Physiology 5: The loop of henle

Question 1

The loop of henle is divided into

Answer 1

2 main parts; descending loop of henle and ascending loop of henle

Question 2

function of the loop of henle

Answer 2

generates a portico-medullary solute concentration gradient enabling formation of HYPERTONIC URINE

Question 3

Together the loop of henle and the vasa recta establish

Answer 3

a hyper-osmotic medullary interstitial fluid

Question 4

descending limb of the loop of henle

Answer 4

does not reabsorb and NaCL and is HIGHLY PERMEABLE TO WATER

Question 5

Ascending limb of the loop of henle

Answer 5

Along the entire length of the ascending limb of the loop of henle Na+ and Cl- ions are being re-absorbed

• in the thin part of the ascending limb this is a passive process
• in the thick part of the ascending limb this is an active process

Question 6

the ascending limb of the loop of henle

Answer 6

is impermeable to water

Question 7

the thick part of the ascending loop of henle contains

Answer 7

• Na+/ K+/ 2 Cl- co-transporter which moves sodium, potassium and 2 chloride ions from the tubule of the ascending limb into the cell
• once within the cell the sodium and chloride moves through there respective channels on the baso-lateral membrane into the renal intersititum which increases its osmolarity
• because the osmolarity of the renal interstitium is increasing this drives the passive re-absorption of water through aquaporins in the descending limb of the loop of henle via osmosis

Question 8

therefore the following has occurred simultaneously

Answer 8

• sodium and chloride have been re-asborbed via the NA/K/2CL transporter in the thick ascending part of the loop of henle into the renal intersitium
• this increases the osmolarity of the renal interstiium which drives the passive movement of water via osmosis in the descending limb of the loop of henle

Question 9

the whole process is known as

Answer 9

countercurrent multipiclation

Question 10

fluid entering the descending limb of the loop of henle is

Answer 10

iso-osmotic with the fluid in the filtrate (300mosmol/litre)

Question 11

as water is progressively lost in the descending limb of the loop of henle

Answer 11

the fluid within the tubules of the descending limb of the loop of henles osmolarity increases (300–> 750–> 900–> 1200 osmol/litre)

Question 12

So the fluid entering the ascending limb of the loop of henle is

Answer 12

at an osmolarity of 1200osmol/litre

Question 13

as the fluid moves through the ascending limb of the loop of henle

Answer 13

sodium, potassium and chloride ions are lost therefore, the osmolarity of the fluid progressively falls until about 120-200omsol/litre which enters the distal convoluted tubule

Question 14

the vasa recta

Answer 14

are peri-tubular capillaries in the renal medulla so they are branches of the efferent arteriole and are known as the countercurrent exchanger

Question 15

as the vasa recta descends

Answer 15

• the renal intersitium is booming hyper-osmoalr so it takes up NaCl and pumps out water

Question 16

as the vasa recta ascends

Answer 16

the renal intersitium is becoming hypoosmolar so it moves sodium and chloride out and water into the vasa recta

Question 17

the process occurring in the vasa recta

Answer 17

does actually contribute anything to the osmotic gradients but it is very important to prevent the rapid removal of sodium, chloride and urea as blood flows through the renal intersitium

Question 18

what else contributes to the osmolarity of the renal medulla

Answer 18

urea recycling which the majority occurs in the collecting ducts

Question 19

so in summary the purpose of the countercurrent multiplier is to

Answer 19

concentrate the medullary interstitial fluid

Question 20

why does it do this?

Answer 20

to allow the kidney to produce different volumes and concentrations of urine depending on the amount of circulating anti-diuretic hormone