Chapter 22: The Respiratory System
The two anatomical divisions of the respiratory system are:
upper respiratory tract and lower respiratory tract
Paired and unpaired cartilages cont.
iv. Arytenoid cartilages - two small pieces of hyaline cartilage which articulate with the superior surface of the cricoid cartilage and help to anchor the vocal cords. v. Cuneiform cartilages - two long, curved pieces of hyaline cartilage; they lie within the folds of tissue that extend between the lateral surface of each arytenoid cartilage and the epiglottis. vi. Corniculate cartilages - two small pieces of hyaline cartilage that articulate with the arytenoid cartilages to function in the opening and closing of the glottis and the production of sound.
Lower respiratory tract consists of
larynx, trachea, bronchial tree, lungs
Upper respiratory tract consists of
nose, nasal cavity, paranasal sinuses, pharynx
c. Tertiary bronchi - each secondary bronchus branches to form tertiary bronchi. The cartilage begins to shrink forming cartilage plates rather than C-shaped rings.
d. Each tertiary bronchus delivers air to a single bronchopulmonary segment and branches repeatedly to give rise to microscopic passageways called bronchioles. i. The terminal bronchioles (which may number as many as 6500) are the LAST branch of the conducting zone and supply a single pulmonary lobule. ii. While the respiratory bronchioles are the FIRST branch of the respiratory zone that extend within the pulmonary lobule and terminate into many tiny alveoli. Respiratory bronchioles open into regions called alveolar ducts which connect many individual alveoli forming an alveolar sac. iii. As cartilage progressively disappears in the bronchioles, smooth muscle increases. Changes in the contraction of this thick muscle layer causes bronchodilation and bronchoconstriction.
Nasal cavity cont.
e. Concha - bony ridges that project towards the nasal septum from the lateral walls of the nasal cavity. There are three conchae: superior, inferior, and middle nasal concha. These create turbulence to help swirl the air so that small, airborne particulate will bump into the mucus-lined walls, trapping it so that it doesn't move further into the respiratory tract. f. Meatuses - as air passes from the external nares to the internal nares, air flows between the adjacent concha, through the superior, middle, and inferior meatuses. g. Internal nares - distinguishes the end of the nasal cavity and the beginning of the pharynx. h. Lined with pseudostratified columnar epithelium which not only secretes mucus but also secretes antimicrobial substances such as defensins and lysozymes which kill potential pathogens.
. Vestibular and Vocal Ligaments - bands of connective tissue that extend between the thyroid cartilage and arytenoid cartilages.
i. Vocal folds - which house the vocal ligaments, lie inferior to the vestibular folds. The vocal folds vibrate as air passes over them and are therefore involved with the production of sound and are also known as the vocal cords or true vocal cords. ii. Vestibular folds - house a relatively inelastic pair of vestibular ligaments that are not associated with sound production. Instead, these folds help prevent foreign objects from entering the glottis and contacting the more delicate vocal folds. Also known as the false vocal cords.
All of the upper and most of the lower respiratory tract make up the conducting zone
That is, they are for the purposes of transporting the air only. The last part of the lower respiratory tract, however, is designed for gas exchange and is therefore called the respiratory zone. The respiratory zone includes the smallest, most delicate branches of the respiratory tree called the respiratory bronchioles and their associated air-filled pockets called the alveoli.
Lower respiratory tract
(LRT) conducts air to and from the gas exchange surfaces and includes: larynx, trachea, bronchi, bronchioles and alveoli.
Upper respiratory tract
- (URT) filters, warms, and humidifies incoming air which protects the more delicate surfaces of the lower respiratory system and reabsorbs heat and water from the outgoing air. Includes the following: nose, nasal cavity, paranasal sinuses, and pharynx
C. High Altitude Effects An increase in altitude results in a decrease in atmospheric pressure. Although the proportion of oxygen relative to gases in the atmosphere remains at 21 percent, its partial pressure decreases. As a result, it is more difficult for a body to achieve the same level of oxygen saturation at high altitude than at low altitude, due to lower atmospheric pressure. In fact, hemoglobin saturation is lower at high altitudes compared to hemoglobin saturation at sea level.
1. Acute mountain sickness (AMS), or altitude sickness, - a condition that results from acute exposure to high altitudes due to a low partial pressure of oxygen at high altitudes. 2. Acclimatization - the process of adjustment that the respiratory system makes due to chronic exposure to a high altitude.
22.2 LUNGS A. Gross Anatomy of the lungs - paired organs of the thoracic cavity composed of approximately 150 million alveoli each giving the lungs a spongy appearance and texture.
