Anatomy & Physiology 2 - Respiratory System

Explain how each of the following affect pulmonary ventilation: bronchiolar smooth muscle contractions, lung and thoracic wall compliance and recoil, and pulmonary surfactant and alveolar surface tension.

Bronchiolar smooth muscle contractions: changes in resistance Lung and thoracic wall compliance and recoil: changes in resistance Pulmonary surfactant and alveolar surface tension: solution to surface tension of water ; surfactant disrupts H bonds

Compare and contrast the central and peripheral chemoreceptors.

Chemorecepters are receptors in the medulla and in the aortic and carotid bodies of the blood vessels that detect changes in blood pH and signal the medulla to correct those changes. Central chemoreceptors are located within the medulla, they are sensitive to the pH of their environment. Peripheral chemoreceptors The aoritic and carotid bodies, which act principally to detect variation of the oxygen concentration in the arterial blood, also monitor arterial carbon dioxide and pH.

Describe the four respiratory processes: ventilation, external respiration (gas exchange at lung), internal respiration (gas exchange at body tissues), and cellular respiration.

· Pulmonary ventilation (breathing): movement of air into and out of the lungs. · External respiration: Involves both bringing air into the lungs (inhalation) and releasing air to the atmosphere (exhalation). O2 and CO2 exchanged between the lungs and the blood. · Internal respiration: O2 and CO2 exchange between systemic blood vessels and tissues · Cellular respiration: refers to intracellular metabolic processes carried out within the mitochondria to produce ATP from nutrients, uses oxygen and produces carbon dioxide as a biproduct, does NOT use respiratory system

Define pulmonary ventilation, inspiration, and expiration.

· Pulmonary ventilation: Mechanical processes that depend on volume changes in the thoracic cavity. As the volume changes, the pressure changes and as the pressure changes, gases flow to equalize the pressure. · Inspiration: gases flow into the lungs · Expiration: gases flow out of the lungs

Describe the major functions of the respiratory system.

· area for gas exchange · move air to & from exchange surfaces · protect exchange surfaces · produce sound · assist in regulation of blood volume, pressure, and body pH

List and describe the major chemical and neural stimuli to the respiratory centers.

A chemoreceptor, also known as chemosensor, is a sensory receptor that transduces a chemical signal into an action potential. The action potential is sent along nerve pathways to parts of the brain, which are the integrating centers for this type of feedback. There are many types of chemoreceptors in the body, but only a few of them are involved in respiration. The respiratory chemoreceptors work by sensing the pH of their environment through the concentration of hydrogen ions. Because most carbon dioxide is converted to carbonic acid (and bicarbonate ) in the bloodstream, chemoreceptors are able to use blood pH as a way to measure the carbon dioxide levels of the bloodstream.

State Boyle's Law and relate this law to the specific sequence of events (muscle contractions/relaxations and pressure/volume changes) causing inspiration and expiration.

Boyle's law defines the relationship between the pressure and volume of a gas Pressure (P) varies inversely with volume (V): P1V1 = P2V2 During inspiration, Inspiratory muscles contract (diaphragm descends; rib cage rises) and the Thoracic cavity volume increases. The lungs are stretched and intrapulmonary volume increases. As the volume increases, the intrapulmonary pressure decreases (Ppul < Patm). The pressure decrease causes air to flow into the lungs until the pressure equalizes (Ppul = Patm). During expiration, Inspiratory muscles relax and the Thoracic cavity volume decreases. Elastic lungs recoil and intrapulmonary volume decreases. As the volume decreases, the pulmonary pressure rises (Ppul > Patm) causing air to flow out of the lungs until the pressure equalizes (Ppul = Patm).

Describe the forces that tend to collapse the lungs and those that normally oppose or prevent collapse.

