The Respiratory System Anatomy Chapter 22 Respiratory System

The Respiratory System Anatomy Chapter 22, Respiratory System 22 1

Respiratory System § Consists of the respiratory and conducting zones § Respiratory zone § Site of gas exchange § Consists of bronchioles, alveolar ducts, and alveoli Chapter 22, Respiratory System 2

Respiratory System § Conducting zone § Provides rigid conduits for air to reach the sites of gas exchange § Includes all other respiratory structures (e. g. , nose, nasal cavity, pharynx, trachea) § Respiratory muscles – diaphragm and other muscles that promote ventilation Chapter 22, Respiratory System 3

Respiratory System Chapter 22, Respiratory System 4 Figure 22. 1

Major Functions of the Respiratory System § To supply the body with oxygen and dispose of carbon dioxide § Respiration – four distinct processes must happen § Pulmonary ventilation – moving air into and out of the lungs § External respiration – gas exchange between the lungs and the blood Chapter 22, Respiratory System 5

Major Functions of the Respiratory System § Transport – transport of oxygen and carbon dioxide between the lungs and tissues § Internal respiration – gas exchange between systemic blood vessels and tissues Chapter 22, Respiratory System 6

Function of the Nose § The only externally visible part of the respiratory system that functions by: § Providing an airway for respiration § Moistening (humidifying) and warming the entering air § Filtering inspired air and cleaning it of foreign matter § Serving as a resonating chamber for speech § Housing the olfactory receptors Chapter 22, Respiratory System 7

Structure of the Nose § The nose is divided into two regions § The external nose, including the root, bridge, dorsum nasi, and apex § The internal nasal cavity § Philtrum – a shallow vertical groove inferior to the apex § The external nares (nostrils) are bounded laterally by the alae Chapter 22, Respiratory System 8

Structure of the Nose Chapter 22, Respiratory System 9 Figure 22. 2 a

Structure of the Nose Chapter 22, Respiratory System Figure 22. 2 b 10

Nasal Cavity § Lies in and posterior to the external nose § Is divided by a midline nasal septum § Opens posteriorly into the nasal pharynx via internal nares § The ethmoid and sphenoid bones form the roof § The floor is formed by the hard and soft palates Chapter 22, Respiratory System 11

Nasal Cavity § Vestibule – nasal cavity superior to the nares § Vibrissae – hairs that filter coarse particles from inspired air § Olfactory mucosa § Lines the superior nasal cavity § Contains smell receptors Chapter 22, Respiratory System 12

Nasal Cavity § Respiratory mucosa § Lines the balance of the nasal cavity § Glands secrete mucus containing lysozyme and defensins to help destroy bacteria Chapter 22, Respiratory System 13

Nasal Cavity Chapter 22, Respiratory System Figure 22. 3 b 14

Nasal Cavity § Inspired air is: § Humidified by the high water content in the nasal cavity § Warmed by rich plexuses of capillaries § Ciliated mucosal cells remove contaminated mucus Chapter 22, Respiratory System 15

Nasal Cavity § Superior, medial, and inferior conchae: § Protrude medially from the lateral walls § Increase mucosal area § Enhance air turbulence and help filter air § Sensitive mucosa triggers sneezing when stimulated by irritating particles Chapter 22, Respiratory System 16

Functions of the Nasal Mucosa and Conchae § During inhalation the conchae and nasal mucosa: § Filter, heat, and moisten air § During exhalation these structures: § Reclaim heat and moisture § Minimize heat and moisture loss Chapter 22, Respiratory System 17

Paranasal Sinuses § Sinuses in bones that surround the nasal cavity § Sinuses lighten the skull and help to warm and moisten the air Chapter 22, Respiratory System 18

Pharynx § Funnel-shaped tube of skeletal muscle that connects to the: § Nasal cavity and mouth superiorly § Larynx and esophagus inferiorly § Extends from the base of the skull to the level of the sixth cervical vertebra Chapter 22, Respiratory System 19

Pharynx § It is divided into three regions § Nasopharynx § Oropharynx § Laryngopharynx Chapter 22, Respiratory System 20

Nasopharynx § Lies posterior to the nasal cavity, inferior to the sphenoid, and superior to the level of the soft palate § Strictly an air passageway § Lined with pseudostratified columnar epithelium § Closes during swallowing to prevent food from entering the nasal cavity § The pharyngeal tonsil lies high on the posterior wall § Pharyngotympanic (auditory) tubes open into the lateral walls Chapter 22, Respiratory System 21

Oropharynx § Extends inferiorly from the level of the soft palate to the epiglottis § Opens to the oral cavity via an archway called the fauces § Serves as a common passageway for food and air § The epithelial lining is protective stratified squamous epithelium § Palatine tonsils lie in the lateral walls of the fauces § Lingual tonsil covers the base of the tongue Chapter 22, Respiratory System 22

Laryngopharynx § Serves as a common passageway for food and air § Lies posterior to the upright epiglottis § Extends to the larynx, where the respiratory and digestive pathways diverge Chapter 22, Respiratory System 23

Larynx (Voice Box) § Attaches to the hyoid bone and opens into the laryngopharynx superiorly § Continuous with the trachea posteriorly § The three functions of the larynx are: § To provide a patent airway § To act as a switching mechanism to route air and food into the proper channels § To function in voice production Chapter 22, Respiratory System 24

