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Physiology (634)
PSL201Y1 (124)
Yue Li (8)


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University of Toronto St. George
Yue Li

1 INTRODUCTION TO PHYSIOLOGY THE OVERALL BODY PLAN: A SIMPLIFIED VIEW  THE BODY’S EXTERNAL ENVIRONMENT o The epithelial barrier includes the skin and the linings of the lungs, gastrointestinal system, and kidney tubules. o The barrier is continuous, there is no read separation between the outer surface of the skin and the inside surfaces of the lungs, gastrointestinal system, and kidney tubules.  THE BODY’S INTERNAL ENVIRONMENT o Cells receive nutrients and oxygen from the bloodstream, which also carries carbon dioxide and waste products away from cells. o Most cells are not in direct contact with the blood but instead are surrounded by a separate fluid (internal environment) that exchanges materials with the blood. THE EXCHANGE OF MATERIALS BETWEEN THE EXTERNAL AND INTERNAL o The blood must obtain oxygen, nutrients, and other needed materials from the external environment and must release carbon dioxide and other unneeded materials into it. o Absorption: water, inorganic salts, and nutrients obtained from digested food are transported from the lumen to the bloodstream. o Secretion: stomach uses materials from blood to produce acids and proteins that are than transported into the lumen. o Excretion: unabsorbed materials remain in the gastrointestinal tract are eliminated in the form of feces. o Filtration: in kidneys, fluid from the bloodstream first enters tubules . o Reabsorption: needed materials are selectively transported back. BODY FLUID COMPARTMENTS
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