Chapter 43 Salt - Chapter 43 Salt-Water Balance and...

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Chapter 43 Salt-Water Balance and Temperature Control I. Maintaining the Extracellular Fluid A. Water Gains and Losses 1 Water is gained by two processes: a. Absorption of water from liquids and solid foods occurs in the gastrointestinal tract. b. Metabolism of nutrients yields water as a byproduct. 2 Water is lost by at least five processes: a. Excretion of water is accomplished by the urinary system. b. Evaporation occurs from respiratory surfaces. c. Evaporation occurs through the skin. d. Sweating occurs on the skin surface. e. Elimination of water in feces is a normal occurrence. 3 The nervous system regulates these processes by regulation of thirst and temperature control (sweating). B. Solute Gains and Losses 1 Solutes are added to the internal environment by three processes: a. Nutrients, mineral ions, drugs, and food additives are absorbed by the gastrointestinal tract. b. Secretion from endocrine glands adds hormones. c. Metabolism reactions contribute waste products. 2 Carbon dioxide waste is disposed of by the respiratory system, but the following must be excreted in urine: a. Ammonia is formed when amino groups are removed from amino acids. b. Urea is formed by reactions in the liver that unite two ammonia molecules with carbon dioxide. c. Uric acid is formed in reactions that degrade nucleic acids. d. Phosphoric acid and sulfuric acid are also produced during protein breakdown. C. Urinary System of Mammals 1 Kidneys (2) filter a variety of substances from the blood. a. Most of the filtrate is returned to the blood; about 1 percent ends up in the kidney’s central cavity (renal pelvis) as urine. b. The kidneys regulate the volume and solute concentrations of extracellular fluid. c. Each kidney is composed of two zones—cortex and medulla—containing numerous blood vessels and working units called nephrons. 2 Urine flows from each kidney through a ureter to a urinary bladder (for storage) and then out of the body through the urethra. 3 Kidney stones are deposits of uric acid that collect in the renal pelvis or lodge in the urethra. D. Nephron Structure 1 Filtration occurs in the glomerulus—a ball of capillaries nestled in the Bowman’s capsule. 2 The Bowman’s capsule collects the filtrate and directs it through the continuous nephron tubules: proximal Æ loop of Henle Æ distal Æ collecting duct. 3 The capillaries exit the glomerulus, converge, then branch again into the peritubular capillaries
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Chapter 43 Salt - Chapter 43 Salt-Water Balance and...

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