1. Apex and base - the apex of the lungs is the narrow pointed region at the top while the base is the wide region at the bottom in contact with the diaphragm. 2. Right lung - composed of three lobes: a superior, middle and inferior lobe divided by two fissures: horizontal fissure divides superior from middle lobe and the oblique fissure divides middle lobe from the inferior lobe. 3. Left lung - composed of only two lobes: a superior and inferior lobe divided by a single fissure: the oblique fissure. The left lung also possesses the cardiac notch which is a curvature that allows for the heart to tilt to the left of the midline.
B. Carbon dioxide transport
1. Approximately 93% of carbon dioxide that enters the blood from the tissues diffuses into RBCs. a. Of this, roughly 23% of the carbon dioxide binds to the amino acids in the globular proteins of the hemoglobin molecules forming carbaminohemoglobin. (HbCO2). b. The remaining 70% is converted to carbonic acid by the enzyme carbonic anhydrase which immediately disassociates into a hydrogen ion (H+) and a bicarbonate ion (HCO3-). The HCO3- then diffuses out of the RBC and into the blood plasma with the aid of a countertransport mechanism that exchanges intracellular bicarbonate ions for extracellular chloride ions (Cl-). This exchange is known as the chloride shift. 2. Approximately 7% of carbon dioxide is dissolved in blood plasma.
22.4 Transport of Gasses A. Oxygen transport in the blood
1. Approximately 98-99% of oxygen in blood is transported bound to hemoglobin within red blood cells as oxyhemoglobin (HbO2). 2. The remaining 1-2% of oxygen in blood is dissolved in the blood plasma. 3. There are several factors affecting the amount of oxygen bound to hemoglobin, or rather, the hemoglobin saturation. a. PO2 - as the partial pressure of oxygen increases, the percent hemoglobin saturation increases. b. PCO2 - as the partial pressure of carbon dioxide increases, the percent hemoglobin saturation decreases. c. pH - as pH decreases (more acidic), the percent of hemoglobin saturation decreases. The relationship between pH and hemoglobin saturation is known as the Bohr Effect. d. Temperature - as temperature increase, the percent of hemoglobin saturation decreases.
C. Factors affecting Pulmonary Ventilation:
1. Compliance - an indication of their expandability or stretch. The greater the compliance, the lower the tension in the walls of the lungs at a given volume, and the more easily air flows along the conducting passages. The lower the compliance, the greater tension in the walls of the lungs at a given volume, and the less easily air flows along the conducting passages. 2. Resistance - an indication of how much force is required to inflate and deflate the lungs. At rest, the muscular activity involved in pulmonary ventilation accounts for 3-5% of the resting energy demand. The higher the resistance, the harder it is to force air along the conducting passages. The lower the resistance, the more easily air flows along the conducting passages. Regulated by bronchodilation and bronchoconstriction 3. Surface tension - the liquid keeping the respiratory membrane moist is primarily composed of water molecules and as such, has the tendency to form hydrogen bonds (i.e. cohesion or surface tension). Surfactant helps reduce this surface tension so that the lungs do not collapse on themselves.
B. Although we use mmHg to report gas pressures, other units are also used in clinical practice:
1. Millimeters of mercury (mmHg): The most common unit for reporting blood pressure and gas pressure. Normal atmospheric pressure at sea level is about 760 mmHg. 2. Torr: this unit of measurement is preferred primarily by respiratory therapists; also commonly used in Europe and in some technical journals. One torr is equivalent to 1 mmHg. 3. Centimeters of water (cmH20): in hospital settings, anesthetic gas pressures and oxygen pressures are commonly measured in centimeters of water. One cmH2O is equivalent to 0.735 mmHg; normal atmospheric pressure is 1033.6 cmH2O. 4. Pounds per square inch (psi): pressure of a compressed gas cylinder and other industrial applications are generally reported in psi. Normal atmospheric pressure at sea level is approximately 15 psi.
Summary of the Changing Respiratory Mucosa:
1. Nasal cavity: the respiratory mucosa is composed of pseudostratified columnar epithelium with numerous goblet cells to secrete mucus. The cilia and mucus create a mucus escalator that sweeps debris forward towards the external nares resulting in boogers. 2. Pharynx: the nasopharynx, like the nasal cavity is lined with pseudostratified columnar epithelium but the oropharynx and laryngopharynx (because these are a common passageway for air and food) is lined with stratified squamous for protection against abrasion and chemical attack. 3. Larynx, trachea, and most of the bronchial tree: because these are passageways for only the transport of gases, the pseudostratified columnar epithelium resumes. Like the nose, the mucus escalator sweeps inhaled debris and microorganisms toward the pharynx, where they will be swallowed and exposed to the acids and enzymes of the stomach. By the time air reaches the respiratory zone, any particles greater than 5 m have been trapped and removed. Hyaline cartilage is abundant. 4. Respiratory bronchioles: in these finer bronchioles, the epithelium becomes shorter forming simple cuboidal epithelium and the cilia disappear. Hyaline cartilage gone. 5. Alveoli: the gas exchange surfaces are composed primarily of simple squamous epithelium. The distance between the air in the air alveoli and blood in the adjacent capillaries is generally less than 1m.
