Transport of other ions and different functions

Question 1

how much sodium is reabsorbed in the loop of Henle?

Answer 1

20% of filtered load

Question 2

function of distal tubule

Answer 2

fine regulation of renal electrolytes and water output

Question 3

important region of the distal tubule

Answer 3

macula densa

Question 4

what is the macula densa sensitive to?

Answer 4

decreased and increased sodium chloride concentration

Question 5

what may increase the concentration of sodium and chloride?

Answer 5

increased flow rate, less time for equilibration in ascending limb

increased GFR

Question 6

percentage absorption in distal tubule

Answer 6

7%

Question 7

transporters in distal tubule

Answer 7

sodium chloride NCC and basolateral sodium potassium pump

Question 8

what happens if there is decreased sodium and chloride?

Answer 8

1. production of prostaglandins which vasodilate the afferent renal arteriole
2. prostaglandins also activate juxtaglomerular cells to release renin
3. renin leads to the constriction of the efferent arteriole

Question 9

explain renin-angiotensin system

Answer 9

1. renin secreted into blood stream from afferent arteriole
2. renin catalyses the conversion of angiotensinogen to angiotensin I in the liver
3. angiotensin I is converted to angiotensin II by ACE within vascular endothelial cells of the lungs
4. angiotensin II acts as a vasoconstrictor of the efferent arteriole, increasing glomerular pressure

Question 10

another function of angiotensin II

Answer 10

stimulates the secretion of the hormone aldosterone from the adrenal cortex

Question 11

Aldosterone function

Answer 11

1. stimulates sodium reabsorption at the principal cells of the collecting duct
2. increased ENaC and basolateral sodium potassium pump, so more sodium and water reabsorbed
3. this increases the blood volume and therefore blood pressure

Question 12

what does aldosterone cause as a side effect?

Answer 12

excess potassium excretion into urine

hypokalemia

Question 13

what happens if there is increased sodium and chloride in macula densa?

Answer 13

1. too much chloride, ATP released from cells in macula densa
2. ATP forms adenosine which inhibits renin release by binding to granular cells

Question 14

what else may lead to renin’s release?

Answer 14

baroreceptors in the afferent arteriole which notice a decrease in blood pressure

Question 15

what else may stimulate aldosterone?

Answer 15

increased plasma potassium

Question 16

what stimulates thirst?

Answer 16

angiotensin iI

Question 17

Where is atrial natriuretic peptide released? + when

Answer 17

atria of the heart

atrial distention

Question 18

atrial natriuretic peptide mechanism of action

Answer 18

1. raises cell cGMP by activating guanylyl cyclase
2. leads to vasodilation of afferent arteriole which increases GFR but inhibits reabsorption

inhibits ENaC on apical side of collecting duct and Na/K+ exchanger

dilutes body fluid and leads to volume extraction

Question 19

atrial natriuretic peptide function

Answer 19

decrease of sodium absorption prevents the reabsorption of water

more water and sodium lost in urine

decreases blood pressure

Question 20

ANP has the opposite affect of what hormone?

Answer 20

angiotensin II which increases renal sodium retention whereas ANP increases renal sodium loss

Question 21

what is secreted by the kidney in response to cellular hypoxia?

Answer 21

erythropoietin

Question 22

where is erythropoietin produced?

Answer 22

interstitial fibroblasts in the kidney in close association with peritubular capillaries and proximal convoluted tubules

Question 23

erythropoietin function

Answer 23

promotes the survival of red blood cell progenitors and precursors from apoptosis

erythropoiesis stimulated, development of stem cells to mature red blood cells

Question 24

which vitamin is activated in the kidneys?

Answer 24

vitamin D

Question 25

explain activation of vitamin D

Answer 25

1. vitamin D synthesised in the skin and then carried to liver
2. converted into prohormone calcifediol
3. calcifediol converted into calcitriol (active form of vit D) in the kidneys, specifically the proximal tubule