Calcium

Question 1

describe the location of calcium in the body

Answer 1

• 99% in bone
• 1% in body fluids
  
  • 50% is free in ionized form
  • rest is bound to proteins

Question 2

describe the organs involved in maintaining Ca within physiologic range

Answer 2

• gut absorption
• bone uptake and release
• kidney Ca reabsorption

Question 3

Ca in bone exists in 2 pools:

Answer 3

1. readily exchangable pool
2. stable pool

Question 4

describe how physiologic pH changes impact Ca levels

Answer 4

• alkalotic pH
  
  • protein charge becomes more negative
  • there is increase in Ca binding
  • alkalosis decreases plasma [Ca]
• acidic pH
  
  • protein charge is less negative
  • there is less Ca binding
  • acidosis increases plasma [Ca]

Question 5

name factors that alter blood Ca levels

Answer 5

• DECREASE in Ca levels
  
  • nephrotic syndrome
  • malnutrition
  • liver disease
• INCREASE Ca levels
  
  • multiple myeloma

Question 6

describe phosphate distribution in the body

Answer 6

• 86% is in bone
  
  • elemental form
• 13-14% in ICF
  
  • organic form

Question 7

______ is not important for Ca regulation in humans but important in fetus

Answer 7

calcitonin is not important for Ca regulation in humans but important in fetus

Question 8

describe PTH

Answer 8

• synthesized and secreted by chief cells in the parathyroid
• the most important regulator of ECF Ca

Question 9

describe trigger for release of PTH

Answer 9

Question 10

describe the mechanism of PTH suppression

Answer 10

high levels of Ca INHIBIT PTH release

Question 11

describe the action of PTH on bone

Answer 11

indirect action on osteoclast

Question 12

describe the aciton of PTH on kidneys

Answer 12

• increase renal tubular reabsorption of Ca in the distal tubules
• decrease renal tubular reabsorption of PO4 (phosphate tinkling hormone)
• indirectly increase intestinal absorption of Ca
  
  • via Vit. D

Question 13

describe vitamin D, where it’s obtained and what is needed to make it active

Answer 13

• steroid
• formed in the skin or obtained in diet
• requires PTH to reach its active form (1,25-dihydroxycholecalciferol/calcitriol)

Question 14

describe the cutaneous synthesis of calcitriol

Answer 14

Question 15

describe calcitrol (vit D) signalling pathway

Answer 15

intracellular receptor (it’s a steroid)

Question 16

describe the effect of vit D on duodenal cell

Answer 16

• calbindin helps to maintain low intracellular calcium levels in order to pump more Ca in

Question 17

describe hypocalcemia

Answer 17

• increases membrane excitability
  
  • paresthesias
  • hypocalcemic tetany
  • Chovstek’s sign of facial twitching
  • Trousseau’s sign when hand goes into tetany
  • EKG shows prolonged QT interval

Question 18

describe hypercalcemia

Question 19

describe primary hyper-parathyroidism

Answer 19

• usually due to parathyroid tumor
• excess PTH causes:
  
  • increased Ca and phosphaturia
  • polyuria and calciuria forms kidney stones
  • develop cystic lesions in the bone
• “stones, bones and abdominal groans”

Question 20

describe secondary hyperparathyroidism

Answer 20

• causes:
  
  • diet deficient in vit. D
  • increased need for Ca (pregnancy/lactation)
• characterized by:
  
  • increased serum PTH
  • decreased to normal Ca
  • decreased serum phosphate levels but normal to increased urine phosphate levels

Question 21

describe rickets and osteomalicia

Answer 21

• causes:
  
  • Vitamin D deficiency
• decreased levels of Ca and PO4 in ECF
• characterized by deminiralization of the osteoid matrix
  
  • children = rickets
  • adults = osteomalicia

Question 22

describe primary hypoparathyroidism

Answer 22

• cause = accidental removal of glands during thyroid/neck surgery
• characterized by:
  
  • low Ca and high plasma phosphate levels
  • tetany due to increased muscle excitability
  • decreased Ca can lead to death