Lect 8

Question 1

where is most potassium (98%) located

Answer 1

inside cells

Question 2

potassium is under control of what three hormones?

Answer 2

• epinephrine
• insulin
• aldosterone

Question 3

potassium is under control of three hormones. Describe the effect of epinephrine on a1 and b2 receptors

Answer 3

• alpha 1 receptor activation
  
  • causes a shift of K+ out of cells -> hyperkalemia
• beta 2 receptor activation
  
  • stimulates K+ uptake into cells -> hypokalemia

Question 4

potassium is under control of three hormones. Describe the effect of insulin

Answer 4

• increases K+ uptake into cells (after a meal)
• stimulates Na+-K+ ATPase

Question 5

potassium is under control of three hormones. Describe the effect of aldosterone

Answer 5

• increases K+ uptake into tubule cells and increases K+ excretion
• stimulates Na+-K+ ATPase

Question 6

hyperosmolarity and exercise favor movement of potassium from where to where?

Answer 6

• from ICF to ECF

Question 7

acidosis stimulates movement of potassium from where to where

Answer 7

• in acidosis, H+ ions move into cell and K+ moves out of the cell

Question 8

alkalosis stimulates movement of potassium from where to where

Answer 8

• stimulates movement of K+ into cells

Question 9

physiological regulation of K+ occurs where in the nephron

Answer 9

distal tubule and collecting duct

• K+ reabsorption in proximal tubule (67%) and loop of henle (20%) does not change in the face of increased or decreased total body K+

Question 10

effect of a low K+ diet

Answer 10

• decrease in K+ excretion
  
  • PT and LOH still reabsorb only 87%
  • remaining K+ reabsorbed in the distal nephron

Question 11

in what cells does the K+ reabsorption occur. What mechanism?

Answer 11

• occurs in the alpha intercalated cells of the distal nephron
• K+ reabsorption in exchange for H+ secretion (via ATP)

Question 12

what is the effect of a high K+ diet

Answer 12

• aldosterone is stimulated
• promotes K+ secretion via
  
  • stimulation of basolateral membrane Na+,K+ ATPase
  • increasing luminal membrane permeability to K+

Question 13

potassium secretion occurs in what cells

Answer 13

• principle cells

Question 14

aldosterone has what effect on K+? What mechanisms?

Answer 14

• two mechanisms
  
  • stimulates Na+-K+ ATPase
  • stimulates diffusion across luminal membrae down its concentration gradient

Question 15

describe the distribution of calcium in the body

Answer 15

• 99% in bone
• 1% in the ICF
• 0.1% in ECF

Question 16

what is the concentration of plasma calcium? what three forms can it exist in

Answer 16

• plasma Ca2+ = 2.5 mM
  
  • 50% ionized Ca2+ = biologically active
  • 10% complexed to anions (CaPO₄)
  • 40% bound to plasma proteins

Question 17

what form of calcium is biologically active

Answer 17

ionized Ca2+

Question 18

how does the filtered load calculation change for Ca2+

Answer 18

• only 60% of plasma Ca2+ is filtered (40% is bound)
  
  • FL = (GFR)(P_Ca)(0.6)

Question 19

What percentage of filtered calcium appears in the urine?

Answer 19

• only 1% of filtered calcium appears in the urine

Question 20

where does the reabsorption of calcium happen in the nephron? give percentages

Answer 20

• proximal tubule 67%
• thick ascending limb 25%
• distal tubule 5-10%
• collecting duct <5%
• does not occur in descending limb of LOH

Question 21

via what mechanism does calcium get transported across apical membrane?

Answer 21

Ca2+ channels

Question 22

via what mechanisms does calcium get transported across basolateral membrane

Answer 22

• active transport via Ca2+-ATPase
• Na-Ca2+ exchange
• *basolateral membrane is on interstitium side

Question 23

parathyroid hormone stimulates Ca2+ uptake in what part of nephron

Answer 23

distal tubule

• mediated by cAMP

Question 24

what effect does thiazide diuretics have on calcium reabsorption

Answer 24

• stimulates Ca2+ reabsorption
• thiazide decreases [Na+] which increases inward movement of Na+ via Na+/Ca2+ exchanger

Question 25

why is phosphate important in the body

Answer 25

• component of organic molecules (DNA, RNA, ATP)
• major component of bone
• urinary PO₄ is an important buffer

Question 26

what percentage of plasma PO₄ is protein bound

Answer 26

10%

• meaning that 90% is filterable at the glomerulus

Question 27

where does reabsorption of phosphate occur in the nephron

Answer 27

• 85% reabsorbed in the proximal tubule
• 15% is excreted - most important buffer anion

Question 28

reabsorption of phosphate in the proximal tuble is inhibited by what

Answer 28

parathyroid hormone