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Flashcards in Rost and Post Renal Phys Deck (10):
1

What is the average glomerular filtration rate in human (mL/d)?
What is the ratio between the volume fitrated and the extracellular fluid volume? Between the volume fitrated and the plasma volume?

Glomerular filtration rate: 135-180 L/day
- Volume fitrated in a day/ extracellular fluid volume : > 10 times
- Volume fitrated in a day/ plasma volume : ~ 60 times

2

What are the two routes for tubular reabsorption?

- Transcellular (tubular lumen, into the cell (across luminal and basolateral membranes), interstitium, peritubular capillary)
- Paracellular (tubular lumen, across the tight junctions between tubular cells, interstitium, peritubular capillary)

3

T/F: Reabsorbed solutes returned to the systemic circulation intact

F: Some reabsorbed solutes are metablized within the tubular cells, particularly low-molecular-weight proteins in the proximal tubules

4

T/F:
- BUN can be excreted (via glomerular filtration), secreted and reabsorbed by the renal tubules
- Creatinine can be excreted (via glomerular filtration), secreted and reabsorbed by the renal tubules

- F: BUN is not secreted by the renal tubules
- F: Creatinine is not reabsorbed by the renal tubules (a small amount can be secreted)

5

Give the 5 major channels responsible for Na+ entry into the tubular cells (specify their location in the tubule)

- Proximal tubule: Na+/Glucose cotransport (can also enter with phosphate and amino-acids), Na+/H+ antiport
- Loop of Henlee: Na+/K+/2Cl- symport
- Distal tubule: Na+/Cl- symport
- Collecting tubule: selective Na+ channel

6

What is the percentage of PARACELLULAR Na+ reabsorbed in the late proximal tubule?

30% (enhanced by paracellular chloride reabsorption)

7

What are the percent net reabsorption (healthy patient on a well-balanced diet) of: water, Na+, Cl-, HCO3-, K+, BUN

- Water: 98-99%
- Na+: >99%
- Cl-: >99%
- HCO3-: ~ 100%
- K+: 85-95%
- BUN: 40-50%

8

What are the 2 major tight junctions effects on tubular reabsorption?

- Relative barrier/gate to the passive diffusion of solutes and water between the cells (proximal tubule >...> collecting tubule). In the proximal tubule, a relative permeability allows more reabsorption (Cl-, Na+, water). In the collecting tubule, a relative impermeability allows the creation and maintainance of a large concentration gradient.
- Boundary/fence between the luminal and basolateral membranes. The prevention of the lateral migration of transporters or channels from a membrane to another maintains the polarity of those membranes.

9

How does tubular ischemia affect the Na+ reabsorption?

Disruption of the anchorage of Na+-K+-ATPase pumps (to actin and fodrin) -> translocation of those pumps from the basolateral membranes to the luminal one -> loss of membrane polarity -> Na+ reabsorption impairment

10

Where does ADH bind? What is the consequence?

ADH binds to the basolateral membrane of collecting tubular cells, stimulating the exocytosis of vesicles with aquaporin-2 allowing the reabsorption of luminal water. (endocytosis in case of absence of ADH stimulation)