Respiratory Physiology Copyright The Mc Graw-Hill

Respiratory Physiology

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Respiration n Includes 3 separate functions: n Ventilation: n n Gas exchange: n n n Breathing. Between air and capillaries in the lungs. Between systemic capillaries and tissues of the body. 02 utilization: n Cellular respiration.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Ventilation n n Mechanical process that moves air in and out of the lungs. [O 2] of air is higher in the lungs than in the blood, O 2 diffuses from air to the blood. C 02 moves from the blood to the air by diffusing down its concentration gradient. Gas exchange occurs entirely by diffusion.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Alveoli n ~ 300 million air sacs (alveoli). n n n Large surface area (60– 80 m 2). Each alveolus is 1 cell layer thick. 2 types of cells: n Alveolar type I: n n Structural cells. Alveolar type II: n Secrete surfactant. Figure 16. 1

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Respiratory Zone n n n Region of gas exchange between air and blood. Includes respiratory bronchioles and alveolar sacs. Must contain alveoli. Figure 16. 4

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Conducting Zone n n n All the structures air passes through before reaching the respiratory zone. Warms and humidifies inspired air. Filters and cleans: n n Insert fig. 16. 5 Mucus secreted to trap particles in the inspired air. Mucus moved by cilia to be expectorated. Figure 16. 5

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Physical Properties of the Lungs n Compliance: n Distensibility (stretchability): n n 100 x more distensible than a balloon. n n Ease with which the lungs can expand. Compliance is reduced by factors that produce resistance to distension. Elasticity: n n Tendency to return to initial size after distension. High content of elastin proteins. n Very elastic and resist distension. n Recoil ability.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Surface Tension n Force exerted by fluid in alveoli to resist distension. n n n Lungs secrete and absorb fluid, leaving a very thin film of fluid. This film of fluid causes surface tension. H 20 molecules at the surface are attracted to other H 20 molecules by attractive forces. n Force is directed inward, raising pressure in alveoli.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Law of Laplace n Pressure in alveoli is directly proportional to surface tension; and inversely proportional to radius of alveoli. n Insert fig. 16. 11 Pressure in smaller alveolus greater. Figure 16. 11

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Surfactant n n Phospholipid produced by alveolar type II cells. Lowers surface tension. n n Insert fig. 16. 12 Reduces attractive forces of hydrogen bonding by becoming interspersed between H 20 molecules. As alveoli radius decreases, surfactant’s ability to lower surface tension increases. Figure 16. 12

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Boyle’s Law n Changes in intrapulmonary pressure occur as a result of changes in lung volume. n n Increase in lung volume decreases intrapulmonary pressure. n n Pressure of gas is inversely proportional to its volume. Air goes in. Decrease in lung volume, raises intrapulmonary pressure above atmosphere. n Air goes out.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Lung Pressures n Intrapulmonary pressure: n n Intrapleural pressure: n n n Intra-alveolar pressure (pressure in the alveoli). Pressure in the intrapleural space. Pressure is negative, due to lack of air in the intrapleural space. Transpulmonary pressure: n n Pressure difference across the wall of the lung. Intrapulmonary pressure – intrapleural pressure. n Keeps the lungs against the chest wall.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Quiet Inspiration n Active process: n n Contraction of diaphragm, increases thoracic volume vertically. Contraction of parasternal and internal intercostals, increases thoracic volume laterally. Increase in lung volume decreases pressure in alveoli, and air rushes in. Pressure changes: n n n Alveolar changes from 0 to – 3 mm Hg. Intrapleural changes from – 4 to – 6 mm Hg. Transpulmonary pressure = +3 mm Hg.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Expiration n Quiet expiration is a passive process. n n n After being stretched, lungs recoil. Decrease in lung volume raises the pressure within alveoli above atmosphere, and pushes air out. Pressure changes: n n n Intrapulmonary pressure changes from – 3 to +3 mm Hg. Intrapleural pressure changes from – 6 to – 3 mm Hg. Transpulmonary pressure = +6 mm Hg.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Ventilation Insert fig. 16. 15 Figure 16. 15

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Function Tests n n n Assessed by spirometry. Subject breathes into a closed system in which air is trapped within a bell floating in H 20. The bell moves up when the subject exhales and down when the subject inhales. Insert fig. 16 Figure 16. 16

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Terms Used to Describe Lung Volumes and Capacities

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Volumes n n n n TV = 500 ml IRV = 2500 -3000 ml ERV = 1100 -1200 ml RV = 1200 ml IC = 3500 ml FRC = 2300 ml VC = 4600 ml TLC = 5800 ml

