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Ch. 13 The Respiratory System

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1 Ch. 13 The Respiratory System
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display

2 Breath of Fresh Air Know what is meant by ventilation and where gas exchange occurs in the lungs Know the respiratory centers of the brain and how the control respiration Know the various lung volumes and lung capacities Know how gas exchange is accomplished and the factors that can affect the rate of gas exchange

3 Respiratory System What are some functions of the respiratory system?
Respiration as a process Ventilation External and internal respiration Cellular respiration

4 Anatomy Principal organs Conducting division Respiratory division
Nose, pharynx, larynx, trachea, bronchi, and lungs Conducting division Function only in airflow Respiratory division Function in gas exchange

5 Organs of Respiratory System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nasal cavity Posterior nasal aperture Hard palate Soft palate Nostril Epiglottis Pharynx Larynx Esophagus Trachea Left lung Left main bronchus Lobar bronchus Right lung Segmental bronchus Pleural cavity Pleura (cut) Diaphragm Figure 22.1

6 Lungs Right lung Left lung Pleurae
Three lobes divided by horizontal and oblique fissures Left lung Two lobes divided by oblique fissure Pleurae Visceral Parietal Pleural cavity Pleural fluid Copyright © The McGraw-Hill Companies (b) Mediastinal surface, right lung

7 Alveoli ~ 150 million sacs for gas exchange Cells types
Why so many? Cells types Squamous alveolar cells (type I) 95% of surface, thinness allows rapid gas exchange Great alveolar cells (type II) Repair alveolar epithelium Secrete surfactant Alveolar macrophages (dust cells) Phagocytize dust particles, bacteria, debris Respiratory membrane Copyright © The McGraw-Hill Companies

8 Ventilation Respiratory cycle Respiratory muscles Inspiration
Expiration Respiratory muscles Diaphragm Intercostals Accessory muscles of respiration Sternocleidomastoids, scalenes, pectoralis muscles, serratus anterior, erector spinae

9 Respiratory Muscles Figure 22.13 Inspiration Sternocleidomastoid
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inspiration Sternocleidomastoid (elevates sternum) Scalenes (fix or elevate ribs 1–2) External intercostals (elevate ribs 2–12, widen thoracic cavity) Pectoralis minor (cut) (elevates ribs 3–5) Forced expiration Internal intercostals, interosseous part (depress ribs 1–11, narrow thoracic cavity) Internal intercostals, intercartilaginous part (aid in elevating ribs) Diaphragm (ascends and reduces depth of thoracic cavity) Diaphragm (descends and increases depth of thoracic cavity) Rectus abdominis (depresses lower ribs, pushes diaphragm upward by compressing abdominal organs) External abdominal oblique (same effects as rectus abdominis) Figure 22.13

10 Neural Control of Breathing
Conscious and sub-conscious control Three pairs of respiratory centers in reticular formation of medulla and pons Ventral respiratory group (VRG) Inspiratory (I) neurons Expiratory (E) neurons Dorsal respiratory group (DRG) External influence of VRG Integrating center Central and peripheral chemoreceptors, stretch receptors, irritant receptors Pontine respiratory group Integrates input from higher brain centers Influences VRG and DRG Modifies breathing to sleep, emotional responses, exercise, other special circumstances

11 Respiratory Control Centers
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Key Inputs to respiratory centers of medulla Outputs to spinal centers and respiratory muscles Respiratory Control Centers Output from hypothalamus, limbic system, and higher brain centers Pons Pontine respiratory group (PRG) Dorsal respiratory group (DRG) Central chemoreceptors Glossopharyngeal n. Ventral respiratory group (VRG) Vagus n. Medulla oblongata Intercostal nn. Spinal integrating centers Phrenic n. Diaphragm and intercostal muscles Figure 22.14 Accessory muscles of respiration

12 Taking a Breath Inspiration Expiration Resistance to airflow
Boyle’s law Pressure of a gas inversely proportional to its volume at constant temp. Charles’s law Volume of a gas directly proportional to its temperature at constant pressure Expiration Passive process, elastic recoil of thoracic cage Resistance to airflow Diameter of bronchioles Pulmonary compliance Surface tension of alveoli

