Calcium Homeostasis Flashcards
What parts of the body are involved in calcium homeostasis?
Bones, kidney, GIT, ECF, thyroid* & parathyroid*
*Hormone production only
What is the normal [Ca] in the ECF?
2.5 mM
Where is PTH produced?
What type of hormone is it & what is its basic mechanism of action?
PTH is produced by the parathyroid hormones
It is a peptide hormone with a cell membrane receptor acting through cAMP pathways
It has a short half life
Acts on the kidneys & bone and indirectly on the GIT via Vitamin D
Where is calcitonin produced?
What type of hormone is it & what is its basic mechanism of action?
Calcitonin is produced by the C-cells/follicular cells of the thyroid gland
It is a peptide hormone with a cell membrane receptor acting through G-protein 2nd messenger systems
Target’s the bone and kidneys
What organ acts most quickly to correct calcium serum levels?
The kidneys - alter excretion/reabsorption of Ca rapidly
How is Vit D produced & activated?
What type of hormone is it & what is its basic mechanism of action?
Vitamin D precursor found in skin and converted by UV to an inactive form
Inactive form undergoes 2 hydroxylation reactions, first in the liver, then in the kidney to become active (calcitriol/Vit D3)
Steroid hormone acting on a nuclear receptor to alter gene expression
Acts on the intestine to increase absorption of Ca
True or False.
Phosphate movement parallels that of calcium?
True
What happens when plasma [Ca] is ELEVATED?
Physiological levels
- Decreased PTH release
- Decreased reabsorption & increased excretion of Ca by the kidneys
- Decreased Vit D activation & decreased Ca absorption at gut
Extreme elevation
- Calcitonin release
- Acts on bones to decrease bone resorption
What happens when plasma [Ca] is DECREASED?
- PTH release from parathyroid glands
- Acts on kidneys - increase tubular reabsorption of Ca & increased activation of Vit D
- Vit D acts at gut to increase Ca absorption
- Acts on bones - increases RANKL/RANK to increase osteoclast activity & bone resorption
