Urinary physiology - loop of Henle

Question 1

How much albumin gets through the glomerulus

Answer 1

30g which is about 0.5% of the amount that is presented to the glomerulus - the albumin is completely reabsorbed by the proximal tubule

Question 2

What is the effect of drugs being non-polar usually

Answer 2

They are very lipid soluble so the removal of water out of the proximal tubule cells establishes a gradient for their reabsorption so they would not be excreted - the liver therefore breakdowns the drugs to polar compounds which make them able to be excreted

Question 3

In quick terms describe filtration

Answer 3

Blood to lumen

Question 4

In quick terms describe reabsorption

Answer 4

Lumen to blood

Question 5

In quick terms describe secretion

Answer 5

Blood to lumen

Question 6

In quick terms describe excretion

Answer 6

lumen to external environment

Question 7

Why is the fluid that leaves the proximal tubule isosmotic

Answer 7

Because every movement of a solute is accompanied by the movement of water

Question 8

What is the isosmotic plasma concentration and define it

Answer 8

Having the same osmotic pressure as plasma which is 300mOmoles/l

Question 9

What is the location of the proximal and distal tubules in the nephron

Answer 9

The renal cortex

Question 10

Where is the loop of Henle in the nephron

Answer 10

Deep within the renal medulla

Question 11

What is the maximum concentration of urine that can be produced by the kidney

Answer 11

1200-1400 mOsmoles/l (4x plasma concentration)

Question 12

What is the concentration of solutes alone which must be excreted per day and how much water loss is required

Answer 12

600mOsmoles and requires at least 500mls loss of water

Question 13

If there is excess water intake - low concentration urine is produced - what is the minimum urine concentration

Answer 13

30-50 mOsmoles/l

Question 14

Why can the kidneys produce urine of varying concentrations

Answer 14

The loop of Henle of juxtamedullary nephrons acts as a counter-current multiplier

Question 15

What is a counter-current multiplier

Answer 15

As fluid flows down the descending limb and up the ascending limb, there is exchange between both limbs - The ascending limb actively co transports sodium and chloride ions out of the lumen into the interstitium, the ascending limb is also impermeable to water - the descending limb is freely permeable to water but not sodium chloride

Question 16

What happens when isosmotic fluid (300mOsmoles) goes up the ascending limb of the loop of Henle

Answer 16

Sodium chloride is pumped out which drops the osmolarity to 200mOsmoles /l - this causes the interstitium osmolarity to rise

Question 17

What happens when the solution goes to the descending limb after the ascending limb

Answer 17

The interstitium osmolarity is higher then the osmolarity in the descending limb so water moves out to the intersitium to reach equilibrium - the water is then reabsorbed by the vasareacta

Question 18

How do the ascending and descending limbs of loop of Henle work

Answer 18

descending limb gets rid of water which increases the osmolarity - the cycle causes the reabsorption of both water and sodium chloride while the Ascending reduces osmolarity by getting rid of sodium chloride

Question 19

What is the function of frusemide

Answer 19

It is a loop diuretic which inhibits the active transport of sodium chloride in the loop of Henle so there is no horizontal osmolarity gradient being produced so the urine will remain isotonic

Question 20

What is the effect of the countercurrent multiplier on the intersitium

Answer 20

Increased concentration

Question 21

What concentration is the fluid which reaches the distal tubule

Answer 21

100mOsmoles - more diluted then plasma

Question 22

What is the vasa recta and how does it work

Answer 22

The specialised arrangement of the peritubular capillaries of the juxtamedullary nephrons which are part of the countercurrent multiplier mechanism

They don’t drain straight through the loop of Henle and interstiium or they would abolish the concentration gradient by removing the sodium chloride and water - Instead they are arranged as hairpin loops which don’t interfere with the gradient

Question 23

What are the functions of the vasa recta

Answer 23

Provide O2 for the renal medulla
Remove fluid and solutes from the interstitium

Question 24

Why is the reabsorption favoured at the vasa recta

Answer 24

The high oncotic pressure is high and so it the tissue pressure due to the tight renal capsule which pushes the fluid into capillaries
The flow rate of the vasa recta is low so equilibration can occur without the medullary gradient being disturbed

Question 25

What is the site of water regulation in the nephron

Answer 25

collecting duct

Question 26

What hormone controls permeability of the collecting duct

Answer 26

ADH - anti diuretic hormone (vasopressin)