Regulation of calcium and phosphate

Question 1

Recommended Calcium intake per day adults

Answer 1

1000mg

Question 2

Calcium proportions in the body

Answer 2

99% skeleton and teeth - hydroxyapatite crystals
1% intracellular
0.1% extracellular

Question 3

Plasma Calcium concentration

Answer 3

-2.5mmol/L
Active
Bound to plasma proteins or anions

Question 4

Importance of calcium in the body: Functions

Answer 4

neuromuscular excitability
bone strength 
factor 4 blood coagulation 
intracellular 2nd messenger
intracellular co-enzyme 
hormone / neurotransmitter coupling secretion

Question 5

Importance of phosphate in the body: Functions

Answer 5

ATP
2nd messengers
DNA
extracellular phosphate is inversely proportional to calcium conc, controlled by same hormones

Question 6

Increase calcium levels in blood

Answer 6

Parathyroid hormone - parathyroid glands
Vitamin D - synthesized in skin or diet
act on kidneys bone and gut

Question 7

Decrease calcium levels in blood

Answer 7

Calcitonin - thyroid parafollicular cells.

No negative effects if cells are removed eg thyroidectomy.

Question 8

Vitamin D2 is from

Answer 8

diet - ergocalciferol

Question 9

Vitamin D3 is from

Answer 9

sunlight - cholecalciferol

Question 10

Production of Calcitriol

Answer 10

25 hydroxylase in liver

1 alpha - hydroxylase in kidney.

Question 11

Measure Vitamin D status

Answer 11

measure serum 25-OH vitamin D.

Question 12

Regulation of Calcitriol synthesis

Answer 12

Negative feedback

Calcitriol decreases transcription of 1 alpha-hydroxylase enzyme

Question 13

Effects of Calcitriol

Answer 13

Increase serum Ca
Kidney - increased reabsorption of Ca2+ and PO43-
Small intestine increased Ca2+ and PO43- reabsorption
Stimulates osteoblasts

Question 14

Parathyroid hormone secretion location and method

Answer 14

Chief cells in parathyroid glands as large precursor

Question 15

Parathyroid hormone regulation

Answer 15

PTH secretion inversely proportional to serum calcium.
G - protein coupled calcium sensing receptor detects serum calcium
High - less PTH
Low - more PTH
Chief cells also have calcitriol receptors - negative feedback

Question 16

Effects of Parathyroid hormone

Answer 16

Increase blood Ca
Kidney - increases Ca reabsoption
Decreases PO reabsorption
Increases 1 alpha-hydroxylase activity - leading to more Vit D synthesis
Increases bone resorption, consuming Ca from bone (osteoclasts)

Question 17

Parathyroid hormone in bone

Answer 17

OsteoBlast - build bone, PTH receptor converts to OsteoClast - consume bone to increase serum Ca

Question 18

Calcitonin secretion and function

Answer 18

Parafollicular cells of thyroid gland - detect high Ca
Reduces serum calcium
thyroidectomy does not affect serum calcium

Question 19

Calcitonin effects

Answer 19

Reduce plasma Ca
Kidney - increase Ca excretion
Decrease osteoclast activity

Question 20

FGF23 function

Answer 20

Inhibits Na/PO co transporter in kidney, decreases reabsorption of PO and inhibits calcitriol -
Leading to less PO reabsorption from gut

Question 21

High serum calcium

Answer 21

Hypercalcaemia

Question 22

Low serum calcium

Answer 22

Hypocalcaemia

Question 23

Hypercalcaemia effects

Answer 23

Ca blocks Na influx, so less membrane excitability - atonal muscles.

Question 24

Hypocalcaemia effects

Answer 24

Greater Na influx, so more membrane excitability - neuromuscular irritability

Question 25

Hypocalcaemia symptoms

Answer 25

``` CATs go numb sensitises excitable tissues - muscle cramps, paraesthesia convulsions arrhythmias Tetany (tetanic seizure) ```

Question 26

Signs of hypocalcaemia

Answer 26

Chvostek's sign - twitching of facial muscles after tap. Trousseau's sign - inflation of BP cuff, carpopedal spasm. Neuromuscular irritability due to hypocalcaemia

Question 27

Causes of hypocalcaemia

Answer 27

``` Low PTH levels - hypoparathyroidsim Surgical Auto-immune Magnesium deficiency Congenital Vitamin D deficiency ```

Question 28

Causes of Vitamin D deficiency

Answer 28

``` Dietary insufficiency Inadequate sun exposure Liver disease - 25 hydroxylase Renal disease - 1 alpha-hydroxylase RARE - Vit D receptor defects ```

Question 29

Consequence of vitamin D deficiency

Answer 29

Lack of bone mineralisation - soft bones Children - rickets Adults - osteomalacia - fractures, proximal myopathy

Question 30

Signs of hypercalcaemia

Answer 30

Stones, abdominal moans and psychic groans. Stones - nephrocalcinosis - kidney stones Abdominal moans - GI effects, anorexia, nausea, constipation Psychic groans - CNS effect, fatigue, depression, coma

Question 31

Causes of hypercalcaemia

Answer 31

``` Primary hyperparathyroidism - too much PTH - parathyroid gland adenoma - no neg feedback, high PTH and high calcium Cancer : - bone metastases - activate osteoclasts - squamous cell carcinomas - PTH related peptide mimics PTH RARE - vit d excess ```

Question 32

Phosphate reabsorbed in the kidney by

Answer 32

sodium phosphate co-transporter