Calcium Regulation 1Dr. Sumera Gul

Associate Professor

Department of Physiology

Learning objectives

• At the end of the lecture all the students should be able to:

• Explain the normal homeostasis related to calcium

• Elucidate the symptoms of hypo and hypercalcemia

• Explain the general features, functions and factors affecting secretion of Calcitonin

• Explain the general features, functions and factors affecting secretion of Parathyroid Hormone

Normal range

Normal Calcium levels in blood: 9.4mg/dl

0.1% in ECF1% in cellsRest in bones

Phosphate

<1% in ECF14-15% in cellsAround 85% in bones

3-4 mg/dl (phosphorus)

Calcium in Plasma

Hormones Affecting Calcium and Phosphate levels• Calcitonin

• Parathyroid Hormone

• Other:

• Vitamin D

Calcitonin

• Cell

• Type

• Receptor

• Mechanism of Action

Calcitonin

• Cell: Parafollicular cells of Thyroid gland

• Type: peptide 32 aa

• Receptor: cell surface receptor

• Mechanism of Action: cAMP and PLC ?

Function

• Inhibits osteoclastic activity

• Inhibits formations of new osteoclasts

• Decreases absorptive activities of osteoclasts

• Initially favors osteoblastic activity

• In long run reduces osteoblastic activity

Functions

• PTH overrides calcitonin

• Increases renal excretion of calcium by inhibiting its reabsorption

• It also facilitates diuresis and increases excretion of sodium and chloride

• Decreases the absorption of calcium from GIT

Functions

• In brain the calcitonin is reported to act via hypothalamus

• It decreases food and water intake

Stimulatory factors

• Calcium

• Gastrin

• Estrogen

• CCK

• Glucagon

Parathyroid Hormone

• Cell

• Type

• Receptor

• Mechanism of Action

Parathyroid Hormone

• Cell: Chief Cells of Parathyroid gland

• Type: peptide 84 aa

• Receptor: cell surface receptor

• Mechanism of Action: cAMP and IP3 and DAG

Function

• Increases osteoclastic activity

• Increases bone resorption

• Initially favors osteoclastic activity

• In long run it also increases osteoblastic activity

• Stimulates production of new osteoclasts

Function• Decreases calcium excretion from kidney

• Increases calcium reabsorption from distal tubules

• Increases phosphate excretion from kidney

• Increase phosphate absorption from GIT

• Increases phosphate absorption from bone

• Increases the formation of 1,25- dihydrocholecalciferol

Stimulatory factors

• Low Calcium

• High phosphate levels

• Decreased Vitamin D

Inhibitory Factors

• Increased PTH

• Increased Calcium

• Increased vitamin D

• Bone resorption by disuse etc