Download Respiratory System: Structure, Function, and Gas Exchange in Organisms - Prof. Douglas N. and more Study notes Biology in PDF only on Docsity! 18 April Respiratory System: Part I Single celled vs. multicellular organisms Fish: gills Evolution to land vertebrates: lungs Focus is normal respiratory physiology as basis for understanding its pathophysiology Respiration External respiration: exchange of gases between the lungs and outside air Internal respiration: the exchange of gases between blood and various tissues Cellular respiration: utilization of oxygen at mitochondria Overview Respiration Organization of airways and lungs Ventilation and lung mechanics Gas exchange between alveoli and blood Gas exchange between blood and tissue Transport of oxygen and carbon dioxide in blood Control of respiration Ventilation-perfusion abnormalities Functions of the Respiratory System Provides oxygen Eliminates carbon dioxide Regulates the blood’s hydrogen ion concentration (pH) in coordination with the kidneys Forms speech sounds (phonation) Defends against microbes Influences arterial concentrations of chemical messengers by removing some from pulmonary capillary blood and producing and adding others to this blood Traps and dissolves blood clots arising from systemic (usually leg) veins Functions of the Conducting Zone of the Airways Provides a low-resistance pathway for air flow; resistance is physiologically regulated by changes in contraction of airway smooth muscle and by physical forces acting upon the airways Defends against microbes, toxic chemicals, and other foreign matter; cilia, mucus, and macrophages perform this function Warms and moistens the air Phonates (vocal cords) Figure 13-1 The major parts of the “airways” used in ventilation (breathing). The lungs have several lobes. Figure 13-2 Conducting zone – the relaxation/contraction of circular smooth muscle lining these “airways” determines how easily airflow can occur (bronchodilation vs. bronchoconstriction) Respiratory zone – most gas exchange occurs in the ~8,000,000 alveolar sacs Mucus elevator Goblet cells secrete mucus Columnar epithelial cells have cilia Cilia move mucus to pharynx About 0.2 μm thick; total surface area is size of tennis court Alveolar pores: alternate gas routes; helps prevent alveolar collapse if an alveoli is obstructed Elastic fibers: stretches like rubber band; lung compliance Ventilation Ventilation: exchange of air between the atmosphere and alveoli Inspiration (inhalation) is the inward movement of air through airways to alveoli Expiration (exhalation) is the outward movement of gases Respiratory cycle comprises inspiration and expiration. About 5 seconds duration if respiratory rate is 12 breaths per minute Minute volume: volume of air that enters and leaves the lungs each minute. (At rest, about 5 L/ min; heavy exercise, about 20-fold greater) Figure 13-5 The space inside the lung is filled with air The intrapleural fluid is found between the lungs and the thoracic and diaphragm wall Movement of the thoracic wall and diaphragm drives the ventilation cycle Lungs, chest wall, diaphragm and pleurae Understood anatomical relationships Intercostal muscles and diaphragm: regulate expansion of the thoracic space and pressure within the intrapleural fluid Pleura Visceral pleura (pleural sac): this thin sheet of cells is attached to and envelops all lung lobes completely Parietal pleura: attached to and completely lines the thoracic cavity including chest wall and diaphragm Intrapleural fluid: Very thin fluid-filled space (pleural space) between the visceral pleura and the parietal pleura. Fluid lubricates between the lung and chest pleural surfaces so they can slide easily during breathing. Example – two glass plates with drop of water between Roles of Pleurae Inspiration: muscles contract, chest wall expands, intrapleural pressure falls, causing lungs to expand Expiration: chest wall recoils passively, intrapleural pressure increases, causing lungs to recoil and contract Pleurisy or pleuritis: inflammation of pleurae; painful to breathe because of the friction between these layers Pleural effusion: excess accumulate of intrapleural fluid. This can limit lung expansion and ventilation. Figure 13-6 Airflow in the lungs is called ventilation Gases exchange by diffusion Bloodflow through the pulmonary capillaries is driven by the contraction of the right ventricle
