (as well as CO2 itself) bind to Hb, triggering the Bohr effect -in this way CO2 loading enhances O2 release. -because of the buffering effect of Hb, the liberated H+ causes little change in pH under resting conditions. as a result, blood becomes only slightly more acidic (the pH declines from 7.4 to 7.34) as it passes through the tissues -once generated, HCO3- moves quickly from the RBCs into the plasma, where it is carried to the lungs -to counterbalance the rapid outrush of these anions from the RBCs, chloride ions (Cl-) move from the plasma into the RBCs -this ion exchange process, called the chloride shift, occur via facilitated diffusion through an RBC membrane protein -in the lungs, the process is reversed. as blood moves through the pulmonary capillaries, its PCO2 declines from 45 mm Hg to 40 mm Hg. -for this to occur, CO2 must first be freed from its bicarbonate housing -HCO3- reenters the RBCs (and Cl- moves into the plasma) and binds with H+ to form carbonic acid -carbonic anhydrase then splits carbonic acid to release CO2 and water -this CO2, along with that released from hemoglobin and from solution in plasma, then diffuses along its partial pressure gradient from the blood into the alveoli

tuberculosis (TB)

-tuberculosis (TB), the infectious disease caused by the bacterium mycobacterium tuberculosis is spread by coughing and primarily enters the body in inhaled air -TB mostly affects the lungs but can spread through the lymphatics to other organs -one-third of the world's population is infected, but most people never develop active TB because a massive inflammatory and immune response usually contains the primary infection in fibrous, or calcified, nodules (tubercles) in the lungs -however, the bacteria survive in the nodules and when the person's immunity is weakened, they may break out and cause symptomatic TB -symptoms include fever, night sweats, weight loss, racking cough, and coughing up blood -deadly strains of drug-resistant TB can develop when treatment is incomplete or inadequate -resistant strains are found elsewhere in the world and have appeared in North America

larynx

-the voice box, extends for about 2 inches from the level of the third to the sixth cervical vertebra -superiorly, it attaches to the hyoid bone and opens into the laryngopharynx -inferiorly it is continuous with the trachea has three functions: -provide a patent (open) airway -act as a switching mechanism to route air and food into the proper channels -voice production (because it houses the vocal folds (vocal cords)) -the framework is an intricate arrangement of nine cartilages connected by membranes and ligaments -except for the epiglottis, all laryngeal cartilages are hyaline cartilages

the respiratory membrane

-the walls of the alveoli are composed primarily of a single layer of squamous epithelial cells, called type I alveolar cells, surrounded by a flimsy basement membrane -the external surfaces of the alveoli are densely covered with a "cobweb" of pulmonary capillaries -together, the capillary and alveolar walls and their fused basement membranes form the respiratory membrane, a 0.5 um-thick blood air barrier that has blood flowing past on one side and gas on the other -gas exchanges occur readily by simple diffusion across the respiratory membrane-- O2 passes from the alveolus into the blood, and CO2 leaves the blood to enter the gas-filled alveolus

chemical factors

among the factors that influence breathing rate and depth, the most important are changing levels of CO2, O2, and H+ in arterial blood sensors responding to such chemical fluctuations, called chemoreceptors, are found in two major body locations: -central chemoreceptors are located throughout the brain stem, including the ventrolateral medulla -peripheral chemoreceptors are found in the aortic arch and carotid arteries

sinusitis

because the mucosa extends tentacle-like into the nasolacrimal (tear) ducts and paranasal sinuses, nasal cavity infections often spread to those regions, causing ______ (inflamed sinuses)

medullary respiratory centers

clustered neurons in two areas of the medulla oblongata appear to be critically important in respiration. these are: -the ventral respiratory group, a network of neurons that extends in the ventral brain stem from the spinal cord to the pons-medulla junction -the dorsal respiratory group (DRG), located dorsally near the root of cranial nerve IX

upper respiratory system

consists of all the structures from the nose to the larynx

therapy for CF

has included mucus-dissolving drugs, "clapping" the chest to loosen the thick mucus, and antibiotics to prevent infection the goal of CF research is to restore normal salt and water movements. this can be done using a number of approaches: -introducing normal CFTR genes into respiratory tract mucosa cells -prodding another channel protein to take over the duties of transporting Cl- -developing techniques to free the CFTR protein from the ER -using hypertonic saline to osmotically move water -this is a novel and surprisingly simple approach that involves inhaling hypertonic saline droplets. this draws water into the mucus, making it more liquid

expiratory reserve volume (ERV)

is the amount of air-- normally 1000 to 1200 ml-- that can be expelled from the lungs after a normal tidal volume expiration

total lung capacity (TLC)

is the sum of all lung volumes

inspiratory capacity (IC)

is the total amount of air that can be inspired after a normal tidal volume expiration, so it is the sum of TV and IRV

vital capacity (VC)

is the total amount of exchangeable air. it is the sum of TV, IRV, and ERV

olfactory mucosa

lines the slitlike superior region of the nasal cavity and contains smell receptors in its olfactory epithelium

forced vital capacity (FVC)

measures the amount of gas expelled when a subject takes a deep breath and then forcefully exhales maximally and as rapidly as possible

histotoxic hypoxia

occurs when body cells are unable to use O2, even though adequate amounts are delivered.metabolic poisons, such as cyanide, can cause this

anemic hypoxia

reflects poor O2 delivery resulting from too few RBCs or from RBCs that contain abnormal or too little Hb

functional residual capacity (FRC)

represents the amount of air remaining in the lungs after a normal tidal volume expiration and is the combined RV and ERV

ischemic (stagnant) hypoxia

results from impaired or blocked blood circulation

inspiratory reserve volume (IRV)

the amount of air that can be inspired forcibly beyond the tidal volume (2100 to 3200 ml) is the _______ _______ _____

alveoli

three major types of cells found in alveoli: -type I alveolar cells are squamous epithelial cells that form the major part of the alveolar walls -type II alveolar cells are cuboidal epithelial cells that are scattered among the type I cells. they secrete a fluid containing a detergent-like substance called a surfactant that coats the gas-exposed alveolar surfaces. type II alveolar cells also secrete a number of antimicrobial proteins that are important elements of innate immunity -alveolar macrophages crawl freely along the internal alveolar surfaces consuming bacteria, dust, and other debris -they are surrounded by fine elastic fibers of the same type that surround the entire bronchial tree -open alveolar pores connecting adjacent alveoli allow air pressure throughout the lung to be equalized and provide alternate air routes to any alveoli whose bronchi have collapsed due to disease -although huge numbers of infectious microorganism are continuously carried into the alveoli, alveolar surfaces are usually sterile. -because the alveoli are "dead ends", aged and dead macrophages must be prevented from accumulating in them -most macrophages simply get swept up by the ciliary current of superior regions and carried to the pharynx

four respiratory volumes

tidal, inspiratory reserve, expiratory reserve, residual

hyperbaric oxygen chambers

- provide clinical applications of henry's law -these chambers contain O2 gas at pressures higher than 1 atm and are used to force greater-than-normal amounts of O2 into the blood of patients suffering from carbon monoxide poisoning -they are also used to treat gas gangrene and tissue damage following radiation therapy

infant respiratory distress syndrome (IRDS)

-When too little surfactant is present, surface tension can collapse the alveoli -once this happens, the alveoli must be completely reinflated during each inspiration, an effort that uses tremendous amounts of energy -This problem is faced in newborns, a condition common to premature babies -Since fetal lungs do not produce adequate amounts of surfactant until the last two months of development, babies born prematurely often are unable to keep their alveoli inflated between breaths -It is treated by spraying natural or synthetic surfactant into the newborn's respiratory passageways -in addition, devices that maintain positive airway pressure throughout the respiratory cycle can keep the alveoli open between breaths -severe cases require mechanical ventilators -many IRDS survivors suffer from bronchopulmonary dysplasia, a chronic lung disease, during childhood and beyond -this condition seems to be caused by a combination of factors including prolonged therapy with oxygen and mechanical ventilation

small cell carcinoma

-about 15% -round lymphocyte-sized cells that originate in the main bronchi and grow aggressively in small grape like clusters within the mediastinum -metastasis from the mediastinum is especially rapid -some small cell carcinomas cause additional problems because they produce certain hormones -for example, some secrete antidiuretic hormone (ADH), resulting in the syndrome of inappropriate ADH secretion

squamous cell carcinoma

-about 20% -arises in the epithelium of the bronchi or their larger subdivisions and tends to form masses that may cavitate (hollow out) and bleed

adenocarcinoma

-about 40% of cases -originate in peripheral lung areas as solitary nodules that develop from bronchial glands and alveolar cells

hypothalamic controls

-acting through the hypothalamus and the rest of the limbic system, strong emotions and pain send signals to the respiratory centers, modifying respiratory rate and depth -for example, have you ever touched something cold and clammy and gasped? that response was mediated through the hypothalamus -so too is the breath-holding that occurs when we are angry and the increased respiratory rate that occurs when we are excited - a rise in body temperature raises the respiratory rate, while a drop in body temperature produces the opposite effect -sudden chilling can stop your breathing (apnea) or at the very least, leave you gasping

physical factors influencing pulmonary ventilation

-airway resistance -alveolar surface tension -lung compliance

intrapleural pressure (Pip)

