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Physiology 1021

Physiology 1021 Mini-Test III 1 Respiratory Physiology Organization and Structure The functions of the respiratory system include: 1. Provides O 2o the blood 2. Removes CO fr2m the blood 3. Regulates [H+], blood pH (range of blood pH is 7.2-7.4) 4. Speech 5. Microbe defence 6. Influences arterial concentration of chemical messengers 7. Traps and dissolves small blood clots (secretes enzymes as blood passes) Gas exchange takes place in the alveoli at the blood-gas-barrier (separates blood in the pulmonary capillary from air in the alveoli) o Air is brought to the other side by pulmonary circulation 2 major divisions of the lungs: 1. Conducting zone (anatomical deadspace): Trachea, primary bronchi, bronchioles, terminal bronchioles Provides low resistance to air flow Microbe defence (mucus, cilia, phagocytes) Warms/ moistens air 2. Respiratory zone: Respiratory bronchioles (about 50 000) Alveolar duct Alveoli: smallest functional unit of the lung, from 300-600 million The pulmonary artery also branches extensively and forms a dense network of capillaries which wrap around the alveoli Air going into the respiratory bronchiole is high2[O ] and low 2CO ] o Due to simple diffusion, CO2wants to move out of the blood and into the alveoli 5 factors that maximize simple diffusion across the blood-gas-barrier: o Short diffusion difference (tiny gap) o Very large surface area of alveoli (75m ) o Gradient for diffusion o Lipid-soluble substances (CO2and O 2 o Slow blood flow Boyles Law: pressure varies inversely with volume chiefly responsible for pulmonary ventilation Mechanics of Pulmonary Ventilation The lungs are suspended in the thoracic cavity, and are surrounded by the chest wall, separated from the abdomen by the diaphragm both the lung and chest wall are elastic structures The space between the lung and chest wall is intrapleural space (filled with about 10mL of fluid, reduces friction, causes adhesion) Pressures: 1. Atmospheric pressure (at sea level) = 760mmHg 2. Alveolar pressure, varies between breaths = 760mmHg 3. Intrapleural space pressure = 756mmHg i. Allows for easy expansion of the lung (no resistance to inflation) ii. The lung does not collapse at the end of expiration Physiology 1021 Mini-Test III 2 4. Transpulmonary pressure = alveolar pressure intrapleural pressure (760-756mmHg = 4 mmHg) the outward force keeps lungs inflated so they dont collapse Pneumothorax: a hole occurs in the lung, so intrapleural and alveolar pressure equalize (therefore 0 pressure keeping the lung inflated, so it collapses) Inflation and deflation of the lung are due to changing the volume of the thoracic cavity (action of respiratory muscles) Moving air into the lungs requires a gradient (air pressure) to get air into the lungs, high inside and low pressure outside, a change in alveolar pressure Inspiration at rest and during exercise involves contraction of diaphragm and external intercostal muscles of the ribs o Contraction of these muscles increases the volume of the thoracic cavity o Alveolar pressure decreases, air moves in Expiration: o At rest: a passive process, only involves the relaxation of diaphragm and external intercostal muscles o During exercise: contraction of rectus abdominus, internal and external obliques, internal intercostal muscles these muscles decrease the volume, causing an increase in alveolar pressure Pulmonary compliance: the change in lung volume as a result of a change in alveolar pressure Compliance = change in lung volume/ change in lung pressure (measure of the stretchability of the lungs) Two major factors that influence the compliance of the lung: 1. Elastic tissue components (increasing this will decrease the compliance, increasing the likelihood that the lung will collapse) Fibres of elastin (and collagen) in the walls of the alveoli, blood vessels and bronchi accounts for 1/3 of the elastic behaviour of the lungs The more elastin, the more the lungs want to collapse/recoil, and the harder it is to inflate the lungs 2. Surface tension: the force at the surface of a liquid due to the intermolecular attraction between water molecules Thin film of liquid that lines the alveoli, huge surface tension Accounts for 2/3 of the elastic behaviour It prevents the lungs from expanding, promotes lung collapse Pulmonary surfactant: a phospholipid protein complex, both hydrophobic and hydrophilic o Can lie on the surface of a liquid and reduce surface tension stimulated by deep breathing, produced late in fetal life Lung Volumes Some of the static lung volumes can be measured using a simple spirometer Tidal volume: the amount of air breathed in or out (at rest it is 500mL), increases with exercise Vital capacity: the maximum amount of air that can be exhaled after a maximal inspiration Forced vital capacity: VC as fast as possible Forced expiratory volume: in one second, FEV-1, the amount of air exhaled in the first second during an FVC In a healthy individual, FEV-1 should be roughly 80% of FVC Asthma: can be triggered by exercise, sudden changes in temperature/ humidity and allergies o Leads to an inflammatory reaction causing broncho-constriction (increase in airway resistance, decrease in air flow)Physiology 1021 Mini-Test III 3 Chronic bronchitis: chronic obstructive pulmonary disease (COPD) o Smoking damages protective cilia lining the airways excess mucous production and general inflammation (increase in airway resistance, decrease in airflow) Emphysema: continued smoking damages elastin fibres in the lungs, walls between alveoli break down, creating large air sacs (surface area decreases) o High compliance but no recoil during exhaling, easy to inflate, but difficult to deflate (air must be forcefully exhaled) Pulmonary fibrosis: chronic inhalation of very fine particles (asbestos, coal dust, silicon, air pollution) that cant be destroyed or removed o Leads to immune reaction, and the formation of collagen (inelastic material) which forms fibrous scars in lungs o Decrease in compliance (hard to inflate) Pulmonary ventilation (VE) is the amount of air entering the entire lung (both conducting and respiratory zones) in one minute o VE= tidal volume x respiratory rate The volume of air entering only the respiratory zone each minute is called alveolar ventilation o (VA) VA = VE VD (VD is anatomical dead space vent) o VA = TVxRR CZxRR o VA = RR (TV-CZ) Alveolar ventilation represents the volume of fresh air available for gas exchange. It is difficult to determine, as dead space is hard to measure assumed volume is 1 lb. = 1mL Partial Pressures and Effects on Respiration The partial pressure of a gas is the pressure exerted by any one gas in a mixture of gas or liquid
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