Endocrine control of Calcium Metabolism Flashcards
Is calcium the most abundant metal in our bodies?
Yes - remember that.
What are the roles of Ca2+ in the body?
Muscle contraction, bone strength, intracellular messenger and co-enzyme, blood coagulation and hormone/NT stimulus-secretion coupling
How is calcium stored?
Most as calcium salts; 99% found in bone
How is calcium transported in the blood?
50% unbound and bioactive
What increases and decreases calcium concentration?
[Ca2+] increased by: parathyroid hormone and calcitriol (active VitD3)
[Ca2+] decreased by: calcitonin
Where are the parathyroid glands?
Back edges of thyroid; secrete parathyroid hormone
What are the effects if Parathormone?
Kidneys: increases phosphate excretion and calcium reabsorption; stimulates 1a-hydroxylase to synthesise active form of VitD3 (by hydroxylation) which acts on small intestine to increase calcium and phosphate absorption
Bone: stimulates osteoclasts (break) and inhibits osteoblasts (build) to increase bone resorption - mobilises Ca2+
Blood: overall increases circulating calcium levels for contraction and signalling
What is calcitrol synthesised from?
vitD3
In skin, UV light can convert cholesterol to vitD3
What are the effects of calcitrol?
Bone: increases osteoblast activity - promotes laying down of calcium/phosphate salts in bones
Small intestine/kidneys: increases calcium and phosphate absorption - to increase levels for bone salts
What does Hypocalcaemia lead to?
Tetany, as sodium enters cell more easily, so more likely to have action potentials - Trousseau’s sign (BP cuff pressure cuts off blood flow and hand will start to contract) and Chvostek’s sign
What are the endocrinological causes of Hypocalcaemia?
Hypoparathyroidism
Pseudohypoparathyroidism
VitD deficiency
What are the endocrinological causes of Hypercalcaemia?
Primary hyperparathyroidism - parathyroid adenoma, producing a lot of PTH (not correctly regulated by increased calcium, so keep releasing)
(Secondary hyperparathyroidism - low plasma calcium e.g. Renal failure, PTH unable to restore calcium levels)
Tertiary hyperthyroidism - initial chronic low plasma [Ca]; started as secondary, and PTH levels were very high, so parathyroid glands became hyperplastic and grew too large; if underlying cause of plasma calcium deficiency (e.g. Renal failure) removed, parathyroid glands become autonomous and are not negatively regulated by plasma calcium
Vitamin D toxicosis - would need a lot chronically
