1 / 23

Calcitonin- A hypocalcaemia hormone Lecture NO: 2 nd MBBS

Calcitonin- A hypocalcaemia hormone Lecture NO: 2 nd MBBS. Dr Muhammad Ramzan. Calcitonin – the definition. Calcitonin is the formal name of a protei n hormone secreted by the Pa ra follic ular cells of Thyr oid gland Also called Thyroc alcitonin

gana
Download Presentation

Calcitonin- A hypocalcaemia hormone Lecture NO: 2 nd MBBS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Calcitonin- A hypocalcaemia hormoneLecture NO: 2nd MBBS Dr Muhammad Ramzan

  2. Calcitonin – the definition • Calcitonin is the formal name of a protein hormone secreted by the Para follicular cells of Thyroid gland • Also called Thyrocalcitonin • Major action of the Calcitonin is to inhibit the boneresorption by the Osteoclasts.

  3. Calcitonin – the background ↓ Ca++ level when it is high • Calcitonin reduces serum Ca++and PO4 level when it is high, opposite to the action of PTH • This action of Calcitonin is through Osteoblasts and Osteocytes that have Calcitonin receptors. • Osteoclasts do not have Calcitonin receptors and so is true about the PTH receptors

  4. Calcitonin – Synthesis32 AAs • Calcitonin is a single chain peptide of 32 AAs • Calcitonin is synthesized as a Prohormone having 115/142 AAs by the RER of : • Para follicular cells • It is cleaved to have 42/37/32Amino acids after passing through Golgi Complex

  5. Calcitonin – Synthesis cont.stored a vesicles • It is stored as secretary granules in the cytoplasm of the Para follicular cells • It Is released in response to an appropriate stimulus like high serum calcium level • Calcitonin has its own GPCR on the plasma membrane of the target organs

  6. Calcitonin - structure

  7. Calcitonin – Target tissuesbone cells, renal tubules and GIT • Target tissues are the ones with Calcitonin receptors • The target organs for the Calcitonin are the : • Osteoblasts; Osteocytes, Renal tubular cells and GIT • Target tissues also bearPTHreceptors and are also involved in binding Calcitonin • There are no Calcitonin receptors on Osteoclasts

  8. Calcitonin – the target organs

  9. Calcitonin - Regulation of secretionserum and ECF Ca++ • It is through negative feed back like PTH • Serum and extracellular calcium level is the majorregulator of Calcitonin secretion • Serum Po4does not play an active role in human • There are 2 pathways for the regulation of Calcitonin • 1. Direct and 2. Indirect

  10. Calcitonin – Direct regulationinteraction B/W Ca and Calcitonin • It is the interactionB/Wserum Ca++ level and the Calcitonin • High Ca level stimulates Para follicular cells to ↑ synthesis of Calcitonin that lowers serum Ca++ level • It will also inhibit the Osteoclastic activity but promotes bone formation ( deposition of Ca) • There is no role of PTH

  11. Calcitonin- Direct regulation

  12. Calcitonin – Indirect regulation via PTH • Low serum Ca++, stimulates the Para thyroids to ↑ PTH secretion and Osteoclastic activity • This elevates serum Ca++ and inhibits Calcitonin synthesis by inhibiting Para follicular cells • Normal Ca level is 9 - 11mg/100ml

  13. Indirect regulation of Calcitonin

  14. Calcitonin - Mechanism of action GPRC • Calcitonin is a peptide and its mechanism of action is like other peptides/proteins – 2nd messenger • Calcitonin binds to the extra cellular domain of GPCR on Osteoblasts, Osteocytes and Renal tubules • Produces conformation changes in membranous subunit

  15. Calcitonin – Mechanism of action cont. • It leads to the activation of G protein and binding of its α-subunit to the GDP in exchange for GTP • Membranous Adenylate Cyclase is stimulated by α-GTP and converts ATP to cAMP – the 2nd messenger • cAMP activates Protein Kinase that Phosphorylates other proteins/enzymes to execute hormonal actions

  16. Mechanism of Action – 2nd messenger GPCR

  17. Metabolic role of Calcitonin • Depends upon its action on target organs • These include : • Bones • Kidneys • and Intestines

  18. Calcitonin – the metabolic role

  19. Effects on bone activity • Calc. inhibits Osteoclastic activity and bone resorption • Less Ca and PO4 are mobilized from the bone to blood • Lowers serum and extracellular calcium ions • Calcitonin promotes Osteogenesis and Osteoblastic activity especially in children

  20. Effects on Kidneys • It inhibits resorption of Ca and Po4 from the distal tubule and ascending loop of Henley 1 • It promotes the renal excretion of Ca and PO4 to reduce the blood calcium level 2 • Calcitonin inhibits the activation of Vitamin D in kidneys

  21. Effects on intestine • Reduction in the activation of Vitamin D that reduces absorption of calcium from GIT • It lowers the blood calcium level

  22. Calcitonin – Secretion abnormalities • A large no of diseases are associated with abnormally excess or deficiency of Calcitonin • However, the pathologic effects of abnormal Calcitonin secretion per se are not generally recognized.

  23. Clinical significance of Calcitonin • Para follicular cells involved in thyroid malignancies • This results in ↑ Calcitonin with no significant hypocalcaemia • It is used for the treatment of osteoporosis after menopause and hysterectomy. • Further it is also used in the hypocalcaemia due to malignancies, hyperparathyroidism and VIT.D intoxication

More Related