Pleura membranes -serous membrane forming two distinct layers:
1. Parietal pleura - serous membrane that lines the interior of the thoracic cavity and extends over the diaphragm and mediastinum. 2. Visceral pleura - serous membrane that lines the external surface of the lungs. 3. Pleural cavity and pleural fluid - the space between the parietal and visceral pleura. The pleural cavity contains a small volume of pleural fluid that coats the pleural surfaces and reduces frictions.
What are the functions of the Respiratory System?
1. Provide an extensive surface area for gas exchange between air and the circulating blood. 2. Moving air to and from the exchange surfaces of the lungs along the respiratory passageways. 3. Protecting respiratory surfaces from dehydration, temperature changes, or other environmental variations, and defending the respiratory system and other tissues from invasion by pathogens. 4. Producing sounds involved in speaking, singing, and other forms of communication. 5. Facilitating the detection of olfactory stimuli by olfactory receptors in the superior portions of the nasal cavity.
B. Respiration can be subdivided into three basic components:
1. Pulmonary ventilation - moving air into and out of the respiratory tract; inhalation and exhalation; the exchange between the atmosphere and the lungs. More simply referred to as "breathing". 2. External respiration - the exchange of gases between the lungs and the blood. Oxygen moves from the lungs into the blood while carbon dioxide moves from the blood into the lungs. 3. Internal respiration - the exchange of gases between the blood and the tissues. Oxygen moves from the blood to the tissues while carbon dioxide moves from the tissues into the blood.
F. Control of Respiration involves interacting mechanisms of the brain stem, higher brain centers, baroreceptors, chemoreceptors, and stretch receptors.
1. Respiratory rhythmicity centers - located with the medulla oblongata and serve as the pacemaker to establish the basic pace of breathing. a. Dorsal respiratory group (DRG) - contains the neurons that control lower motor neurons innervating the primary inspiratory muscles (the external intercostal muscles and the diaphragm). This center functions in every respiratory cycle and is therefore called the pacemaker. b. Ventral respiratory group (VRG) - has inspiratory and expiratory centers that function only when ventilation demands increase and accessory respiratory muscles are needed.
22.4 Gas Exchange A. Gas diffusion depends on the partial pressures and solubility of gases.
1. The partial pressure (P) of a gas is the pressure contributed by a single gas in a mixture of gases. Represented as PO2 or PCO2. 2. The principles that govern the movement and diffusion of gas molecules are relatively straightforward. These principles are known as the gas laws and include Boyle's Law (already mentioned), Dalton's Law, and Henry's Law. a. Boyle's Law - the volume (V) of a gas is inversely proportional to its pressure (P). As the gas volume increases, its pressure decreases. b. Henry's Law - at a given temperature, the amount of a particular gas in solution is directly proportional to the partial pressure of that gas. As the concentration of a gas increases, its partial pressure increases. c. Dalton's Law - the sum of all the partial pressures equals the total pressure exerted by a gas mixture.
E. Pulmonary ventilation must be closely regulated to meet the tissue's demand for oxygen.
1. The respiratory system adjusts pulmonary ventilation to meet oxygen demands during changing activities. These adjustments involve varying the number of breaths per minute and the amount of air moved per breath. 2. Respiratory rate (f) - the number of breaths you take each minute. The normal respiratory rate of a resting adult ranges from 12 to 18 breaths per minute. Children breathe more rapidly, at rates of about 18 to 20 breaths per minute. 3. Respiratory minute volume (VE) - the amount of air moved per minute. Calculated by multiplying the number of breaths per minute times the tidal volume. VE = f X VT For example, if f = 12 per minute and VT = 500 mL, then VE = 12 X 500 mL = 6000 mL 4. Alveolar ventilation (VA) - the amount of air reaching the alveoli each minute. The alveolar ventilation is less than the respiratory minute volume, because some of the air never reaches the alveoli, but instead, remains in the conduction zone of the lungs and bronchial tree. This is known as anatomical dead space (VD) and at rest it amounts to roughly 150 mL of the 500 mL of tidal air not reaching the alveoli. Alveolar ventilation (VA) is calculated by: VA = f X (VT - VD). For example, if f = 12 per minute, VT = 500 mL, and VD = 150 mL, then VA = 12 (500 mL - 150 mL) = 4200 mL. 5. If the respiratory rate jumps to 20 per minute but the tidal volume drops to 300 mL, the respiratory minute volume will remain unchanged BUT the alveolar ventilation rate drops from 4200 mL per minute to 3000 mL per minute and widespread hypoxia can occur.