-also fluctuates with breathing phases, but it is always about 4 mm Hg less than Ppul. it is always negative relative to Ppul two forces act to pull the lungs (visceral pleura) away from the thorax wall (parietal pleura) and cause the lungs to collapse: -the lungs' natural tendency to recoil. because of their elasticity, lungs always assume the smallest size possible -the surface tension of the alveolar fluid. the molecules of the fluid lining the alveoli attract each other. this produces surface tension that constantly acts to draw the alveoli to their smallest possible dimension -however, these lung-collapsing forces are opposed by the natural elasticity of the chest wall, force that tends to pull the thorax outward and enlarge the lungs -so which force wins? in a healthy person, the answer is neither, because of the strong adhesive force between the parietal and visceral pleurae -pleural fluid secures the pleurae together in the same way a drop of water holds two glass slides together -the pleurae slide from side to side easily, but they remain stuck together, and separating them requires extreme force -the net result of the dynamic interplay between these forces is a negative Pip -the amount of pleural fluid in the pleural cavity must remain minimal to maintain a negative Pip -the pleural fluid is actively pumped out of the pleural cavity into the lymphatics continuously -if it wasn't, fluid would accumulate in the intrapleural space

oxygen toxicity

-although breathing O2 gas at 2 atm is not a problem for short periods, _______ ______ develops rapidly when PO2 is greater than 2.5-3 atm -excessively high O2 concentrations generate huge amounts of harmful free radicals, resulting in profound CNS disturbances, coma, and death

pontine respiratory centers

-although the VRG generates the basic respiratory rhythm, the _________ ________ ________ influence and modify the activity of medullary neurons -for example, pontine centers appear to smooth out the transitions from inspiration to expiration, and vice versa -when lesions are made in its superior region, inspirations become very prolonged, a phenomenon called apneustic breathing -the pontine respiratory group and other pontine centers transit impulses to the VRG of the medulla -this input modifies and fine-tunes the breathing rhythms generated by the VRG during certain activities such as vocalization, sleep, and exercise -as you would expect from these functions, the __________ _________ ________, like the DRG, receive input from higher brain centers and from various sensory receptors in the periphery

cortical controls

-although the brain stem respiratory centers normally regulate breathing involuntarily, we can also exert conscious (voluntary) control over the rate and depth of our breathing -we can choose to hold our breath to take an extra-deep breath, for example -during voluntary control, the cerebral motor cortex sends signals to the motor neurons that stimulate the respiratory muscles, bypassing the medullary centers -our ability to voluntarily hold our breath is limited, however, because the brain stem respiratory centers automatically reinitiate breathing when the blood concentration of CO2 reaches critical levels. that explains why drowning victim typically have water in their lungs

fibrosis

-any decrease in the natural resilience of the lungs diminishes lung compliance -chronic inflammation, or infections such as tuberculosis, can cause nonelastic scar tissue to replace normal lung tissue (________) -decreased production of surfactant can also impair lung compliance -the lower the lung compliance, the more energy is needed just to breathe

ventral respiratory group (VRG)

-appears to be a rhythm-generating and integrative center -it contains groups of neurons that fire during inspiration and others that fire during expiration in a dance of mutual inhibition -when its inspiratory neurons fire, a burst of impulses travels along the phrenic and intercostal nerves to excite the diaphragm and external intercostal muscles, respectively -as a result, the thorax expands and air rushes into the lungs -when the VRG's expiratory neurons fire, the output stops, and expiration occurs as the inspiratory muscles relax and the lungs recoil -this cyclic on/off activity of the inspiratory and expiratory neurons repeats continuously and produces a respiratory rate of 12-16 breaths per minute, with inspiratory phases lasting about 2 seconds followed by expiratory phases lasting about 3 seconds -this normal respiratory rate and rhythm is called eupnea -during severe hypoxia, VRG networks generate gasping (perhaps in a last-ditch effort to restore O2 to the brain) -respiration stops when a certain cluster of VRG neurons is completely suppressed, as by an overdose of morphine or alcohol

alveolar surface tension

-at any gas-liquid boundary, the molecules of the liquid are more strongly attracted to each other than to the gas molecules -this unequal attraction produces a state of tension at the liquid surface, called _______ _____ that 1) draws the liquid molecules closer together and reduces their contact with the dissimilar gas molecules, and 2) resists any force that tends to increase the surface area of the liquid -water is composed of highly polar molecules and has a very high surface tension -as the major component of the liquid film that coats the alveolar walls, water is always acting to reduce the alveoli to their smallest possible size -if the film were pure water, the alveoli would collapse between breaths -but the alveolar film also contains surfactant, a detergent-like complex of lipids and proteins produced by the type II alveolar cells -surfactant decreases the cohesiveness of water molecules -as a result, the surface tension of areolar fluid is reduced, and less energy is needed to overcome those forces to expand the lungs and discourage alveolar collapse -breaths that are deeper than normal stimulate type II cells to secrete more surfactant

respiratory zone structures

-defined by the presence of thin-walled air sacs called alveoli, the respiratory zone begins as the terminal bronchioles feed into respiratory bronchioles within the lung -protruding from these smallest bronchioles are scattered alveoli -the respiratory bronchioles lead into winding alveolar ducts, whose walls consist of diffusely arranged rings of smooth muscle cells, connective tissue fibers, and out pocketing alveoli -the alveolar ducts lead into terminal clusters of alveoli called alveolar sacs or alveolar saccule -many people confuse alveoli, the site of gas exchange, with alveolar sacs, but they are not the same thing -the alveolar sac is analogous to a bunch of grapes, and the alveoli are the individual grapes -the 300 million or so gas-filled alveoli in the lungs account for most of our lung volume and provide a tremendous surface area for gas exchange

developmental aspects of the respiratory system

-because embryos develop in a cephalocaudal (head-to-tail) direction, the upper respiratory structures appear first -by the fourth week of development, two thickened plates of ectoderm, the olfactory placodes are present on the anterior aspect of the head -these quickly invaginate to form olfactory pits that form the nasal cavity -the olfactory pits then extend posteriorly to connect with the developing pharynx, which forms at the same time from the endodermal germ layer -the epithelium of the lower respiratory organs develops as outpocketing of the foregut endoderm, which becomes the pharyngeal mucosa -this protrusion, called the laryngotracheal bud, is present by the fifth week of development -the proximal part of the bud forms the tracheal lining, and its distal end splits and forms the mucosal of the bronchi and all their subdivisions , including the lung alveoli -mesoderm covers these endoderm-derived linings and forms the walls of the respiratory passageways and the stroma of the lungs -by 28 weeks, the respiratory system has developed sufficiently to allow most babies born prematurely to breathe on their own -during fetal life, the lungs are filled with fluid and the placenta makes all respiratory exchanges -vascular shunts cause circulating blood to largely bypass the lungs -at birth, the respiratory passageways fill with air -as the PCO2 in the baby's blood rises, the respiratory centers are excited, causing the baby to take its first breath -the alveoli inflate and begin to function in gas exchange, but it is nearly two weeks before the lungs are fully inflated

bronchial circulation of the lungs

-bronchial arteries provide oxygenated systemic blood to lung tissue -the bronchial arteries arise from the aorta, enter the lungs at the hilum, and then run along the branching bronchi -they provide a high-pressure, low-volume supply of oxygenated blood to all lung tissues except the alveoli -the tiny bronchial veins drain some systemic venous blood from the lungs, but there are multiple anastomoses between the two circulating, and most venous blood returns to the heart via the pulmonary veins

influence of local PCO2 on ventilation

-bronchioles servicing areas where alveolar Co2 levels are high dilate, allowing CO2 to be eliminated from the body more rapidly -bronchioles serving areas where PCO2 is low constrict

emphysema

-certain pulmonary diseases dramatically reduce the alveolar surface area -for instance, in _______, the walls of adjacent alveoli break down and the alveolar chambers enlarge -tumors, mucus, or inflammatory material also reduce surface area by blocking gas flow into the alveoli -is distinguished by permanent enlargement of the alveoli, accompanied by destruction of the alveolar walls invariably the lungs lose their elasticity. this has three important consequences: -accessory muscles must be enlisted to breathe, and victims are perpetually exhausted because breathing requires 15-20% of their total body energy supply (as opposed to 5% in healthy individuals) -for complex reasons, the bronchioles open during inspiration but collapse during expiration, trapping huge volumes of air in the alveoli. this hyperinflation leads to development of a permanently expanded "barrel chest" and flattens the diaphragm, thus reducing ventilation efficiency -damage to the pulmonary capillaries as the alveolar walls disintegrate increases resistance in the pulmonary circuit, forcing the right ventricle to overwork and consequently become enlarged -is usually caused by smoking, but hereditary factors cause emphysema in some patients

influence of arterial pH

-changes in arterial pH can modify respiratory rate and rhythm even when CO2 and O2 levels are normal -because H+ does not cross the blood brain barrier, the increased ventilation that occurs in response to falling arterial pH is mediated through the peripheral chemoreceptors -although changes in PCO2 and H+ concentration are interrelated, they are distinct stimuli -a drop in blood pH may reflect CO2 retention, but it may also result from metabolic causes, such as accumulation of lactic acid during exercise or of fatty acid metabolites (ketone bodies) in patients with poorly controlled diabetes mellitus -regardless of cause, as arterial pH declines, respiratory system controls attempt to compensate and raise the pH -they do this by increasing respiratory rate and depth to eliminate CO2 (and carbonic acid) from the blood

rhinitis

-cold viruses, streptococcal bacteria, and various allergens can cause ____, inflammation of the nasal mucosa accompanied by excessive mucus production, nasal congestion, and postnasal drip -the nasal mucosa is continuous with the mucosa of other respiratory passageways, explaining the typical nose to throat to chest progression of colds

conducting zone

-consists of all the respiratory passageways from the nose to the respiratory bronchioles -these provide fairly rigid conduits for air to reach the gas exchange sites -the _________ ________ organs also cleanse, humidify, and warm incoming air -as a result, air reaching the lungs has fewer irritants than when it entered the body, and it is warm and damp

lower respiratory system

-consists of the larynx and all the structures below it -also consists of conducting and respiratory zone structures

breathing or pulmonary ventilation

-consists of two phases: inspiration, the period when air flows into the lungs, and expiration, the period when gases exit the lungs -is a mechanical process that depends on volume changes in the thoracic cavity -volume changes lead to pressure changes, and pressure changes lead to the flow of gases to equalize the pressure boyle's law gives the relationship between the pressure and volume of a gas: at a constant temperature, the pressure of a gas varies inversely with its volume: P1V1=P22 where P is the pressure of the gas, V is its volume, and subscripts 1 and 2 represent the initial and resulting conditions -gases always fill their container. consequently, in a large container, the molecules in a given amount of gas will be far apart and the pressure will be low -but if the volume of the container is reduced, the gas molecules will be forced closer together and the pressure will rise

seramucous nasal glands

-contain mucus-secreting mucous cells and serous cells that secret a watery fluid containing enzymes -each day, these glands secrete about a quart (a liter) of mucus containing lysozyme, an antibacterial enzyme -the sticky mucus traps inspired dust, bacteria, and other debris, while lysozyme attacks and chemically destroys bacteria

forced expiratory volume (FEV)

