Parathyroid physiology Flashcards
What stimulates the parathyroid gland to release PTH?
Decreased calcium
Where is vitamin D3 produced?
Skin
How is calcidiol produced?
Converted from Vit D3 in the liver
What enzyme converts calcidiol to calcitriol?
a-hydroxylase
What does PTH stimulate?
Kidney (a-hydroxylase to convert calcidiol to calcitriol)
Bone (release calcium & phosphate)
DCT (increase calcium reabsorption)
What exhibits a negative feedback mechanism on PTH?
Calcitriol
Whatdoes calcitriol stimulate?
Bone (release calcium & phosphate)
GI tract (absorb calcium & phosphate)
PCT (reabsorb calcium)
What stimulates release of calcitonin from the thyroid gland?
Decreased calium
What is the parathyroid gland composed of?
Chief cells
Symptoms/signs of hyperparathyroidism
Bone disease (pain, fracture, osteoporosis)
Renal stones
GI (constipation, nausea, peptic ulcer, gallstones, pancreatitis)
CNS (depression, lethargy, seizures)
Muscular weakness & fatgue
CVS (Calcification of aortic + mitral valves)
Causes of hperparathyroidism
Adenoma
Hyperplasia
Management of hyperparathyroidism
Surgery
Indications for parathyroid surgery
End organ damage
Very high calcium (>2.85)
What is primary hyperparathyroidism?
Primary overactivity of parathyroid (e.g.adenoma)
What are the biochemical findings of primary hyperparathyroidism?
High PTH
High Calcium
Normal Alk Phos
Low phosphate
What is secondary hyperparathyroidism?
Physiological response to low calcium due to chronic hypocalcaemia
(parathyroid is hyperplastic)
Causes of secondary hyperparathyroidism
Renal failure
Low calcium intake
Vit D deficiency
Biochemical findings of secondary hyperparathyroidism
Low calcium
High PTH
What is tertiary hyperparathyroidism?
Parathyroid becomes autonomous after many years of secondary
Biochemical findings of tertiary hyperparathyroidism
High calcium
High PTH
What can be a congenital cause of absent parathyroid glands?
Di George syndrome
Causes of hypoparathyroidism
Congenital abscence
Destruction (surgery, malignancy, radiotherapy)
Autoimmune
Hypomagnaesmia
Treatment of hypoparathyroidism
Calcium & Vitamin D supplements
What is a mild type of osteogenesis imperfecta?
Type I
What are the severe types of osteogenesis imperfecta?
Types III & IV
Which type of osteogenesis imperfecta causes nneonatsl death?
Type II
What is osteogenesis imperfecta associated with?
Blue sclerae
Dentinogenesis
Management of osteogenesis imperfecta
No cure
Bisphosphonates
Causes of vitamin D deficiency
Dietary deficiency
Malabsorption
Chronic renal failure
Drugs (anti-convulsants)
Features of osteomalacia
Low calcium
Proximla muscle wasting
Dental defects
Bone tenderness
What mutation causes vitamin D resistant rickets?
PHEX gene mutation
Treatment of vitamin D resistant rickets
Phosphate + Vit D3
Why does hypomagnasaemia affect calcium levels?
Calcium release from cells is dependent on magnesium
Means increased intracellular calcium
PTH release is inhibited
Skeletal + muscles receptors less sensitive to PTH
Cuases of hypomagnasaemia
Alcohol (+/- PPI)
Drugs (thiazide, PPI)
GI illness (malabsorption)
Pancreatitis
What is pseudohyperparathyroidism a genetic defect of?
GNAS 1
Biochemical findings of pseudohyperparathyroidism
Low calcium
High PTH
Features of pseudohyperparathyroidism
Bone abnormalities (McCune Labright) Obesity Subcutaneous calcification Learning diability Brachdactyly (4th metacarpal)
Difference between pseudohyperparathyroidism & pseudo-pseudohyperparathyroidism
Pseudo-pseudo has normal calcium
patients can change from pseudo to pseudo-pseudo
What is Paget’s disease?
Abnormal osteoclastic activity followed by increased osteoblastic activity = abnormal bone structure
Which bones are typically affected by Paget’s?
Long bones
Pelvis
Lumbar spine
Skull
How does Paget’s present?
Incidenc increases with age
Bone pain
Deformity
Deafness
What is a rare complication of Paget’s?
Osteosarcoma
Treatment of Paget’s
Treat with bisphosphates if pain not responding to analgesia
Biochemical findings of FHH
High calcium
Normal PTH
Normal Alk Phos
Normal phosphate
Biochemical findings of hypoparathyroidism
Low calcium
Low PTH
Normal Alk Phos
Normal phosphate
Biochemical findings of osteomalacia
Low calcium
High PTH
High Alk Phos
Low phosphate
Biochemical findings of Paget’s
Normal calcium
Normal PTH
High Alk Phos
Normal phosphate
