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Chapter 23: The Respiratory System

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1 Chapter 23: The Respiratory System
Copyright 2009, John Wiley & Sons, Inc.

2 Respiratory System Anatomy
Structurally Upper respiratory system Nose, pharynx and associated structures Lower respiratory system Larynx, trachea, bronchi and lungs Functionally Conducting zone – conducts air to lungs Nose, pharynx, larynx, trachea, bronchi, bronchioles and terminal bronchioles Respiratory zone – main site of gas exchange Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli Copyright 2009, John Wiley & Sons, Inc.

3 Structures of the Respiratory System
Copyright 2009, John Wiley & Sons, Inc.

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Nose External nose – portion visible on face Internal nose – large cavity beyond nasal vestibule Internal nares or choanae Ducts from paranasal sinuses and nasolacrimal ducts open into internal nose Nasal cavity divided by nasal septum Nasal conchae subdivide cavity into meatuses Increase surface are and prevents dehydration Olfactory receptors in olfactory epithelium Copyright 2009, John Wiley & Sons, Inc.

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Pharynx Starts at internal nares and extends to cricoid cartilage of larynx Contraction of skeletal muscles assists in deglutition Functions Passageway for air and food Resonating chamber Houses tonsils 3 anatomical regions Nasopharynx Oropharynx Laryngopharynx Copyright 2009, John Wiley & Sons, Inc.

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Larynx Short passageway connecting laryngopharynx with trachea Composed of 9 pieces of cartilage Thyroid cartilage or Adam’s apple Cricoid cartilage hallmark for tracheotomy Epiglottis closes off glottis during swallowing Glottis – pair of folds of mucous membranes, vocal folds (true vocal cords, and rima glottidis (space) Cilia in upper respiratory tract move mucous and trapped particles down toward pharynx Cilia in lower respiratory tract move them up toward pharynx Copyright 2009, John Wiley & Sons, Inc.

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Larynx Copyright 2009, John Wiley & Sons, Inc.

9 Structures of Voice Production
Mucous membrane of larynx forms Ventricular folds (false vocal cords) – superior pair Function in holding breath against pressure in thoracic cavity Vocal folds (true vocal cords) – inferior pair Muscle contraction pulls elastic ligaments which stretch vocal folds out into airway Vibrate and produce sound with air Folds can move apart or together, elongate or shorten, tighter or looser Androgens make folds thicker and longer – slower vibration and lower pitch Copyright 2009, John Wiley & Sons, Inc.

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Trachea Extends from larynx to superior border of T5 Divides into right and left primary bronchi 4 layers Mucosa Submucosa Hyaline cartilage Adventitia 16-20 C-shaped rings of hyaline cartilage Open part faces esophagus Copyright 2009, John Wiley & Sons, Inc.

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Location of Trachea Copyright 2009, John Wiley & Sons, Inc.

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Bronchi Right and left primary bronchus goes to right lung Carina – internal ridge Most sensitive area for triggering cough reflex Divide to form bronchial tree Secondary lobar bronchi (one for each lobe), tertiary (segmental) bronchi, bronchioles, terminal bronchioles Structural changes with branching Mucous membrane changes Incomplete rings become plates and then disappear As cartilage decreases, smooth muscle increases Sympathetic ANS – relaxation/ dilation Parasympathetic ANS – contraction/ constriction Copyright 2009, John Wiley & Sons, Inc.

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Lungs Separated from each other by the heart and other structures in the mediastinum Each lung enclosed by double-layered pleural membrane Parietal pleura – lines wall of thoracic cavity Visceral pleura – covers lungs themselves Pleural cavity is space between layers Pleural fluid reduces friction, produces surface tension (stick together) Cardiac notch – heart makes left lung 10% smaller than right Copyright 2009, John Wiley & Sons, Inc.

16 Relationship of the Pleural Membranes to Lungs
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Anatomy of Lungs Lobes – each lung divides by 1 or 2 fissures Each lobe receives it own secondary (lobar) bronchus that branch into tertiary (segmental) bronchi Lobules wrapped in elastic connective tissue and contains a lymphatic vessel, arteriole, venule and branch from terminal bronchiole Terminal bronchioles branch into respiratory bronchioles which divide into alveolar ducts About 25 orders of branching Copyright 2009, John Wiley & Sons, Inc.

19 Microscopic Anatomy of Lobule of Lungs
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Alveoli Cup-shaped outpouching Alveolar sac – 2 or more alveoli sharing a common opening 2 types of alveolar epithelial cells Type I alveolar cells – form nearly continuous lining, more numerous than type II, main site of gas exchange Type II alveolar cells (septal cells) – free surfaces contain microvilli, secrete alveolar fluid (surfactant reduces tendency to collapse) Copyright 2009, John Wiley & Sons, Inc.

