Alveolar Gas Exchange Chapter 19.5

Microscopic air sac clusters at the distal ends of the finest respiratory tubes (alveolar ducts) Alveoli Sites of the vital process of gas exchange between the air and the blood Alveolus - tiny space within a thin wall that separates it from adjacent alveoli (SHOW ON DIAGRAM) Megan

Alveolar Pores Alveolar Macrophages Tiny openings in the walls of some alveoli may permit air to pass from one alveolus to another Phagocytic cells in the alveoli and pores that phagocytize airborne agents Job = clean the alveoli Megan

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Respiratory Membrane Fill in Diagram A on Page 2 of Your Packet Macey

Respiratory Membrane Wall of Alveolus Made up of cells that secrete pulmonary surfactant Bulk of the wall consists of a layer of simple squamous epithelium Alveolus Each alveolus is associated with a dense network of capillaries. Alveolar Capillary Membrane Two thicknesses of epithelial cells and basement membranes separate the air in an alveolus and the blood in a capillary. Layers = respiratory membrane (alveolar capillary membrane) Gas exchange occurs through these layers between the alveolar air and the blood. Macey

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Diffusion Through the Respiratory Membrane Solutes Diffuse from higher concentration to lower concentration Determine the direction of solute = must know the concentration gradient Dissolved Gases Partial pressure gradients A gas will diffuse from an area of higher partial pressure to lower partial pressure. When a mixture of gases dissolves in blood, the concentration of each dissolved gas is proportional to its partial pressure. Ally

This happens not just inside the respiratory system! Gas Diffusion Each gas diffuses between blood and its surroundings from areas of higher partial pressure to areas of lower partial pressure until the partial pressures in the two regions reach equilibrium. This happens not just inside the respiratory system! Example: PCO2 of blood entering the pulmonary capillaries is 45 mm Hg, BUT the PCO2 in alveolar air is 40 mm Hg. Carbon dioxide diffusion = blood alveolar air (higher to lower) Increased Diffusion More surface area Shorter distance Greater solubility of gases Steeper partial pressure gradient For example, the PCO2 of blood entering the pulmonary capillaries is 45 mm Hg., but the PCO2 in alveolar air is 40 mm Hg. Carbon dioxide diffuses from blood since the partial pressure is higher, into the alveolar air, where partial pressure is lower. Ally

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Because of this, breath analysis can reveal alcohol in the blood or acetone can be smelled on the breath of a person who has untreated diabetes mellitus. Extra Information The respiratory membrane is very thin, and soluble chemicals other than carbon dioxide may diffuse into alveolar air and be exhaled. Ally

These conditions may require increased PO2 treatment. Pneumonia = inflammation and lots of unnecessary fluid in alveoli Emphysema = damaged alveoli Megan

Disorders that Impair Gas Exchange Pneumonia Alveolar linings swell with edema & are abnormally permeable Allow fluids and WBC’s to accumulate in the air sacs Surface area available for gas exchange diminishes Breathing is difficult Tuberculosis Caused by bacterium Mycobacterium tuberculosis Fibrous connective tissue develops around the sites of infection Form structures called tubercles Atelectasis Collapse of a lung, or some part of it Collapse of the blood vessels that supply the affected region as well Tuberculosis: by walling off the bacteria, the tubercules help stop their spread. Megan

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Electricity = Blood Low in Oxygen but High in Carbon Dioxide Lightbulb = Alveoli Electricity = Blood Low in Oxygen but High in Carbon Dioxide Light = Blood Low in Carbon Dioxide but High in Oxygen Magnetic Field = Air moving in and out of alveolus/Carbon Dioxide and Oxygen diffusing into the blood Heat = oxygen is transported around the body Power = Carbon dioxide diffusing from blood to be exhaled Inside of lightbulb = gas-filled air space Macey