D. Pulmonary Volumes and Capacities
1. Tidal volume (VT) - the amount of air moved into the lungs during inhalation and out of the lungs during exhalation. The tidal volume is approximately 500 mL. 2. Inspiratory reserve volume (IRV) - the amount of air that can be forcibly inhaled after a normal tidal volume inhalation. Inspiratory reserve volume ranges from 1900 to 3300 mL. 3. Expiratory reserve volume (ERV) - the amount of air that can be forcibly exhaled after a normal tidal volume exhalation. Expiratory volume ranges from 700 to 1000 mL. 4. Residual volume (RV) - the amount of air that remains in your lungs even after a forcible exhalation. The residual volume ranges from 1100 to 1200 mL. 5. Minimal volume - a component of the residual volume, is the amount of air that would remain in your lungs if they were allowed to collapse. The minimal volume ranges from 30 to 120 mL.
ALVEOLAR EPITHELIUM - primarily a simple squamous epithelium.
1. Type I pneumocytes - the simple squamous cells that form the wall of each alveolus and serve as the respiratory membrane. 2. Type II pneumocytes - simple cuboidal cells scattered among the squamous cells; produce surfactant - an oily secretion that disrupts surface tension and prevents the collapse of the alveoli. A collapsed lung is called atelectasis. 3. Alveolar macrophages - patrols the epithelial surfaces, phagocytizing any particulate that has eluded other respiratory defenses and reached the alveolar surfaces. 4. Pulmonary capillaries: differ functionally from other capillaries: they dilate when alveolar oxygen levels are high, and constrict when alveolar oxygen levels are low. This response directs blood flow to the alveoli containing the most oxygen. 5. Respiratory membrane - the simple squamous epithelium of the alveoli plus the simple squamous of the pulmonary capillaries plus the basal lamina connecting the two. Diffusion across the respiratory membrane proceeds very rapidly because the distance is short and both oxygen and carbon dioxide are lipid soluble. The total distance separating alveolar air from blood can be as little as 0.1 m; it averages about 0.5 m. The respiratory membrane forms an air-blood barrier.
Embryotic timeline cont.
3. Weeks 16-24: Once the respiratory bronchioles form, further development includes extensive vascularization, or the development of the blood vessels, as well as the formation of alveolar ducts and alveolar precursors. At about week 19, the respiratory bronchioles have formed. In addition, cells lining the respiratory structures begin to differentiate to form type I and type II pneumocytes. Once type II cells have differentiated, they begin to secrete small amounts of pulmonary surfactant. Around week 20, fetal breathing movements may begin. 4. Weeks 24-Term: Major growth and maturation of the respiratory system occurs from week 24 until term. More alveolar precursors develop, and larger amounts of pulmonary surfactant are produced. Surfactant levels are not generally adequate to create effective lung compliance until about the eighth month of pregnancy. The respiratory system continues to expand, and the surfaces that will form the respiratory membrane develop further. At this point, pulmonary capillaries have formed and continue to expand, creating a large surface area for gas exchange. The major milestone of respiratory development occurs at around week 28, when sufficient alveolar precursors have matured so that a baby born prematurely at this time can usually breathe on its own. However, alveoli continue to develop and mature into childhood. A full complement of functional alveoli does not appear until around 8 years of age.
2. Apneustic and Pneumotaxic centers - located within the pons; paired nuclei that adjust the output of the respiratory rhythmicity centers. a. Apneustic centers - promotes inhalation by stimulating the DRG. During forced breathing, the apneustic centers adjust the degree of stimulation in response to sensory information from the vagus nerve concerning the amount of lung inflation. b. Pneumotaxic centers - inhibit the apneustic centers and thereby promote passive or active exhalation. 3. Higher brain centers - located within the cerebral cortex, limbic system and hypothalamus; alter the activity of the Pneumotaxic centers but essentially normal respiratory cycles continue even if the brain stem superior to the pons has been severely damaged.