-determines the amount of air expelled during specific time intervals of the FVC test -for example, the volume exhaled during the first second is FEV1 -those with healthy lungs can exhale about 80% of the FVC within 1 second -those with obstructive pulmonary disease exhale considerably less than 80% of the FVC within one second, while those with restrictive disease can exhale 80% of more of FVC in 1 second even though their FVC is reduced

the pleurae

-form a thin, double-layered serosa -the layer called the parietal pleura covers the thoracic wall and superior face of the diaphragm -it continues around the heart and between the lungs, forming the lateral walls of the mediastinal enclosure and snugly enclosing the lung root -from here, the pleurae extends as the layer called the visceral pleura to cover the external long surface, dipping into and lining the its fissures -produce pleural fluid, which fills the slitlike pleural cavity between them -this lubricating secretion allows the lungs to glide easily over the thorax wall during our breathing movements -although the pleurae slide easily across each other, the surface tension of the pleural fluid strongly resists their separation -consequently, the lungs cling tightly to the thorax wall and expand and recoil passively as the volume of the thoracic cavity alternately increases and decreases during breathing -the pleurae also help divide the thoracic cavity into three chambers-- the central mediastinum and the two lateral pleural compartments, each containing a lung -this compartmentalization helps prevent one mobile organ from interfering with another -it also limits the spread of local infections

lung compliance (CL)

-healthy lungs are unbelievably stretchy, and this distensibility is called _________ _____ -is a measure of the change in lung volume (delta VL) that occurs with a given change in transpulmonary pressure (delta Ppul- Pip) -the more a lung expands for a given rise in transpulmonary pressure, the greater its compliance -said another way, the higher the lung compliance, the easier it is to expand the lungs at any given transpulmonary pressure is determined largely by two factors: 1) distensibility of the lung tissue 2) alveolar surface tension -because lung distensibility is generally high and surfactant keeps alveolar surface tension low, healthy lungs tend to have high compliance, which favors efficient ventilation -factors that reduce the compliance of the thoracic wall hinder lung expansion -the total compliance of the respiratory system is comprised of lung compliance and thoracic wall compliance -deformities of the thorax, ossified costal cartilages (common during old age), and paralyzed intercostal muscles all hinder thoracic expansion, reducing total respiratory compliance

association of oxygen and hemoglobin

-hemoglobin (Hb) is composed of four polypeptide chains, each bound to an iron-containing heme group -because the iron atoms bind oxygen, each hemoglobin molecule can combine with four molecules of O2, and oxygen loading is rapid and reversible -the hemoglobin-oxygen combination, called oxyhemoglobin, is written HbO2 -hemoglobin that has released oxygen is called reduced hemoglobin or deoxyhemoglobin and is written HHb -after the first O2 molecule binds to iron, the Hb molecule changes shape. as a result, it more readily takes up two more O2 molecules, and uptake of the fourth is even more facilitated -when one, two, or three oxygen molecules are bound, a hemoglobin molecule is partially saturated -when all four of its heme groups are bound to O2, the hemoglobin is fully saturated -by the same token, unloading of one oxygen molecule enhances the unloading of the next. in this way, the affinity (binding strength) of hemoglobin for oxygen changes with the extent of oxygen saturation, and both loading and unloading of oxygen are very efficient -the rate at which Hb reversibly binds or releases O2 is regulated by PO2 temperature, blood pH, PCO2, and blood concentration of an organic chemical called BPG -these factors interact to ensure the adequate O2 is delivered to tissue cells

influence of local PO2 on perfusion

-if alveolar ventilation is inadequate, local PO2 is low because blood takes O2 away more quickly than ventilation can replenish it -as a result, the terminal arterioles constrict, redirecting blood to respiratory areas where PO2 is high and oxygen pickup is more efficient -in alveoli where ventilation is maximal, high PO2 dilates pulmonary arterioles and blood flow into the associated pulmonary capillaries increases

alveolar dead space

-if some alveoli cease to act in gas exchange (due to alveolar collapse or obstruction by mucus), the __________ _________ _____ is added to the anatomical dead space -the sum of the nonuseful volumes is the total dead space

expiration

-in healthy individuals, quiet expiration is a passive process that depends more on lung elasticity than on muscle contraction -as the inspiratory muscles relax and resume their resting length, the rib cage descends and the lungs recoil -as a result, both the thoracic and intrapulmonary volumes decrease -this volume decrease compresses the alveoli, and Ppul rises to about 1 mm Hg above atmospheric pressure -when Ppul > Patm, the pressure gradient forces gas to flow out of the lungs -forced expiration is an active process produced by contracting abdominal wall muscles, primarily the oblique and transversus muscles -these contractions 1) increase the intraabdominal pressure, which forces the abdominal organs superiorly against the diaphragm and 2) depress the rib cage -the internal intercostal muscles also help depress the rib cage and decrease thoracic volume -to precisely regulate air flow from the lungs, it is necessary to control the accessory muscles of expiration -for instance, the ability of a trained vocalist to hold a musical note depends on the coordinated activity of several muscles normally used in forced expiration

thickness and surface area of the respiratory membrane

-in healthy lungs, the respiratory membrane is only 0.5 to 1 um thick, and gas exchange is usually very efficient -the effective thickness of the respiratory membrane increases dramatically if the lungs become waterlogged and edematous, as in pneumonia or left heart failure -under such conditions, even the 0.75 s that RBCs spend in transit through the pulmonary capillaries may not be enough for adequate gas exchange, and body tissues suffer from oxygen deprivation -the greater the surface area of the respiratory membrane, the more gas can diffuse across it in a given time period -in healthy lungs, the alveolar surface area is enormous -spread flat, the total gas exchange surface of these tiny sacs in an adult male's lungs is about 90 m^2-- approx. 40 times greater than the surface area of his skin

thyroid cartilage

-large, shield-shaped ________ ______ is formed by the fusion of two cartilage plates at the midline -it resembles an upright open book, with the book's "spine" lying in the anterior midline of the neck -this "book spine" is the laryngeal prominence which can be seen externally as the Adam's apple -is typically larger in males than in females because male sex hormones stimulate its growth during puberty -inferior to it is the ring-shaped cricoid cartilage, perched atop and anchored to the trachea inferiorly

COPD: symptoms and treatment

-in the clinical setting you might see two very different patterns that represent the extremes of patients with COPD -one pattern has traditionally been called the "pink puffer": these patients work so hard to maintain adequate ventilation that they lose weight, becoming thin but still having nearly normal blood gases -in contrast, "blue bloaters" commonly of stocky build, become sufficiently hypoxic that they are obviously cyanotic. the hypoxia causes constriction of pulmonary blood vessels, leading to pulmonary hypertension and right-sided heart failure -traditionally, "pink puffers" were associated with emphysema while "blue bloaters" were associated with chronic bronchitis -it turns out that patients with the same underlying disease can display either of these clinical patterns, and this may depend on a third factor--the strength of their innate respiratory drive -most COPD patients fall between these two extremes -COPD is routinely treated with inhaled bronchodilators and corticosteroids -severe dyspnea and hypoxia mandate oxygen use, but oxygen must be administered with care -in some of these patients, giving pure oxygen can increase the blood PCO2 (and lower blood pH) to life-threatening levels -the solution is to use the minimum concentration of oxygen that relieves the person's hypoxia

hypoxia

-inadequate oxygen delivery to body tissues -is more visible in fair-skinned people because their skin and mucosa take on a bluish cast (become cyanotic) when Hb saturation falls below 75% -the mucosa and nail beds are often the easiest places to observe this color change is classified based on cause: -anemic hypoxia -ischemic (stagnant) hypoxia -histotoxic hypoxia -hypoxemic hypoxia -carbon monoxide poisoning

external nose

-includes the root (area between the eyebrows), bridge, and dorsum nasi (anterior margin), the latter terminating in the apex (tip of the nose) -the external openings of the nose, the nostrils or nares are bounded laterally by the flared alae -the skeletal framework for the external nose is fashioned by the nasal and frontal bones superiorly (forming the bridge and root, respectively), the maxillary bones laterally, and flexible plates of hyaline cartilage (the alar and septal cartilages, and the lateral processes of the septal cartilage) inferiorly -the skin covering the nose's anterior and lateral aspects is thin and contains many sebaceous glands

pleurisy

-inflammation of the pleurae -often results from pneumonia -inflamed pleurae become rough, resulting in friction and stabbing pain with each breath -as the disease progresses ,the pleurae may produce excessive amounts of fluid -this increased fluid relieves the pain caused by pleural surfaces rubbing together, but may exert pressure on the lungs and hinder breathing movements

laryngitis

-inflammation of the vocal folds -causes the vocal folds to swell, interfering with their vibration -this changes the vocal tone, causing hoarseness, or in severe cases limiting us to a whisper -is most often caused by viral infections, but may also be due to overusing the voice, very dry air, bacterial infections, tumors on the vocal folds, or inhalation of irritating chemicals

