Review Bsf Exam 4: Calcium And Phosphate Homeostasis

Front 1

Ca2+/Pi balance refers to the exchange of Ca and Pi between blood and three major target organs:

Back 1

Bone
Kidney
small Intestine

Front 2

This form of calcium is active and can cross the membrane.

Back 2

Ionized (free)

Bound forms do not cross membranes!

Front 3

Alkalosis (increases|decreases) protein-binding Ca and (increases|decreases) ionized Ca in the blood.

Back 3

Increases
Decreases

(thus decreases plasma Ca)
(normally ECF Ca should be higher than ICF)

Front 4

Form that Ca is stored in the bone.

Back 4

hydroxyapatite

Front 5

Effect on Ca and Pi by calcitrol (Vit D), PTH, & Calcitonin

Back 5

calcitrol (vit D) - Increases Ca & Pi
PTH- Increases Ca & Decreases Pi
Calcitonin- Decreases Ca & Pi

Front 6

PTH secretion is regulated by what two plasma particles?

Back 6

Ca2+ and VitD


(inverse relationship, if Ca 2+ and/or Vit D are high, PTH secretion will be low)

Front 7

Two locations of PTH receptors

Back 7

Bone (osteoblasts):
(PTH activates osteoblasts--> convert to osteoclasts for reabsorptiion)

Kidney (proximal tubule):
(PTH decreases Pi reabsorption & increases Ca reabsorption)

Front 8

PTH effect on intestine

Back 8

NO DIRECT EFFECT

(only Vit D acts on small intestine)

Front 9

Enzyme responsible for activating vit D

Where is vit D activated?

Back 9

1a-hydroxylase
(PTH activates this enzyme)

activated in kidney
(taken in via skin (sun) & liver)

Front 10

What stimulates and inhibits calcitriol synthesis

Back 10

Stimuates:
PTH
Low Ca
Low Pi

Inhibits:
High VitD (Neg feedback)
High Ca

Front 11

Calcitriol effect on intestine

Back 11

Increases Ca absorption
Increases Pi absorption

Stimulates synthesis of calbindin (shuttle protein)

Front 12

Calcitriol (vit D) effect on bone

Back 12

INDIRECTLY promotes bone calcification by increasing available substrates (Ca2+ & Pi)
DIRECTLY by stimulating osteoblasts

(extreme quantities cause resportion by converting osteoblasts to osteoclasts)

Front 13

Indirect effect on kidneys by Vitamin D

Back 13

Stimulates re-absorption of Pi by inhibiting PTH

Front 14

Calcitonin effect on kidney & bone

Back 14

kidney- Induces 1a-hydroxylase transcription (vit D synthesis)

bone- inhibits osteoclast activity

Front 15

____________ leads to tetany

Back 15

hypocalcemia

Front 16

What does Vit D deficiency result in?

Back 16

rickets (children) & osteomalacia (adults)

= failure of osteoid to calcify (soft bones)

Front 17

What does primary hyperparathyroidism lead to?

Back 17

hypercalcemia (muscle weakness, bradycardia)
bone loss (weak, pain, too much resorption)
kidney stones (too much resorption

Front 18

Effects of GH on bone growth.

Back 18

Increases Ca absorption in the intestine
Increases renal Pi reabsorption

(increases substrates needed for bone formation)

Front 19

Effect of low TH levels in children

Back 19

Delayed ossification of cartilaginous bone = more cartilage

(*if TH is too high, bone resporption will increase= less bone)

Front 20

Effects of excess glucocorticoid

Back 20

Decrease renal Ca reabsorption
Decrease intestinal Ca absorption
Stimulates bone resorption
Inhibits bone formation
(decreases Ca)