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Alveolus Respiratory membrane Alveolar wall – type I and type II alveolar cells Epithelial basement membrane Capillary basement membrane Capillary endothelium Very thin – only 0.5 µm thick to allow rapid diffusion of gases Lungs receive blood from Pulmonary artery - deoxygenated blood Bronchial arteries – oxygenated blood to perfuse muscular walls of bronchi and bronchioles Copyright 2009, John Wiley & Sons, Inc.

22 Components of Alveolus
Copyright 2009, John Wiley & Sons, Inc.

23 Pulmonary ventilation
Respiration (gas exchange) steps Pulmonary ventilation/ breathing Inhalation and exhalation Exchange of air between atmosphere and alveoli External (pulmonary) respiration Exchange of gases between alveoli and blood Internal (tissue) respiration Exchange of gases between systemic capillaries and tissue cells Supplies cellular respiration (makes ATP) Copyright 2009, John Wiley & Sons, Inc.

24 Inhalation/ inspiration
Pressure inside alveoli lust become lower than atmospheric pressure for air to flow into lungs 760 millimeters of mercury (mmHg) or 1 atmosphere (1 atm) Achieved by increasing size of lungs Boyle’s Law – pressure of a gas in a closed container is inversely proportional to the volume of the container Inhalation – lungs must expand, increasing lung volume, decreasing pressure below atmospheric pressure Copyright 2009, John Wiley & Sons, Inc.

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Boyle’s Law Copyright 2009, John Wiley & Sons, Inc.

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Inhalation Inhalation is active – Contraction of Diaphragm – most important muscle of inhalation Flattens, lowering dome when contracted Responsible for 75% of air entering lungs during normal quiet breathing External intercostals Contraction elevates ribs 25% of air entering lungs during normal quiet breathing Accessory muscles for deep, forceful inhalation When thorax expands, parietal and visceral pleurae adhere tightly due to subatmospheric pressure and surface tension – pulled along with expanding thorax As lung volume increases, alveolar (intrapulmonic) pressure drops Copyright 2009, John Wiley & Sons, Inc.

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28 Exhalation/ expiration
Pressure in lungs greater than atmospheric pressure Normally passive – muscle relax instead of contract Based on elastic recoil of chest wall and lungs from elastic fibers and surface tension of alveolar fluid Diaphragm relaxes and become dome shaped External intercostals relax and ribs drop down Exhalation only active during forceful breathing Copyright 2009, John Wiley & Sons, Inc.

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Airflow Air pressure differences drive airflow 3 other factors affect rate of airflow and ease of pulmonary ventilation Surface tension of alveolar fluid Causes alveoli to assume smallest possible diameter Accounts for 2/3 of lung elastic recoil Prevents collapse of alveoli at exhalation Lung compliance High compliance means lungs and chest wall expand easily Related to elasticity and surface tension Airway resistance Larger diameter airway has less resistance Regulated by diameter of bronchioles & smooth muscle tone Copyright 2009, John Wiley & Sons, Inc.

32 Lung volumes and capacities
Minute ventilation (MV) = total volume of air inhaled and exhaled each minute Normal healthy adult averages 12 breaths per minute moving about 500 ml of air in and out of lungs (tidal volume) MV = 12 breaths/min x 500 ml/ breath = 6 liters/ min Copyright 2009, John Wiley & Sons, Inc.

33 Spirogram of Lung Volumes and Capacities
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Lung Volumes Only about 70% of tidal volume reaches respiratory zone Other 30% remains in conducting zone Anatomic (respiratory) dead space – conducting airways with air that does not undergo respiratory gas exchange Alveolar ventilation rate – volume of air per minute that actually reaches respiratory zone Inspiratory reserve volume – taking a very deep breath Copyright 2009, John Wiley & Sons, Inc.

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Lung Volumes Expiratory reserve volume – inhale normally and exhale forcefully Residual volume – air remaining after expiratory reserve volume exhaled Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume Total lung capacity = vital capacity + residual volume Copyright 2009, John Wiley & Sons, Inc.

36 Exchange of Oxygen and Carbon Dioxide
Dalton’s Law Each gas in a mixture of gases exerts its own pressure as if no other gases were present Pressure of a specific gas is partial pressure Px Total pressure is the sum of all the partial pressures Atmospheric pressure (760 mmHg) = PN2 + PO2 + PH2O + PCO2 + Pother gases Each gas diffuses across a permeable membrane from the are where its partial pressure is greater to the area where its partial pressure is less The greater the difference, the faster the rate of diffusion Copyright 2009, John Wiley & Sons, Inc.

37 Partial Pressures of Gases in Inhaled Air
PN2 =0.786 x 760mm Hg = mmHg PO2 =0.209 = mmHg PH2O =0.004 = 3.0 mmHg PCO2 =0.0004 = 0.3 mmHg Pother gases =0.0006 = 0.5 mmHg TOTAL = mmHg Copyright 2009, John Wiley & Sons, Inc.

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Henry’s law Quantity of a gas that will dissolve in a liquid is proportional to the partial pressures of the gas and its solubility Higher partial pressure of a gas over a liquid and higher solubility, more of the gas will stay in solution Much more CO2 is dissolved in blood than O2 because CO2 is 24 times more soluble Even though the air we breathe is mostly N2, very little dissolves in blood due to low solubility Decompression sickness (bends) Copyright 2009, John Wiley & Sons, Inc.

