Calcium Homeostasis (physiology) Flashcards
What stimulates the release of PTH??
Low blood calcium levels
In which cells is calcitonin released and what stimulates the release?
In the parafollicular cells, high calcium levels
What do we call the stimuli caused by ions, nutrients and chemicals?
Humoral stimuli
What are the two bone cells and their antagonistic functions?
Osteoblasts- resp for calcium deposition in bone.
Osteoclasts- resp for bone resorption in order to produce calcium and phosphate ions.
What are some of the functions of calcium?(5)
Contraction of muscle cells.
Cell proliferation
Mineralization of bones and teeth.
Tight junctions
Blood clotting
What are the three forms of circulating calcium?(3)
Ionized from- most biologically active form.
(50%)
Protein bound- Bound to negatively charged albumin. (40%)
Complexes form- bound to substances such as citrate and phosphate. (10%)
What are the cells resp for production of PTH?
Chief cells of the parathyroid gland
Two disorders of the parathyroids, explain further.(4)
Hyperparathyroidism:
- Tumour of parathyroid gland.
- Increased levels of PTH, caused high calcium levels.
- Weakening of bones, softening of bones, muscle weakness and kidney stones formation.
Hypoparathyroidism:
-Mostly due to accidental removal of parathyroid glands.
-Low levels of PTH, causes low levels of calcium.
- Tetany, suffocation, spams of laryngeal muscles.
What are the causes of vitamin d deficiency?(4)
Reduced exposure to the sun.
Poor dietary intake
Malabsorption
Vitamin D metabolism abnormality
Which other hormone stimulates osteoclast-mediated resorption of bone?
Thyroxine
How does oestrogen and testosterone affect ca metabolism?
They inhibit osteoclast function, and stimulate osteoblast function.
What role does cortisol play in ca metabolism?
It inhibits intestinal absorption and stimulate renal elimination.
What role does GH play in ca metabolism?
It increases urinary excretion of ca, while decreasing the urinary excretion of phosphate.
What are the causes of hypercalcaemia?
Thyrotoxicosis
Renal failure
Drug induced
Iatrogenic
Malignancy
What are the hypothyroid causes of hypocalcaemia?(5)
Post operative
Idiopathic
Acquired hypomagnesaemia
Neck irritation
Anticonvulsive therapy
