Calcium

Question 1

Symptoms of hypoglycaemia

Answer 1

Increased muscle or nerve excitability
Muscle spasm

Question 2

Symptoms of hypercalcaemia

Answer 2

Decreased muscle or nerve excitability
Cardiac arrhythmia

Question 3

What is bone turnover?

Answer 3

Osteoblasts are attracted to osteoclasts due to osteoclasts releasing growth factors, either IGF or TGF-B. This causes more differentiation of osteoblasts. Osteoblasts build. Osteoclasts break down bone for calcium.

Question 4

What is RANKL?

Answer 4

Increases osteoclasts differentiation, therefore, promotes bone resorption/ breakdown

Question 5

What is OsteoProteGrin OPG?

Answer 5

Decoy receptor for RANKL, therefore decreases osteoclast differentiation and promotes bone growth

Question 6

How does oestrogen regulate osteoclasts?

Answer 6

Oestrogen stimulates OsteoProteGrin (OPG) and therefore decreases osteoclasts and promotes bone growth

Question 7

State the 3 hormones that control Ca2+ Homeostasis

Answer 7

Parathyroid
Calcitonin
Vitamin D

Question 8

How does the ParaThyroid Hormone (PTH) control calcium homeostasis?

Answer 8

Calcium concentration detected by GPCRs in parathyroid cells. When low, PTH causes calcium release in one of two ways:

FAST EXCHANGE- stimulation of GPCR receptors causes increase in cAMP, causing calcium to move into cells from bone fluid via gap junctions between osteoblasts.

SLOW EXCHANGE- Only when prolonged hypocalcaemia- PTH activates osteoblasts to increase RANKL. Therefore, osteoclasts are increased and bone breakdown is promoted, whilst osteoblast building activity is inhibited.

Question 9

What does presence of PTH on kidneys do in regards to calcium homeostasis?

Answer 9

Promotes calcium retention
Activates Vitamin D
Vit D causes increase in calcium absorption in GIT and therefore PTH indirectly causes increase in uptake of calcium in diet.

Question 10

How does Vitamin D control calcium homeostasis?

Answer 10

Increases conc. of calcium absorption in GIT from diet.
Activated in the liver and kidney.
Vitamin D promotes gene expression.
This causes increased absorption of calcium in GIT.
Also increases resorption of calcium in kidney.

Question 11

How does Calcitonin control calcium homeostasis?

Answer 11

Antagonistic to PTH
Secreted by thyroid gland C-cells
Secretion increases when calcium levels increase
How it works: Decreases calcium by inhibiting osteoclast activity, Also inhibits reabsorption of calcium in the kidney.