13 Measurements of Ventilation
Spirometer Dead space Approx. 150 ml of air remain in conductive division Alveolar ventilation rate (AVR) – volume of air used in gas exchange X breaths/min Tidal volume (TV) – one cycle of quite breathing, about 500 ml Inspiratory reserve volume (IRV) – amount that can be inhaled beyond TV inhalation, 3000 ml Expiratory reserve volume (ERV) – amount that can be forcefully exhaled beyond TV exhalation, 1200 ml Residual volume (RV) – volume of air that remains even after maximal expiration, 1300 ml

14 Lung Volumes and Capacities
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Maximum possible inspiration 6,000 5,000 Inspiratory reserve volume Inspiratory capacity Vital capacity 4,000 Tidal volume Lung volume (mL) 3,000 Total lung capacity 2,000 Expiratory reserve volume Functional residual capacity 1,000 Maximum voluntary expiration Residual volume

15 Spirometry Restrictive disorders Obstructive disorders
Reduce pulmonary compliance Appear as a reduced vital capacity Obstructive disorders Blockage or narrowing of airway More difficult to inhale/exhale given amount of air Measure by forced expiratory volume (FEV) Percentage of vital capacity that can be exhaled in a given time interval 75-85% in 1 second for healthy adult

16 Gas Exchange Involves oxygen and carbon dioxide Composition of air
78.6% N2, 20.9% O2, .04% CO2, 0.5% H2O Dalton’s law – total atmospheric pressure is sum of partial pressures of individual gases Composition of gases will vary depending on where air is in the respiratory tract Inhaled air differs from alveolar air differs from exhaled air

17 Driving Force Behind Alveolar Exchange
Diffusion down concentration gradient Have to consider that we are going from air to water Henry’s law – for a given temperature, at the air-water interface the amount of gas that dissolves in the water is determined by its solubility in water and its partial pressure in air Erythrocytes load O2 and unload CO2 Efficiency of exchange may be affected by: Pressure gradients, solubility, membrane thickness and area, ventilation-perfusion coupling

18 Gas Transport Oxygen binds to hemoglobin (98.5%) Carbon dioxide
Oxyhemoglobin (HbO2) Carbon dioxide Carbonic acid (90%) Carbamino compounds (carbaminohemoglobin, HbCO2) Dissolved gases

19 Systemic Gas Exchange Systemic gas exchange - the unloading of O2 and loading of CO2 at the systemic capillaries CO2 loading CO2 diffuses into the blood carbonic anhydrase in RBC catalyzes CO2 + H2O  H2CO3  HCO3- + H+ chloride shift keeps reaction proceeding, exchanges HCO3- for Cl- H+ binds to hemoglobin O2 unloading H+ binding to HbO2 reduces its affinity for O2 tends to make hemoglobin release oxygen HbO2 arrives at systemic capillaries 97% saturated, leaves 75% saturated – venous reserve – oxygen remaining in the blood after it passes through the capillary beds Utilization coefficient – given up 22% of its oxygen load

20 Systemic Gas Exchange Figure 22.24 Respiring tissue Capillary blood 7%
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiring tissue Capillary blood 7% CO2 Dissolved CO2 gas CO2 + plasma protein Carbamino compounds 23% CO2 CO2 + Hb HbCO2 Chloride shift Cl– 70% CAH CO2 CO2 + H2O H2CO3 HCO3– + H+ 98.5% O2 O2 + HHb HbO2+ H+ 1.5% Dissolved O2 gas Key O2 Hb Hemoglobin HbCO2 Carbaminohemoglobin HbO Oxyhemoglobin Figure 22.24 HHb Deoxyhemoglobin CAH Carbonic anhydrase

21 Alveolar Gas Exchange Reactions that occur in the lungs are reverse of systemic gas exchange CO2 unloading As Hb loads O2 its affinity for H+ decreases, H+ dissociates from Hb and bind with HCO3- CO2 + H2O  H2CO3  HCO3- + H+ Reverse chloride shift HCO3- diffuses back into RBC in exchange for Cl-, free CO2 generated diffuses into alveolus to be exhaled

22 Alveolar Gas Exchange Figure 22.25 Alveolar air Respiratory membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alveolar air Respiratory membrane Capillary blood 7% CO2 Dissolved CO2 gas CO2 + plasma protein Carbamino compounds 23% Chloride shift CO2 CO2 + Hb HbCO2 Cl- 70% CAH CO2 CO2 + H2O H2 CO3 HCO3- + H+ 98.5% O2 O2 + HHb HbO2 + H+ 1.5% O2 Dissolved O2 gas Key Hb Hemoglobin HbCO2 Carbaminohemoglobin Figure 22.25 HbO Oxyhemoglobin HHb Deoxyhemoglobin CAH Carbonic anhydrase