Framework of the Larynx § Cartilages (hyaline) of the larynx § Shield-shaped anterosuperior thyroid cartilage with a midline laryngeal prominence (Adam’s apple) § Signet ring–shaped anteroinferior cricoid cartilage § Three pairs of small arytenoid, cuneiform, and corniculate cartilages § Epiglottis – elastic cartilage that covers the laryngeal inlet during swallowing Chapter 22, Respiratory System 25

Framework of the Larynx Chapter 22, Respiratory System Figure 22. 4 a, b 26

Vocal Ligaments § Attach the arytenoid cartilages to the thyroid cartilage § Composed of elastic fibers that form mucosal folds called true vocal cords § The medial opening between them is the glottis § They vibrate to produce sound as air rushes up from the lungs Chapter 22, Respiratory System 27

Vocal Ligaments § False vocal cords § Mucosal folds superior to the true vocal cords § Have no part in sound production Chapter 22, Respiratory System 28

Vocal Production § Speech – intermittent release of expired air while opening and closing the glottis § Pitch – determined by the length and tension of the vocal cords § Loudness – depends upon the force at which the air rushes across the vocal cords § The pharynx resonates, amplifies, and enhances sound quality § Sound is “shaped” into language by action of the pharynx, tongue, soft palate, and lips Chapter 22, Respiratory System 29

Movements of Vocal Cords Chapter 22, Respiratory System Figure 22. 5 30

Sphincter Functions of the Larynx § The larynx is closed during coughing, sneezing, and Valsalva’s maneuver § Air is temporarily held in the lower respiratory tract by closing the glottis § Causes intra-abdominal pressure to rise when abdominal muscles contract § Helps to empty the rectum § Acts as a splint to stabilize the trunk when lifting heavy loads Chapter 22, Respiratory System 31

Trachea § Flexible and mobile tube extending from the larynx into the mediastinum § Composed of three layers § Mucosa – made up of goblet cells and ciliated epithelium § Submucosa – connective tissue deep to the mucosa § Adventitia – outermost layer made of C-shaped rings of hyaline cartilage Chapter 22, Respiratory System 32

Trachea Chapter 22, Respiratory System Figure 22. 6 a 33

Conducting Zone: Bronchi § The carina of the last tracheal cartilage marks the end of the trachea and the beginning of the right and left bronchi § Air reaching the bronchi is: § Warm and cleansed of impurities § Saturated with water vapor § Bronchi subdivide into secondary bronchi, each supplying a lobe of the lungs § Air passages undergo 23 orders of branching in the lungs Chapter 22, Respiratory System 34

Conducting Zone: Bronchial Tree § Tissue walls of bronchi mimic that of the trachea § As conducting tubes become smaller, structural changes occur § Cartilage support structures change § Epithelium types change § Amount of smooth muscle increases Chapter 22, Respiratory System 35

Conducting Zone: Bronchial Tree § Bronchioles § Consist of cuboidal epithelium § Have a complete layer of circular smooth muscle § Lack cartilage support and mucus-producing cells Chapter 22, Respiratory System 36

Respiratory Zone § Defined by the presence of alveoli; begins as terminal bronchioles feed into respiratory bronchioles § Respiratory bronchioles lead to alveolar ducts, then to terminal clusters of alveolar sacs composed of alveoli § Approximately 300 million alveoli: § Account for most of the lungs’ volume § Provide tremendous surface area for gas exchange Chapter 22, Respiratory System 37

Respiratory Zone Chapter 22, Respiratory System Figure 22. 8 a 38

Respiratory Zone Chapter 22, Respiratory System Figure 22. 8 b 39

Respiratory Membrane § This air-blood barrier is composed of: § Alveolar and capillary walls § Their fused basal laminas § Alveolar walls: § Are a single layer of type I epithelial cells § Permit gas exchange by simple diffusion § Secrete angiotensin converting enzyme (ACE) § Type II cells secrete surfactant Chapter 22, Respiratory System 40

Alveoli § Surrounded by fine elastic fibers § Contain open pores that: § Connect adjacent alveoli § Allow air pressure throughout the lung to be equalized § House macrophages that keep alveolar surfaces sterile PLAY Inter. Active Physiology®: Respiratory System: Anatomy Review: Respiratory Structures Chapter 22, Respiratory System 41

Respiratory Membrane Chapter 22, Respiratory System 42 Figure 22. 9 b

Respiratory Membrane Chapter 22, Respiratory System Figure 22. 9. c, d 43

Gross Anatomy of the Lungs § Lungs occupy all of the thoracic cavity except the mediastinum § Root – site of vascular and bronchial attachments § Costal surface – anterior, lateral, and posterior surfaces in contact with the ribs § Apex – narrow superior tip § Base – inferior surface that rests on the diaphragm § Hilus – indentation that contains pulmonary and systemic blood vessels Chapter 22, Respiratory System 44

Lungs § Cardiac notch (impression) – cavity that accommodates the heart § Left lung – separated into upper and lower lobes by the oblique fissure § Right lung – separated into three lobes by the oblique and horizontal fissures § There are 10 bronchopulmonary segments in each lung Chapter 22, Respiratory System 45

