Parathyroid Gland

Question 1

Calcium in the body

Answer 1

▪️total body calcium- 1-2kg

• insoluble (99%)- hydroxyapatite
• soluble (1%)-extracellular (0.1%), intracellular (0.9%)

Question 2

Soluble calcium distribution

Answer 2

▪️extracellular (blood) - 2.20-2.60mmol/L
-40% bound to albumin
-10% bound with anions (phosphate)
-50% ionised (active)- 1.10-1.30mmol/L
▪️intracellular (cytoplasm)- <100nmol/L
-most is stored in ER so levels in cytoplasm are quite small- needed for signal responses

Question 3

Calcium key roles

Answer 3

▪️blood clotting- cofactors of clotting cascade
▪️nerve transmission- dumps down neural excitability-action potentials
▪️hormone secretion- stimulates insulin to be released
▪️muscle function. Required at neuromuscular junction

Question 4

Symptoms of Hypocalcaemia

Answer 4

▪️paraesthesia- pins and needles
▪️carpo-pedal spasm- muscle spasm at deep and hands
▪️seizures- uncontrolled neural excitability
▪️laryngospasm- spasm of laryngeal muscles- noisy breathing
▪️bronchospasm- causes wheezing

Question 5

Symptoms of hypercalcaemia

Answer 5

▪️lethargy
▪️anorexia- reduced appetite
▪️constipation
▪️brachycardia
▪️heart block- loss of electric conduction in atria and ventricles
▪️kidney failure- increase in calcium in urine

Question 6

Phosphate distribution

Answer 6

▪️85% in bone
▪️Pi major intracellular anion
▪️energy production:
-glycolysis, ATP, creative phosphate
▪️2,3-DPG in RBC- allows Hb to dissociate from oxy and release into cells
▪️nucleic acid production- backbone of DNA
▪️cell membranes phospholipids
▪️extracellular Pi is not as tightly regulated as calcium- can vary by 30% during the day

Question 7

Symptoms of Hypophosphataemia

Answer 7

▪️plasma <0.4 mmol/L
▪️affects ATP production
▪️muscle weakness
▪️rhabdomyolysis- muscle break down

Question 8

Symptoms of hyperphosphataemia

Answer 8

▪️caused by medicine and treatments
▪️acute due to Pi enema for constipation:
-hypocalcaemia- Pi binds to Ca2+ to make calcium phosphate so less active calcium
▪️chronic due to chronic kidney disease:
-soft tissue calcifications- calcium phosphate precipitates and settles in blood vessels- can be seen on x-rays

Question 9

Parathyroid gland regulating Calcium

Answer 9

▪️when Ca2+ levels are low in blood, PTH is released by PTG
▪️PTH works on bone-osteoclastic activity- break down to realise Ca2+
▪️PTH works on the DCT of nephron to reabsorb more Ca2+
▪️PTH works on PCT of nephron to produce active VD (calbinin)
▪️VD acts on duodenum and proximal jejunum to absorb Ca2+ from diet
-to stop Ca2+ from binding with Pi and calcifying, PTG also helps excrete Pi from the kidneys

Question 10

Hypoparathyroidism

Answer 10

▪️⬇️Ca, ⬆️Pi, ⬇️PTH
-low amounts of PTH leads to low amounts of Ca and high amounts of Pi
▪️causes:
-destruction of PTG- neck surgery (75%)
-autoimmune- APS1 (25-40%)
-developmental abnormalities 
-hypomagnesaemia 
▪️leads to high bone mass, hypocalcaemia, hyperphosphataemia

Question 11

Primary hyperparathyroidism

Answer 11

▪️most common cause of Hypercalcaemia
▪️⬆️Ca, ⬇️Pi, ⬆️PTH
▪️85%- PT adenoma
▪️leads to- excessive bone reabsorption, fractures, osteoporosis, kidney stones