chronic bronchitis

-inhaled irritants lead to chronic production of excessive mucus -the mucosa of the lower respiratory passageways become inflamed and fibroses -these responses obstruct the airways, severely impairing lung ventilation and gas exchange -pulmonary infections are frequent because bacteria thrive in the stagnant pools of mucus -smoking is a major risk factor -environmental pollution also promotes chronic bronchitis

factors influencing breathing rate and depth

-inspiratory depth is determined by how actively the respiratory centers stimulate the motor neurons serving the respiratory muscles -the greater the stimulation, the greater the number of motor units excited and the greater the force of respiratory muscle contractions -respiratory rate is determined by how long the inspiratory center is active or how quickly it is switched off -changing body demands can modify depth and rate of breathing -the respiratory centers in the medulla and pons are sensitive to both excitatory and inhibitory stimuli

internal respiration

-involves capillary gas exchange in body tissues -the factors promoting gas exchanges between systemic capillaries and tissue cells are essentially identical to those acting in the lungs -tissue cells continuously use O2 for their metabolic activities and produce CO2 -because PO2 is always lower in tissues than it is in systemic arterial blood, O2 moves rapidly from blood into tissues until equilibrium is reached -at the same time, CO2 moves quickly along its pressure gradient into blood -as a result, venous blood draining the tissue capillary beds and returning to the heart has a PO2 of 40 mm Hg and a PCO2 of 45 mm Hg -in summary, the gas exchanges that occur between blood and alveoli and between blood and tissue cells take place by simple diffusion -they are driven by the partial pressure gradients of O2 and CO2 that exist on the opposite sides of the exchange membranes

sleep apnea

-is a common disorder that is characterized by the temporary cessation of breathing during sleep -although they are not usually aware of it, people with ________ _____ wake themselves up many times each night (in severe cases, more than 30 times per hour) -as a result, these people may feel as tired when they get up as when they went to sleep, leaving them with excessive daytime sleepiness -loud snoring, particularly when respiration resumes, is often reported by others sleeping in the same room because it disturbs their sleep as well -consequences of disrupted sleep are an increased susceptibility to accidents and increase in a variety of chronic illnesses such as hypertension, heart disease, stroke, and diabetes -obstructive sleep apnea is often treated using a continuous positive airway pressure (CPAP) device -by gentling blowing air into the airway, it provides a positive air pressure that holds the airway open and prevents its collapse

carbon monoxide poisoning

-is a unique type of hypoxemic hypoxia and is a leading cause of death from fire -carbon monoxide (CO) is an odorless, colorless gas -because Hb's affinity for CO is more than 200 times greater than its affinity for oxygen CO outcompetes O2 for the heme binding sites -even at miniscule partial pressures, carbon monoxide can drastically reduce hemoglobin's ability to carry O2 -is particularly dangerous because it does not produce the characteristic signs of hypoxia-- cyanosis and respiratory distress -instead, the victim is confused and has a throbbing headache -in rare cases, fair skin becomes cherry red. -patients with this are given hyperbaric therapy if available or 100% O2 until the CO has been cleared from the body

hyperventilation

-is an increase in the rate and depth of breathing that exceeds the body's need to remove CO2 -a person experiencing an anxiety attack may hyperventilate involuntarily -as the person blows off CO2, the low CO2 levels in the blood (hypocapnia) constrict cerebral blood vessels -this reduces brain perfusion, producing cerebral ischemia that causes dizziness or fainting -earlier symptoms of hyperventilation are tingling and involuntary muscle spasms (tetany) in the hands and face caused by blood Ca2+ levels falling as pH rises -symptoms may be averted by breathing into a paper bag -the air inspired from the bag is expired air, rich in carbon dioxide, which causes carbon dioxide to be retained in the blood -sometimes swimmers voluntarily hyperventilate so they can hold their breath longer during swim meets. this is dangerous -blood O2 content rarely drops much below 60% of normal during regular breath-holding, because as PO2 drops, PCO2 rises enough to make breathing unavoidable -however, strenuous hyperventilation can lower PCO2 so much that a lag period occurs before PCO2 rebounds enough to stimulate respiration again -this lag may allow oxygen levels to fall well below 50 mm Hg, causing the swimmer to black out (and perhaps drown) before he or she has the urge to breathe

central sleep apnea

-is caused by a reduced drive from the respiratory centers of the brain stem during sleep rather than by obstruction of the airway

asthma

-is characterized by episodes of coughing, dyspnea, wheezing, and chest tightness-- alone or in combination -a sense of panic accompanies most acute attacks -although sometimes classed with COPD because it is an obstructive disorder, ______ is marked by acute episodes followed by symptom-free periods-- that is, the obstruction is reversible -the cause has been hard to pin down -initially it was viewed as a consequence of bronchospasm triggered by various factors such as cold air, exercise, or allergens -however, researchers have found that in allergic asthma (the most common kind), active inflammation of the airways comes first -the inflammation is an immune response controlled by a subset of T lymphocytes that stimulate the production of IgE antibodies and recruit inflammatory cells to the site -once someone has allergic asthma, the inflammation persists even during symptom-free periods and makes the airways hypersensitive (the most common triggers are in the home) -once the airway walls are thickened with inflammatory exudate, the effect of bronchospasm is vastly magnified and can dramatically reduce air flow -about one in ten people in north america suffer from asthma-- more children than adults -over the past 20 years, the number of cases rose dramatically, plateaued, and may now be declining -while asthma remains a major health problem, better treatment options have reduced the number of asthma-related deaths -instead of merely treating the symptoms with fast acting bronchodilators, we now treat the underlying inflammation using inhaled corticosteroids and a variety of other drugs

hypoxemic hypoxia

-is indicated by reduced arterial PO2 -Possible causes include disordered or abnormal ventilation-perfusion coupling, pulmonary diseases that impair ventilation, and breathing air containing scant amounts of O2.

nasopharynx

-is posterior to the nasal cavity, inferior to the sphenoid bone, and superior to the level of the soft palate -because it lies above the point where food enters the body, it serves only as an air passageway -during swallowing, the soft palate and its pendulous uvula move superiorly, an action that closes off the ______ and prevents food from entering the nasal cavity -is continuous with the nasal cavity through the posterior nasal apertures -its pseudostratified ciliated epithelium takes over the job of propelling mucus where the nasal mucosa leaves off -high on its posterior wall is the pharyngeal tonsil which traps and destroys pathogens entering the ______ in air -infected and swollen adenoids block air passage in here, making it necessary to breathe through the mouth -as a result, air is not properly moistened, warmed, or filtered before reaching the lungs -when the adenoids are chronically enlarged, both speech and sleep may be disturbed -the pharyngotympanic (auditory) tubes, which drain the middle ear cavities and allow middle ear pressure to equalize with atmospheric pressure, open into the lateral walls of the _____ -a ridge of pharyngeal mucosa posterior to each of these openings marks the site of the tubal tonsil. its location helps protect the middle ear against infections likely to spread from the nasopharynx

transpulmonary pressure

-is the difference between the intrapulmonary and intrapleural pressures (Ppul- Pip) -this pressure keeps the air spaces of the lungs open/ keeps the lungs from collapsing -the size of the __________ _________ determines the size of the lungs at any time-- the greater the __________ pressure, the larger the lungs -any condition that equalizes Pip with the intrapulmonary (or atmospheric) pressure causes immediate lung collapse

lung cancer

-is the leading cause of cancer death for both men and women in North America, killing more people every year than breast, prostate, and colorectal cancer combined -this is tragic, because lung cancer is largely preventable-- nearly 90% of cases result from smoking -the cure rate for lung cancer is notoriously low, with most people dying within one year of diagnosis -the five-year survival rate is about 16% -because lung cancer is aggressive and metastasizes rapidly and widely, most cases are not diagnosed until they are well advanced -appears to follow closely the oncogene-activating steps -ordinarily, nasal hairs, sticky mucus, and cilia do a fine job of protecting the lungs from chemical and biological irritants, but when a person smokes, these defenses are overwhelmed and eventually stop functioning -in particular, smoking paralyzes the cilia that clear mucus from the airways, allowing irritants and pathogens to accumulate -the "cocktail" of free radicals and other carcinogens in tobacco smoke eventually translates into lung cancer most common types: -adenocarcinoma -squamous cell carcinoma -small cell carcinoma -the key to survival is early detection -if the cancer has not metastasized before it is discovered, complete removal of the diseased lung has the greatest potential for prolonging life and providing a care -with metastatic lung cancer, radiation therapy and chemotherapy are the only options, but these have low success rates

intrapulmonary pressure (Ppul)

