Loop Of Henle

Question 1

What is the function of the loop of henle?

Answer 1

More Na+ reabsorption, urinary dilution & generation of medullary hyperosmocity

Question 2

The thin descending limb is permeable/impermeable to…

Answer 2

Water permeable

Ion impermeable

Question 3

The thick ascending limb is permeable/impermeable to…

Answer 3

Water impermeable

Ion permeable

Question 4

Where does solute reabsorption occur?

Answer 4

Thick ascending limb

Question 5

How is a hyperosmotic interstitium generated?

Answer 5

Via countercurrent multiplication

Question 6

Urinary concentration occurs as tubular fluid flows through…

Answer 6

Medullary collecting ducts

Question 7

The interstitial fluid surrounding these ducts are….. in the presence of…..
Water diffuses put the ducts into blood vessels of medulla

Answer 7

Very hyperosmotic

ADH (vasopressin)

Question 8

What is the countercurrent multiplier system?

Answer 8

Fluid enters PCT, flows down descending limb then up ascending limb, opposing flows in the 2 limbs

Question 9

What does the countercurrent multiplier system create?

Answer 9

A hyperosmotic medullary interstitial fluid to enable water to be drawn out of Collecting ducts by ADH, concentrating urine

Question 10

What happens in the ascending limb?

Answer 10

Na+ and Cl- are reabsorbed from the lumen into the medullary IF
H2O remains inside
Decreased conc inside

Question 11

What happens to all the ions in the ascending limb?

Pumps? Types of transport?

Answer 11

Na+ and Cl- are pumped from lumen into loop of henle cell via a NKCC2 channel/pump (transports 1Na+, 1K+ & 2Cl-)
Na+ and Cl- into capillary
K+ returns to lumen + coats entire inside lining so Ca2+ and Mg2+ are repelled from leaving

Question 12

In the upper thick portions of the ascending limb, how is Na+ and Cl- reabsorbed?
Where are these transporters not present?

Answer 12

Actively cotransport them

Not present lower ascending limb so occurs via simple diffusion

Question 13

As the ascending limb is impermeable to water, what is the IF of the medulla described as and why?

Answer 13

Very hyperosmotic compared to fluid in the ascending limb as solutes are reabsorbed without water

Question 14

What happens in the descending limb?

Answer 14

Water is reabsorbed
Ions stay
Osmosis of water out until osmolarities in limb and IF are equal

Question 15

How is the IF osmolarity maintained during equilibrium ?

Answer 15

Ascending limb continues to pump out Na+ and Cl- to maintain conc difference
So the loop countercurrent multiplier system produces a hyperosmotic medullary interstitium
Draw out water from collecting ducts

Question 16

What are NKCC2 pumps acted on by to increase NaCl reabsorption?

Answer 16

Aldosterone (from RAAS)

Question 17

What is low NaCl detected by and the process?

Answer 17

Detected by macula densa cells
Renin
Angiotensinogen 
Angiotensin 1
Angiotensin 2
Aldosterone 
Acts on NKCC2 (increases expression)