resorption and secretion 1

Question 1

how much sodium is reabsorbed in the proximal tubule

Answer 1

70%

Question 2

how does Na and Cl leave the lumen of the proximal tubule

Answer 2

• Na diffuses across membrane
• removal of Na leaves lumen -ve compared to interstitium
• repels Cl ions
• Na actively pumped out of cell into interstitium
• Na absorbed by peritubular cap

Question 3

what happens to Na and Cl in the thick ascending limb of the loop of henly

Answer 3

• Na, Cl and K all removed from lumen using a NKCC2 transporter

Question 4

how much sodium is reabsorbed in the thick ascending limb of the loop of henle

Answer 4

20%

Question 5

how is Na anc Cl reabsorbed in the distal tubules

Answer 5

Na and Cl co-transport system

Question 6

what happens to sodium in the collecting ducts

Answer 6

• Na reabsorbed via ENaC channel on principle cells
• Na reabsorption is increased by aldosterone
• 9% Na is reabsorbed in the diatal tubules and collecting ducts

Question 7

what happens to potassium in the proximal tubule

Answer 7

K follows Na and water

Question 8

how much potassium is reabsorbed in the proximal tubule

Answer 8

65%

Question 9

what happens to potassium in the thick ascending limb of the loop of henle

Answer 9

• moves via paracellular movemtn
• NKCC2 transporter

Question 10

what happens to potassium in the collecting ducts

Answer 10

• some K reabsorption from intercalatated cells
• K secretion (blood to tubular lumen) via principle cells
• aldosterone increases activity of Na/K pumt and increases number of K channels

Question 11

how does insulin affect the exchange of potassium

Answer 11

• used to shift K into cells
• increases the activity of the Na and K pump
• can be used to treat hyperkalaemia

Question 12

how is calcium moved in the kidneys

Answer 12

• free ions are freely filtered
• important in lots of cellular processes
• bound to proteins or stored in ER to mitochondria
• passive reabsorption in proximal tubules and ascending limb of LoH driven by Na
• active transcellular reabsorption in distal tubules
• parathyroid hormone can increase Ca reabsorption

Question 13

discuss the movement of phosphate in the kidneys

Answer 13

• free ion is freely filtered
• 80% reabsorbed in the proximal tubule
• transcellular process: co transport with Na ions
• PTH decreases PO4 reabsorption

Question 14

describe the movement of magnesium in the kidney

Answer 14

• free ion is freely filtered
• 30% reabsorbed in proximal tubules: paracellular movement driven by Na
• 65% reabsorpion in the thick ascending limb of LoH due to transepithelial potential
• 5% in distal tubules via Mg ATPases
• regulation via PTH

Question 15

discuss the movement of glucose in the kidneys

Answer 15

• freely filtered
• only reabsorbed in proximal tubule via secondary active reabsorption
• increasing portion of proximal tubule participates in reabsorption as glucose concentration increases
• Tmax = all glucose transporting carrier molecules in apical membrane occupied (see glucose in urine)