-is the pressure in the alveoli -rises and falls with the phases of breathing, but it always equalizes with atmospheric pressure eventually

minute ventilation

-is the total amount of gas that flows into or out of the respiratory tract in 1 min -during normal quiet breathing, the minute ventilation in healthy people is about 6 L/min (500 ml per breath multiplied by 12 breaths per minute) -during vigorous exercise, this ventilation may reach 200 L/min

nasal cavity

-lies in and posterior to the external nose -during breathing, air enters the cavity by passing through the nostrils or nares -is divided by a midline nasal septum, formed anteriorly by the septal cartilage and posteriorly by the vomer bone and perpendicular plate of the ethmoid bone -is continuous posteriorly with the nasal portion of the pharynx through the posterior nasal apertures -the roof is formed by the ethmoid and sphenoid bones of the skull -the floor is formed by the palate, which separates the ______ ____ from the oral cavity below -anteriorly, where the palate is supported by the palatine bones and processes of the maxillary bones, it is called the hard palate. the unsupported posterior portion is the muscular soft palate -the part of the nasal cavity just superior to each nostril, called the nasal vestibule, is lined with skin containing sebaceous and sweat glands and numerous hair follicles -the hairs, or virbissae, filter coarse particles from inspired air -the rest of the cavity is lined with two types of mucous membrane: olfactory and respiratory mucosa -the nasal mucosa is richly supplied with sensory nerve endings, and contact with irritating particles triggers a sneeze reflex -rich plexuses of capillaries and thin-walled veins underlie the nasal epithelium and warm incoming air as it flows across the mucosal surface -when the inspired air is cold, the vascular plexus becomes engorged with blood, intensifying the air-heating process

oropharynx

-lies posterior to the oral cavity and is continuous with it through an archway called the isthmus of the fauces -because it extends inferiorly from the level of the soft palate to the epiglottis, both swallowed food and inhaled air pass through it -as the nasopharynx blends into the ______, the epithelium changes from pseudo stratified columnar to a more protective stratified squamous epithelium -this structural adaptation accommodates the increased friction and chemical trauma (characteristic of hot and spicy foods) accompanying food passage -the paired palatine tonsils lie embedded in the lateral walls of the oropharyngeal mucosa just posterior to the oral cavity -the lingual tonsil covers the posterior surface of the tongue

laryngopharynx

-like the oropharynx above it, this serves as a passageway for food and air and is lined with a stratified squamous epithelium -it lies directly posterior to the larynx, where the respiratory and digestive pathways diverge, and extends to the inferior edge of the cricoid cartilage -is continuous with the esophagus posteriorly

respiratory mucosa

-lines most of the nasal cavity -is a pseudo stratified ciliated columnar epithelium, containing scattered goblet cells, that rests on a lamina propria richly supplied with seromucous nasal glands -the epithelial cells of this mucosa also secrete defensins, natural antibiotics that help kill invading microbes -the high water content of the mucus film humidifies incoming air -the ciliated cells create a gentle current that moves the sheet of contaminated mucus posteriorly toward the throat, where it is swallowed and digested -when our nasal cilia are exposed to cold air, they become sluggish, allowing mucus to accumulate in the nasal cavity and dribble out the nostrils -this, along with with the fact that water vapor in expired air tends to condense at lower temperatures, explains why you have a runny nose on a crisp wintry day

atelectasis

-lung collapse -occurs when a bronchiole becomes plugged (as may follow pneumonia) -its associated alveoli then absorb all of their air and collapse -can also occur when air enters the pleural cavity either through a chest wound or a rupture of the visceral pleura, which allows air from the respiratory tract to enter the pleural cavity

spirometer

-lung volumes and capacities are often abnormal in people with pulmonary disorders -the original clinical measuring tool, a ______, was a cumbersome instrument utilizing a hollow bell inverted over water -now patients simply blow into a small electronic measuring device

vocal folds

-lying under the laryngeal mucosa on each side are the vocal ligaments, which attach the arytenoid cartilages to the thyroid cartilage -these ligaments, composed of elastic fibers, form the core of mucosal folds called the _______ ______, or true vocal cords, which appear pearly white because they lack blood vessels -they vibrate, producing sounds as air rushes up from the lungs -the ________ ______ and the medial opening between them through which air passes are called the glottis -superior to them is a similar pair of mucosal folds called the vestibular folds or false vocal cords -these play no direct part in sound production but help to close the glottis when we swallow

respiratory system

-major function is to supply the body with oxygen and dispose of carbon dioxide -to accomplish this function, at least four functions, collectively called respiration must happen -the _______ system is responsible for only the first two processes, but it cannot accomplish its primary goal of obtaining oxygen and eliminating carbon dioxide unless the third and fourth processes also occur -the ________ and circulatory systems are closely coupled, and if either system fails, the body's cells begin to die from oxygen starvation -is also involved with the sense of smell and with speech -includes the nose and paranasal sinuses; the pharynx; the larynx; the trachea; the bronchi and their smaller branches; and the lungs, which contain tiny air sacs called alveoli

non respiratory air movements

-many processes other than breathing move air into or out of the lungs, altering the normal respiratory rhythm -these occur when you cough, sneeze, cry, laugh, hiccup or yawn -some can be produced voluntarily , but some are reflexive

alveolar ventilation rate (AVR)

-minute ventilation values provide a rough yardstick for assessing respiratory efficiency, but the ________ _______ _______ is a better index of effective ventilation -takes into account the volume of air wasted in the dead space and measures the flow of fresh gases in and out of the alveoli during a particular time interval AVR (ml/min) = frequency (breaths/min) x (TV- dead space) (ml/breath) -in healthy people, AVR is usually about 12 breaths per minute times the difference of 500-150 ml per breath, or 4200 ml/ min -because anatomical dead space is constant in a particular individual, increasing the volume of each inspiration (breathing depth) enhance AVR and gas exchange more than raising the respiratory rate -AVR drops dramatically during rapid shallow breathing because most of the inspired air never reaches the exchange sites -furthermore, as tidal volume approaches the dead space value, effective ventilation approaches zero, regardless of how fast a person is breathing

influence of PCO2

-of all the chemicals influencing respiration, CO2 is the most potent and the most closely controlled -normally arterial PCO2 is 40 mm Hg and is maintained within 3 mm Hg of this level by an exquisitely sensitive homeostatic mechanism that is mediated mainly by the effect of rising CO2 levels on the central chemoreceptors of the brain stem -as PCO2 levels rise in the blood, a condition referred to as hypercapnia, CO2 accumulates in the brain -as CO2 accumulates, it is hydrated to form carbonic acid -the acid dissociates, H+ is liberated, and the pH drops -this is the same reaction that occurs when CO2 enters RBCs -the increase in H+ excites the central chemoreceptors, which make abundant synapses with the respiratory regulatory centers -as a result, the depth and rate of breathing increase -this enhanced alveolar ventilation quickly flushes CO2 out of the blood, raising blood pH -an elevation of only 5 mm Hg in arterial PCO2 doubles alveolar ventilation, even when arterial O2 levels and pH haven't changed -when PO2 and pH are below normal, the response to elevated PCO2 is even greater -increased ventilation is normally self-limiting, ending when homeostatic blood PCO2 levels are restored -while rising blood CO2 levels act as the initial stimulus, it is rising levels of H+ generated within the brain that prod the central chemoreceptors into increased activity -CO2 readily diffuses across the blood brain barrier between the brain and the blood, but H+ does not -in the final analysis, control of breathing during rest is aimed primarily at regulating the H+ concentration in the brain -when PCO2 is abnormally low, respiration is inhibited and becomes slow and shallow -in fact, periods of apnea (breathing cessation) may occur until arterial PCO2 rises and again stimulates respiration

pleural effusion

-other fluids that may accumulate in the pleural cavity include blood (leaked from damaged blood vessels) and blood filtrate (the watery fluid that oozes from the lung capillaries when left-sided heart failure occurs ) -the term for fluid accumulation in the pleural cavity is _________ _______

partial pressure gradients and gas solubilities

-partial pressure gradients of O2 and CO2 drive the diffusion of these gases across the respiratory membrane -a steep gradient for the partial pressure of oxygen exists across the respiratory membrane because the PO2 of deoxygenated blood in the pulmonary arteries is only 40 mm Hg, as opposed to a PO2 of approximately 104 mm Hg in the alveoli -as a result, O2 diffuses rapidly from the alveoli into the pulmonary capillary blood -equilibrium-- that is, a PO2 of 104 mm Hg on both sides of the respiratory membrane-- usually occurs in 0.25 seconds, which is about a third of the time an RBC spends in a pulmonary capillary -blood can flow through the pulmonary capillaries three times as quickly and still be adequately oxygenated -carbon dioxide diffuses in the opposite direction along a much gentler partial pressure gradient of about 5 mm Hg until equilibrium occurs at 40 mm Hg -expiration then gradually expels carbon dioxide from the alveoli -even though the O2 pressure gradient for oxygen diffusion is much steeper than the CO2 gradient, equal amounts of these gases are exchanged. why? the reason is that CO2 is 20 times more soluble in plasma and alveolar fluid than O2

nasal conchae

-protruding medially from each lateral wall of the nasal cavity are the superior, middle, and inferior _______ _____ -the groove inferior to each concha is a nasal meatus -greatly increase the mucosal surface area exposed to air and enhance air turbulence in the cavity -the gases in inhaled air swirl through the twists and turns, deflecting heavier, nongaseous particles onto the mucus-coated surfaces, where they become trapped -the ____ and nasal mucosa not only function during inhalation to filter, heat, and moisten the air, but also act during exhalation to reclaim this heat and moisture -this reclamation process minimizes the amount of moisture and heat lost from the body through breathing, helping us to survive in dry and cold climates

three neural factors that interact in the abrupt increase in ventilation that occurs as exercise begins