Gross Anatomy of Lungs § Base, apex (cupula), costal surface, cardiac notch § Oblique & horizontal fissure in right lung results in 3 lobes § Oblique fissure only in left lung produces 2 lobes Chapter 22, Respiratory System 46

Mediastinal Surface of Lungs § Blood vessels & airways enter lungs at hilus § Forms root of lungs § Covered with pleura (parietal becomes visceral) Chapter 22, Respiratory System 47

Blood Supply to Lungs § Lungs are perfused by two circulations: pulmonary and bronchial § Pulmonary arteries – supply systemic venous blood to be oxygenated § Branch profusely, along with bronchi § Ultimately feed into the pulmonary capillary network surrounding the alveoli § Pulmonary veins – carry oxygenated blood from respiratory zones to the heart Chapter 22, Respiratory System 48

Blood Supply to Lungs § Bronchial arteries – provide systemic blood to the lung tissue § Arise from aorta and enter the lungs at the hilus § Supply all lung tissue except the alveoli § Bronchial veins anastomose with pulmonary veins § Pulmonary veins carry most venous blood back to the heart Chapter 22, Respiratory System 49

Pleurae § Thin, double-layered serosa § Parietal pleura § Covers the thoracic wall and superior face of the diaphragm § Continues around heart and between lungs Chapter 22, Respiratory System 50

Pleurae § Visceral, or pulmonary, pleura § Covers the external lung surface § Divides the thoracic cavity into three chambers § The central mediastinum § Two lateral compartments, each containing a lung Chapter 22, Respiratory System 51

Breathing § Breathing, or pulmonary ventilation, consists of two phases § Inspiration – air flows into the lungs § Expiration – gases exit the lungs Chapter 22, Respiratory System 52

Pressure Relationships in the Thoracic Cavity § Respiratory pressure is always described relative to atmospheric pressure § Atmospheric pressure (Patm) § Pressure exerted by the air surrounding the body § Negative respiratory pressure is less than Patm § Positive respiratory pressure is greater than Patm Chapter 22, Respiratory System 53

Pressure Relationships in the Thoracic Cavity § Intrapulmonary pressure (Ppul) – pressure within the alveoli § Intrapleural pressure (Pip) – pressure within the pleural cavity Chapter 22, Respiratory System 54

Pressure Relationships § Intrapulmonary pressure and intrapleural pressure fluctuate with the phases of breathing § Intrapulmonary pressure always eventually equalizes itself with atmospheric pressure § Intrapleural pressure is always less than intrapulmonary pressure and atmospheric pressure Chapter 22, Respiratory System 55

Pressure Relationships § Two forces act to pull the lungs away from the thoracic wall, promoting lung collapse § Elasticity of lungs causes them to assume smallest possible size § Surface tension of alveolar fluid draws alveoli to their smallest possible size § Opposing force – elasticity of the chest wall pulls the thorax outward to enlarge the lungs Chapter 22, Respiratory System 56

Pressure Relationships Chapter 22, Respiratory System 57 Figure 22. 12

Lung Collapse § Caused by equalization of the intrapleural pressure with the intrapulmonary pressure § Transpulmonary pressure keeps the airways open § Transpulmonary pressure – difference between the intrapulmonary and intrapleural pressures (Ppul – Pip) Chapter 22, Respiratory System 58

Pulmonary Ventilation § A mechanical process that depends on volume changes in the thoracic cavity § Volume changes lead to pressure changes, which lead to the flow of gases to equalize pressure Chapter 22, Respiratory System 59

Boyle’s Law § Boyle’s law – the relationship between the pressure and volume of gases P 1 V 1 = P 2 V 2 § P = pressure of a gas in mm Hg § V = volume of a gas in cubic millimeters § Subscripts 1 and 2 represent the initial and resulting conditions, respectively Chapter 22, Respiratory System 60

Inspiration § The diaphragm and external intercostal muscles (inspiratory muscles) contract and the rib cage rises § The lungs are stretched and intrapulmonary volume increases § Intrapulmonary pressure drops below atmospheric pressure ( 1 mm Hg) § Air flows into the lungs, down its pressure gradient, until intrapleural pressure = atmospheric pressure Chapter 22, Respiratory System 61

Inspiration Chapter 22, Respiratory System Figure 22. 13. 1 62

Expiration § Inspiratory muscles relax and the rib cage descends due to gravity § Thoracic cavity volume decreases § Elastic lungs recoil passively and intrapulmonary volume decreases § Intrapulmonary pressure rises above atmospheric pressure (+1 mm Hg) § Gases flow out of the lungs down the pressure gradient until intrapulmonary pressure is 0 Chapter 22, Respiratory System 63

Expiration Chapter 22, Respiratory System 64 Figure 22. 13. 2

Physical Factors Influencing Ventilation: Airway Resistance § Friction is the major nonelastic source of resistance to airflow § The relationship between flow (F), pressure (P), and resistance (R) is: P F = R Chapter 22, Respiratory System 65

Physical Factors Influencing Ventilation: Airway Resistance § The amount of gas flowing into and out of the alveoli is directly proportional to P, the pressure gradient between the atmosphere and the alveoli § Gas flow is inversely proportional to resistance with the greatest resistance being in the medium-sized bronchi Chapter 22, Respiratory System 66

