L9. Calcium homeostasis, growth hormone and pineal gland Flashcards
4 roles of Ca2+
• Excitation-contraction coupling
Excitation-secretion coupling
Excitability of nerves and muscle •
Clotting of blood (haemostasis)
what level of Ca2+ is rquired for muscle contraction?
increase in intracellular ca2+
what does an increase in extracellular ca2+ cause?
decerase in neuromuscular contracility
normal plasma ca2+ levels
9-10mg/dl
where is 99% of ca2+ stored
bone
3 hormones which control Ca2+ homeostais
PTH
Vit D
calcitonin
where is PTH synthesised?
chief cells of PT glands
describe steps of PTH synthesis
- preproparathormone
- proparathormone
- PTH
how is PTH removed?
liver & kidney
half life of PTH
2-5mins
what regulates PTH secretion
Ca2+
what causes increased PTH secretion?
low plasma Ca2+
what causes decreased PTH secretion?
high plasma Ca2+
2 effects of chronic hypocalcaemia?
hyperplasia
hypertrophy of PT gland
role of pTH
increase ECF Ca2+
3 target organs of PTH
- kidney
- inetsine
- bone
effect of pTH on kidney
decreased ca exretion
increased phosphate excretion
effect of PTH on intestinr
activates VitD3 to increase absorption of Ca and phos
normal effecrt of PTH on bone
fast efflux of ca from bone fluid into plasma
effect of PTH on bone during chronic hypocalcameia
dissolution of bone to allow slow tranfer of Ca2+ into plasma
cause of PTH deficiency
operative procedure on thyroid/PT gland
cause of PTH excess
tumour in PT gland
effects of PTH deficiency
hypocalcaemia
effects of PTH excess
hypercalcaemia + hypophosphataemia
3 signs + sxs of hypocalcaemia
- tetany of hands and feet
- removal of glands = death due to asphyxiation due to tetany of resp muscle
- seizures due to excitiablity in brain
sxs of hypercalcaemia on bone
extensive bone decalcification
sxs of hypercalcaemia is reduced neuromuscular excitiability. what 6 sxs does this lead to?
- muscle weakness
- decreased mentation
- poor memory
- constipation, abdo pain graons
- peptic ulcer
- depressed relaxation of heart during diastole
sxs of hypercalcaeimai on kidney
increased risk of kidney stones
treatment for hypocalcaemia
vit D and calcium supplements
treatment for hypercalcaemia
surgical removal of tumour
2 roles of Vit D
- intestinal absorption of Ca2+
2. responsivenes of bone to PTH
is vit D action fast or slow?
slow
describe steps in activation of Vit D3
- Vit D3
- 25-hydroxy Vit D3 (liver)
- 1,25-dihydroxy Vid D3 (kidney) via PTH
Vit D deficiency effects on Ca2+ absoprtion
reduced - causes PTH to maintain Ca2+ levels ; demineralisation of bone
vit D effects on children
rickets
Vit d effects on adults
osteomalacia
what is osteoporosis
reduction in bone mass - as bone resoption > bone formation
function of calcitonin
reduce Ca2+
how does calcitonin reduce Ca2+
inhibiting osteoclastic bone resorption - ca2+ is not released
where is calcitonin synethsised
parafollicular/c cells of thyroid
what increased calcitonin secretion
hypercalcaemia
what decreases calcitonin secretion
hypocalcaemia
therapeutic use of calcitonin
disorders of increased skeletal remodlling - paget’s disease
where is growth hormone secreted?
anterior pituitary
where is calcitonin secreted from?
thyroid gland
T/F: Growth hormone causes fat accumulation within adipocytes
false
T/F: Growth hormone is glucose sparing.
true
how do liver cells respond to growth factor?
release insulin-like-GF
where in the skin is vitamin D synthesised?
epidermis
T/F: Vitamin D exhibits property similar to a steroid hormone.
true
what gland secretes melatonin?
pineal
what does melatonin secretion increase in response to?
darkness
Before the discovery of these glands, thyroid surgery often led to a rapid drop in blood calcium levels, which triggered muscle contractions and cardiac arrhythmias. What glands are these and which hormone is lacking?
parathyroid; PTH
2 other names of growth hormone (GH)
somatotropic hormone/somatotropin
where is GH sec from
ant pit
2 normal growth spurts
post natal, puberty
2 effects of GH
- metabolic effect
2. growth effect
describe 2 metabolic effects of GH
- increase FA levels
2, increase BG levels by dec glucose uptake
GH effect on soft tissues
hyperplasia, hypertrophy, protein synthesis
what 2 components make up bone
bone cells + Ca phosphase crystsls in organic matrix
what is part of the organic matrix of bone
collagen fibres + ground substance
3 types of bone cells
osteoblasts, osteoclasts, osteocytes
which bone cells are responsible for bone resorption
osteoclasts
what affect does GH have on liver
release glucose and IGF-1
which is the GH-inhibiting hormone
somatostatin
2 drugs to treat excess GH
somatostain + bromocriptine
precursor of melatonin
5-hydroxy tryptamine
which enzyme converts 5-hydroxy tryptamine into melatonin
5-methoxytryptamine
