5. Endocrine Control of Calcium Homeostasis

Question 1

importance of calcium

Answer 1

exocytosis (NT/hormone secretion)

physical properties of bone

Question 2

physical signs of hypoglycaemia

Answer 2

capopedal spasm (Trosseau's sign) 
Chvostek's sign

Question 3

carpopedal spasm

Answer 3

Trosseau’s sign

carpal spasm can be induced by occluding brachial artery in people with hypocalcaemia

Question 4

Chvostek’s sign

Answer 4

tapping facial nerve exaggerates neuronal excitation - facial nerved momentarily contract
present in 10% of healthy people low plasma calcium increases neuronal permeability to sodium - progressive depolarisation

Question 5

consequences of acute hypocalcaemia

Answer 5

thirst and polyuria

abdominal pain

Question 6

consequences of chronic hypocalcaemia

Answer 6

constipation
musculoskeletal aches/weakness
neurobehavioral symptoms 
renal calculi
osteoporosis

Question 7

serum calcium

Answer 7

protein bound: 40% (90% albumin, 10% globulin)
bound to cations: 10% (phosphate, citrate)
ionised (free): 50%
lab reports total calcium - corrected for albumin

Question 8

normal calcium level in blood

Answer 8

controlled within a tight range

2.15 - 2.25 moles/l

Question 9

parathyroid hormone

Answer 9

produced by chief cells in parathyroid glands

acts to increase serum level of calcium

Question 10

calcium sensing receptor

Answer 10

in parathyroid chief cells
G-protein coupled receptor
activation causes phospholipase C activation
also found in C cells of thyroid (calcitonin)

Question 11

how parathyroid hormone works

Answer 11

binds to PTH1 receptor - changes its shape
activates adenylyl cyclase
receptors found in bone and kidney

Question 12

PTH in bone

Answer 12

PTH binds, osteocytic membrane pumps calcium ions from bone fluid into extracellular fluid

Question 13

osteocytic membrane

Answer 13

interconnected network of cells overlying bone matrix

small layer of interposed fluid = bone fluid

Question 14

rapid calcium reabsorption

Answer 14

increased calcium reabsorption in loop of Henle, distal tubule, collecting ducts
decreased PO4 reabsorption in proximal tubule

Question 15

primary hyperparathyroidism

Answer 15

caused by enlargement of one or more parathyroid gland

rarely caused by parathyroid cancer

Question 16

hyperparathyroidism symptoms and complications

Answer 16

fatigue
fractures
muscular weakness/pain
decreased height

osteoporosis
bone cysts

Question 17

hypoparathyroidism

Answer 17

investigations: serum calcium low, PTH low/normal, Chvostek’s sign
causes: iatrogenic, autoimmune, hypomagnesaemia

Question 18

secondary hyperparathyroidism common causes

Answer 18

low/low normal serum calcium and high pTH
low serum 25 OH vitamin D (lack of sun, GI problems)
renal failure

Question 19

influence of vitamin D

Answer 19

induces synthesis of calcium binding protein in intestinal epithelial cells