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary volumes n n Minute respiratory volume = TV x RR TV (500 ml) x RR (12 breaths/min) = 6000 ml/min

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Anatomical Dead Space n n Not all of the inspired air reached the alveoli. As fresh air is inhaled it is mixed with air in anatomical dead space. n n Conducting zone and alveoli where [02] is lower than normal and [C 02] is higher than normal. Alveolar ventilation = F x (TV- DS). n n n F = frequency (breaths/min. ). TV = tidal volume. DS = dead space.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Restrictive and Obstructive Disorders n Restrictive disorder: n n n Vital capacity is reduced. FVC is normal. Obstructive disorder: n n VC is normal. FEV 1 is < 80%. Figure 16. 17 Insert fig. 16. 17

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Disorders n Dyspnea: n n Shortness of breath. COPD (chronic obstructive pulmonary disease): n Asthma: n Obstructive air flow through bronchioles. n Caused by inflammation and mucus secretion. n Inflammation contributes to increased airway responsiveness to agents that promote bronchial constriction. n Ig. E, exercise.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Disorders n Emphysema: n n Alveolar tissue is destroyed. Chronic progressive condition that reduces surface area for gas exchange. n n (continued) Decreases ability of bronchioles to remain open during expiration. n Cigarette smoking stimulates macrophages and leukocytes to secrete protein digesting enzymes that destroy tissue. Pulmonary fibrosis: n Normal structure of lungs disrupted by accumulation of fibrous connective tissue proteins. n Anthracosis.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Gas Exchange in the Lungs n Partial pressure: n The pressure that an particular gas exerts independently. PATM = PN + P 0 + PC 0 + PH 0= 760 mm Hg. n 02 is humidified = 105 mm Hg. n 2 2 2 H 20 contributes to partial pressure (47 mm Hg). n n n 2 P 02 (sea level) = 150 mm Hg. PC 0 = 40 mm Hg. 2 Figure 16. 20

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Significance of Blood P 0 and PC 0 Measurements 2 n n n At normal P 02 arterial blood = 100 mm Hg. P 02 level in the systemic veins is = 40 mm Hg; PC 02 = 46 mm Hg. Provides a good index of lung function. Figure 16. 23 2

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Circulation n Rate of blood flow through the pulmonary circulation is = flow rate through the systemic circulation. n n Pulmonary vascular resistance is low. n n Driving pressure is about 10 mm Hg. Low pressure pathway produces less net filtration than produced in the systemic capillaries. Autoregulation: n n Pulmonary arterioles constrict when alveolar P 0 decreases. Matches ventilation/perfusion ratio. 2

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Lung Ventilation/Perfusion Ratios n Functionally: n n Alveoli at apex are underperfused (overventilated). Alveoli at the base are underventilated (overperfused). Insert fig. 16. 24 Figure 16. 24

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Brain Stem Respiratory Centers n Rhythmicity center: n n Controls automatic breathing. Iinteracting neurons that fire either during inspiration (I neurons) or expiration (E neurons). Insert fig. 16. 25 Figure 16. 25

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Rhythmicity Center n I neurons located primarily in dorsal respiratory group (DRG): n n E neurons located in ventral respiratory group (VRG): n n Regulate activity of phrenic nerve. Passive process. Activity of E neurons inhibit I neurons. n Rhythmicity of I and E neurons may be due to pacemaker neurons.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Pons Respiratory Centers n n Medullary rhythmicity center influenced by pons. Apneustic center: n n Promotes inspiration by stimulating the I neurons in the medulla. Pneumotaxic center: n n Antagonizes the apneustic center. Inhibits inspiration.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Chemoreceptors n Monitor changes in blood PC 0 , P 0 , and p. H. Central: 2 n n n 2 Medulla. Insert fig. 16. 27 Peripheral: n Carotid and aortic bodies. n Control breathing indirectly. Figure 16. 27

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Central Chemoreceptors n n More sensitive to changes in arterial PC 0. H 20 + C 02 H 2 C 03 H+ H+ cannot cross the blood brain barrier. C 02 can cross the blood brain barrier and will form H 2 C 03. 2 n Lowers p. H of CSF. n Directly stimulates central chemoreceptors.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Peripheral Chemoreceptors n Are not stimulated directly by changes in arterial PC 0. H 20 + C 02 H 2 C 03 H+ Stimulated by rise in [H+] of arterial blood. 2 n n n Increased [H+] stimulates peripheral chemoreceptors.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Chemoreceptor Control of Breathing Insert fig. 16. 29 Figure 16. 20

