Lecture 7 & 16 - Calcium and Phosphate metabolism

Question 1

PTH action

• how this works with low serum calcium
• how is it regulated

Answer 1

• Cells in PT gland can sense low serum CA, this binds to the receptors and causes PTH to be made and secreted
• This will cause a change in the main organs (kidney - reabsorb calcium, make vit D to help absorb in cut more, breakdown bone to release calcium)
• This restores serum calcium

Regulated - serum calcium (negative feedback)

• serum phosphate (positive)
• vit D (negative)

Question 2

Significance of Parathyroid hormone related peptide?

Answer 2

• Most common cause of cancer related hypercalcemia (Produce in excess by some cancers)
• acts similarly to PTH (increase absorption of calcium from kidney, decrease absorption of Pi)
• is not involved in calcium homeostasis

e.g get cancer - lots of PTHrP and then get hypercaclemia

Question 3

• Main causes of hypercalcemia

Answer 3

PTH dependent - primary hyperparathyroidism

PTH independent

• Cancer e.g PTHrP
• Vit D intoxication

Question 4

• Cause of hypocalcemia

Answer 4

Hypoparathyoridsm
-surgery to neck, genetic (mutation in genes)

Parathyroid hormone resistance - doesn’t work, so cannot get increase in calcium

Abnormality in vit D metabolism

Question 5

• Phosphate metabolism
• Hormones, organs
• how does pH effect this?

Answer 5

Hormones - vit D, PTH, Phosphatonins

High pH - drives phosphate into the cells (from ecf into icf) - resp alkalosis - hyperventilating, get low serum phosphate because phosphate goes into icf , then restores when get better

Low phosphate - inhibits PTH and increases calitrol

Question 6

Hyperphosphatemia

Answer 6

• Advanced renal failure, ability to secrete phosphate is reduced
• hypoparathyoridism
• PTH resistance

Question 7

Hypophosphatemia

Answer 7

vit D deficiencey - elderly

• resp alkalosis (Drives phosphate into cells)
• renal loss

-increased PTH

Question 8

Phosphatonins

Answer 8

-comes from bone
PHEX inhibits this

FGF23 - derived from bone
-decreases kidney and gut absorption of phosphate to cause hypophosphatemia

Can get aquired and genetic problems - abnormality in transport across gut (hypophosphatemia)

Question 9

Symptoms - hypercalcaemia, high PTH hormone

Answer 9

Hyperparathyroidism

• had a parathyroid adenoma removed on neck
• calcium went back to normal

Question 10

Patient with Hypercalcemia, but low PTH

Answer 10

Due to PTHrP tumour secretion

-this acts similar to PTH so will increase serum calcium

Question 11

Old lady - bone pain, very skinny, hypocalcemia, anaemia due to folate and iron deficiencey

Answer 11

High parathyroid hormone, no vit D from sun

• unminderalized osteiod - osteomalacia
• has coeliac disease - malabsportion causing anaemia , also malabsorptuon of caclium, vit D ect.
• getting ill, becoming deficient

Question 12

Osteomalacia

Answer 12

Failure of bone to mineralise

• accumulation of unmineralised osteoid
• bone pain, easily fractured

-rickets in children,

Question 13

What happens if increase phosphate, but decreased calcium

Answer 13

Not vit D deficinecy

Question 14

PTH resistance

Answer 14

• Short bones
• high phosphate and PTH, low Calcium
• mutation in a PTH receptor

Question 15

Autosomal dominant hypercalciuric hypocaclcemia

Answer 15

Activation of calcium sensitive receptor

• Parathyroids read plasma ionised calcium level as being higher than it really is
• will switch off processes that drive absorption and reabsorption of urine

-if this receptor doesnt work then patients look like they have mild parathyrodism

• no treatment if asymptomatic
• can give vit D

Question 16

Very high FGF23

Answer 16

• very low phosphate and high parathyroid
• the enzyme is stoping reabsorption from kidney and gut

caused by tumour induced osteomalacia