#Endocrinology

Bone related biochemistry

evan Jan. 21, 2024

Disease	ALP	Ca	Phos	PTH
HyperPTH	$↑$	$↑$	$↓$	$↑$
Osteomalacia	$↑$	$↓$	$↓$	$↑$
Osteoporosis	N	N	N	N
Paget's	$↑$	N	N	N
Bone mets	$↑$	$↑$	N	$↓$

Calcium biochemistry

Calcium values dependant on albumin (protein bound component)
If albumin low cannot use adjusted calcium so use ionised calcium instead

Phosphate biochemistry

Predominantly intracellular
ATP, DNA backbone, membrane phospholipids

Homeostasis of calcium and phosphate

PTH and vitamin D and metabolites controlling factors
Balance of - GI absorption, bone storage/resorption, renal excretion/reabsorption

Parathyroid hormone

Net effect:

Increase serum calcium
Decrease serum phosphate

PTH causes osetoclasts to breakdown bone releasing Ca and PO4
$↪$ kidneys increase reabsorption of Ca but increase PO4 excretion

Kidneys also increase active form of vitamin D to absorb more from gut

Other regulators

- Calcitonin - opposes the effect of PTH by acting on osteoclasts to inhibit bone resorption. Function is usually insignificant
- Oestrogen inhibits bone resorption