Competing forces within the thorax cause the formation of the negative intrapleural pressure. One of these forces relates to the elasticity of the lungs themselves—elastic tissue pulls the lungs inward, away from the thoracic wall. Surface tension of alveolar fluid, which is mostly water, also creates an inward pull of the lung tissue. This inward tension from the lungs is countered by opposing forces from the pleural fluid and thoracic wall. Surface tension within the pleural cavity pulls the lungs outward. Too much or too little pleural fluid would hinder the creation of the negative intrapleural pressure; therefore, the level must be closely monitored by the mesothelial cells and drained by the lymphatic system. Since the parietal pleura is attached to the thoracic wall, the natural elasticity of the chest wall opposes the inward pull of the lungs. Ultimately, the outward pull is slightly greater than the inward pull, creating the -4 mm Hg intrapleural pressure.

State Dalton's Law and Henry's Law, and relate both laws to the events of external and internal respiration and to the amounts of oxygen and carbon dioxide dissolved in plasma

Daltons law: Total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas. The partial pressure of each gas is directly proportional to its percentage in the mixture Henry's law: When a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure With respect to external respiration, O2 diffuses because of large partial pressure difference across alveoli and blood, CO2 diffuses because it is highly soluble With respect to internal respiration ventilation must be sufficient to create a high partial pressure of O2 in the alveoli, there the CO2, O2 gas exchange can occur. O2 diffuses because of large partial pressure difference across alveoli and blood, CO2 diffuses because it is highly soluble

Define hyperventilation, hypoventilation, panting, eupnea, hyperpnea and apnea

Hyperventilation: ventilation in excess of metabolic demand; lowers the blood CO2 and raises blood pH Hypoventilation: reduced pulmonary ventilation; increased blood CO2 and decreases blood pH Panting - short, quick breaths Eupnea - relaxed quiet breathing Hyperpnea - increased rate and depth of breathing Apnea - temporary cessation of breathing

List, in order, the respiratory structures that air passes through during inspiration

Nasal cavity Pharynx Epiglottis Larynx Trachea Primary Bronchi Secondary Bronchi Tertiary Bronchi Terminal Bronchioles Respiratory Bronchioles Alveolar Ducts Alveolar Sacs

Identify the muscles used during quiet inspiration, during forced inspiration, and during forced expiration, as well as the nerves responsible for stimulating those muscles.

Quiet inspiration, also known as eupnea, is a mode of breathing that occurs at rest and does not require the cognitive thought of the individual. During quiet breathing, the diaphragm and external intercostals must contract. During forced breathing, other accessory muscles must contract in addition to the contraction of the diaphragm and intercostal muscles. During forced inspiration, muscles of the neck, including the scalenes, contract and lift the thoracic wall, increasing lung volume. During forced expiration, accessory muscles of the abdomen, including the obliques, contract, forcing abdominal organs upward against the diaphragm. This helps to push the diaphragm further into the thorax, pushing more air out. In addition, accessory muscles (primarily the internal intercostals) help to compress the rib cage, which also reduces the volume of the thoracic cavity

Describe and distinguish between the conducting and respiratory zones of the respiratory tract.

The conducting zone is a passageway for air to reach the lungs. It cleanses, humidifies, and warms incoming air such that fewer irritants reaching respiratory zone. The respiratory zone is site of gas exchange through respiratory bronchioles, alveolar ducts, and alveoli (including microscopic structures).

Describe and distinguish between the upper and lower respiratory tracts

The upper respiratory tract includes the nose, nasal cavity, sinuses, pharynx, larynx, and the upper portion of the trachea. The lower respiratory tract consists of the lower portion of the trachea, the bronchial tree, and the lungs The main difference between upper and lower respiratory tract is that upper respiratory tract is mainly involved in the conduction of air to the bottom parts whereas lower respiratory tract is mainly involved in the gas exchange.

Define the respiratory volumes (IRV, TV, ERV, and RV) and the respiratory capacities (IC, FRC, VC, and TLC).

