Renal 2 Flashcards
How does kidney handle solutes and water? (overview)
- Dump plasma and most of the solutes (e.g. glucose, Na, Cl, K, Ca, etc) outside the body into the lumen of the tubule.
- Reabsorb what you want to keep
- Leave undesired plasma and solutes in lumen to form urine
- Secrete some solutes from blood plasma into lumen of tubule (much smaller numbers of molecules handled this way)
(Kidney tubules are mini digestive tracts.)
Transport of glucose across the apical membrane
- It can be transported across the apical membrane (arrows on left) and then the basolateral membrane (arrows on right)
- It can pass through the gap between the cells
Co-transport with sodium
- Sodium has a downhill gradient: there’s a high concentration of Na and plasma) and there’s a negative membrane potential inside the cell
- This gradient (source of energy) can be used to bring along other solutes (e.g. glucose or amino acids) in secondary active transport
- This system is so effective that before you’re out of the proximal tubule, all of the sugar in the blood has been reabsorbed
How does the permeability of water change throughout the tubule system?
- There are certain segments where water is not permeable (there are no aquaporins) in the cells
- In some segments, the permeability of water can be regulated
If solutes come in to the tubular epithelial cells, ___ follows osmotically
Water
Flow through tubule graph
Watch lecture at 9 mins
In the ___ ___ ___, there are no aquaporins
Thick ascending limb
Sodium reabsorption
- water follows (except for thick ascending)
- thick ascending reabsorption of Na+ sets up osmotic gradient that results in more water reabsorbed (discussed later)
Proximal Tubule (65 - 80%)
Descending Loop (no but sets up gradient)
Thick Ascending Loop (10 – 20%)
Distal Tubule (5 – 10%)
Collecting Duct (3 – 5%)
Diuretics
- Block the reabsorption of sodium, so more sodium is left in the lumen of the tubule
- More chloride is left in the lumen of the tubule
- Osmotically, more water will be left in the lumen –> bladder
- Decreases plasma volume –> decreases BP
- If the diuretic acts in the collecting duct, it has a smaller impact (3-5%) (look at prev flashcard)
- Thick ascending loop would have bigger impact
Analysis of sodium through tubule
Watch lectrure at 22:50
Sodium reabsorption is affected by the ___ system
RAAS
Movement of glucose through nephron
- There’s 500 ml of plasma per minute going into the kidney
- Each ml of plasma has 1 mg of glucose, there’s 500 mg of glucose per minute going into the kidney
- There is no glucose in the urine, so there’s 500 mg of glucose in the renal vein per minute
- There’s 375 mg of glucose that wasn’t filtered (stayed in capillaries)
- Whatever was filtered is reabsorbed completely into the peritubular capillaries (it’s permeable)
Inulin
- It is filtered (freely permeable in the glomerulus) so goes into the Bowman’s capsule
- Inulin is not reabsorbed or secreted so reabsorption is 0 and excretion is 125 (all that was in the tubule goes into the bladder)
- 375 mg/min come out through the renal vein
PAH
- Just like inulin and glucose, it is filtered into the nephron (125 mg)
- Just like inulin, it is not reabsorbed and it is actively secreted in multiple places along the tubule (from the blood into the lumen of the nephron)
- So the 375 that stayed in the capillaries is filtered into the lumen, so in the end, all of the PAH shows up in the urine
- Actually, only about 90% of PAH is cleared. There are some peritubular capillaries that aren’t close enough to the tubule to actively secrete it
What is clearance?
The volume of plasma that is 100% cleared of a solute (measured in ml/min)
Transport max
Watch lecture at 1 hour
