Topic 15 Flashcards
Kidney functions
- maintain plasma voltume (bp MAP)
- regulate ion and H2O
- acid base balance
- eliminate waste, drugs and hormones
- endocrine
Nephron
functional unit of kidney = renal corpuscle and tubule.
Processes in nephron leading to urine formation
- glomerular filtration
- tubular reabsorption
- tubular secretion
Glomerular filtration
20% of plasma in glomerulus is filtered into bowman capsule (bulk flow across filtration membrane)
Filtration membrane of glomerular
- fenestrated endothelium
- fused basement membranes
- podocytes with filtration slits between
Glomerular filtrate
- identical to plasma minus large protein
- H2O, glucose, aa, vitamins, ions, urea, some small proteins
- pH 7.45
Net filtration pressure (NFP) =
(55+0) - (30+15) = 10 mmHg
Glomerular filtration pressure (GFP)
at this NFP, 180L/day filtrate both kidneys = 125 mL/min (entire plasma vol. filtered 65x/day). however <1% of filtered volume remains at end of collecting duct (reabsorption)
Regulation of GFR
keeps GFR from changing when bp changes. if not increase MAP and increase GFR (vice versa)
Intrinsic regulation (auto regulation) of GFR
for bp in range of resting to moderate exercise.
Intrinsic regulation of GFR in the myogenic
⇑MAP ⇒ stretch ⇒ afferent arteriole smooth muscle contracts ⇒ prevents ⇑BP in glomerulus (+ vice versa)
Extrinsic regulation
primarily SNS (arteriolar vasocon.)
- afferent low flow into glom
- efferent blood backs up in glom
Moderate SNS activation
both balance and GFR dent change much. (extreme stress, heavy exercise, hemorrhage is high GFR)
NFP can change blood OP (proteins)
- dehydration causes high BOP and low GFR
- burns, nephrotic syndrome causes low BOP and high GFR
NFP can change capsular hydrostatic P
-urinary tract obstruction (kidney stone, inflammation, rotate enlargement) causes high CHP and low GFR
Tubular reabsorption
1-1.5 L/day urine but 180 L/day filtered so 99% filtrate reabsorbed from tubules into peritubular and vasa recta capillaries
Active tubular reabsorption
requires energy. (Na, ions, glucose, aa)
Passive tubular reabsorption
no energy required. (Cl, H2O, urea.
Proximal convoluted tubule (PCT) (unregulated)
- -glucose, aa – 100% - act. transport
- -NaCl - 66% - act. transport
- -small proteins (endocytosis ⇒ aa ⇒ blood)
- -vitamins
- -obligatory (unregulated) reabsorption of H2O (osmosis as solutes reabsorbed ⇒ water “obliged” to follow)
Result of proximal convoluted tubule
- large amount of solute removed + ⇓ filtrate volume
- filtrate is isotonic to plasma = 300 mOsmoles/L (mOsm/L = unit of OP)
Loose of henle
reabsorbs into vasa recta from:
- descending limb (DL): h2o only
- ascending limb (AL): NaCl only
Distal convoluted tubule (ACT)
initial part. reabsorbs Na, Cl, Ca. impermeable to h2o
Late DCT and collecting duct (CD)
reabsorb Na which increases aldosterone and decreases atrial natriuretic peptide ANP. facultative reabsorption of h2o. ADG increase (ANP inhibits ADH)
Nephrons normally reabsorb…
→ 99% of filtered H2O
→ 99.5% of filtered NaCl
→ 100% of filtered glucose
→ 50% of filtered urea