Tidal Volume: Amount of air inhaled or exhaled with each breath under resting conditions (Average Values - Adult Male: 500 ml, Adult Female: 500 ml) Inspiratory reserve volume (IRV): Amount of air that can be forcefully inhaled after a normal tidal volume inhalation (Average Value - Adult Male: 3100 ml, Adult Female: 1900 ml) Inspiratory reserve volume (IRV): Amount of air that can be forcefully exhaled after a normal tidal volume exhalation (Average Value - Adult Male: 1200 ml, Adult Female: 700 ml) Residual volume (RV): Amount of air remaining in the lungs after a forced exhalation (Average Value - Adult Male: 1200 ml, Adult Female: 1100 ml) Total lung capacity (TLC): Maximum amount of air contained in lungs after a maximum inspiratory effort: TLC = TV + IRV + ERV + RV (Average Values - Adult Male: 6000 ml, Adult Female: 4200 ml) Vital capacity (VC): Maximum amount of air that can be expired after a maximum inspiratory effort: VC = TV + IRV + ERV (Average Values - Adult Male: 4800 ml, Adult Female: 3100 ml) Inspiratory capacity (IC): Maximum amount of air that can be inspired after a normal expiration: IC = TV + IRV (Average Values - Adult Male: 3600 ml, Adult Female: 2400 ml) Functional residual capacity (FRC): Volume of air remaining in the lungs after a normal tidal volume expiration: FRC = ERV + RV (Average Values - Adult Male: 2400 ml, Adult Female: 1800 ml)

Describe the locations and functions of the brainstem respiratory centers.

Ventral Respiratory group (VRG): · Rhythm-generating and integrative center · Sets eupnea (12-15 breaths/minute). · Inspiratory neurons excite the inspiratory muscles via the phrenic and intercostal nerves. · Expiratory neurons inhibit the inspiratory neurons. · Located in the nucleus of the Medulla. Dorsal Respiratory Group (DRG): · Modifies rhythm of VRG. · Near the root of cranial nerve IX · Integrates input from peripheral stretch and chemoreceptors Pontine Respiratory Group (PRG): · modifies rhythm of VRG; Receives input from higher brain centers:-hypothalamus, limbic system, cerebral corte · Issues output to both DRG and VRG · Hastens or delays transition from inspiration to expiration; Sleep, exercise, vocalization, and emotional responses

With respect to the oxygen-hemoglobin saturation curve: a. Interpret the curve at low and high partial pressures of oxygen. b. List factors that shift the curve down and to the right, and explain how this results in increased oxygen delivery to the tissues. c. List factors that shift the curve up and to the left, and explain how this facilitates oxygen binding to hemoglobin in the lungs. d. Describe the oxygen-fetal hemoglobin saturation curve and its impact on oxygen delivery to fetal tissues.

a. At high PO2, large changes in PO2 cause small changes in Hb saturation (the cure is relatively flat). This is effectively a safety margin that ensures Hb remains nearly saturated even with large changes in PO2. At low PO2, large changes in PO2 cause large changes in Hb (the curve is steep). Tissues other than lungs have low PO2 because they consume O2. Hb's properties ensure that oxygen is delivered when it is needed most. When tissues need more they get more. b. An increase in temperature, PCO2, H+, or BPG levels in blood lowers Hb's affinity for O2, enhancing oxygen unloading from the blood. This is shown by the rightward shift of the oxygen-hemoglobin dissociation curve. c. A decrease in any of these factors increases hemoglobin's affinity for oxygen, decreasing oxygen unloading. This change shifts the dissociation curve to the left. d. There is not as much diffusion of oxygen into the fetal blood supply. The fetus' hemoglobin overcomes this problem by having a greater affinity for oxygen than maternal hemoglobin (the oxygen-fetal hemoglobin disassociation curve is shifted to the left and upward). Both fetal and adult hemoglobin have four subunits, but two of the subunits of fetal hemoglobin have a different structure that causes fetal hemoglobin to have a greater affinity for oxygen than does adult hemoglobin.

