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

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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 – 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 Nostril Hard palate Larynx Trachea Right lung Posterior nasal aperture Soft palate Pharynx Epiglottis Esophagus Left lung Left main bronchus Lobar bronchus Segmental bronchus Pleural cavity Pleura (cut) Diaphragm Figure 22.1

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

7 Alveoli ~ 150 million sacs for gas exchange – 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 – Inspiration – Expiration Respiratory muscles – Diaphragm – Intercostals – Accessory muscles of respiration Sternocleidomastoids, scalenes, pectoralis muscles, serratus anterior, erector spinae

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

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. Central chemoreceptors Spinal integrating centers Glossopharyngeal n. Vagus n. Diaphragm and intercostal muscles Accessory muscles of respiration Ventral respiratory group (VRG) Dorsal respiratory group (DRG) Medulla oblongata Pontine respiratory group (PRG) Pons Output from hypothalamus, limbic system, and higher brain centers Phrenic n. Intercostal nn. Key Inputs to respiratory centers of medulla Outputs to spinal centers and respiratory muscles Figure 22.14

12 Taking a Breath Inspiration – 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. Lung volume (mL) 6,000 5,000 4,000 3,000 2,000 1,000 0 Maximum possible inspiration Inspiratory reserve volume Expiratory reserve volume Residual volume Maximum voluntary expiration Functional residual capacity Total lung capacity Tidal volume Inspiratory capacity Vital capacity

15 Spirometry Restrictive 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% N 2, 20.9% O 2,.04% CO 2, 0.5% H 2 O 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 O 2 and unload CO 2 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%) – Oxyhemoglobin (HbO 2 ) Carbon dioxide – Carbonic acid (90%) – Carbamino compounds (carbaminohemoglobin, HbCO 2 ) – Dissolved gases

19 Systemic Gas Exchange Systemic gas exchange - the unloading of O 2 and loading of CO 2 at the systemic capillaries CO 2 loading – CO 2 diffuses into the blood – carbonic anhydrase in RBC catalyzes CO 2 + H 2 O  H 2 CO 3  HCO H + – chloride shift keeps reaction proceeding, exchanges HCO 3 - for Cl - H + binds to hemoglobin O 2 unloading – H + binding to HbO 2 reduces its affinity for O 2 tends to make hemoglobin release oxygen HbO 2 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiring tissueCapillary blood Dissolved CO 2 gas CO 2 + plasma protein CO 2 O2O2 Dissolved O 2 gas Carbamino compounds Cl – 7% 23% 70% 98.5% 1.5% CO 2 + Hb CO 2 + H 2 O O 2 + HHb HbO 2 + H + H 2 CO 3 HCO 3 – + H + HbCO 2 CAH Key Chloride shift CO 2 O2O2 HbCO 2 Carbaminohemoglobin Hb Hemoglobin HHb Deoxyhemoglobin CAH Carbonic anhydrase HbO 2 Oxyhemoglobin Figure 22.24

21 Alveolar Gas Exchange Reactions that occur in the lungs are reverse of systemic gas exchange CO 2 unloading – As Hb loads O 2 its affinity for H + decreases, H + dissociates from Hb and bind with HCO 3 - CO 2 + H 2 O  H 2 CO 3  HCO H + – Reverse chloride shift HCO 3 - diffuses back into RBC in exchange for Cl -, free CO 2 generated diffuses into alveolus to be exhaled

22 Alveolar Gas Exchange Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiratory membraneCapillary blood CO 2 O2O2 Alveolar air Carbamino compounds 7% 23% 70% 98.5% 1.5% HbCO 2 CAH Key Cl  Chloride shift CO 2 O2O2 Dissolved O 2 gas O 2 + HHb HbO 2 + H + HCO 3  + H + H 2 CO 3 CO 2 + H 2 O CO 2 + Hb CO 2 + plasma protein Dissolved CO 2 gas Hb Hemoglobin HbCO 2 Carbaminohemoglobin HbO 2 Oxyhemoglobin HHb Deoxyhemoglobin CAH Carbonic anhydrase Figure 22.25

23 Concentration Gradients of Gases Figure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alveolar gas exchange O 2 loading CO 2 unloading Gas transport O 2 carried from alveoli to systemic tissues CO 2 carried from systemic tissues to alveoli Systemic gas exchange O 2 unloading CO 2 loading Expired air Inspired air P O mm Hg P CO 2 32 mm Hg Alveolar air P O mm Hg P CO 2 40 mm Hg Tissue fluid P O 2 40 mm Hg P CO 2 46 mm Hg Deoxygenated blood P O 2 40 mm Hg P CO 2 46 mm Hg Oxygenated blood P O 2 95 mm Hg P CO 2 40 mm Hg P O mm Hg P CO mm Hg CO 2 Pulmonary circuit Systemic circuit CO 2 O2O2 O2O2

24 Adjustment to the Metabolic Needs of Individual Tissues Hemoglobin unloads O 2 to match metabolic needs of different states of activity of the tissues Four factors that adjust the rate of oxygen unloading – ambient P O 2 active tissue has  P O 2 ; O 2 is released from Hb – temperature active tissue has  temp; promotes O 2 unloading – Bohr effect active tissue has  CO 2, which lowers pH of blood ; promoting O 2 unloading – bisphosphoglycerate (BPG) RBCs produce BPG which binds to Hb; O 2 is unloaded Haldane effect – rate of CO 2 loading is also adjusted to varying needs of the tissues, low level of oxyhemoglobin enables the blood to transport more CO 2  body temp (fever), thyroxine, growth hormone, testosterone, and epinephrine all raise BPG and cause O 2 unloading  metabolic rate requires  oxygen

25 Blood Gases and the Respiratory Rhythm Rate and depth of breathing adjust to maintain levels of: – pH 7.35 – 7.45 – P CO 2 40 mm Hg – P O 2 95 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 CO 2, and least significant is O 2

26 Hydrogen Ions Acidosis – blood pH lower than 7.35 Alkalosis – blood pH higher than 7.45 Hypocapnia – P CO 2 less than 37 mm Hg (normal 37 – 43 mm Hg) most common cause of alkalosis Hypercapnia – P CO 2 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 CO 2 production Hyperventilation is a corrective homeostatic response to acidosis – “blowing off ” CO 2 faster than the body produces it – pushes reaction to the left CO 2 (expired) + H 2 O  H 2 CO 3  HCO  H + – reduces H + (reduces acid) raises blood pH towards normal Hypoventilation is a corrective homeostatic response to alkalosis – allows CO 2 to accumulate in the body fluids faster than we exhale it – shifts reaction to the right – CO 2 + H 2 O  H 2 CO 3  HCO H + – raising the H + concentration, lowering pH to normal

28 Effects of Oxygen P O 2 usually has little effect on respiration Chronic hypoxemia, P O 2 less than 60 mm Hg, can significantly stimulate ventilation – Hypoxic drive – respiration driven more by low P O 2 than by CO 2 or pH – Emphysema, pneumonia – High elevations after several days

29 Respiration and Exercise Causes of increased respiration during exercise 1.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 2.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 O 2 consumption and CO 2 generation by the muscles

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


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