structure and function of renal tubule Flashcards
At what rate is the glomerular filtrate formed?
120ml/min
List techniques to investigate tubular function
- Clearance studies
- Micropuncture & Isolated Perfused Tubule
- Electrophysiological Analysis
- Potential measurement
- Patch clamping
Only 1 is applied to man
Explain the process of micropuncture
- Puncture
- Inject viscous oil
- Inject fluid for study
- Study and analyse
ELECTROPHYSIOLOGY – ELECTRICAL POTENTIAL
Electrodes (micropipettes of very small diameter <0.5μm) inserted into cell and the Potential difference measured across whole cell epithelium
ELECTROPHYSIOLOGY – PATCH CLAMPING
blunt-tip pipette (opening ~0.5-1 µm) is pressed against the cell membrane until a seal forms between electrode tip and membrane surface.
Plasma membrane can be pulled away from the cell and placed in a test solution of desired composition or measurements made in situ
What are the two types of nephrons?
Cortical and Juxtamedullary
Name the differences between two types of nephrons
-
Cortical Nephrons:
- Short-looped Henle’s loops
- Entire tubular system surrounded by an extensive network of capillaries.
-
Juxtamedullary Nephrons:
- Long-looped Henle’s loops that penetrate deep into the medulla.
- Long efferent arterioles extend from glomeruli to the outer medulla.
- Specialized capillaries (vasa recta) extend downward into the medulla and run alongside loops of Henle.
Why are juxtamedullary nephrons better at concentrating urine?
Longer loops of henle
How are small proteins reabsorbed in the PCT
endocytosis, degraded by lysosomal enzymes, and converted into amino acids and simple sugars.
what is Fanconi’s syndrome?
- Defects in all proximal tubule reabsorptive mechanisms.
- Glucose, amino acids, Na, K, etc., found in urine due to the inability to reabsorb these substances effectively.
What does the vasa recta do ?
Delivers O2 and nutrients to cells of the loop of henle
The vasa recta, like other capillaries, is permeable to both H2O and salts and could disrupt the salt gradient established by the loop of Henle. How is this avoided?
As the vasa recta descends into the renal medulla, water diffuses out into the surrounding fluids, and salts diffuse in. When the vasa recta ascends, the reverse occurs.
What are the two types of cells in the collecting duct?
Intercalculated cells- Involved in acidification of urine and acid-base balance
Principal cells - Role to play in Na balance & ECF volume regulation
ADH causes increased water permeability. How?
ADH induces synthesis and insertion of water channels (aquaporins) into the luminal membrane of the collecting duct.
Origin and storage of ADH?
Produced in hypothalamus
Stored in pituitary gland
How is ADH stimulated for secretion?
Via plasma osmolarity sensed by osmoreceptors in hypothalamus
ADH mode of action
ADH acts through a G protein coupled receptor
Increases insertion of aquaporin-2 channels to apical membrane of the DCT and CD cells
4 major factors leading to build up of solute concentration in renal medulla
- Active transport of Na+ and co-transport of K+ & Cl- out of thick ascending limb into medullary interstitium
- Active transport of ions from collecting ducts into medullary interstitium
- Facilitated diffusion of large amounts of urea from collecting ducts into medullary interstitium
- Very little diffusion of water from ascending limbs of tubules into medullary interstitium