With respect to carbon dioxide transport: a. Describe the ways in which carbon dioxide is transported in blood and discuss the relative importance of each to total carbon dioxide transport. b. State the reversible chemical equation for carbon dioxide binding to deoxyhemoglobin and predict how changing carbon dioxide concentrations will affect deoxyhemoglobin levels in the tissues and the lungs. c. Explain how each of the following relates to carbon dioxide transport: carbonic anhydrase, hydrogen ions binding to hemoglobin and plasma proteins, the chloride ion shift, and the oxygen-hemoglobin saturation level.

a. Blood transports CO2 from the tissue cells to the lungs in three forms: 1. Dissolved in plasma (7-10%). The smallest amount of O2 is transported simply dissolved in plasma. 2. Chemically bound to hemoglobin (just over 20%). Dissolved CO2 is bound and carried in the RBCs as carbaminohemoglobin 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 b. CO2+Hb⇌HbCO2 CO2 loading and unloading are directly influenced by the PCO2 and the degree of Hb oxygenation. Carbon dioxide rapidly dissociates from 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 the PCO2 is higher than that in blood. Deoxygenated hemoglobin combines more readily with carbon dioxide than does oxygenated hemoglobin c. Carbonic anhydrase is 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. 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, occurs 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.

With respect to internal respiration: a. Describe oxygen and carbon dioxide concentration gradients and net gas movements. b. Explain the factors that maintain oxygen and carbon dioxide gradients between blood and tissue cells.

a. Internal respiration involves capillary gas exchange in body tissues. In internal respiration, the partial pressure and diffusion gradients are reversed from the external respiration and pulmonary gas exchange. b. 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 (40 mm Hg versus 100 mm Hg), 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.

With respect to oxygen transport: a. Describe the ways in which oxygen is transported in blood and discuss the relative importance of each to total oxygen transport. b. State the reversible chemical equation for oxygen binding to hemoglobin and predict how raising or lowering the partial pressure of oxygen will shift the equilibrium.

a. Molecular oxygen is carried in blood in two ways: bound to hemoglobin within red blood cells 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 b. See picture. Raising or lowering the Partial pressure of oxygen means that more or less O2 is available to bind with hemoglobin. More binding means that the saturation of hemoglobin increases, less binding means it decreases

With respect to external respiration: a. Describe oxygen and carbon dioxide concentration gradients and net gas movements. b. Analyze how oxygen and carbon dioxide movements are affected by changes in partial pressure gradients (e.g., at high altitude), surface area, diffusion distance, and solubility and molecular weight of the gases. c. Describe the mechanisms of ventilation-perfusion coupling and predict the effect that reduced alveolar ventilation has on pulmonary blood flow and the effect that reduced pulmonary blood flow has on bronchiole diameter and alveolar ventilation.

a. Partial pressure gradients of O2 and CO2 drive the diffusion 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 . Carbon dioxide diffuses in the opposite direction along a much gentler partial pressure gradient of about 5 mm Hg (45 mm Hg to 40 mm Hg) until equilibrium occurs at 40 mm Hg. Expiration then gradually expels carbon dioxide from the alveoli. b. The greater the surface area of the respiratory membrane, the more gas can diffuse across it in a given time period. At high altitudes, partial pressures decline in direct proportion to the decrease in atmospheric pressure. 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. When a liquid's temperature rises, gas solubility decreases. c. For optimal gas exchange, there must be a close match 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. 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. 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.

Define and state relative values for atmospheric pressure, intrapulmonary pressure, intrapleural pressure, and transpulmonary pressure.

· Atmospheric Pressure (Patm): Pressure exerted by the air surrounding the body (760 mm of Mercury (Hg) at sea level). Written as Patm · Intrapulmonary Pressure (Ppul): Pressure in the alveoli, which fluctuates with breathing. It always eventually equalizes with Patm · Intrapleural Pressure (Pip): Pressure in the pleural cavity which fluctuates with breathing. It is always a negative pressure (less than Patm and Ppul). Typically 756 mm Hg. · Transpulmonary Pressure: The difference between the pulmonary pressure and the intrapleural pressure (Ppul - Pip). This pressure keeps the airways open. Typically -4 mm Hg. The greater the transpulmonary pressure, the larger the lungs. If Pip = Ppul the lungs collapse.