Airway Resistance § As airway resistance rises, breathing movements become more strenuous § Severely constricted or obstructed bronchioles: § Can prevent life-sustaining ventilation § Can occur during acute asthma attacks which stops ventilation § Epinephrine release via the sympathetic nervous system dilates bronchioles and reduces air resistance Chapter 22, Respiratory System 67

Alveolar Surface Tension § Surface tension – the attraction of liquid molecules to one another at a liquid-gas interface § The liquid coating the alveolar surface is always acting to reduce the alveoli to the smallest possible size § Surfactant, a detergent-like complex, reduces surface tension and helps keep the alveoli from collapsing Chapter 22, Respiratory System 68

Lung Compliance § The ease with which lungs can be expanded § Specifically, the measure of the change in lung volume that occurs with a given change in transpulmonary pressure § Determined by two main factors § Distensibility of the lung tissue and surrounding thoracic cage § Surface tension of the alveoli Chapter 22, Respiratory System 69

Factors That Diminish Lung Compliance § Scar tissue or fibrosis that reduces the natural resilience of the lungs § Blockage of the smaller respiratory passages with mucus or fluid § Reduced production of surfactant § Decreased flexibility of the thoracic cage or its decreased ability to expand Chapter 22, Respiratory System 70

Factors That Diminish Lung Compliance § Examples include: § Deformities of thorax § Ossification of the costal cartilage § Paralysis of intercostal muscles PLAY Inter. Active Physiology®: Respiratory System: Pulmonary Ventilation Chapter 22, Respiratory System 71

The Respiratory System Physiology Chapter 22, Respiratory System 22 72

Respiratory Volumes § Tidal volume (TV) – air that moves into and out of the lungs with each breath (approximately 500 ml) § Inspiratory reserve volume (IRV) – air that can be inspired forcibly beyond the tidal volume (2100– 3200 ml) § Expiratory reserve volume (ERV) – air that can be evacuated from the lungs after a tidal expiration (1000– 1200 ml) § Residual volume (RV) – air left in the lungs after strenuous expiration (1200 ml) Chapter 22, Respiratory System 73

Respiratory Capacities § Inspiratory capacity (IC) – total amount of air that can be inspired after a tidal expiration (IRV + TV) § Functional residual capacity (FRC) – amount of air remaining in the lungs after a tidal expiration (RV + ERV) § Vital capacity (VC) – the total amount of exchangeable air (TV + IRV + ERV) § Total lung capacity (TLC) – sum of all lung volumes (approximately 6000 ml in males) Chapter 22, Respiratory System 74

Dead Space § Anatomical dead space – volume of the conducting respiratory passages (150 ml) § Alveolar dead space – alveoli that cease to act in gas exchange due to collapse or obstruction § Total dead space – sum of alveolar and anatomical dead spaces Chapter 22, Respiratory System 75

Pulmonary Function Tests § Spirometer – an instrument consisting of a hollow bell inverted over water, used to evaluate respiratory function § Spirometry can distinguish between: § Obstructive pulmonary disease – increased airway resistance § Restrictive disorders – reduction in total lung capacity from structural or functional lung changes Chapter 22, Respiratory System 76

Pulmonary Function Tests § Total ventilation – total amount of gas flow into or out of the respiratory tract in one minute § Forced vital capacity (FVC) – gas forcibly expelled after taking a deep breath § Forced expiratory volume (FEV) – the amount of gas expelled during specific time intervals of the FVC Chapter 22, Respiratory System 77

Pulmonary Function Tests § Increases in TLC, FRC, and RV may occur as a result of obstructive disease § Reduction in VC, TLC, FRC, and RV result from restrictive disease Chapter 22, Respiratory System 78

Alveolar Ventilation § Alveolar ventilation rate (AVR) – measures the flow of fresh gases into and out of the alveoli during a particular time AVR (ml/min) = frequency (breaths/min) X (TV – dead space) (ml/breath) § Slow, deep breathing increases AVR and rapid, shallow breathing decreases AVR Chapter 22, Respiratory System 79

Nonrespiratory Air Movements § Most result from reflex action § Examples include: coughing, sneezing, crying, laughing, hiccupping, and yawning Chapter 22, Respiratory System 80

Basic Properties of Gases: Dalton’s Law of Partial Pressures § Total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture § The partial pressure of each gas is directly proportional to its percentage in the mixture Chapter 22, Respiratory System 81

What is Composition of Air? § Air = 21% O 2, 78% N 2 and. 04% CO 2 § Alveolar air = 14% O 2, 78% N 2 and 5. 2% CO 2 § Expired air = 16% O 2, 78% N 2 and 4. 5% CO 2 § Observations § alveolar air has less O 2 since absorbed by blood § mystery-----expired air has more O 2 & less CO 2 than alveolar air? § Anatomical dead space = 150 ml of 500 ml of tidal volume Chapter 22, Respiratory System 82

Basic Properties of Gases: 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 § The amount of gas that will dissolve in a liquid also depends upon its solubility § Various gases in air have different solubilities: § Carbon dioxide is the most soluble § Oxygen is 1/20 th as soluble as carbon dioxide § Nitrogen is practically insoluble in plasma Chapter 22, Respiratory System 83