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Effects of Pulmonary Receptors on Ventilation n Lungs contain receptors that influence the brain stem respiratory control centers via sensory fibers in vagus. n Unmyelinated C fibers can be stimulated by: n Capsaicin: n n Histamine and bradykinin: n n n Produces apnea followed by rapid, shallow breathing. Released in response to noxious agents. Irritant receptors are rapidly adaptive receptors. Hering-Breuer reflex: n Pulmonary stretch receptors activated during inspiration. n Inhibits respiratory centers to prevent undue tension on lungs.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin n 280 million hemoglobin/RBC. Each hemoglobin has 4 polypeptide chains and 4 hemes. In the center of each heme group is 1 atom of iron that can combine with 1 molecule 0 2. Insert fig. 16. 32 Figure 16. 32

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin n Methemoglobin: n Lacks electrons and cannot bind with 02. n n (continued) Blood normally contains a small amount. Carboxyhemoglobin: n The bond with carbon monoxide is 210 times stronger than the bond with oxygen. n Transport of 02 to tissues is impaired.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin n Oxygen-carrying capacity of blood determined by its [hemoglobin]. n Anemia: [Hemoglobin] below normal. n n Polycythemia: [Hemoglobin] above normal. n n Hemoglobin production controlled by erythropoietin. Production stimulated by PC 0 delivery to kidneys. n n (continued) 2 Loading/unloading depends: n P 0 of environment. n Affinity between hemoglobin and 0 2. 2

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Oxyhemoglobin Dissociation Curve n Graphic illustration of the % oxyhemoglobin saturation at different values of P 02. n n Loading and unloading of 02. n Steep portion of the sigmoidal curve, small changes in P 02 produce large differences in % saturation (unload more 02). Decreased p. H, increased temperature, and increased 2, 3 DPG: n Affinity of hemoglobin for 02 decreases. n Greater unloading of 02: n Shift to the curve to the right. Figure 16. 34

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Effects of p. H and Temperature n n Affinity is decreased when p. H is decreased. Increased temperature and 2, 3 -DPG: n Shift the curve to the right. Insert fig. 16. 35 Figure 16. 35

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. C 02 Transport n C 02 transported in the blood: HC 03 - (70%). n Dissolved C 02 (10%). n Carbaminohemoglobin (20%). n H 20 + C 02 ca H 2 C 03 High PC 0 2

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Chloride Shift at Systemic Capillaries n n H 20 + C 02 H 2 C 03 H+ + HC 03 At the tissues, C 02 diffuses into the RBC; shifts the reaction to the right. n Increased [HC 03 -] produced in RBC: n n RBC becomes more +. n n n HC 03 - diffuses into the blood. Cl- attracted in (Cl- shift). H+ released buffered by combining with deoxyhemoglobin. Hb. C 02 formed. n Unloading of 02.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Carbon Dioxide Transport and Chloride Shift Insert fig. 16. 38 Figure 16. 38

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. At Pulmonary Capillaries n n n H 20 + C 02 H 2 C 03 H+ + HC 03 At the alveoli, C 02 diffuses into the alveoli; reaction shifts to the left. Decreased [HC 03 -] in RBC, HC 03 - diffuses into the RBC. n RBC becomes more -. n n Deoxyhemoglobin converted to oxyhemoglobin. n n Cl- diffuses out (reverse Cl- shift). Has weak affinity for H+. Gives off Hb. C 02.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Reverse Chloride Shift in Lungs Insert fig. 16. 39 Figure 16. 39

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Ventilation During Exercise n n During exercise, breathing becomes deeper and more rapid. Produce > total minute volume. Neurogenic mechanism: n Sensory nerve activity from exercising muscles stimulates the respiratory muscles. n Cerebral cortex input may stimulate brain stem centers. Humoral mechanism: n PC 0 and p. H may be different at chemoreceptors. n Cyclic variations in the values that cannot be detected by blood samples. Insert fig. 16. 41 2 Figure 16. 41

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Lactate Threshold and Endurance Training n Maximum rate of oxygen consumption that can be obtained before blood lactic acid levels rise as a result of anaerobic respiration. n n 50 -70% maximum 02 uptake has been reached. Endurance trained athletes have higher lactate threshold, because of higher cardiac output. n n Have higher rate of oxygen delivery to muscles. Have increased content of mitochondria in skeletal muscles.

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Acclimatization to High Altitude n n Adjustments in respiratory function when moving to an area with higher altitude: Changes in ventilation: n Hypoxic ventilatory response produces hyperventilation. n n n Affinity of hemoglobin for 02: n n Increases total minute volume. Increased tidal volume. Action of 2, 3 -DPG decreases affinity of hemoglobin for 02. Increased hemoglobin production: n Kidneys secrete erythropoietin.