calcium and bone

Question 1

PTH

Answer 1

secreted in response to decreased calcium
immediately increases Ca reabsorbed in the renal tubule
also causes Ca release from the bone
activates vit D and increases Ca absorption in the gut

overall role is to increase serum calcium and reduce phosphate
stimulates osteoclast activity
increase calcium, and decrease phosphate reabsorption from the kidney
increase renal production of 1,25-dihydroxy-vitaminD3 (calcitriol)

Question 2

vitamin D

Answer 2

cholecalciferol

7-dehydrocholesterol converted in the skin into vit D by UVB in the sunlight

Question 3

osteoclasts

Answer 3

form a seal and secrete acid onto the underlying bone leaving a pit behind, on which osteoblasts act to build new bone

Question 4

hypercalcaemia

Answer 4

common
thirst, polyuria, renal stones, weakness, myalgia, bone pain, diarrhoea, anorexia

stones, bones, groans and moans

Question 5

primary hyperparathyroidism

Answer 5

F:M 3:1
peak 50-70yrs
85% solitary parathyroid adenoma
15% 4-gland parathyroid hyperplasia
<1% parathyroid carcinoma

can lead to:
kidney stones and renal impairment
osteoporosis at wrist and hip
osteitis fibrosa cystica

the high PTH removes Ca from the bone and moves it to the blood. this is then excreted by the kidneys, causing kidney stones as it passes through

Question 6

severe hypercalcaemia

Answer 6

when someone first presents, blood tests can indicate cause

if PTH is high - primary hyperparathyroidism
if PTH low - cancer

Question 7

albumin

Answer 7

calcium in the blood is bound to albumin. therefore patients who have low albumin will have an apparent hypocalcaemia on blood tests. their calcium is not low, rather their albumin is reduced

Question 8

vit D and calcitriol

Answer 8

vit D hydroxylated in the liver into 25-hydroxy-vit D and again in the kidney into calcitriol, the biologically active form
calcitriol production is stimulated by decreased calcium, decreased phosphate and PTH
it increases calcium and phosphate absorption from the gut
inhibits PTH release (negative feedback)
it increases bone turnover
increases calcium and phosphate reabsorption in the kidney

Question 9

role of phosphate

Answer 9

85% of the bodies stores found in bone as hydroxyapatite
15% stored as phosphoproteins, phospholipids and nucleic acids
involved in energy production and bone and tooth formation
levels are opposite to calcium. ie as calcium falls, phosphate will rise and vice versa
controlled less tightly than calcium, with wider variations due to diet
increased by vitD, decreased by calcitonin
serum phosphate controlled by reabsorption in the kidney,. which is decreased by PTH

Question 10

bone

Answer 10

despite the role of bone as a structure, its metabolic function as a reservoir for calcium, phosphate, magnesium is its primary function
ie calcium will be removed from bone if needed regardless of the loss of structural integrity

Question 11

magnesium

Answer 11

low magnesium prevents PTH release and may play a role in hypocalcaemia