Calcium Phosphate Metabolism and PTH

Question 1

Role of PTH and vitamin D on >>> calcium and phosphate

Answer 1

• PO₄ >>> change of absorption/reabsorption >>> only kidney
• Calcium >>> change of absorption/reabsorption >>> kidney and GIT
• Bones are also affected (by raising osteoclastic activity)

Question 2

Phosphate reabsorption occurs in- ?

Answer 2

Kidney

Question 3

Calcium absorption and reabsorption occurs in- ?

Answer 3

• Absorption in gut
• Reabsorption in kideny

Question 4

Hormones of calcium metabolism

Answer 4

• Primary hormones (2):
  
  • PTH (Parathyroid hormones) >>> raises calcium
  • Vitamin D >>> raises calcium
• Other hormones:
  
  • Calcitonin (Secreted from C cells of the thyroid gland) >>> reduces calcium
  • Thyroxine >>> raises calcium
  • GH (Growth hormone)

Question 5

Hormones that raises calcium

Answer 5

• PTH (Parathyroid hormone)
• Vitamin D
• Thyroxine

Question 6

Hormones that lowers calcium

Answer 6

Calcitonin

Question 7

Effect of PTH on vitamin D

Answer 7

PTH activates vitamin D

(converts 25, hydroxy vitamin D to 1, 25 dihydroxy vitamin D)

Question 8

C cells of thyroid >>> function and significance

Answer 8

• It secrets calcitonin ; calcitonin reduces calcium level
• Medullary thryroid carcinoma (alone or as part of MEN-2a) arises from it

Question 9

Action of PTH (Parathyroid hormone) on calcium and phosphate metabolism

Answer 9

• It reduces plasma PO₄ (kindeys)
  
  • Reduces renal tubular reabsorption of phosphate
• It raises plasma calcium (kidneys and bones)
  
  • Raises renal tubular reabsorption of calcium
  • Raises osteoclastic activity
• It activates vitamin D
  
  • Raises conversion of 25-hydroxy vitamin D to 1, 25 dihydroxy vitamin D

Question 10

Action of vitamin D on calcium and phosphate metabolism

Answer 10

• It raises PO₄ level
  
  • Raises renal tubular reabsorption of PO₄
• It raises calcium level (kidneys, GIT, bones)
  
  • Raises renal tubular reabsorption of calcium
  • Raises gut absorption of calcium
  • Raises osteoclastic activity

Question 11

What does activate vitamin D OR convert 25-hydroxy vitamin D to 1, 25-dihydroxy vitamin D?

Answer 11

PTH (Parathyroid hormones)

Question 12

Similarities between “Role of vitamin D” and “Role of PTH”

Answer 12

• Both raise plasma calcium level
• Both act upon kindeys
  
  • Raises renal tubular absorption of calcium
• Both act upon bones
  
  • Raises osteoclastic activity

Question 13

Differences between “Role of vitamin D” and “Role of PTH”

Answer 13

• Vitamin D raises PO₄ level, but PTH reduces PO₄ level (by renal) [P goes against P]
• Vitamin D acts upon GIT (PTH does NOT)
  
  • ​Raises gut absorption of calcium

Question 14

Site of activation of vitamin D =

Site of conversion of 25,hydroxy vitamin D → 1,25 hydroxy vitamin D

Answer 14

Kidney (Renal system)

(by PTH)

Question 15

Formula of corrected calcium

Answer 15

Corrected calcium = measured calcium_mmol/L + [40 — S. Albimun_g/dL] x 0.027

Question 16

Different parathyroid conditions >>> Ca, PTH, PO₄ levels

Answer 16

• High Ca, High/N PTH, Low PO₄: Primary hyperparathyroidism
• High Ca, High PTH, High PO₄: Tertiary hyperparathyroidism (+ CKD, high sr. cr.)​
• Low Ca, High PTH, High PO₄: Secondary hyperparathyroidism (+ CKD, high sr. cr.)
• Low Ca, High PTH, High PO₄: Pseudohypoparathydoidism (short stature, short 4th-5th metacarpals)
• Low Ca, Low PTH, High PO₄: Primary hypoparathyroidism
• N. Ca, N. PTH, N. PO₄: Pseudopseudohypoparathyroidism (+ phenotypes like pseudohypoparathyroidism)

Question 17

Vitamin D intoxicity, Osteomalacia, Paget’s disease >>> Levels of Ca, PO₄, ALP

Answer 17

• Vitamin D intoxicity >>> High Ca, High PO₄, (ALP maybe normal)
• Osteomalacia >>> Low Ca, Low PO₄, High ALP
• Paget’s disease >>> Normal Ca, High ALP