Hyperbaric Oxygenation § Clinical application of Henry’s law § Use of pressure to dissolve more O 2 in the blood § treatment for patients with anaerobic bacterial infections (tetanus and gangrene) § anaerobic bacteria die in the presence of O 2 § Hyperbaric chamber pressure raised to 3 to 4 atmospheres so that tissues absorb more O 2 § Used to treat heart disorders, carbon monoxide poisoning, cerebral edema, bone infections, gas embolisms & crush injuries Chapter 22, Respiratory System 84

Composition of Alveolar Gas § The atmosphere is mostly oxygen and nitrogen, while alveoli contain more carbon dioxide and water vapor § These differences result from: § Gas exchanges in the lungs – oxygen diffuses from the alveoli and carbon dioxide diffuses into the alveoli § Humidification of air by conducting passages § The mixing of alveolar gas that occurs with each breath Chapter 22, Respiratory System 85

External Respiration: Pulmonary Gas Exchange § Factors influencing the movement of oxygen and carbon dioxide across the respiratory membrane § Partial pressure gradients and gas solubilities § Matching of alveolar ventilation and pulmonary blood perfusion § Structural characteristics of the respiratory membrane Chapter 22, Respiratory System 86

Partial Pressure Gradients and Gas Solubilities § The partial pressure oxygen (PO 2) of venous blood is 40 mm Hg; the partial pressure in the alveoli is 104 mm Hg § This steep gradient allows oxygen partial pressures to rapidly reach equilibrium (in 0. 25 seconds), and thus blood can move three times as quickly (0. 75 seconds) through the pulmonary capillary and still be adequately oxygenated Chapter 22, Respiratory System 87

Partial Pressure Gradients and Gas Solubilities § Although carbon dioxide has a lower partial pressure gradient: § It is 20 times more soluble in plasma than oxygen § It diffuses in equal amounts with oxygen Chapter 22, Respiratory System 88

Partial Pressure Gradients Chapter 22, Respiratory System Figure 22. 17 89

Chapter 22, Respiratory System 90

Oxygenation of Blood Chapter 22, Respiratory System 91 Figure 22. 18

Ventilation-Perfusion Coupling § Ventilation – the amount of gas reaching the alveoli § Perfusion – the blood flow reaching the alveoli § Ventilation and perfusion must be tightly regulated for efficient gas exchange § Changes in PCO 2 in the alveoli cause changes in the diameters of the bronchioles § Passageways servicing areas where alveolar carbon dioxide is high dilate § Those serving areas where alveolar carbon dioxide is low constrict Chapter 22, Respiratory System 92

Ventilation-Perfusion Coupling Chapter 22, Respiratory System 93 Figure 22. 19

Surface Area and Thickness of the Respiratory Membrane § Respiratory membranes: § Are only 0. 5 to 1 m thick, allowing for efficient gas exchange § Have a total surface area (in males) of about 60 m 2 (40 times that of one’s skin) § Thicken if lungs become waterlogged and edematous, whereby gas exchange is inadequate and oxygen deprivation results § Decrease in surface area with emphysema, when walls of adjacent alveoli break through Chapter 22, Respiratory System 94

Internal Respiration § The factors promoting gas exchange between systemic capillaries and tissue cells are the same as those acting in the lungs § The partial pressures and diffusion gradients are reversed § PO 2 in tissue is always lower than in systemic arterial blood § PO 2 of venous blood draining tissues is 40 mm Hg and PCO 2 is 45 mm Hg PLAY Inter. Active Physiology®: Respiratory System: Gas Exchange Chapter 22, Respiratory System 95

Oxygen Transport § Molecular oxygen is carried in the blood: § Bound to hemoglobin (Hb) within red blood cells § Dissolved in plasma Chapter 22, Respiratory System 96

Oxygen Transport: Role of Hemoglobin § Each Hb molecule binds four oxygen atoms in a rapid and reversible process § The hemoglobin-oxygen combination is called oxyhemoglobin (Hb. O 2) § Hemoglobin that has released oxygen is called reduced hemoglobin (HHb) Lungs HHb + O 2 Hb. O 2 + H+ Tissues Chapter 22, Respiratory System 97

Hemoglobin (Hb) § Saturated hemoglobin – when all four hemes of the molecule are bound to oxygen § Partially saturated hemoglobin – when one to three hemes are bound to oxygen § The rate that hemoglobin binds and releases oxygen is regulated by: § PO 2, temperature, blood p. H, PCO 2, and the concentration of BPG (an organic chemical) § These factors ensure adequate delivery of oxygen to tissue cells Chapter 22, Respiratory System 98

Influence of PO 2 on Hemoglobin Saturation § Hemoglobin saturation plotted against PO 2 produces a oxygen-hemoglobin dissociation curve § 98% saturated arterial blood contains 20 ml oxygen per 100 ml blood (20 vol %) § As arterial blood flows through capillaries, 5 ml oxygen are released § The saturation of hemoglobin in arterial blood explains why breathing deeply increases the PO 2 but has little effect on oxygen saturation in hemoglobin Chapter 22, Respiratory System 99

Hemoglobin Saturation Curve § Hemoglobin is almost completely saturated at a PO 2 of 70 mm Hg § Further increases in PO 2 produce only small increases in oxygen binding § Oxygen loading and delivery to tissue is adequate when PO 2 is below normal levels Chapter 22, Respiratory System 100

