Hormones Involved In Bone By Yapa Wijeratne

HORMONES INVOLVED IN BONE

METABOLISM

by Yapa Wijeratne

Faculty of MedicineUniversity of Peradeniya Sri Lanka

1. PTH

2. Calcitriol

3. Calcitonin

4. Oestrogen

5. Cortisol ( glucocorticoids)

6. Thyroid hormones

7. Insulin

8. GH

9. IGF

1.PTH

Secreted by Chief cells of the parathyroid gland 84 amino acid(AA) ↓ [Ca+2]ECF (+) secretion ↑ [PO4

-3]serum

PTH active PTH(amino terminal fragment)

1-84 1-34

carboxy terminal fragment

35-84

PTH

Act directly on bones –

1. ↑osteoclast (OC) activity to ↑bone resorption → ↑mobilize [Ca+2] → ↑[Ca+2]serum

2. ↓Reabsorption of [PO4-3]in PCT

3. ↑Reabsorption of [Ca+2] in DCT

4. ↑ formation of 1,25 DHCC & this ↑ [Ca+2] absorption from the intestine.

2.Calcitriol

1. ↑Transcription of calbinding D protein in the intestine.

2. ↑Intestinal Ca+2 absorption by facilitating Ca+2

transport.

3. Facilitates Ca+2 reabsorption in the kidney.

4. ↑The synthetic activity of osteoblast (OB) & is necessary for normal calcification of matrix

3.Calcitonin

By Parafollicular cells of thyroid gland. 32 AA Secretion is regulated by serum[Ca+2].

1. Inhibit OC bone resorption

2. ↑Ca+2 Excretion in the urine

4.Estrogen

1. ↑OB functions

2. ↓OC functions

3. ↓Renal excretion of Ca+2 & PO4-3

4. ↓intestinal excretion of Ca+2 & PTH function

5. Cortisol ( glucocorticoids)

lower plasma Ca2+ levels by inhibiting osteoclast formation and activity.

Over long periods they cause osteoporosis by ↓bone formation & ↑bone resorption.

1. ↓bone formation by inhibiting protein synthesis in OB.

2. ↓Absorption of Ca+2 & PO4-3 from the intestine

3. ↑Renal excretion of Ca+2 & PO4-3

6. Thyroid hormones

Promote normal growth and skeletal development. May cause hypercalcemia, hypercalciuria, and, in

some instances, osteoporosis.

7. Insulin

↑Bone formation (via OB activity) DM → ↓insulin → Significant bone loss in

untreated DM.

8.GH Anabolic effect on bone Promotes the growth of the skeleton These effects in are believed to be mediated by IGF I & II

acting on cells of the OB.

↑urinary excretion of Ca+2 & hydroxyproline ↑Intestinal absorption of Ca+2

NET EFFECT (+) Ca+2 balance

↓urinary excretion of PO4-3

9.IGF -I

Long arm of chromosome 12 & produces a 70 AA polypeptide.

Receptor (®) IGF-I = insulin ® → stimulates Tyr kinase activity &

autophosporylation of the Tyr residue in ® → cell differentiation & division

IGF-I

1. Stimulate Growth without GH

2. Stimulate Protein synthesis in bone

3. Has stimulatory effect on1. Hematopoiesis

2. Ovarian steroidogenesis

3. Myoblast proliferation

4. Differentiation of lens

IGF-II

67 AA peptide Short arm of chromosome 11 [IGF II]plasma vary with

Age Physiological condition (peak during puberty)

Neonates children puberty adult

IGF-BPS

IGF molecules in the circulation are mostly bound to variety.

IGF-BPS I (-) action of IGF I It is present in ↑ [ ] in fetal serum & amniotic fluid.