-psychological stimuli (our conscious anticipation of exercise) -simultaneous cortical motor activation of skeletal muscles and respiratory centers -excitatory input reaching respiratory centers from proprioceptors in moving muscles, tendons, and joints

exercise

-respiratory adjustments during exercise are geared to both the intensity and duration of the exercise -working muscles consume tremendous amounts of O2 and produce large amounts of CO2, so ventilation can increase 10- to 20- fold during vigorous exercise -increased ventilation in response to metabolic needs is called hyperpnea -how does hyperpnea differ from hyperventilation? the respiratory changes in hypernea do not alter blood O2 and CO2 levels significantly. in contrast, hyperventilation is excessive ventilation, and is characterized by low PCO2 and alkalosis exercise-enhanced ventilation does not appear to be prompted by rising PCO2 and declining PO2 , and pH in the blood for two reasons: -ventilation increases abruptly as exercise begins, followed by a gradual increase, and then reaches a steady stage. when exercise stops, there is a small but abrupt decline in ventilation rate, followed by a gradual decrease to the pre-exercise value -although venous levels change, arterial PCO2 and PO2 levels remain surprisingly constant during exercise. in fact, PCO2 may fall below normal and PO2 may rise slightly because the respiratory adjustments are so efficient -the subsequent gradual increase and then plateauing of respiration probably reflect the rate of CO2 delivery to the lungs -the rise in lactic acid levels during exercise results from anaerobic respiration. however, it is not a result of inadequate respiratory function, because alveolar ventilation and pulmonary perfusion are as well matched during exercise as during rest (hemoglobin remains fully saturated) -rather, it reflects cardiac output limitations or inability of the skeletal muscles to further increase their oxygen consumption -in light of this fact, the practice of inhaling pure O2 by mask, used by some football players to replenish their "oxygen-starved" bodies as quickly as possible, is useless -the panting athlete does need more oxygen, but inspiring extra oxygen will not help, because the shortage is in the muscles not the lungs

atmospheric pressure

-respiratory pressures are always described relative to _________ pressure, which is the pressure exerted by the air (gases) surrounding the body -at sea level, it is 760 mm Hg (the pressure exerted by a column of mercury 760 mm high) -this pressure can also be expressed in atmosphere units. 760 mm Hg= 1 atm -a negative respiratory pressure in any respiratory area indicates that the pressure in that region is lower than atmospheric pressure -a positive respiratory pressure is higher than atmospheric pressure -a zero respiratory pressure is equal to atmospheric pressure

epiglottis

-the ninth cartilage, the flexible, spoon-shaped ________, is composed of elastic cartilage and is almost entirely covered by a taste bud-containing mucosa -extends from the posterior aspect of the tongue to its anchoring point on the anterior rim of the thyroid cartilage -when only air is flowing into the larynx, the inlet to the larynx is wide open and the free edge of the epiglottis projects upward -during swallowing, the larynx is pulled superiorly and the epiglottis tips to cover the laryngeal inlet -because this action keeps food out of the lower respiratory passages, the epiglottis has been called the guardian of the pathways -anything other than air entering the larynx initiates the cough reflex to expel the substance

asthma attack

-smooth muscle of the bronchiolar walls is exquisitely sensitive to neural controls and certain chemicals -for example, inhaled irritants activate a reflex of the parasympathetic division of the nervous system that cause vigorous constriction of the bronchioles and dramatically reduces air passage -during an acute ______ ______, histamine and other inflammatory chemicals can cause such strong bronchoconstriction that pulmonary ventilation almost completely stops, regardless of the pressure gradient -conversely, epinephrine release during sympathetic nervous system activation or administered as a drug dilates bronchioles and reduces airway resistance -local accumulations of mucus, infectious material, or solid tumors in the passageways are important sources of airway resistance in those with respiratory disease -whenever airway resistance rises, breathing movements become more strenuous, but such compensation has its limits -when the bronchioles are severely constricted or obstructed, even the most extreme respiratory efforts cannot restore ventilation to life-sustaining levels

dead space

-some of the inspired air fills the conducting respiratory passageways and never contributes to gas exchange in the alveoli -the volume of these conducting zone conduits, which make up the anatomical ________ _______, typically amounts to about 150 ml -the anatomical _________ _________ volume in a healthy young adult is equal to 1 ml per pound of ideal body weight -if TV is 500 ml, only about 250 ml of the tidal breath is in the anatomical _________ _____

voice production

-speech involves the intermittent release of expired air as the glottis opens and closes -the length of the vocal folds and the size of the glottis change with the action of the intrinsic laryngeal muscles that clothe the cartilages -most of these muscles move the arytenoid cartilages -as the length and tension of the vocal folds change, the pitch of the sound varies -the tenser the vocal folds, the faster they vibrate and the higher the pitch -as a boy's larynx enlarges during puberty, his vocal folds become longer and thicker. because this causes them to vibrate more slowly, his voice becomes deeper -loudness of the voice depends on the force with which the airstream rushes across the vocal folds -the vocal folds do not move at all when we whisper, but they vibrate vigorously when we yell -the muscle of the chest, abdomen, and back provide the power for the airstream -the vocal folds actually produce buzzing sounds -the perceived quality of the voice depends on the coordinated activity of many structures above the glottis -the entire length of the pharynx acts as a resonating chamber, to amplify and enhance the sound quality -the oral, nasal, and sinus cavities also contribute to vocal resonance -good enunciation depends on muscles in the pharynx, tongue, soft palate, and lips that "shape" sounds in recognizable consonants and vowels

pulmonary function tests

-spirometry is most useful for evaluating losses in respiratory function and for following the course of certain respiratory diseases -it cannot provide a specific diagnosis, but it can distinguish between obstructive pulmonary diseases involving increased airway resistance (such as chronic bronchitis) and restrictive diseases involving reduced total lung capacity (these changes might be due to diseases such as tuberculosis, or to fibrosis due to exposure to certain environmental agents such as abestos) -in obstructive diseases, TLC, FRC, and RV may increase because the lungs hyperinflate, whereas in restrictive diseases, VC, TLC, and FRC, and RV decline because lung expansion is limited

dalton's law of partial pressures

-states that the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture -further, the pressure exerted by each gas--its partial pressure-- is directly proportional to the percentage of that gas in the gas mixture -nitrogen makes up about 79% of air, and the partial pressure of nitrogen PN2 is 78.6% x 760 mm Hg, or 597 mm Hg -oxygen, which accounts for nearly 21% of air, has a partial pressure PO2, of 159 mm Hg (20.9% x 760 mm Hg) -together, nitrogen and oxygen contribute about 99% of the total atmospheric pressure -air also contains 0.04% carbon dioxide, up to 0.5% water vapor, and insignificant amounts of inert gases -at high altitudes, partial pressures decline in direct proportion to the decrease in atmospheric pressure -moving in the opposite direction, atmospheric pressure increases by 1 atm (760 mm Hg) for each 33 feet of descent below sea level -at 99 feet below sea level, the total pressure exerted on the body is equivalent to 4 atm, or 3040 mm Hg, and the partial pressure exerted by each component gas is also quadrupled

henry's law

-states that when a gas is in contact with a liquid, the gas will dissolve in the liquid in proportion to its partial pressure -accordingly, the greater the concentration of a particular gas in the gas phase, the more and the faster that gas will go into solution in the liquid -at equilibrium, the partial pressures in the gas and liquid phases are the same -if, however, the partial pressure of the gas later becomes greater in the liquid than in the adjacent gas phase, some of the dissolved gas molecules will reenter the gaseous phase -so the direction and amount of movement of a gas are determined by its partial pressure in the two phases -this flexible solution is exactly what occurs when gases are exchanged in the lungs an d tissues -how much of a gas will dissolve in a liquid at any given partial pressure also depends on the solubility of the gas in the liquid and the temperature of the liquid -the gases in air have very different solubilities in water (and in blood plasma) -carbon dioxide is most soluble. oxygen is only 1/20 as soluble as CO2, and N2 is only half as soluble as O2. for this reason, at a given partial pressure, much more CO2 than O2 dissolves in water, and practically no N2 goes into solution -when a liquid's temperature rises, gas solubility decreases in summary, the amount of gas that will dissolve in a liquid depends on: -the partial pressure of the gas in contact with the liquid -the solubility of the gas in the liquid -the temperature of the liquid

epithelium of larynx

-stratified squamous epithelium lines the superior portion of the larynx, an area subject to food contact -below the vocal folds the epithelium is a pseudo stratified ciliated columnar type that filters dust -the power stroke of its cilia is directed upward toward the pharynx to continually move mucus away from the lungs

the nose and paranasal sinuses

-the nose is the only external visible part of the respiratory system the nose: 1) provides an airway for respiration 2) moistens and warms entering air 3) filters and cleans inspired air 4) serves as a resonating chamber for speech and 5)houses the olfactory (smell) receptors -the structures of the nose are divided into the external nose and the internal nasal cavity

structural changes of the conducting tubes

-support structures change. irregular patches, or plates, of cartilage replace the cartilage rings, and by the time the bronchioles are reached, the tube walls no longer contain supportive cartilage. however, the tube walls throughout the bronchial tree contain elastic fibers -epithelium type changes. the mucosal epithelium thins as it changes from pseudo stratified columnar to simple columnar and then to simple cuboidal in the terminal bronchioles. mucus-producing cells and cilia are sparse in the bronchioles. for this reason, most airborne debris found at or below the level of the bronchioles must be removed by macrophages in the alveoli -amount of smooth muscle increases. the relative amount of smooth muscle in the tube walls increases as the passageways become smaller. a complete layer of circular smooth muscle in the bronchioles and the lack of supporting cartilage allows the bronchioles to provide substantial resistance to air passage under certain conditions

paranasal sinuses

-surround the nasal cavity -are located in the frontal, sphenoid, ethmoid, and maxillary bones -lighten the skull, and they may help warm and moisten the air -the mucus they produce ultimately flows into the nasal cavity, and the suctioning effect created by nose blowing helps drain the sinuses

pulmonary circulation of the lungs

-systemic venous blood that is to be oxygenated in the lungs is delivered by the pulmonary arteries, which lie anterior to the main bronchi -in the lungs, the pulmonary arteries branch profusely along with the bronchi and finally feed into the pulmonary capillary networks surrounding the alveoli -the pulmonary veins convey the freshly oxygenated blood from the respiratory zone of the lungs to the heart -their tributaries course back to the hilum both with the corresponding bronchi and in the connective tissue septa separating the bronchopulmonary segments -the pulmonary circuit is a low-pressure, high-volume circulation -because all of the body's blood passes through the lungs about once each minute, the lung capillary endothelium is an ideal location for enzymes that act on materials in the blood -examples include angiotensin converting enzyme, which activates an important blood pressure hormone, and enzymes that inactivate certain prostaglandins