Hemoglobin Saturation Curve § Only 20– 25% of bound oxygen is unloaded during one systemic circulation § If oxygen levels in tissues drop: § More oxygen dissociates from hemoglobin and is used by cells § Respiratory rate or cardiac output need not increase Chapter 22, Respiratory System 101

Hemoglobin Saturation Curve Chapter 22, Respiratory System 102 Figure 22. 20

Other Factors Influencing Hemoglobin Saturation § Temperature, H+, PCO 2, and BPG § Modify the structure of hemoglobin and alter its affinity for oxygen § Increases of these factors: § Decrease hemoglobin’s affinity for oxygen § Enhance oxygen unloading from the blood § Decreases act in the opposite manner § These parameters are all high in systemic capillaries where oxygen unloading is the goal Chapter 22, Respiratory System 103

Factors That Increase Release of Oxygen by Hemoglobin § As cells metabolize glucose, carbon dioxide is released into the blood causing: § Increases in PCO 2 and H+ concentration in capillary blood § Declining p. H (acidosis), which weakens the hemoglobin-oxygen bond (Bohr effect) § Metabolizing cells have heat as a byproduct and the rise in temperature increases BPG synthesis § All these factors ensure oxygen unloading in the vicinity of working tissue cells Chapter 22, Respiratory System 104

Hemoglobin and Oxygen Partial Pressure Blood is almost fully saturated at p. O 2 of 60 mm § people OK at high altitudes & with some disease Between 40 & 20 mm Hg, large amounts of O 2 are released as in areas of need like contracting muscle tissues lungs Chapter 22, Respiratory System 105

p. CO 2 & Oxygen Release As p. CO 2 rises with exercise, O 2 is released more easily CO 2 converts to carbonic acid & becomes H+ and bicarbonate ions & lowers p. H. Chapter 22, Respiratory System 106

Acidity & Oxygen Affinity for Hb As H+ increases (decrease in p. H), O 2 affinity for Hb decreases Bohr effect allows the blood to unload oxygen H+ binds to hemoglobin & alters it O 2 left behind in needy tissues Chapter 22, Respiratory System 107

Temperature & Oxygen Release As temperature increases, more O 2 is released Metabolic activity & heat increases Chapter 22, Respiratory System 108

Hemoglobin-Nitric Oxide Partnership § Nitric oxide (NO) is a vasodilator that plays a role in blood pressure regulation § Hemoglobin is a vasoconstrictor and a nitric oxide scavenger (heme destroys NO) § However, as oxygen binds to hemoglobin: § Nitric oxide binds to a cysteine amino acid on hemoglobin § Bound nitric oxide is protected from degradation by hemoglobin’s iron Chapter 22, Respiratory System 109

Hemoglobin-Nitric Oxide Partnership § The hemoglobin is released as oxygen is unloaded, causing vasodilation § As deoxygenated hemoglobin picks up carbon dioxide, it also binds nitric oxide and carries these gases to the lungs for unloading Chapter 22, Respiratory System 110

Carbon Dioxide Transport § Carbon dioxide is transported in the blood in three forms § Dissolved in plasma – 7 to 10% § Chemically bound to hemoglobin – 20% is carried in RBCs as carbaminohemoglobin § Bicarbonate ion in plasma – 70% is transported as bicarbonate (HCO 3–) Chapter 22, Respiratory System 111

Transport and Exchange of Carbon Dioxide § Carbon dioxide diffuses into RBCs and combines with water to form carbonic acid (H 2 CO 3), which quickly dissociates into hydrogen ions and bicarbonate ions CO 2 Carbon dioxide + H 2 O Water H 2 CO 3 Carbonic acid H+ Hydrogen ion + HCO 3– Bicarbonate ion § In RBCs, carbonic anhydrase reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid Chapter 22, Respiratory System 112

Transport and Exchange of Carbon Dioxide Chapter 22, Respiratory System Figure 22. 22 a 113

Transport and Exchange of Carbon Dioxide § At the tissues: § Bicarbonate quickly diffuses from RBCs into the plasma § The chloride shift – to counterbalance the outrush of negative bicarbonate ions from the RBCs, chloride ions (Cl–) move from the plasma into the erythrocytes Chapter 22, Respiratory System 114

Transport and Exchange of Carbon Dioxide § At the lungs, these processes are reversed § Bicarbonate ions move into the RBCs and bind with hydrogen ions to form carbonic acid § Carbonic acid is then split by carbonic anhydrase to release carbon dioxide and water § Carbon dioxide then diffuses from the blood into the alveoli Chapter 22, Respiratory System 115

Transport and Exchange of Carbon Dioxide Chapter 22, Respiratory System Figure 22. 22 b 116

Haldane Effect § The amount of carbon dioxide transported is markedly affected by the PO 2 § Haldane effect – the lower the PO 2 and hemoglobin saturation with oxygen, the more carbon dioxide can be carried in the blood Chapter 22, Respiratory System 117

Haldane Effect § At the tissues, as more carbon dioxide enters the blood: § More oxygen dissociates from hemoglobin (Bohr effect) § More carbon dioxide combines with hemoglobin, and more bicarbonate ions are formed § This situation is reversed in pulmonary circulation Chapter 22, Respiratory System 118

