endocrine lecture4

Question 1

what do you need Ca++ for?

Answer 1

• structure (bone)
• cellular signaling
• muscle contraction

Question 2

what general symptoms do you get if you dont have Ca++

Answer 2

hyper excitability leading to tetani, seizures

Question 3

what general symptoms do you get if you have too much Ca++?

Answer 3

sluggishness

Question 4

What is the Ca++ charge screening effect?

Answer 4

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

Question 5

what is phosphate used for in the body?

Answer 5

• 2nd messenger
• structure for bone
• energy store (high energy phosphates ATP, GTP)

Question 6

The net uptake resulting from 1000mg of dietary Ca++ is only about ______

Answer 6

175mg (825mg gets excreted)

Question 7

Serum Ca++ must be maintained at what level?

Answer 7

8-10mg per dL

• about 50% of which is free
• 40% bound to albumin
• 10% salts

Question 8

bone matrix is made of what?

Answer 8

calcium phosphate salt

Question 9

canulicular fluid in the bone has (lower/higher) ca++ than the blood?

Answer 9

lower

-so Ca++ enters from blood, down its concentration gradient

Question 10

phosphate is (better/worse) absorbed than Ca++?

Answer 10

better

Question 11

what is the key hormone for regulating Ca++ and K+ homeostasis?

Answer 11

PTH

Question 12

PTH is released from where?

Answer 12

cheif cells of the parathyroid gland

Question 13

what stimulates release of PTH?

Answer 13

low blood Ca++, acts to raise Ca++ levels

Question 14

What exactly does PTH do to increase Ca++ levels?

Answer 14

-acts INDIRECTLY via Vit D

Question 15

how does Vitamin D affect Ca++ levels? K+?

Answer 15

• 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

Question 16

how does low serum Ca++ cause vessicle exocytosis of PTH?

Answer 16

• Ca++ sensor on surface of cheif cells
• Ca++ normally keeps this sensor inactivated
• low Ca++ activates Gq (g protein) causing exocytosis

Question 17

how is Vit D3 activated?

Answer 17

must be hydroxylated in 2 positions

• Liver does one
• Kidneys does the second one

Question 18

what is the active form of Vit D?

Answer 18

1, 25-(OH)2 Vitamin D

Question 19

what role does PTH play on the activation of Vit D?

Answer 19

it catalyzes the hydroxylation reactions of Vit D in the Liver and Kidney. SO without PTH you wouldnt get enough active Vit D

Question 20

What does Vit D do to increase gut uptake of Vit D?

Answer 20

increases levels of a protein “CALBINDIN” which is a Ca++ transport protein

Question 21

How does cortisol affect Vit D’s effects?

Answer 21

It opposes the action of Vit D

Question 22

What would happen with HYPER PTH?

Answer 22

hypercalcemia (sluggishness)

• bone destruction
• excess calcium uptake from gut
• excess calcium retention
• stones

Question 23

What would happen with HYPO PTH

Answer 23

hypocalcemia (tetani, seizures)

• low serum Ca++
• low Vit D
• Ca++ excretion at kidneys

Question 24

what is pseudo hypo parathyroidism?

Answer 24

defect in the PTH receptor

• leads to hypo Ca++
• PTH levels dont matter, could be super high