Wk 27 Flashcards
Where is Na+ and Cl- reabsorbed the most?
Proximal tubule
Tubule reabsorption takes place by both transcellular and paracellular pathways.
What is transcellular? =
What is paracellular?=
Trans is through the cell via sodium channels and coupled cotransporters and exchangers
Paracellular is between epithelial cells via tight junctions
What does Na+ reabsorption involve? (The different channels and transporters)
Apical transporters
Epithelial sodium channels
Basolateral Na-K pump
Na-H exchanger
Electrogenic Na/HCO3 cotransporter
Balance between paracellular and transcellular absorption along the tubular system depends on what?
The electrochemical gradient at that level
How does regulation of Na+ absorption happen? (Glomerulotubular balance)
If the glomerulus lets too much Na through, the tubules increase their reabsorption rate to stablize the filtered amount
How does Angiotensin II work in the nephron?
related to Na
Binds to AT1 receptors at the apical and basolateral membranes of proximal tubule cells= PROMOTE Na+ REBSORPTION INTO BLOOD (so water will follow and you pee out less water)
How does aldosterone work in the kidney?
related to Na
Stimulates Na+ reabsorption by the Collecting Duct (Initial collecting tubule, cortical collecting tubule and medullary collecting ducts)
How does sympathetic nerve stimulation act on the nephron?
related to Na
Decreases renal blood flow and GFR which means less Na+ excretion into urine
ALSO, alpha adrenoceptors on proximal tubules increase Na+ reabsorption
(you want to keep Na so your BP stays high in fight or flight)
How does arginine vasopressin (antidiuretic hormone) affect water excretion from kidneys?
It stimulates the retention of water and very concentrated urine (with hardly any water in it)
How does atrial natriuretic peptide affect sodium levels in the nephron?
It promotes natriuresis (sodium secretion in urine) due to increasing blood flow to nephrons and also direct effects on collecting duct
If GFR increases, what happens to reabsorption?
Increases proportionally (this is Glomerulotubular [GT} balance)
What is the major substance the kidneys filter and then totally reabsorb?
What is the major substance the kidneys filter, reabsorb and secrete?
Glucose
Urea
Where is glucose reabsobed in the nephron and by what 2 mechanisms?
Proximal convoluted tubule
Apical, electrogenic Na/Glucose cotransporter and a basolateral facilitated diffusion mechanism
Where is phosphate reabsobed in the nephron and by what mechanism?
Proximal convoluted tubule reabsorbs most
Via Na/ Phosphate cotransporter
Where is calcium reabsorbed in the nephron and how much of the filtered amount is reabsorbed?
Proximal convoluted tubule
99% is absorbed back into blood
Where does most magnesium absorbed in nephron?
Thick ascending limb of Henle’s loop
Where are amino acids absorbed?
Proximal tubule (using many transporters on apical and basolateral membranes of epithelial cells)
Where is potassium reabsorbed and secreted in the nephron?
Proximal tubule reabsorbs most of the filtered K and the distal tubule may reabsorb or secrete K depending on level in body
(When someone has high K, the collecting duct secretes K into lumen for excretion = called the distal K + secretory system)
What does the renal excretion rate (EX) depend on? (3 factors)
- rate of filtration of X (FX)
- rate of reabsorption of X (RX) by tubules
- rate of secretion of X (SX) by tubules
How do you estimate the net amount reabsorbed or secreted by the renal tubules and why is this important?
By measuring the difference between the amount of X filtered with the amount of X excreted into urine
Important so you can understand how glomerular filtration, tubule reabsorption and tubular secretion is working
(can’t provide info on specific sites though)
What are the limitations with using clearance methods to estimate overall nephron function?
They can’t provide any information on exact sites and mechanisms of transport