Calcium/Phosphate Regulation

Question 1

Hypocalcemia symptoms

Answer 1

HYPER stuff- increased membrane excitability because of lower activation threshold
Hyperreflexia, muscle cramps, numbness/tingling
Chvostek sign- face muscle twitching when tapping on facial nerve
Trousseau sign- carpopedal spasm when BP cuff inflated

Question 2

Hypercalcemia symptoms

Answer 2

Higher activation threshold so decreased membrane excitability
Decreased QT interval
Constipation
Lack of appetite
Muscle weakness, hyporeflexia, lethargy

Question 3

Severe hypomagnesemia and PTH

Answer 3

PTH production will be inhibited

Question 4

PTH action on kidneys

Answer 4

Decreased Pi reabsorption
Increased calcium reabsorption by distal tubule and ascending limb
Increased urinary cAMP
Stimulates 1a-hydroxylase activity

Question 5

Vitamin D effects

Answer 5

Increases calcium and phosphate concentrations which promotes new bone formation
Suppressed PTH gene transcription
Increase RANKL production
Upregulate Calcium sensing receptor
Vit D must by hydroxylated to be an active metabolite, this is regulated by negative feedback mechanism

Question 6

Cholecalciferol synthesis

Answer 6

Different name for vitamin D
Converted to 25-OH-cholecalciferol (inactive
Kidney converts to 1-25-OH-cholecalciferol using 1a-hydroxylase
24a-hydroxylase converts it to 24-25-oh-cholecalciferol

Question 7

PTH short term function

Answer 7

Increases bone formation because it activates osteoblasts, which EVENTUALLY (long term action) will cause osteoclast proliferation

Question 8

Osteoclast formation and OPG

Answer 8

Osteoblasts release RANKL which binds to RANK on osteoclast precursors and then they turn into osteoclasts
After enough bone resorption, osteoblasts will release OPG which is a decoy receptor of RANKL so less RANKL will bind RANK and form osteoblasts

Question 9

Calbindin/TRPV6

Answer 9

Calbindin- Binds calcium while inside the epithelial cell during reuptake from intestine so that it does not effect the resting membrane potential and ruin the gradient
It is upregulated by Vitamin D
TRPV6- Calcium transporter in intestines, upregulated by vitamin D

Question 10

Vitamin D action concerning intestinal phosphate absorption

Answer 10

Activates the sodium/phosphate cotransporter so that it can be reabsorbed by epithelial cells

Question 11

Calcitonin

Answer 11

Promotes bone deposition/formation
Reduces renal calcium uptake
Released by thyroid gland