23 Concentration Gradients of Gases
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Expired air Inspired air PO2 116 mm Hg PO2 159 mm Hg PCO2 32 mm Hg PCO2 0.3 mm Hg Alveolar gas exchange Alveolar air O2 loading PO2 104 mm Hg CO2 unloading PCO2 40 mm Hg CO2 O2 Gas transport Pulmonary circuit O2 carried from alveoli to systemic tissues Deoxygenated blood CO2 carried from systemic tissues to alveoli Oxygenated blood PO2 40 mm Hg PO2 95 mm Hg PCO2 46 mm Hg PCO2 40 mm Hg Systemic circuit Systemic gas exchange CO2 O2 O2 unloading CO2 loading Figure 22.19 Tissue fluid PO2 40 mm Hg PCO2 46 mm Hg

24 Adjustment to the Metabolic Needs of Individual Tissues
Hemoglobin unloads O2 to match metabolic needs of different states of activity of the tissues Four factors that adjust the rate of oxygen unloading ambient PO2 active tissue has  PO2 ; O2 is released from Hb temperature active tissue has  temp; promotes O2 unloading Bohr effect active tissue has  CO2, which lowers pH of blood ; promoting O2 unloading bisphosphoglycerate (BPG) RBCs produce BPG which binds to Hb; O2 is unloaded Haldane effect – rate of CO2 loading is also adjusted to varying needs of the tissues, low level of oxyhemoglobin enables the blood to transport more CO2  body temp (fever), thyroxine, growth hormone, testosterone, and epinephrine all raise BPG and cause O2 unloading  metabolic rate requires  oxygen

25 Blood Gases and the Respiratory Rhythm
Rate and depth of breathing adjust to maintain levels of: pH – 7.45 PCO mm Hg PO mm Hg Brainstem respiratory centers receive input from central and peripheral chemoreceptors that monitor the composition of blood and CSF Most potent stimulus for breathing is pH, followed by CO2, and least significant is O2 H+ does not easily cross blood-brain barrier, but CO2 does. Reacts with water and produces carbonic acid (H+).

26 Hydrogen Ions Acidosis – blood pH lower than 7.35
Alkalosis – blood pH higher than 7.45 Hypocapnia – PCO2 less than 37 mm Hg (normal 37 – 43 mm Hg) most common cause of alkalosis Hypercapnia – PCO2 greater than 43 mm Hg most common cause of acidosis

27 Effects of Hydrogen Ions
Respiratory acidosis and respiratory alkalosis – pH imbalances resulting from a mismatch between the rate of pulmonary ventilation and the rate of CO2 production Hyperventilation is a corrective homeostatic response to acidosis “blowing off ” CO2 faster than the body produces it pushes reaction to the left CO2 (expired) + H2O  H2CO3  HCO3- +  H+ reduces H+ (reduces acid) raises blood pH towards normal Hypoventilation is a corrective homeostatic response to alkalosis allows CO2 to accumulate in the body fluids faster than we exhale it shifts reaction to the right CO2 + H2O  H2CO3  HCO3- + H+ raising the H+ concentration, lowering pH to normal

28 Effects of Oxygen PO2 usually has little effect on respiration
Chronic hypoxemia, PO2 less than 60 mm Hg, can significantly stimulate ventilation Hypoxic drive – respiration driven more by low PO2 than by CO2 or pH Emphysema, pneumonia High elevations after several days

29 Respiration and Exercise
Causes of increased respiration during exercise When the brain sends motor commands to the muscles Also sends this information to the respiratory centers Increase pulmonary ventilation in anticipation of the needs of the exercising muscles Exercise stimulates proprioceptors of the muscles and joints Transmit excitatory signals to the brainstem respiratory centers Increase breathing because they are informed that the muscles have been told to move or are actually moving Increase in pulmonary ventilation keeps blood gas values at their normal levels in spite of the elevated O2 consumption and CO2 generation by the muscles

30 Effect of Smoking Figure 22.27 a-b Tumors
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tumors (a) Healthy lung, mediastinal surface (b) Smoker's lung with carcinoma a: © The McGraw-Hill Companies/Dennis Strete, photographer; b: Biophoto Associates/Photo Researchers, Inc. Figure a-b


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