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18 terms

CH 26 Tubular Reabsorption and Tubular Secretion

CHAPTER 26 • THE URINARY SYSTEM
STUDY
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tubular reabsorption
is a selective process that reclaims materials from tubular fluid and returns them to the bloodstream
Reabsorbed substances
include water, glucose, amino acids, urea, and ions, such as sodium, chloride, potassium, bicarbonate, and phosphate
tubular secretion
Some substances not needed by the body are removed from the blood and discharged into the urine
tubular fluid
filtered fluid that has entered the proximal convoluted tubule; composition of tubular fluid changes as it flows along the nephron tubule and through the collecting duct due to reabsorption and secretion
urine
fluid that drains from papillary ducts into the renal pelvis
apical membrane
contacts the tubular fluid
basolateral membrane
contacts interstitial fluid at the base and sides of the cell
paracellular route
between tubule cells; tight junctions do not completely seal off the interstitial fluid from the fluid in the tubule lumen
transcellular route
across tubule cells; substance passes from the fluid in the tubular lumen through the apical membrane of a tubule cell, across the cytosol, and out into interstitial fluid through the basolateral membrane
primary active transport
energy derived from hydrolysis of ATP is used to "pump" a substance across a membrane
secondary active transport
energy stored in an ion's electrochemical gradient, rather than hydrolysis of ATP, drives another substance across a membrane
secondary active transport
Symporters and antiporters
antiporters
move two or more substances in opposite directions across a membrane
symporters
move two or more substances in the same direction across the membrane
transport maximum (Tm)
maximum amount of a substance that can be reabsorbed per unit time
water reabsorption
obligatory water reabsorption and facultative water reabsorption
obligatory water reabsorption
90% of water reabsorption is obligatory; occurs via osmosis together with reabsorption of solutes; is not hormonally regulated; is the water reabsorbed with solutes in tubular fluid; occurs in the proximal convoluted tubule and the descending limb of the loop of Henle
facultative water reabsorption
10% of water reabsorption is facultative; varies according to body needs; is regulated by ADH