influence of other factors on hemoglobin saturation

-temperature, blood pH, PCO2, and the amount of BPG in the blood all influence hemoglobin saturation at a given PO2 -RBCs produce BPG as they metabolize glucose -BPG binds reversibly with hemoglobin, and its levels rise when oxygen levels are chronically low -all of these factors influence Hb saturation by modifying hemoglobin's three-dimensional structure, thereby changing its affinity for O2 -an increase in temperature, PCO2, H+, OR BPG levels in blood lowers Hb'S affinity for O2, enhancing oxygen unloading from the blood -conversely, a decrease in any of these factors increases hemoglobin's affinity for oxygen, decreasing oxygen unloading -all these factors tend to be highest in the systemic capillaries, where oxygen unloading is the goal -as cells metabolize glucose and use O2, they release CO2, which increases the PCO2, and H+ levels in capillary blood -both declining blood pH (acidosis) and increasing PCO2 weaken the HB-O2 bond, a phenomenon called the Bohr effect. this enhances oxygen unloaded where it is most needed -heat is a by-product of metabolic activity, and active tissue are warmer than less active ones -a rise in temperature decreases hemoglobin's affinity for O2 both directly and indirectly (via its influence on RBC metabolism and BPG synthesis

respiratory zone

-the actual site of gas exchange -is composed of the respiratory bronchioles, alveolar ducts, and alveoli, all microscopic structures

cellular respiration

-the actual use of oxygen and production of carbon dioxide by tissue cells -is the cornerstone of all energy-producing chemical reactions in the body

bronchial tree

-the air passageways in the lungs branch again and again, about 23 times overall -at the tips of the bronchial tree, conducting zone structures give way to respiratory zone structures

respiratory capacities

-the amount of air flushed in and out of the lungs depends on the conditions of inspiration and expiration -consequently, several respiratory volumes can be described -specific combinations of these respiratory volumes, called ________ _______, are measured to gain info about a person's respiratory status -include inspiratory, functional residual, vital, and total lung capacities -always consist of two or more lung volumes -lung volumes and capacities tend to be smaller in women than in men because of women's smaller size

the Haldane effect

-the amount of carbon dioxide transported in blood is markedly affected by the degree to which blood is oxygenated -the lower the PO2 and the lower the Hb saturation with oxygen, the more CO2 that blood can carry -this phenomenon, called the _____ ______ reflects the greater ability of reduced hemoglobin to form carbaminohemoglobin and to buffer H+ by combining with it -as CO2 enters the systemic bloodstream, it causes more oxygen to dissociate from Hb (Bohr effect) -the dissociation of O2 allows more CO2 to combine with Hb (Haldane effect) -this effect encourages CO2 exchange in both the tissues and lungs -in the pulmonary circulation, the situation that we just described is reversed-- uptake of O2 facilitates release of CO2 -as Hb becomes saturated with O2, the H+ released combines with HCO3-, helping to unload CO2 from the pulmonary blood

summary of interactions of PCO2, PO2, and arterial pH

-the body's need to rid itself of CO2 is the most important stimulus for breathing in a healthy person -however, CO2 does not act in isolation, and various chemical factors enforce or inhibit one another's effects these interactions are summarized here: - rising CO2 levels are the most powerful respiratory stimulant. as CO2 is hydrated in brain tissue, liberated H+ acts directly on the central chemoreceptors, causing a reflexive increase in breathing rate and depth. low PCO2 levels depress respiration -under normal conditions, blood PO2 affects breathing only indirectly. it does so by influencing peripheral chemoreceptor sensitivity to changes in PCO2. low PO2 augments PCO2 effects, and high PO2 levels diminish the effectiveness of CO2 stimulation -when arterial PO2 falls below 60 mm Hg, it becomes the major stimulus for respiration. the peripheral chemoreceptors respond, reflexively increasing ventilation. this may increase O2 loading into the blood, but it also causes hypocapnia (low PCO2 blood levels) and an increase in blood pH, both of which inhibit respiration -changes in arterial pH due to CO2 retention or metabolic factors act through the peripheral chemoreceptors. the resulting changes in ventilation in turn modify arterial PCO2 and pH. arterial pH does not influence the central chemoreceptors directly

balancing ventilation and perfusion

-the changing diameter of local bronchioles and arterioles synchronizes alveolar ventilation and pulmonary perfusion -poor alveolar ventilation results in low oxygen and high carbon dioxide levels in the alveoli -consequently, pulmonary arterioles constrict and airways dilate, bringing blood flow and air flow into closer physiological match -high PO2 and low PCO2 in the alveoli cause bronchioles serving the alveoli to constrict, and promote flushing of blood into the pulmonary capillaries -although these homeostatic mechanisms provide appropriate conditions for efficient gas exchange, they never completely balance ventilation and perfusion in every alveolus due to other factors -in particular, 1) gravity causes regional variations in blood and air flow in the lungs and 2) the occasional alveolar duct plugged with mucus creates unventilated areas -these factors, together with blood shunted from the bronchial veins, account for the slight drop in PO2 from alveolar air to pulmonary venous blood

pharynx

-the funnel-shaped ___ connects the nasal cavity and mouth superiorly to the larynx and esophagus inferiorly -commonly called the throat, it vaguely resembles a short length of garden hose as it extends for about 5 inches from the base of the skull to the level of the sixth cervical vertebra -is divided into three regions: nasopharynx, oropharynx, and laryngopharynx -the muscular pharynx wall is composed of skeletal muscle throughout its length -however, the cellular composition of its mucosa varies from one pharyngeal region to another

composition of alveolar gas

-the gaseous makeup of the atmosphere is quite different than that in the alveoli -the atmosphere is almost entirely O2 and N2; the alveoli contain more CO2 and water vapor and much less O2 these differences reflect the effects of: -gas exchanges occurring in the lungs (O2 diffuses from the alveoli into the pulmonary blood and CO2 diffuses in the opposite direction) -humidification of air by conducting passages -the mixing of alveolar gas that occurs with each breath. because only 500 ml of air enter with each tidal inspiration, gas in the alveoli is actually a mixture of newly inspired gases and gases remaining in the respiratory passageways between breaths -the alveolar partial pressures of O2 and CO2 are easily changed by increasing breathing depth and rate -a high AVR brings more O2 into the alveoli, increasing alveolar PO2 and rapidly eliminating CO2 from the lungs

innervation of the lungs

-the lungs are innervated by parasympathetic and sympathetic motor fibers, and visceral sensory fibers -these nerve fibers enter each lung through the pulmonary plexus on the lung root and run along the bronchial tubes and blood vessels in the lungs -parasympathetic fibers cause the air tubes to constrict, whereas sympathetic fibers dilate them

pulmonary irritant reflexes

-the lungs contain receptors that respond to an enormous variety of irritants -when activated, these receptors communicate with the respiratory centers via vagal nerve afferents -accumulated mucus, inhaled debris, such as dust, or noxious fumes stimulate receptors in the bronchioles that promote reflex constriction of those air passages -in the trachea or bronchi, the same irritants stimulate a cough -stimulation in the nasal cavity triggers a sneeze

airway resistance

-the major nonelastic source of resistance to gas flow is friction, or drag, encountered in the respiratory passageways -the following equation gives the relationship between gas flow (F), pressure (P), and resistance (R): F= delta P / R -the factors determining gas flow in the respiratory passages and blood flow in the blood vessels are equivalent -the amount of gas flowing into and out of the alveoli is directly proportional to delta P, the difference in pressure, or pressure gradient, between the external atmosphere and the alveoli -normally, very small differences in pressure produce large changes in gas flow -the average pressure gradient during normal quiet breathing is 2 mm Hg or less, and yet it is sufficient to move 500 ml of air in and out of the lungs with each breath -but, as the equation also indicates, gas flow changes inversely with resistance -gas flow decreases as resistance increase -resistance in the respiratory tree is determined mostly by the diameters of the conducting tubes however, airway resistance is insignificant for two reasons: -airway diameters in the first part of the conducting zone are huge, relative to the low viscosity of air -as the airways get progressively smaller, there are progressively more branches. as a result, although individual bronchioles are tiny, there is an enormous number of them in parallel, so the total cross-sectional area is huge -the greater resistance to gas flow occurs in the medium-sized bronchi -at the terminal bronchioles, gas flow stops and diffusion takes over as the main force driving gas movement, so resistance is no longer an issue

obstructive sleep apnea

-the most common kind -is caused by collapse of the upper airway -this occurs because the muscles of the pharynx relax during sleep, which allows the soft tissues of the pharynx to sag and obstruct the airway -is more common in men and is made worse by obesity

cystic fibrosis (CF)

-the most common lethal genetic disease in North America, strikes in one out of every 3000 births -abnormally viscous mucus clogs the respiratory passages, providing a breeding ground for airborne bacteria and predisposing the child to respiratory infections -at the root of _______ ______ is a faulty gene that codes for the CFTR (cystic fibrosis transmembrane conductance regulator) protein -the normal CFTR protein works as a membrane channel to control Cl- flow in and out of cells -in one common mutation, CFTR lacks a critical amino acid and so does not fold correctly -as a result, it gets stuck in the endoplasmic reticulum, is marked for degradation, and never reaches the plasma membrane to perform its normal role -consequently, less Cl- is secreted and less water follows, resulting in the thick mucus typical of CF -this thick mucus forms a perfect harbor for bacterial infection -by early childhood, 80% of patients are colonized by pseudomonas aeruginosa, which cause chronic inflammation and triggers the disabled cells to churn out a thick sludge of abnormal mucus -repeated cycles of infection and inflammation eventually result in extensive tissue damage that can be treated only by a lung transplant -defects in the CFTR protein can affect other organ systems too -the ducts of the pancreas become clogged with secretions, impairing food digestion -obstructed reproductive ducts render 97% of males with CF infertile -characteristically, sweat glands of CF patients produce extremely salty perspiration

