Flashcards in Lecture 28 Kidneys Deck (32)
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1
Functions of the Kidneys
1. osmoregulation = water and solute balance (ECF osmolarity -290mOsm and volume total H20
2. ion (electrolyte) balance (Na+, K+, Ca2+, etc.)
3. acid-base regulation (H+, HCO3-)
4. excretion - urea + other soluble waste products
5. endocrine function - erythropoietin
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Regions
Cortex
medulla
renal pelvis -> ureter
3
Nephron
functional unit of the kidney
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Renal corpuscle
glomerulus
glomerular (Bowman's) capsule
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Renal Tubule
proximal convoluted tubule (PCT)
loop of Henle - descending limb, ascending limb
distal convoluted tubule
collecting duct
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Blood Supply
glomerulus - afferent arteriole
glomerular capsule- efferent arteriole
renal tubule- peritubular capillaries
PCT - vasa recta
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cortical nephrons
mostly in cortex, short loops of henle
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juxtamedullary nephrons
long loops of Henle extend deep into the medulla
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three primary processes of the Nephron
filtration
reabsorption
secretion
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Filtration: Glomerulus and Glomerular Capsule
formation of protein-free filtrate
filtrate contains H20 + small to medium sized solutes (ions, glucose, urea, etc.)
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Filtration membrane
consists of three layers
fenestrated capillaries
basement membrane
filtration slits of podocytes
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Net filtration pressure
Blood pressure 55mm Hg (in glomerular capillaries)
-C.O.P -30 mm Hg (from plasma proteins in cap.)
-Tissue P -15mm Hg (fluid backpressure in glomerulacap)
=NFP 10 mm Hg
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Glomerular filtration rate
GFR = 125 mL/min
14
GFR
can be estimated by measuring clearance of a substance that is filtered into the nephron but not reabsorbed or secreted. e.g. inulin, creatinine
GFR= insulin clearance = [inulin]urine X urine flow (mL/min) / [inulin]plasma
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Reabsorption: PCT
"mass reabsorption" in the PCT, isosmotic with ECF (300 mOsm)
approx. 70% filtered fluid is reabsorbed from the PCT into the ECF (peritbular capillaries)
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Epithelial Transport in the PCT
transport proteins (pumps, carriers, channels) in apical and basolateral membranes
microvilli on apical surface face into lumen of tubule (increase surface area)
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Transport mechanisms
Na+
diffusion through channels in the apical membrane
primary active transport: Na+/K+ ATPase in the basolateral mambrane
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Transport mechanisms glucose
secondary active transport with Na+ (SGLT) across apical membrane
facilitated diffusion (GLUT) across basolateral membrane
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Transport mechanisms amino acids
cotransport with Na+ similar to glucose
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Transport mechanisms H20
via osmosis, follows movement of solutes
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Glucose reabsorption in the PCT
normally, all glucose filtered into nephrons is reabsorbed
at very high glucose levels, glucose transporters become saturated
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transport maximum
maximal rate of glucose reabsorption
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renal plasma threshold
minimum plasma [glucose] at which glucose appears in urine
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normal plasma
normal plasma [glucose] 90 mg/dL << renal plasma threshold - 180 mg/dL
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in diabetes mellitus
high plasma [glucose] > renal plasma threshold -> glucose in urine
-> osmotic diuresis
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Vertical Osmotic Gradient: Loop of Henle
Counteractive multiplier mechanism
active transport of NaCl
osmotic movement of H20
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Active transport of NaCl
NaCl pumped out of ascending limb (thick region)
decrease osmolarity of tubular fluid and increase osmolarity of surrounding ECF
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Osmotic movement of H20
H20 moves out of descending limb due to increase ECF osmolarity
differential permeability properties along the loop of Henle:
descending limb : permeable to H20, impermeable to NaCl Ascending limb: impermeable to H20, permeable to NaCl (active transport)
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Countercurrent flow
opposite direction of flow in descending and ascending limbs
concentrated fluid (1200 mOsm) formed at base of loop and surrounding ECF
dilute fluid (100 mOsm) at top of ascending limb enters DCT
vasa recta around loop of Henle helps maintain vertical osmotic gradient
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