MEDI7111 Lecture Notes - Lecture 3: Descending Limb Of Loop Of Henle, Alkalosis, Polyuria
Renal 3
Tubular Physiology
Renal function is primarily controlled by glomerular filtration rate (GFR) and tubular function
(absorptive and secretory capacity). GFR was covered in Renal 2; here we discuss tubular function.
Each section of the nephron has a different function with regard to filtration of the blood, pH
balance and sensitivities to hormones/drugs. The schematic below outlines the functional segments
of the nephron.
It is important to note that water cannot be actively transported; it is moved across an osmotic
gradient when appropriate channels are available (e.g. trans-cellular movement or aquaporins).
Proximal Convoluted Tubule
70% of the tubular filtrate is reabsorbed in the PCT
oFiltrate remains isosmotic to blood/interstitium
oMakes the fluid load for the rest of the nephron more manageable
Filtration/secretion is NOT finely regulated
oSome hormones effect Na+/K+ ATPase on basolateral membrane but that’s about it
for regulation of PCT filtration
oATII upregulates Na+/K+ ATPase activity
Reclaims:
oNaCl
oWater
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oBicarbonate
oGlucose
oAmino acids
Secretes
oPenicillin
Absorption of fluid in the PCT primarily occurs from the active transport of sodium out of the filtrate,
with a partial input from the colloid osmotic pressure of the albumin in the peri-tubular capillaries.
The tight junctions between the cells are not very tight at this point in the tubule so water can move
through this space with only a small driving force. Some water that flows through these junctions
brings solutes with it, a process called “solvent drag”.
Proximal Straight Tubule
This is the final portion of the proximal tubule before it meets the loop of Henle, normally no glucose
or amino acids reach this point in the tubule. This section is particularly important for secretory
processes however; weak organic acids such as penicillins and cephalosporins are secreted here.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Renal function is primarily controlled by glomerular filtration rate (gfr) and tubular function (absorptive and secretory capacity). Gfr was covered in renal 2; here we discuss tubular function. Each section of the nephron has a different function with regard to filtration of the blood, ph balance and sensitivities to hormones/drugs. The schematic below outlines the functional segments of the nephron. It is important to note that water cannot be actively transported; it is moved across an osmotic gradient when appropriate channels are available (e. g. trans-cellular movement or aquaporins). 70% of the tubular filtrate is reabsorbed in the pct: filtrate remains isosmotic to blood/interstitium, makes the fluid load for the rest of the nephron more manageable. Filtration/secretion is not finely regulated: some hormones effect na+/k+ atpase on basolateral membrane but that"s about it for regulation of pct filtration, atii upregulates na+/k+ atpase activity. Reclaims: nacl, water, bicarbonate, glucose, amino acids.