4. Baroreceptors, chemoreceptors, and stretch receptors: a. Chemoreceptors sensitive to the pH, PO2, or PCO2 of the blood or cerebrospinal fluid alter the activities of the respiratory centers. b. Baroreceptors in the aortic arch or carotid sinuses sensitive to changes in blood pressure alter the activities of the respiratory centers. c. Stretch receptors that respond to changes in the volume of the lungs are responsible for inflation and deflation reflexes. d. Protective reflexes are triggered with an irritating physical or chemical stimuli are present within the nasal cavity, larynx, or bronchial tree; initiates coughing or sneezing.
anatomy of lungs cont.
4. Pulmonary hilum - an indention in each lung which allows for the passage of the primary bronchi, pulmonary blood vessels, nerves, and lymphatics into and out of the lungs. The root of the lung is a meshwork of dense connective tissue that fixes the position of the bronchi, major nerves, blood vessels, and lymphatic within the pulmonary hilum. 5. Pulmonary arteries and veins - the pulmonary arteries (blue) exit the right atrium of the heart and transport deoxygenated blood to the lungs; the pulmonary veins (red) leave the lungs and transport oxygenated blood to the left atrium. 6. Pulmonary surfaces - landmarks of the exterior surface of the lungs. a. Costal surface - the surface that faces the rib cage. b. Mediastinal surface - the surface that faces the mediastinum. c. Diaphragmatic surface - the surface that faces the diaphragm.
Pulmonary volumes and capacities cont.
6. Total Lung Capacity (TLC) - the volume of your lungs, the sum of all four respiratory volumes. TLC = IRV + VT + ERV + RV. Total lung capacity averages around 6000 mL in males and 4200 mL in females. 7. Vital Capacity (VC) = the maximum amount of air that you can move into or out of your lungs in a single respiratory cycle. VC = IRV + VT + ERV. The vital capacity ranges from 4000 to 4800 mL in males and 3000 to 4000 mL in females. 8. Inspiratory Capacity (IC) - maximum amount of air that can be inspired after a normal expiration. IC = IRV + VT A normal inspiratory capacity ranges from 2400 to 3800 mL. 9. Functional Residual Capacity (FRC) - the amount of air remaining in your lungs after you have completed a quiet respiratory cycle. FRC = ERV + RV. The functional residual capacity ranges between 1800 to 2200 mL.
Disorders of the Respiratory System
A. Chronic Obstructive Pulmonary Diseases (COPD) - a general term indicating a progressive disorder of the airways that restricts airflow and reduces alveolar ventilation. B. Asthma - respiratory passages are extremely sensitive to irritants resulting in constriction of the airways, inflammation and edema within the mucosa of the passageways, and accelerated mucus production. Can be caused by allergies, toxins, or exercise. C. Chronic bronchitis - a long-term inflammation and swelling of the bronchial lining, leading to overproduction of mucous secretions. The characteristic sign is frequent coughing with copious sputum production. Commonly related to cigarette smoking but also results from other environmental irritants. Often described as "blue bloater" as a result of the edema from heart failure and skin turning blue from lack of oxygenation.
22.4 Embryonic Development of the Respiratory System Begins at about week 4 of gestation. By week 28, enough alveoli have matured that a baby born prematurely at this time can usually breathe on its own. The respiratory system, however, is not fully developed until early childhood, when a full complement of mature alveoli is present.
A. Embryonic Timeline 1. Week 4 - Ectodermal tissue from the anterior head region invaginates posteriorly to form olfactory pits, which fuse with endodermal tissue of the developing pharynx. An olfactory pit enlarges to become the nasal cavity. The lung bud is a dome-shaped structure composed of tissue that bulges from the foregut. The foregut is endoderm just inferior to the pharyngeal pouches. The laryngotracheal bud forms from the longitudinal extension of the lung bud as development progresses. The portion of this structure nearest the pharynx becomes the trachea, whereas the distal end becomes more bulbous, forming bronchial buds. A bronchial bud will eventually become the bronchi and all other lower respiratory structures. 2. Weeks 7-16: Bronchial buds continue to branch as development progresses until all of the segmental bronchi have been formed. Beginning around week 13, the lumens of the bronchi begin to expand in diameter. By week 16, respiratory bronchioles form. The fetus now has all major lung structures involved in the airway.
22.4 Modifications in Respiratory Functions
A. Hyperpnea is an increased depth and rate of ventilation to meet an increase in oxygen demand as might be seen in exercise or disease, particularly diseases that target the respiratory or digestive tracts. This does not significantly alter blood oxygen or carbon dioxide levels, but merely increases the depth and rate of ventilation to meet the demand of the cells. B. Hyperventilation is an increased ventilation rate that is independent of the cellular oxygen needs and leads to abnormally low blood carbon dioxide levels and high (alkaline) blood pH.
