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how is the capillary bed of the glomerulus different from the capillary beds of the peripheral tissues and the pulmonary circulation?
- the glomerular capillaries drain into a high pressure system (the efferent arteriole) rather than a low pressure vein
- this causes the hydrostatic pressure in the glomerulus to remain high (above osmotic pressure) for its entire length. this ensures that fluid will go out, not in
what is the juxtagolomerular apparatus?
- the point of contact between the distal convoluted tubule and the afferent arteriole.
- in the DCT this point has specialized cells called the macula densa (sensing cells) that sense the sodium concentration in the fluid and the fluid volume.
- in the afferent arterole this point has large smooth muscle cells that encircle the vessel and contain granules of renin.
- if flow in the distal tubule is high, the macula densa signals the smooth muscle cells to constrict, decreasing the blood flow and the filtration rate. if the flow in the distal is too low, the macula densa signals the cells to release their renin which raise the blood pressure by producing angiotensin.
solute and water re-absorption is based on _____.
re-absorption of sodium (co-transporters)
how does sodium re-absorption occur?
through symports in the apical membrane down a concentration gradient produced by sodium pumps on the basal membrane of the tubular cell
how does bicarbonate reabsorpiton occur?
- by combining with hydrogen that is pumped into the tublar fluid by the tubular cell to produce carbon dioxide and water.
- the carbon dioxice can cross the apical membrane into the cell where it combines with water to produce hydrogen and bicarbonate. the bicarbonate then diffuses through the basilar membrane and into the capillary.
- H+ + HC03- > H2C03 > H20 + CO2 in the fluid
- CO2 + H20 > H2CO3 > H+ + HCO3- in cell