Haldane Effect Chapter 22, Respiratory System Figure 22. 23 119

Influence of Carbon Dioxide on Blood p. H § The carbonic acid–bicarbonate buffer system resists blood p. H changes § If hydrogen ion concentrations in blood begin to rise, excess H+ is removed by combining with HCO 3– § If hydrogen ion concentrations begin to drop, carbonic acid dissociates, releasing H+ Chapter 22, Respiratory System 120

Influence of Carbon Dioxide on Blood p. H § Changes in respiratory rate can also: § Alter blood p. H § Provide a fast-acting system to adjust p. H when it is disturbed by metabolic factors PLAY Inter. Active Physiology®: Respiratory System: Gas Transport Chapter 22, Respiratory System 121

Control of Respiration: Medullary Respiratory Centers § The dorsal respiratory group (DRG), or inspiratory center: § Is located near the root of nerve IX § Appears to be the pacesetting respiratory center § Excites the inspiratory muscles and sets eupnea (1215 breaths/minute) § Becomes dormant during expiration § The ventral respiratory group (VRG) is involved in forced inspiration and expiration Chapter 22, Respiratory System 122

Control of Respiration: Medullary Respiratory Centers Chapter 22, Respiratory System Figure 22. 24 123

Control of Respiration: Pons Respiratory Centers § Pons centers: § Influence and modify activity of the medullary centers § Smooth out inspiration and expiration transitions and vice versa § The pontine respiratory group (PRG) – continuously inhibits the inspiration center Chapter 22, Respiratory System 124

Respiratory Rhythm § A result of reciprocal inhibition of the interconnected neuronal networks in the medulla § Other theories include § Inspiratory neurons are pacemakers and have intrinsic automaticity and rhythmicity § Stretch receptors in the lungs establish respiratory rhythm Chapter 22, Respiratory System 125

Depth and Rate of Breathing § Inspiratory depth is determined by how actively the respiratory center stimulates the respiratory muscles § Rate of respiration is determined by how long the inspiratory center is active § Respiratory centers in the pons and medulla are sensitive to both excitatory and inhibitory stimuli Chapter 22, Respiratory System 126

Medullary Respiratory Centers Chapter 22, Respiratory System Figure 22. 25 127

Depth and Rate of Breathing: Reflexes § Pulmonary irritant reflexes – irritants promote reflexive constriction of air passages § Inflation reflex (Hering-Breuer) – stretch receptors in the lungs are stimulated by lung inflation § Upon inflation, inhibitory signals are sent to the medullary inspiration center to end inhalation and allow expiration Chapter 22, Respiratory System 128

Depth and Rate of Breathing: Higher Brain Centers § Hypothalamic controls act through the limbic system to modify rate and depth of respiration § Example: breath holding that occurs in anger § A rise in body temperature acts to increase respiratory rate § Cortical controls are direct signals from the cerebral motor cortex that bypass medullary controls § Examples: voluntary breath holding, taking a deep breath Chapter 22, Respiratory System 129

Depth and Rate of Breathing: PCO 2 § Changing PCO 2 levels are monitored by chemoreceptors of the brain stem § Carbon dioxide in the blood diffuses into the cerebrospinal fluid where it is hydrated § Resulting carbonic acid dissociates, releasing hydrogen ions § PCO 2 levels rise (hypercapnia) resulting in increased depth and rate of breathing Chapter 22, Respiratory System 130

Depth and Rate of Breathing: PCO 2 Chapter 22, Respiratory System Figure 22. 26 131

Depth and Rate of Breathing: PCO 2 § Hyperventilation – increased depth and rate of breathing that: § Quickly flushes carbon dioxide from the blood § Occurs in response to hypercapnia § Though a rise CO 2 acts as the original stimulus, control of breathing at rest is regulated by the hydrogen ion concentration in the brain Chapter 22, Respiratory System 132

Depth and Rate of Breathing: PCO 2 § Hypoventilation – slow and shallow breathing due to abnormally low PCO 2 levels § Apnea (breathing cessation) may occur until PCO 2 levels rise Chapter 22, Respiratory System 133

Depth and Rate of Breathing: PCO 2 § Arterial oxygen levels are monitored by the aortic and carotid bodies § Substantial drops in arterial PO 2 (to 60 mm Hg) are needed before oxygen levels become a major stimulus for increased ventilation § If carbon dioxide is not removed (e. g. , as in emphysema and chronic bronchitis), chemoreceptors become unresponsive to PCO 2 chemical stimuli § In such cases, PO 2 levels become the principal respiratory stimulus (hypoxic drive) Chapter 22, Respiratory System 134

Depth and Rate of Breathing: Arterial p. H § Changes in arterial p. H can modify respiratory rate even if carbon dioxide and oxygen levels are normal § Increased ventilation in response to falling p. H is mediated by peripheral chemoreceptors Chapter 22, Respiratory System 135

Peripheral Chemoreceptors Chapter 22, Respiratory System Figure 22. 27 136

Depth and Rate of Breathing: Arterial p. H § Acidosis may reflect: § Carbon dioxide retention § Accumulation of lactic acid § Excess fatty acids in patients with diabetes mellitus § Respiratory system controls will attempt to raise the p. H by increasing respiratory rate and depth Chapter 22, Respiratory System 137