influence of PO2 on hemoglobin saturation

-the oxygen-hemoglobin dissociation curves shows how local PO2 controls oxygen loading and unloading from hemoglobin -under normal resting conditions (PO2=100 mm Hg), arterial blood hemoglobin is 98% saturated, and 100 ml of systemic arterial blood contains about 20 ml of O2 -this oxygen content of arterial blood is written as 20 vol % -as arterial blood flows through systemic capillaries, it releases about 5 ml of O2 per 100 ml of blood, yielding an Hb saturation of 75% and an O2 content of 15 vol % in venous blood -this means that substantial amounts of O2 are normally still available in venous blood (the venous reserve) which can be used if needed -the nearly complete saturation of Hb in arterial blood explains why breathing deeply increases both the alveolar and arterial blood PO2 but causes very little increase in the O2 saturation of hemoglobin -remember, PO2 measurements indicate only the amount of O2 dissolved in plasma, not the amount bound to hemoglobin -however, PO2 values are a good index of lung function, and when arterial PO2 is significantly less than alveolar PO2, some degree of respiratory impairment exists

gross anatomy of the lungs

-the paired lungs occupy all of the thoracic cavity except the mediastinum, which houses the heart, great blood vessels, bronchi, esophagus, and other organs -each cone-shaped lung is surrounded by pleurae and connected to the mediastinum by vascular and bronchial attachments, collectively called the lung root -the anterior, lateral, and posterior lung surfaces lie in close contact with the ribs and form the continuously curving costal surface -just deep to the clavicle is the apex, the narrow superior tip of the lung. the concave, inferior surface that rests on the diaphragm is the base -on the mediastinal surface of each lung is an indentation, the hilum, through which pulmonary and systemic blood vessels, bronchi, lymphatic vessels, and nerves enter and leave the lungs -each main bronchus plunges into the hilum on its own side and begins to branch almost immediately -all conducting and respiratory passageways distal to the main bronchi are found in the lungs -the two lungs differ slightly in shape and size because the apex of the heart is slightly to the left of the median plane -the left lung is smaller than the right, and the cardiac notch-a concavity in its medial aspect-- is molded to and accommodates the heart -the left lung is subdivided into superior and inferior lobes by the oblique fissure, whereas the right lung is partitioned into superior, middle, and inferior lobes by the oblique and horizontal fissures

influence of PO2

-the peripheral chemoreceptors--found in the aortic bodies of the aortic arch and in the carotid bodies at the bifurcation of the common carotid arteries--contain cells sensitive to arterial O2 levels -the main oxygen sensors are in the carotid bodies -under normal conditions, declining PO2 has only a slight effect on ventilation, mostly limited to enhancing the sensitivity of peripheral receptors to increased PCO2 -arterial PO2 must drop substantially, to at least 50 mm Hg, before O2 levels become a major stimulus for increased ventilation -there is a huge reservoir of O2 bound to Hb, and Hb remains almost entirely saturated unless or until the PO2 of alveolar gas and arterial blood falls below 60 mm Hg -the brain stem centers then begin to suffer from O2 starvation, and their activity is depressed -at the same time, the peripheral chemoreceptors become excited and stimulate the respiratory centers to increase ventilation, even if PCO2 is normal -in this way, the peripheral chemoreceptor system can maintain ventilation even though the brain stem centers are depressed by hypoxia

pneumothorax

-the presence of air in the pleura cavity is referred to as a _______ and is reversed by drawing air out of the intrapleural space with chest tubes -this procedure allows the pleurae to heal and the lung to reinflate and resume normal function

developmental aspects of the respiratory system (continued)

-the respiratory rate is highest in newborn infants (40-80 breaths/min) -at five years of age, it is around 25 per minute, and in adults, it is between 12 and 16 per minute. in old age, the rate often increases again -at birth, only about one-sixth of the final number of alveoli are present - the lungs continue to mature and form more alveoli until young adulthood -however, if a person begins smoking in the early teens, the lungs never completely mature, and those additional alveoli are lost forever -in infants, the ribs take a nearly horizontal course -for this reason, infants rely almost entirely on descent of the diaphragm to increase thoracic volume for inspiration -by the second year, the ribs are more obliquely positioned, and the adult form of breathing is established -the maximum amount of oxygen we can use during aerobic metabolism, VO2max, declines about 9% per decade in inactive people beginning in their mid-20s -in those who remain active, VO2max still declines but much less -as we age, the thoracic wall becomes more rigid and the lungs gradually lose their elasticity, decreasing the ability to ventilate the lungs -vital capacity declines by about one-third by age 70 -blood O2 levels decline slightly, and many elderly people tend to become hypoxic during sleep -sleep apnea becomes more common

conducting zone structures

-the trachea divides to form the right and left main (primary) bronchi approximately at the level of T7 in an erect (standing) person -each bronchus runs obliquely in the mediastinum before plunging into the medial depression (hilum) of its lung -the right main bronchus is wider, shorter, and more vertical than the left. it is more common for an inhaled foreign object to get stuck there. -once inside the lungs, each main bronchus subdivides into lobar (secondary) bronchi-- three on the right and two on the left-- each supplying one lung lobe -the lobar bronchi branch into third-order segmental (tertiary) bronchi, which divide repeatedly into smaller bronchi -passageways smaller than 1 mm in diameter are called bronchioles and the tiniest of these, the terminal bronchioles, are less than 0.5 mm in diameter

the inflation reflex

-the visceral pleurae and conducting passages in the lungs contain numerous stretch receptors that are vigorously stimulated when the lungs are inflated -these receptors signal the medullary respiratory centers via afferent fibers of the vagus nerves, sending inhibitory impulses that end inspiration and allow expiration to occur -as the lungs recoil, the stretch receptors become quiet, and inspiration is initiated once again -this reflex, called the ________ _______, or hering-breuer reflex, is thought to be more a protective response (to prevent the lungs from being stretched excessively) than a normal regulatory mechanism

influence of CO2 on blood pH

-typically, the H+ released during carbonic acid dissociation is buffered by Hb or other proteins within the RBCs or in plasma -the HCO3- generated in the RBCs diffuses into the plasma, where it acts as the alkaline reserve (weak base) part of the blood's bicarbonate buffer system -the bicarbonate buffer system is very important in resisting shifts in blood pH -for example, if the hydrogen ion concentration in blood begins to rise, excess H+ is removed by combining with HCO3- to form carbonic acid (a weak acid) -if H+ concentration in blood drops below desirable levels, carbonic acid dissociates, releasing hydrogen ions and lowering the pH again -changes in respiratory rate or depth can alter blood pH dramatically by altering the amount of carbonic acid in blood -slow, shallow breathing allows CO2 to accumulate in blood -as a result, carbonic acid levels increase and blood pH drops -conversely, rapid, deep breathing quickly flushes CO2 out of blood, reducing carbonic levels and increasing blood pH -in this way, respiratory ventilation provides a fast-acting system to adjust blood pH (and PCO2) when it is disturbed by metabolic factors -respiratory adjustments play a major role in the acid-base balance of the blood

sphincter functions of the larynx

-under certain conditions, the vocal folds act as a sphincter that prevents air passage -during abdominal straining associated with defecation, the glottis closes to prevent exhalation and the abdominal muscles contract, causing the intra-abdominal pressure to rise -these events, known as the valsalva maneuver, help empty the rectum and can also splint (stabilize) the body trunk when lifting a heavy load

dorsal respiratory group (DRG)

-until recently, it was thought that the DRG acts as an inspiratory center, performing many of the tasks now known to be performed by the VRG -in almost all mammals, including humans, the DRG integrates input from peripheral stretch and chemoreceptors and communicates this info to the VRG

sinus headache

-when mucus or infectious materials block the passageways connecting the sinuses to the nasal cavity, the pressure within the sinuses may no longer be the same as atmospheric pressure -a change in pressure can result in a ________ ______

acclimatization

-when you move on a long-term basis from sea level to the mountains, your body makes respiratory and hematopoietic adjustments via an adaptive response called ______- -decreases in arterial PO2 cause the peripheral chemoreceptors to become more responsive to increases in PCO2, and a substantial decline in PO2 directly stimulates them -as a result, ventilation increases as the brain attempts to restore gas exchange -increased ventilation also reduces arterial CO2 levels, so the PCO2 of individuals living at high altitudes is typically below 40 mm Hg (its value at sea level)

trachea

-windpipe, descends from the larynx through the neck and into the mediastinum -it ends by dividing into the main bronchi at mid thorax -it is about 4 inches long and 3/4 inch in diameter, and is very flexible and mobile -its wall consists of several layers that are common to many tubular body organs-- the mucosa, submucosa, and adventitia-- plus a layer of hyaline cartilage -the mucosa has the same goblet cell-containing pseudo stratified epithelium that occurs throughout most of the respiratory tract -its cilia continually propel debris-laden mucus toward the pharynx -this epithelium rests on a fairly thick lamina propria that has a rich supply of elastic fibers -smoking inhibits and ultimately destroys cilia. without ciliary activity, coughing is the only way to prevent mucus from accumulating in the lungs -the submucosa, a connective tissue layer deep to the mucosa, contains seromucus glands that help produce the mucus "sheets" within the trachea -the submucosa is supported by 16 to 20 C-shaped rings of hyaline cartilage encased by the adventitia, the outermost layer of connective tissue -the trachea's elastic elements make it flexible enough to stretch and move inferiorly during inspiration and recoil during expiration, but the cartilage rings prevent it from collapsing and keep the airway patent despite the pressure changes that occur during breathing -the open posterior parts of the cartilage rings which lie next to the esophagus are connected by smooth muscle fibers of the trachealis and by soft connective tissue -because this portion of the tracheal wall is flexible, the esophagus can expand anteriorly as swallowed food passes through it -contraction of the trachealis decreases the trachea's diameter, causing expired air to rush upward from the lungs with greater force -this action helps expel mucus from the trachea when we cough -the last tracheal cartilage is expanded, and a spar of cartilage, called the carina, projects posteriorly from its inner face, marking the point where the trachea branches into the two main bronchi -the mucosa of the carina is highly sensitive, and violent coughing is triggered when a foreign object makes contact with it -by the time incoming air reaches the end of the trachea, it is warm, cleansed of most impurities, and saturated with water vapor