Lecture 28 Kidneys Flashcards
Functions of the Kidneys
- osmoregulation = water and solute balance (ECF osmolarity -290mOsm and volume total H20
- ion (electrolyte) balance (Na+, K+, Ca2+, etc.)
- acid-base regulation (H+, HCO3-)
- excretion - urea + other soluble waste products
- endocrine function - erythropoietin
Regions
Cortex
medulla
renal pelvis -> ureter
Nephron
functional unit of the kidney
Renal corpuscle
glomerulus
glomerular (Bowman’s) capsule
Renal Tubule
proximal convoluted tubule (PCT)
loop of Henle - descending limb, ascending limb
distal convoluted tubule
collecting duct
Blood Supply
glomerulus - afferent arteriole
glomerular capsule- efferent arteriole
renal tubule- peritubular capillaries
PCT - vasa recta
cortical nephrons
mostly in cortex, short loops of henle
juxtamedullary nephrons
long loops of Henle extend deep into the medulla
three primary processes of the Nephron
filtration
reabsorption
secretion
Filtration: Glomerulus and Glomerular Capsule
formation of protein-free filtrate
filtrate contains H20 + small to medium sized solutes (ions, glucose, urea, etc.)
Filtration membrane
consists of three layers
fenestrated capillaries
basement membrane
filtration slits of podocytes
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
Glomerular filtration rate
GFR = 125 mL/min
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
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)
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)
Transport mechanisms
Na+
diffusion through channels in the apical membrane
primary active transport: Na+/K+ ATPase in the basolateral mambrane
Transport mechanisms glucose
secondary active transport with Na+ (SGLT) across apical membrane facilitated diffusion (GLUT) across basolateral membrane
Transport mechanisms amino acids
cotransport with Na+ similar to glucose
Transport mechanisms H20
via osmosis, follows movement of solutes
Glucose reabsorption in the PCT
normally, all glucose filtered into nephrons is reabsorbed
at very high glucose levels, glucose transporters become saturated
transport maximum
maximal rate of glucose reabsorption
renal plasma threshold
minimum plasma [glucose] at which glucose appears in urine
normal plasma
normal plasma [glucose] 90 mg/dL «_space;renal plasma threshold - 180 mg/dL