B. Fetal Breathing -
Can be observed starting at 20-21 weeks of development. Fetal breathing movements involve muscle contractions that cause the inhalation of amniotic fluid and exhalation of the same fluid, with pulmonary surfactant and mucus.
Disorders of the Respiratory System
D. Emphysema - a chronic, progressive condition characterized by shortness of breath and an inability to tolerate physical exertion. The underlying problem is the destruction of alveolar surfaces and inadequate surface area for oxygen and carbon dioxide exchange. To compensate, the individual breathes more rapidly to maintain near normal oxygenation. Often described as "pink puffers". E. Laryngitis - inflammation of the vocal cords. F. Cystic Fibrosis - the most common lethal inherited disorder among Caucasians of Northern European descent. Causes an increase in mucus produced by the mucus membranes of the respiratory and digestive tracts. Within the lungs, the excess mucus inhibits gas exchanged and clogged respiratory passages. Frequency is 1 in 2500 births.
Disorders of the Respiratory System
G. Infant Respiratory Distress Syndrome - inadequate surfactant production in newborns or premature babies. Leads to increased surface tension and alveolar collapse. H. Pneumothorax - air within the intrapleural space resulting in an increased pressure on the outer surface of the lungs which can cause the lung to collapse. I. Atelectasis - collapsed lung. J. Pleurisy - inflammation of the pleural membranes. K. Apnea - a period in which respiration is suspended. Can be associated with sleep which is called sleep apnea. Also occurs as a reflex shortly before a sneeze or a cough. L. Dyspnea - difficult or labored breathing. M. Tuberculosis - an infectious disease caused by the bacterium Mycobacterium tuberculosis resulting in fibroid masses in the lungs and an increase in dead space. N. Pneumonia - a bacterial or viral infection of the lungs.
Disorders of the Respiratory System
O. Hypoxia - inadequate oxygen delivery to tissues. Three primary types: 1. Hypoxemic hypoxia - not enough oxygen in blood due to low oxygen concentrations within the air or due to reduced respiratory minute volume. Being in high altitudes or hypoventilation are examples. 2. Anemic hypoxia - not enough oxygen in blood due to low RBC counts or due to the inability of hemoglobin to bind oxygen. Blood loss or carbon monoxide poisoning are examples. 3. Ischemic hypoxia - adequate oxygen in blood but oxygen is not reaching the tissues due to reduced blood flow to the tissues. Heart failure or clogged blood vessels can cause ischemic hypoxia. 4. Histotoxic hypoxia - quantity of oxygen reaching the cells is normal, but the cells are unable to use the oxygen effectively, due to disabled oxidative phosphorylation enzymes. Cyanide poisoning is one example.
Disorders of the respiratory system
P. Lung cancer - now accounts for 12.6 percent of new cancer cases in both men and women and kills more people each year than colon, breast, and prostate cancer combined. Over 50% of lung cancer patients die within a year of diagnosis. Research has shown that 85-90% of all cases of lung cancer are the direct result of cigarette smoking. Life expectancy of a smoker is shorter than that of a non-smoker. Although some decrease in respiratory performance is inevitable, you can prevent serious respiratory deterioration by stopping smoking or never starting. 1. Dysplasia - cells are damaged and their functional characteristics change; smoking paralyzes the cilia of the pseudostratified columnar epithelium lining the respiratory passages and causes a local buildup of mucus. May be reversed. 2. Metaplasia - tissue changes its structure in response to injury or chemical stresses. The pseudostratified columnar changes to stratified epithelium. May be reversed. 3. Neoplasia or Anaplasia - abnormal cells form a cancerous tumor, the most dangerous stage where the cells become malignant and metastasize (spread) to other parts of the body. Not reversible but can be treated with chemicals, radiation, and/or surgery.
C. Birth -
Prior to birth, the lungs are filled with amniotic fluid, mucus, and surfactant. As the fetus is squeezed through the birth canal much of this fluid is expelled. The first inhalation occurs within 10 seconds after birth and not only serves as the first inspiration, but also acts to inflate the lungs. Pulmonary surfactant is critical for inflation to occur, as it reduces the surface tension of the alveoli. Preterm birth around 26 weeks frequently results in severe respiratory distress.
What is Respiration?
