Physiology Final Essay Questions.Answers

Physiology Final Essay Questions.Answers - Physiology Essay...

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Physiology Essay Questions for Ch. 16, 17, and 18 Ch. 16 1. Describe the structures of the respiratory system and how gas exchange occurs. Gas exchange between the alveolar air and the pulmonary capillaries results in an increased oxygen concentration and a decreased carbon dioxide concentration in the blood leaving the lungs. This blood enters the systemic arteries, where blood gas measurements are taken. Gas exchange in the lungs occurs across an estimated 300 million tiny air sacs known as alveoli. Their enormous number provides a large surface area for diffusion of gases. The diffusion rate is further increased by the fact that each alveolus is only one cell- layer thick so that the total “air-blood barrier” is only two cells across. In order to maximize the rate of gas diffusion between the air and blood, the air-blood barrier provided by the alveoli is extremely thin and has a very large surface area. The alveolar wall isn’t fragile but is strong enough to withstand high stress during heavy exercise and high lung inflation. There are two types of alveolar cells. Type I alveolar cells comprise 95% to 97% of the total surface area of the lung; gas exchange with blood thus occurs primarily through type I alveolar cells. These cells are very thin. Type II alveolar cells are the cells that secrete pulmonary surfactant and that reabsorb Na and H2O, thereby preventing fluid buildup within the alveoli. The air passages of the respiratory system are divided into two functional zones. The respiratory zone is the region where gas exchange occurs, and it therefore includes the respiratory bronchioles and the terminal alveolar sacs. The conducting zone includes all of the anatomical structures through which air passes before reaching the respiratory zone. Air enters the respiratory bronchioles from terminal bronchioles, which are the narrowest of the airways that do not have alveoli and no not contribute to gas exchange. The terminal bronchioles receive air from larger airways, which are formed from successive branchings of the right and left primary bronchi. These two large air passages, in turn, are continuous with the trachea, or windpipe, which is located in the neck in front of the esophagus. Air enters the trachea from the pharynx. In order for air to enter or leave the trachea and lungs, however, it must pass through a valve-like opening called the glottis between the vocal folds. 2. Explain how ventilation is regulated by the CNS and by arterial Pco2 Po2, and pH.
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Chemoreceptor input to the brain stem modifies the rate and depth of breathing so that, under normal conditions, arterial Pco2, pH, and Po2 remain relatively constant. If hypoventilation occurs, Pco2 quickly rises and pH falls. The fall in pH
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