Parathyroid & Bone Physiology

Question 1

Hypoparathyroidism develops after removal of at least…..glands

Answer 1

3

Question 2

Explain pseudohypoprathyroidism

Answer 2

A receptor disease in which tissues fail to respond to the hormone due to defective Gs protein with dec cAMP

Question 3

Causes of hypocalcemia

Answer 3

1. Hypoparathyroidism
2. Renal failure
3. Alkalemia
4. Vitamin D deficiency

Question 4

Mainfest tetany occurs at…..while latent tetnay occurs at…..

Answer 4

7 mg%
7-8.5mg%

Question 5

Mention provocative tests of latent tetany

Answer 5

1. Trouseau sign: occlusion of circulation of forearm by sphygmomanometer for few minutes causing ischemia of peripheral nerves resulting in wrist & thumb flexion & finger extension
2. Chvostek’s sign: tapping over facial nerve at angle of the jaw causes quick contraction of facial muscles

Question 6

Treatment of hypocalcemic tetany

Answer 6

1. Manifest tetany: calcium gluconate is given by slow IV
2. Latent tetany: diet rich in Ca & active vit D3 supplementation

Question 7

Describe distribution of plasma Ca

Answer 7

1. Diffusible (60%): ionized is 50%, non-ionized/complexed with HPO4/HCO3 or citrate (10%)
2. Non-diffusible (40%) bound to PPs exp albumin

Question 8

Describe Ca filtration/reabsorption of Ca through kidney

Answer 8

Only diffusible form is filtered, 99% is reabsorbed:
60% absorbed actively & obligatorily in PCT
Rest is absorbed under PTH influence in DCT
About 100 mg/day are excreted in urine

Question 9

Describe effect of the following on Ca:
1. Glucocorticoids
2. Estrogens
3. GH

Answer 9

1. Lower Ca++ in plasma by dec intestinak absorption & inc remal excretion. Dec bone formation by dec protein synthesis. Prolonged glucocorticoid administration leads to osteoporosis.
2. Dec osteoclast proliferation & activation by inc osteoprotegerin which is osteoclast inhibitory factor; glycoprotein that inhibit recruitment & proliferation of osteoclasts.
3. Inc Ca level as it inc its intestinal absorption.

Question 10

Normal vit D level is…..

Answer 10

20-50 ng/ml

Question 11

Describe actions of calcitriol on:
1. Intestine
2. Kidney
3. Bones

Answer 11

1. Inc calbindin in intestinal epithelium & inc Ca stimulated ATPase, so it helps Ca absorption also helps PO4 absorption.
2. Promotes Ca++ reabsorption in DCT by calbindin D formation, promotes PO4 reabsorption in PCT.
3. High Ca & PO4, stimulate bone deposition & vice versa.

Question 12

Serum calcitonin level is……

Answer 12

10-50 pg/ml

Question 13

Describe actions of calcitonin on:
1. Bone
2. Kidneys

Answer 13

1. Dec no & activity of osteoclasts so inhibit bone resorption, stimulate osteoblasts & alkaline phosphatase activity dec Ca movement from bone fluid to plasma & facilitates Ca deposition on long-term
2. Inhibit alpha-1 hydroxylase activity, stimlates secretion of both Ca & PO4

Question 14

Describe control of calcitonin secretion

Answer 14

Inc by: hypercalcemia, many GIT hormones such as (gastrin, glucagon, secretin, CCK) & estrogen
Dec Ca in plasma inhibits calcitonin release

Question 15

Structure of hydroxyapatite

Answer 15

Ca10(PO4)6(OH)2

Question 16

Importance of bone remodelling

Answer 16

1. Allows bone thickening
2. It replaces the old organic degenerated weak matter by strong one.
3. During childhood formation is more tyan resorption while the opposite is true during menopause
4. During adult life: bone formation is parallel to bone breakdown

Question 17

Causes of osteoporosis

Answer 17

1. Advancing age after menopause
2. Glucocorticoids (Cushing syndrome)
3. Immobilization

Question 18

The first line of defense against change in Ca level is….while 2nd is…..

Answer 18

Exchangeable calcium in bones
Hormonal control on bone deposition & resorption

Question 19

Describe the 2 mechanisms of raising PO4 blood level

Answer 19

1st: bec of inverse relation between Ca & PO4, a fall in PO4 causes rise Ca which inhibits PTH causing inc PO4 reabsorption from PCT
2nd, fall in PO4 causes inc vit D activation which inc PO4 reabsorption from kidney