Respiration is defined as the exchange of gases (most notably oxygen and carbon dioxide) between the atmosphere, lungs, blood, and tissues
22.3 The Process of Breathing A. Pulmonary ventilation is driven by pressure changes within the pleural cavities. 1. Several different pressures must be considered:
a. Atmospheric pressure - the force exerted by the mixture of air surrounding the body; Normal atmospheric pressure at sea level is 760 mmHg. b. Alveolar pressure - also known as intrapulmonary pressure; the force exerted by the air within the alveoli of the lungs; this pressure rises and falls as the phases of breathing progress. c. Intrapleural pressure - the pressure within the pleural cavity; always 4 mmHg lower than the alveolar pressure so the alveoli will be able to inflate. If the pressure in the pleural cavity rises, it causes pneumothorax which can result in atelectasis. d. Boyle's Law - volume is inversely proportional to pressure. That is, as volume increase, pressure decreases. AND as volume decreases, pressure increase. If you reduce the volume of the thoracic cavity by half, the pressure within the thoracic cavity will double. If you double the volume of the thoracic cavity, the pressure within will decline by half.
1. NOSE - the primary passageway for air entering the respiratory when you are resting and breathing quietly.
a. Bridge of the nose is formed from the nasal bones (2) and is supported by the anterior portions of the nasal septum and nasal cartilages. b. Nasal septum - composed of the vomer and perpendicular plate of the ethmoid bone and divides the nasal cavity into a right and left portion. c. Nasal cartilages - small, hyaline cartilages that extend laterally from the bridge of the nose. These cartilages help to keep the external nares (nostrils) open and prevent their collapse during a strong inhalation. d. External nares - or nostrils, open into the nasal cavity.
2. TRACHEA - or "windpipe", is a tough, flexible tube that conducts air towards the lungs. It has a diameter of 2.5 cm and lies within the mediastinum.
a. Composed of three distinct layers: i. Mucosa - pseudostratified columnar epithelium containing numerous goblet cells and cilia to create the mucus escalator. ii. Submucosa - connective tissue region underlying the mucosa layer. Contains numerous exocrine glands that secrete mucus and blood vessels. iii. Adventitia - connective tissue layer that anchors the trachea to the surrounding tissues and helps to prevent overexpansion of the trachea.
4. Oxygen reversibly binds to hemoglobin. The affinity of oxygen to hemoglobin changes in the lungs to stimulate loading of oxygen onto hemoglobin while the tissues stimulate the unloading of oxygen from the hemoglobin so that it can diffuse from the blood and out to the tissues.
a. During external respiration - PO2 is high, PCO2 is low, pH is high, and temperature is low. All of these factors increase oxygen's affinity for hemoglobin and therefore oxygen loading occurs and hemoglobin saturation increases. b. During internal respiration - PO2 is low, PCO2 is high, pH is low, and temperature is high. All of these factors decrease oxygen's affinity for hemoglobin and therefore oxygen unloads from the hemoglobin and the hemoglobin saturation declines.
3. The partial pressures and solubility of gases affects gas exchange between the lungs and blood (external respiration) as well as the blood and tissues (internal respiration).
a. During external respiration - in the lungs, the PO2 is high (100 mmHg) and the PCO2 is low (40 mmHg) but in the blood, the PO2 is low (40 mmHg) and PCO2 is high (45 mmHg). Therefore oxygen is forced into the blood from the lungs and carbon dioxide is forced from the blood into the lungs. b. During internal respiration - in the blood, the PO2 is high (95 mmHg) and the PCO2 is low (40 mmHg) but in the tissues, the PO2 is low (40 mmHg) and PCO2 is high (45 mmHg). Therefore oxygen is forced out of the blood and into the tissues while carbon dioxide is forced from the tissues into the blood.
3. Air flows from an area of higher pressure to an area of lower pressure.
a. Inspiration = as the diaphragm contracts, it moves downward which increases the volume of the thoracic cavity. In turn, alveolar pressure decreases [758 mm Hg] which causes atmospheric air to be sucked into the lung spaces. b. Expiration = as the diaphragm relaxes, it moves upward which decreases the volume of the thoracic cavity. In turn, alveolar pressure increases [762 mm Hg] which causes air to be squeezed out of the lung spaces and into the atmosphere. c. A pressure differential of 0 mmHg exists when atmospheric and alveolar pressures are equal. Positive alveolar pressure will push air out of the lungs while negative alveolar pressure will pull air into the lungs.
2. The changes in alveolar pressure that occur with breathing are created by variations in the lung and thoracic volume. Respiratory muscles alter the volume of the thoracic cavity.
a. Inspiratory muscles - muscles used to control inhalation: i. Primary inspiratory muscles: contraction of the external intercostal muscles elevates the ribs which contributes about 25% to the volume of air in the lungs at rest. Contraction of the diaphragm flattens the floor of the thoracic cavity which is responsible for 75% of the air movement in normal breathing at rest. ii. Accessory inspiratory muscles: sternocleidomastoid muscles, scalene muscles, pectoralis minor muscles, and serratus anterior muscles. b. Expiratory muscles - the muscles used to control exhalation: i. Exhalation is a passive activity. Elastic forces and gravity are sufficient enough to reduce the volume of the lungs. ii. Accessory expiratory muscles: internal intercostal muscles, transverse thoracis muscles, external oblique muscles, rectus abdominus muscles, internal oblique muscles. These are used for forcible exhalations.