39 External Respiration in Lungs
Oxygen Oxygen diffuses from alveolar air (PO2 105 mmHg) into blood of pulmonary capillaries (PO2 40 mmHg) Diffusion continues until PO2 of pulmonary capillary blood matches PO2 of alveolar air Small amount of mixing with blood from conducting portion of respiratory system drops PO2 of blood in pulmonary veins to 100 mmHg Carbon dioxide Carbon dioxide diffuses from deoxygenated blood in pulmonary capillaries (PCO2 45 mmHg) into alveolar air (PCO2 40 mmHg) Continues until of PCO2 blood reaches 40 mmHg Copyright 2009, John Wiley & Sons, Inc.

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Internal Respiration Internal respiration – in tissues throughout body Oxygen Oxygen diffuses from systemic capillary blood (PO2 100 mmHg) into tissue cells (PO2 40 mmHg) – cells constantly use oxygen to make ATP Blood drops to 40 mmHg by the time blood exits the systemic capillaries Carbon dioxide Carbon dioxide diffuses from tissue cells (PCO2 45 mmHg) into systemic capillaries (PCO2 40 mmHg) – cells constantly make carbon dioxide PCO2 blood reaches 45 mmHg At rest, only about 25% of the available oxygen is used Deoxygenated blood would retain 75% of its oxygen capacity Copyright 2009, John Wiley & Sons, Inc.

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42 Rate of Pulmonary and Systemic Gas Exchange
Depends on Partial pressures of gases Alveolar PO2 must be higher than blood PO2 for diffusion to occur – problem with increasing altitude Surface area available for gas exchange Diffusion distance Molecular weight and solubility of gases O2 has a lower molecular weight and should diffuse faster than CO2 except for its low solubility - when diffusion is slow, hypoxia occurs before hypercapnia Copyright 2009, John Wiley & Sons, Inc.

43 Transport of Oxygen and Carbon Dioxide
Oxygen transport Only about 1.5% dissolved in plasma 98.5% bound to hemoglobin in red blood cells Heme portion of hemoglobin contains 4 iron atoms – each can bind one O2 molecule Oxyhemoglobin Only dissolved portion can diffuse out of blood into cells Oxygen must be able to bind and dissociate from heme Copyright 2009, John Wiley & Sons, Inc.

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45 Relationship between Hemoglobin and Oxygen Partial Pressure
Higher the PO2, More O2 combines with Hb Fully saturated – completely converted to oxyhemoglobin Percent saturation expresses average saturation of hemoglobin with oxygen Oxygen-hemoglobin dissociation curve In pulmonary capillaries, O2 loads onto Hb In tissues, O2 is not held and unloaded 75% may still remain in deoxygenated blood (reserve) Copyright 2009, John Wiley & Sons, Inc.

46 Oxygen-hemoglobin Dissociation Curve
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Hemoglobin and Oxygen Other factors affecting affinity of Hemoglobin for oxygen Each makes sense if you keep in mind that metabolically active tissues need O2, and produce acids, CO2, and heat as wastes Acidity PCO2 Temperature Copyright 2009, John Wiley & Sons, Inc.

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Bohr Effect As acidity increases (pH decreases), affinity of Hb for O2 decreases Increasing acidity enhances unloading Shifts curve to right PCO2 Also shifts curve to right As PCO2 rises, Hb unloads oxygen more easily Low blood pH can result from high PCO2 Copyright 2009, John Wiley & Sons, Inc.

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Temperature Changes Within limits, as temperature increases, more oxygen is released from Hb During hypothermia, more oxygen remains bound 2,3-bisphosphoglycerate BPG formed by red blood cells during glycolysis Helps unload oxygen by binding with Hb Copyright 2009, John Wiley & Sons, Inc.

50 Fetal and Maternal Hemoglobin
Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin Hb-F can carry up to 30% more oxygen Maternal blood’s oxygen readily transferred to fetal blood Copyright 2009, John Wiley & Sons, Inc.

51 Carbon Dioxide Transport
Dissolved CO2 Smallest amount, about 7% Carbamino compounds About 23% combines with amino acids including those in Hb Carbaminohemoglobin Bicarbonate ions 70% transported in plasma as HCO3- Enzyme carbonic anhydrase forms carbonic acid (H2CO3) which dissociates into H+ and HCO3- Copyright 2009, John Wiley & Sons, Inc.

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CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- Chloride shift HCO3- accumulates inside RBCs as they pick up carbon dioxide Some diffuses out into plasma To balance the loss of negative ions, chloride (Cl-) moves into RBCs from plasma Reverse happens in lungs – Cl- moves out as moves back into RBCs Copyright 2009, John Wiley & Sons, Inc.

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End of Chapter 23 Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein. Copyright 2009, John Wiley & Sons, Inc.


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