Rost and Post Renal Phys

Question 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?

Answer 1

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

Question 2

What are the two routes for tubular reabsorption?

Answer 2

• 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)

Question 3

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

Answer 3

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

Question 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

Answer 4

• F: BUN is not secreted by the renal tubules

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

Question 5

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

Answer 5

• 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

Question 6

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

Answer 6

30% (enhanced by paracellular chloride reabsorption)

Question 7

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

Answer 7

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

Question 8

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

Answer 8

• 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.

Question 9

How does tubular ischemia affect the Na+ reabsorption?

Answer 9

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

Question 10

Where does ADH bind? What is the consequence?

Answer 10

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)