L04 - Calcium Homeostasis

Question 1

Where is calcium important?

what does hypocalcaemia do?

Answer 1

Exocytosis (neurotransmitter & hormone secretion), bone

Hypocalcaemia destablises neurones. can cause seizures

Question 2

Physical signs of Hypocalcaemia?

Why

Answer 2

Cardopedal spasm
— occlusion of brachial artery causes

Chvostek’s sign
— low plasma Ca increases permeability of neuronal membranes to Na - action potentials more likely

Question 3

Consequences of hypercalcaemia (acute and chronic)

Answer 3

ACUTE - thirst and polyuria, abdominal pain

CHRONIC - constipation, musk aches / weakness, renal calculi, osteoporosis

Question 4

Why can Ca conc be inaccurate

what to do

Answer 4

LAb reports total Ca bound to albumin - corrected Ca may be inaccurate if albumin is super low (less than 20g/l) in severe acute illness

measure ionised Ca directly

Question 5

What hormone can serum Ca effect

how does it release in response?

what can prevent release of the hormone

Answer 5

PTH release from chief cells

calcium sensing receptor in the parathyroid chief cells

Once chief cells modify their cell processes, Mg facilitates the secretion of PTH. low prevents.

Question 6

How does Parathyroid hormone work.

Where are the receptors

Answer 6

PTH Type 1 receptor is activated by PTH by changing its shape

are in bone and kidney

Question 7

Calcium release from bone

how

Answer 7

osteocytic membrane pump

PTH –> osteoblast –> rank ligand –> rank connected to OSTEOCLAST activation.

osteoclasts break down bone, release Ca

Question 8

Actions of PTH on kidney and where exactly

how??

Answer 8

rapid calcium reabsorption in LOH, DT, col ducts

decresed PO4 reabsorption in prox tub

Question 9

How does PTH increase ca reabsorption?

Answer 9

how
Kidney and vitamin D

with PTH, 25OH Vit D—-> 1,25OH Vit D

Vit D increases calcium absorbtion in

calcium transporters and binding & protein calbindin in gut cells

Question 10

how is vitamin d activation regulated

Answer 10

1,25OH Vit D activates osteocytes and PTH.

PTH increases vit D activation, osteocyte increases FGF23 which decreases activation

Question 11

Clinical problems of Calcium metabolism

Answer 11

Hypercalcaemia (1ary and 2ary)

Hypoparathyroidism

Question 12

Primary hyperparathyroidism

diagnosis and complications

Answer 12

serum Ca increased
serum phosphate reduced
PTH increased

osteoporosis, bone cysts

Question 13

Hypercalcaemia complications

Answer 13

Renal stones

Question 14

How to locate parathyroid adenoma?

Answer 14

sesta mibi parathyroid scan

or neck ultrasound

Question 15

HypOparathyroidism

causes

Answer 15

serum Ca low, PTH low/normal

iatrogenic causes (thyroidectomy, radical neck surgery), autoimmune, hypomagnesaemia, genetic mutations

Question 16

secondary hyperparathyroidism

causes

Answer 16

low serum Ca and high PTH

low serum 25 OH Vit D
– lack of sun exposure, GI problems (malabsorp,surgery), renal failure

Question 17

reduced vitamin D can cause what

Answer 17

rickets in children, osteomalacia in adults (looser’s zone)

Question 18

Vit D and elderly

Answer 18

have lower Vit D levels

deficiency combined with elderly skin increases falls and fracture risk