PSL201 - Renal.docx

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21 Apr 2012
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PSL201 - Renal
Funtions of the Urinary System
- filter blood
- regulate ionic composition of plasma
- regulate osmolarity of plasma
- regulate volume of plasma
- regulate pH of plasma
o this all causes the formation of urine
Anatomy of the Urinary System
- the functional units of the kidneys are the nephrons (bowman’s capsule,
proximal tubule, descending limb on henle, ascending loop of henle, and the
distal tubule
- the DT drains into the collecting duct
- filtration occurs at the renal corpuscle which includes the bowman’s capsule
and glomerulus
o glomerular filtrate is the same as plasma but lacking protein
- reabsorption and secretion occurs within the tubules of the nephron (see
slides for diagrams)
- kidneys receive a large part of cardiac output via the renal artery
Basic Renal Exchange Processes
- glomerular filtration is driven by the four starling forces:
o glomular capillary hydrostatic pressure
o hydrostatic pressure inside the bowman’s capsule
o the osmotic pressure of fluids in BC
o the osmotic pressure in the glomerulus
- normal filtration is 125 mL/min
- the filtered load is the quantity of a certain solute that is filtered at the
glomerulus
- GFR stays constant with 3 intrinsic mechanisms:
o Myogenic regulation of smooth muscle in the afferent arteriole
o Tubuglomular feedback
o Mesangial cell contraction
- Extrinsic mechanisms:
o Sympathetic control of smooth muscle in the afferent and efferent
arterioles
- When solutes are transported across the tubular epithelium by carrier
proteins during reabsorption or secretion a transport maximum can be
reached
o When all carriers are saturated
o Plasma concentration at which solute appears in urine is the renal
threshold
Regional Specialization of Renal Tubules
- proximal tubule is specialized to reabsorb large quantities of solutes and
water, and returns it to the blood
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