The Respiratory System

1. The Respiratory System CHAPTER 23

2. Introduction • Body cells must obtain oxygen and eliminate carbon dioxide. • This gas exchange occurs at the alveoli of the lungs. • Functions are: • providing an area for gas exchange between air and circulating fluid. • Moving air to and from exchange surfaces. • protecting respiratory surfaces from environmental variations and pathogens. • permitting vocal communications. • providing olfactory sensations to the CNS.

3. Organization • The respiratory system includes the nose, nasal cavity, paranasal sinuses, pharynx, larynx, trachea, bronchi, bronchioles and alveoli of the lungs. • The respiratory tract consists of the conducting passageways that carry air to and from the alveoli. • Upper respiratory system:filter and humidify the air. • Lower respiratory system: includes delicate conduction passages and the alveolar exchange surfaces.

4. The upper respiratory system • Components are the nose, nasal cavity, paranasal sinuses and pharynx. • Air enters the external nares which open into the nasal cavity. • The vestibule is guarded by hair that screen out large particles. • Incoming air flows through the superior, inferior and middle meatuses and bounces off the conchal surfaces. • The hard palate separates the oral and nasal cavities. The connections between the nasal cavity and nasopharynx are the internal nares.

5. The upper respiratory system • Nasal mucosa-traps particles, warms incoming and cools outgoing. • The pharynx: this is a chamber shared by the digestive and respiratory systems. • The nasopharynx is the superior part of the pharynx. • The oropharynx is continuous with the oral cavity. • The laryngopharynx includes the narrow zone between the hyoid and entrance to the esophagus.

6. The Larynx • The larynx surrounds and protects the glottis. • Inspired air passes through the glottis en route to the lungs. • The larynx is made of cartilages-large are thyroid, cricoid and epiglottis and smaller arytenoid, corniculate and cuneiform • The ext.laryngeal muscles position and stabilize the larynx. • The int.laryngeal muscles regulate tension in the vocal folds and open and close the glottis. • During swallowing, both sets of muscles help prevent particles from entering the glottis.

7. The Trachea • The trachea extends from the sixth cervical vertebra to the fifth thoracic vertebra. • The posterior tracheal wall can distort to permit large masses of food to pass through the esophagus. • The trachea branches within the mediastanium to for the left and right primary bronchi. • Each bronchus then enters the lung at a hilus. • The root of the lung is a connective tissue mass including the bronchus, pulmonary vessels and nerves.

8. The Lungs • Each lung occupies a single pleur; cavity lined by a pleura (serous memebrnae). • There are two pleurae-a parietal pleura covering the inner surface of the thoracic wall and a visceral pleura that covers the lungs. • Each lung has lobes that are separated by fissures. The right has three lobes and the left has two lobes. • The primary bronchi and their branches for the braonchila tree. • The sec. And tert. Are branches within the lungs. The tert. Supplies to a bronchopulmonary segment. • Bronchioles within this ultimately branch into terminla bronchioles.

9. The Lungs • Each terminal bronchiole delivers air to a single pulmonary lobule. • Within the lobule this branches into respiratory bronchioles which open into alveolar ducts. • Many alveoli are interconnected at each duct. • The respiratory membrane consists of simple squamous epithelium. Surfactant cells that are scattered produce an oily secretion that keeps the alveoli form collapsing. • Alveolar macrophages patrol the epithelium and engulf foreign particles. • Blood supply:ext.carotid arteries, thyrocervical trunks and bronchial arteries.

10. Respiratory Physiology • Respiratory physiology focuses on a series of integrated processes. • External respiration: the exchange of oxygen and carbon dioxide between the interstitial fluids and the external environment. • Pulmonary ventilation-breathing • internal respiration: exchange of oxygen and carbon dioxide between the interstitial fluid and living cells. • If oxygen content declines-hypoxia • if oxygen completely shut off-anoxia

11. Pulmonary Ventilation • As pressure on a gas decreases, its volume expands and as pressure increases, volume contracts-this is Boyle’s Law. • The relationship between intrapulmonary pressure and atmospheric pressure determines the direction of air flow. Intrapleural pressure is the pressure in the space between the parietal and visceral pleurae. • Eupnea is quiet breathing that involves the diaphragm and the intercostals. • Hyperpnea:forced breathing. Here accessory muscles become active during inspiratory and expiratory movements.

12. Alveolar Ventilation • Alveolar ventilation is the amount of air reaching the alveoli per minute. • Vital capacity includes the tidal volume plus the expiratory and inspiratory reserve volume. • The air left in the lungs at the end of maximum expiration is the residual volume. • Dalton’s Law: in a mixed gas, the individual gases exert a pressure proportional to their abundance in the mixture. The pressure contributed is partial pressure. • Henry’s Law: the amount of gas in solution is directly proportional to the partial pressure of that gas.

13. Respiratory Volumes and Pulmonary function Tests • The four respiratory volumes are tidal, inspiratory reserve, expiratory reserve and residual. • The four respiratory capacities are vital, functional residual, inspiratory and total lung. • Respiratory volumes and capacities may be measured by spirometry. • Anatomical and alveolar dead space: some of the inspired air fills the conducting respiratory passageways and never contributes to gas exchange-anatomical dead space. (150 mL). • If some of the alveoli cease to function-alveolar dead space. Sum of the two =total dead space.

14. Gas Pickup and Delivery • Blood entering peripheral capillaries delivers oxygen and absorbs carbon dioxide. • The transport of these two gases in the blood involves reactions that are completely reversible. • Over the range of oxygen pressures normally present in the body, a small change in the PO2 will lead to a large change in the amount of oxygen bound or released. • At alveolar PO2, hemoglobin is almost fully saturated. • At the PO2 of peripheral tissues it retains a substantial oxygen reserve. • When PO2 low. RBC’s generate2,3 bisphosphoglycerate which reduces Hb affinity for oxygen.

15. Gas Pickup and delivery • Fetal hemoglobin has a stronger affinity for oxygen than does adult hemoglobin. This aids the removal of oxygen from the maternal blood. • Aerobic metabolism generates CO2. About 7%dissolved in plasma, 23%carbaminohemoglobin and the rest as carbonic acid that dissociated into H+ and HCO3-

16. Control of Respiration • Local factors regulate blood flow(perfusion) and airflow (ventilation). • Alveolar capillaries constrict under conditions of low oxygen, and bronchioles dilate under conditions of high carbon dioxide. • The respiratory centers include three pairs of nuclei in the reticular formation of pons and medulla oblongata. • The respiratory rhythmicity set the pace for respiration. • The apneustic centers-strong sustained inspiratory movements. • The pneumotaxic centers-promote exhalation.

17. Control of Respiration • The inflation reflex-prevents over expansion of the lungs during forced breathing. • The deflation reflex-stimulates inspiration when the lungs are collapsing. • Chemoreceptor reflexes-changes in PO2 and PCO2 of blood and CSF. • Conscious and unconscious thought can also affect respiration by affecting the respiratory centers.

18. Aging and the Respiratory System • Less efficient in the elderly. • Elastic tissue deteriorates. Lowering the vital capacity of the lungs. • Movements of the chest are restricted by arthritic changes and decreased flexibility of costal cartilages. • Emphysema develops.