BIOL 431 Urinary System study guide.docx

If gfr high filtrate flow rate increases decreasing

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densa cells; respond to filtrate NaCl concentration. If GFR high filtrate flow rate increases decreasing reabsorption time high filtrate NaCl levels constriction of afferent arteriole decrease NFP & GFR more time for NaCl reabsorption. Opposite for decrease GFR 14. How does the sympathetic nervous system control GFR? (extrinsic controls) under normal conditions at rest, renal blood vessels dilate, renal autoregulation mechanisms prevail. If extracellular fluid volume extremely low (low bp) then
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Norepinephrine released by sympathetic nervous system, epinephrine released by adrenal medulla Systemic vasoconstriction increased blood pressure COntriction of afferent arterioles lower GFR increased blood volume and pressure 15. What is the hormonal control of the GFR? (extrinsic) Renin-angiotensin-aldosterone mechanism Main mechanism for increasing blood pressure, 3 pathways to renin release by granular cells Direct stimulation of granular cells by sympathetic nervous system Stimulation by activated macula densa cells when filtrate NaCl concentration low Reduced stretch of granular cells Other factors affecting GFR, kidneys release chemicals, some act as paracrine that affect renal arterioles -Adenosine – Prostaglandin E2 – Intrinsic angiotensin II reinforces effects of hormonal angiotensin II 16. How is sodium reabsorbed in the renal tubules? Sodium is the most abundant cation in filtrate, Na+ reabsorption by primary active transport provides energy and means for reabsorbing most other substances. Creates electrical gradient passive ereabsorption of anions. 17. What is obligatory water reabsorption? Water is reabsorbed by osmosis, aided by water filled pores called aquaporins. When aquaporins are always present in PCT obligatory water reabsorption 18. What is facultative water reabsorption? When aquaporins inserted in collecting ducts only if ADH is present facultative water reabsorption 19. What is a transport maximum and what role does this play in tubular reabsorption? Transport maximum is the maximum amount of substance that can be reabsorbed based on the number of transport proteins available. It depends on the amount of substance and the number of transport proteins available. Whatever solute in present that is in excess the rest is then excreted through urine. 20. How does ADH alter water reabsorption? Antidiuretic hormone binds to receptors on cells in the collecting ducts of the kidney and promotes reabsorption of water back into the circulation. In the absense of antidiuretic hormone, the collecting ducts are virtually impermiable to water, and it flows out as urine. 21. On what cells does aldosterone act? What are the effects of aldosterone? Causes principle cells of collecting ducts to insert aquaporins in apical membranes water reabsorption. As ADH levels increase, there is an increase in water reabsorption.
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