2. NASAL CAVITY - space between the external nares and the internal nares at the back of the nasal cavity. Lined with pseudostratified columnar epithelium.
a. Nasal vestibule - the space contained within the flexible tissues of the nose. Filled with coarse hairs called vibrissae that trap large airborne particles preventing them from entering the nasal cavity. b. Cribriform plate of the ethmoid bone - forms the roof of the nasal cavity. The tiny holes in the cribriform plate allow the olfactory bulbs to extend their neural fibers down into the nasal cavity for sensation of smell. c. Hard palate - forms the anterior portion of the floor of the nasal cavity; formed by the palatine process of the maxillae and the palatine bones. d. Soft palate - a membranous and muscular flap with attached reticular tissue called the uvula; forms the posterior portion of the floor of the nasal cavity. During swallowing the soft palate and uvula flex upward to block the nasal cavity.
PHARYNX - a chamber more commonly called the "throat," is shared by the digestive and respiratory tracts. The curving superior and posterior walls of the pharynx are closely bound to the axial skeleton, but the lateral walls are flexible and muscular. The pharynx is divided into three regions:
a. Nasopharynx - the superior portion of the pharynx located between the soft palate and the internal nares. Lined with pseudostratified columnar epithelium and houses the pharyngeal tonsils. b. Oropharynx - extends between the soft palate and the base of the tongue at the level of the hyoid bone. At the boundary between the nasopharynx and the oropharynx, the epithelial tissue changes from pseudostratified columnar to stratified squamous epithelium; this accommodates the movement of food through this region and protects against abrasion. Houses the palatine tonsils on either side of the fauces (archways formed by the soft palate and uvula) and the lingual tonsils attached to the back of the tongue. c. Laryngopharynx - includes that portion of the pharynx between the hyoid bone and the entrance to the larynx and esophagus. Like the oropharynx, the laryngopharynx is lined with stratified squamous epithelium.
1. LARYNX - a cartilaginous structure that surrounds and protects the glottis and is more commonly called the "voice box". Lined with pseudostratified columnar epithelium. Glottis - inhaled air leaves the pharynx and enters the larynx through a narrow opening called the glottis.
a. Paired and unpaired cartilages: i. Epiglottis - only piece formed of elastic cartilage forming a flexible flap that covers over the glottis during swallowing so that food cannot enter the respiratory passageways. ii. Thyroid cartilage - a large single piece of hyaline cartilage forms the anterior and lateral walls of the larynx. The prominent anterior surface which is more commonly called the "Adam's Apple" is known as the laryngeal prominence. The superior portion of the thyroid cartilage is connected to the hyoid bone by the thyrohyoid membrane. iii. Cricoid cartilage - a single piece of hyaline cartilage which has a greatly expanded posterior portion to provide support. Together the cricoid and thyroid cartilages protect the glottis and the entrance to the trachea, and their broad surfaces provide sites for the attachment of important muscles and ligaments.
3. BRONCHIAL TREE - the highly branching pattern of the bronchi and bronchioles as they approach and travel through the lungs.
a. Primary bronchi - at the site of carina, the trachea branches to form a right and left primary bronchus. The right primary bronchus transports air to and from the right lung while the left primary bronchus transports air to and from the left lung. b. Secondary bronchi - the right primary bronchus branches to form three secondary bronchi while the left primary bronchus branches to form two secondary bronchi.
b. Tracheal cartilages - 15 to 20 C-shaped rings of hyaline cartilage which stiffen the tracheal walls and protect the airway. The also prevent its collapse or overexpansion as pressure changes within the respiratory system.
c. Trachealis muscle - contraction of this smooth muscle reduces the diameter of the trachea which increases resistance to airflow. The diameter of the trachea changes from moment to moment. For example, sympathetic stimulation relaxes the trachealis muscle, increasing the diameter of the trachea and making it easier to move air along the respiratory passageways (such as during exercise). d. Site of Carina - at the bottom of the trachea; a triangular piece of cartilage that helps to support the branching of the trachea to form the primary bronchi.
paranasal sinuses
recall from AP I, the maxilla, frontal, ethmoid, and sphenoid bones have hollow, membrane-lined cavities called sinuses. The mucous secretions produced in these sinuses, aided by tears draining through the nasolacrimal ducts, keep the surfaces of the nasal cavity moist and clean.