Respiratory Adjustments: Exercise § Respiratory adjustments are geared to both the intensity and duration of exercise § During vigorous exercise: § Ventilation can increase 20 fold § Breathing becomes deeper and more vigorous, but respiratory rate may not be significantly changed (hyperpnea) § Exercise-enhanced breathing is not prompted by an increase in PCO 2 or a decrease in PO 2 or p. H § These levels remain surprisingly constant during exercise Chapter 22, Respiratory System 138

Respiratory Adjustments: Exercise § As exercise begins: § Ventilation increases abruptly, rises slowly, and reaches a steady state § When exercise stops: § Ventilation declines suddenly, then gradually decreases to normal Chapter 22, Respiratory System 139

Respiratory Adjustments: Exercise § Neural factors bring about the above changes, including: § Psychic stimuli § Cortical motor activation § Excitatory impulses from proprioceptors in muscles PLAY Inter. Active Physiology®: Respiratory System: Control of Respiration Chapter 22, Respiratory System 140

Respiratory Adjustments: High Altitude § The body responds to quick movement to high altitude (above 8000 ft) with symptoms of acute mountain sickness – headache, shortness of breath, nausea, and dizziness Chapter 22, Respiratory System 141

Respiratory Adjustments: High Altitude § Acclimatization – respiratory and hematopoietic adjustments to altitude include: § Increased ventilation – 2 -3 L/min higher than at sea level § Chemoreceptors become more responsive to PCO 2 § Substantial decline in PO 2 stimulates peripheral chemoreceptors Chapter 22, Respiratory System 142

Pneumothorax § Pleural cavities are sealed cavities not open to the outside § Injuries to the chest wall that let air enter the intrapleural space § causes a pneumothorax § collapsed lung on same side as injury § surface tension and recoil of elastic fibers causes the lung to collapse Chapter 22, Respiratory System 143

Smokers Lowered Respiratory Efficiency Smoker is easily “winded” with moderate exercise § nicotine constricts terminal bronchioles § carbon monoxide in smoke binds to hemoglobin § irritants in smoke cause excess mucus secretion § irritants inhibit movements of cilia § in time destroys elastic fibers in lungs & leads to emphysema § trapping of air in alveoli & reduced gas exchange Every thirteen seconds someone dies from a smoking-related disease. Chapter 22, Respiratory System 144

Chapter 22, Respiratory System 145

Chapter 22, Respiratory System 146

Chronic Obstructive Pulmonary Disease (COPD) § Exemplified by chronic bronchitis and obstructive emphysema § Patients have a history of: § Smoking § Dyspnea, where labored breathing occurs and gets progressively worse § Coughing and frequent pulmonary infections § COPD victims develop respiratory failure accompanied by hypoxemia, carbon dioxide retention, and respiratory acidosis Chapter 22, Respiratory System 147

Chronic Obstructive Pulmonary Disease § progressive airflow limitations caused by an abnormal inflammatory reaction to the chronic inhalation of particles § chronic bronchitis and emphysema § Signs of COPD are consequences of the anatomical changes caused by the disease: § barrel chest § pursed-lip breathing § productive cough § cyanosis. Chapter 22, Respiratory System 148

Pathogenesis of COPD Chapter 22, Respiratory System Figure 22. 28 149

Asthma § Characterized by dyspnea, wheezing, and chest tightness § Active inflammation of the airways precedes bronchospasms § Airway inflammation is an immune response caused by release of IL-4 and IL-5, which stimulate Ig. E and recruit inflammatory cells § Airways thickened with inflammatory exudates magnify the effect of bronchospasms Chapter 22, Respiratory System 150

Tuberculosis § Infectious disease caused by the bacterium Mycobacterium tuberculosis § Symptoms include fever, night sweats, weight loss, a racking cough, and splitting headache § Treatment entails a 12 -month course of antibiotics Chapter 22, Respiratory System 151

Lung Cancer § Accounts for 1/3 of all cancer deaths in the U. S. § 90% of all patients with lung cancer were smokers § The three most common types are: § Squamous cell carcinoma (20 -40% of cases) arises in bronchial epithelium § Adenocarcinoma (25 -35% of cases) originates in peripheral lung area § Small cell carcinoma (20 -25% of cases) contains lymphocyte-like cells that originate in the primary bronchi and subsequently metastasize Chapter 22, Respiratory System 152

Developmental Aspects § Olfactory placodes invaginate into olfactory pits by the 4 th week § Laryngotracheal buds are present by the 5 th week § Mucosae of the bronchi and lung alveoli are present by the 8 th week § By the 28 th week, a baby born prematurely can breathe on its own § During fetal life, the lungs are filled with fluid and blood bypasses the lungs § Gas exchange takes place via the placenta Chapter 22, Respiratory System 153

Respiratory System Development Chapter 22, Respiratory System 154 Figure 22. 29

Developmental Aspects § At birth, respiratory centers are activated, alveoli inflate, and lungs begin to function § Respiratory rate is highest in newborns and slows until adulthood § Lungs continue to mature and more alveoli are formed until young adulthood § Respiratory efficiency decreases in old age Chapter 22, Respiratory System 155