endocrine lecture4 Flashcards
what do you need Ca++ for?
- structure (bone)
- cellular signaling
- muscle contraction
what general symptoms do you get if you dont have Ca++
hyper excitability leading to tetani, seizures
what general symptoms do you get if you have too much Ca++?
sluggishness
What is the Ca++ charge screening effect?
Ca++ normally neutralizes negative charges on the plasma membrane surface. When you have low Ca++ thenthe negative charges are exposed, tricking the v-gated Na+ channels to think that the cell is more depolarized than it actually is
what is phosphate used for in the body?
- 2nd messenger
- structure for bone
- energy store (high energy phosphates ATP, GTP)
The net uptake resulting from 1000mg of dietary Ca++ is only about ______
175mg (825mg gets excreted)
Serum Ca++ must be maintained at what level?
8-10mg per dL
- about 50% of which is free
- 40% bound to albumin
- 10% salts
bone matrix is made of what?
calcium phosphate salt
canulicular fluid in the bone has (lower/higher) ca++ than the blood?
lower
-so Ca++ enters from blood, down its concentration gradient
phosphate is (better/worse) absorbed than Ca++?
better
what is the key hormone for regulating Ca++ and K+ homeostasis?
PTH
PTH is released from where?
cheif cells of the parathyroid gland
what stimulates release of PTH?
low blood Ca++, acts to raise Ca++ levels
What exactly does PTH do to increase Ca++ levels?
-acts INDIRECTLY via Vit D
how does Vitamin D affect Ca++ levels? K+?
- increases Ca++ uptake from gut by upregulating Ca++ uptake protein “CALBINDIN”
- activates osteoclasts to breakdown bone and drive Ca++ and K+ into the blood
- increases reuptake of Ca++ in the kidneys
- DECREASES reuptake of K+ in the kidneys (this prevents formation of Ca/K salts in the blood
how does low serum Ca++ cause vessicle exocytosis of PTH?
- Ca++ sensor on surface of cheif cells
- Ca++ normally keeps this sensor inactivated
- low Ca++ activates Gq (g protein) causing exocytosis
how is Vit D3 activated?
must be hydroxylated in 2 positions
- Liver does one
- Kidneys does the second one
what is the active form of Vit D?
1, 25-(OH)2 Vitamin D
what role does PTH play on the activation of Vit D?
it catalyzes the hydroxylation reactions of Vit D in the Liver and Kidney. SO without PTH you wouldnt get enough active Vit D
What does Vit D do to increase gut uptake of Vit D?
increases levels of a protein “CALBINDIN” which is a Ca++ transport protein
How does cortisol affect Vit D’s effects?
It opposes the action of Vit D
What would happen with HYPER PTH?
hypercalcemia (sluggishness)
- bone destruction
- excess calcium uptake from gut
- excess calcium retention
- stones
What would happen with HYPO PTH
hypocalcemia (tetani, seizures)
- low serum Ca++
- low Vit D
- Ca++ excretion at kidneys
what is pseudo hypo parathyroidism?
defect in the PTH receptor
- leads to hypo Ca++
- PTH levels dont matter, could be super high
