Calcium Homeostasis

Question 1

IC Ca vs. EC ca

Answer 1

IC - signal transduction, enzyme, muscle contraction, exocytosis

Plasma - Nerve and muslce excitability, low = tetany
membrane permeability, coagulation of blood, tight junction maintenanc,e synaptic trnasmission, bones and teeth

Question 2

Where is calcium located?

Answer 2

99% in bone

50% of plasma calcium is ionic…40% protein bound and 10% not

Plasma is only fraction that is hormonlally reguoated

Question 3

Metabolic state and calcium

Answer 3

Ca competes with H ions so at lower pH (acidosis), Ca is higher

Question 4

Sites of caclium exchange

Answer 4

Plasma

Very tightly regulated

Gut, kidney, bone

Question 5

GI tract

Answer 5

a and PO4 absorbed in small intestine

Majority is excreted in feces

If gastric emptying too fast (partial gastrectomy), then less calcium absorbed

Major determinant of net Ca uptake is absorption…Vit D3 increases Ca absorption in GI

Question 6

kidneys

Answer 6

Usually 99% reabsorbed, 60% in proximal tubule

Fine regulation in the distal nephron - major site of regulation in normal calcium balance

PTH in creases reabsorption

Question 7

Stable pool

Answer 7

Slow exchangei due to remodeling

Uses osteoclasts and osteoblasts

Release both Ca and PO4

Question 8

Labile pool

Answer 8

Repid exchange from bone fluid

Osteocytes have cnaaliculi that contain bone fluid and Ca

Osteocytic osteolysis where transfer Ca but NOT PO4 from bone fluid to plasma

Mechanical stress will increase flow of bone fluid and increase osteocytic activiation

Absence of stress inhibits osteblasts

Question 9

Phosphate exchange

Answer 9

Levels vary widley

Most ingested phosphate is absorbed

Renal phopshate reabsorption is primary site of regulation

Question 10

PTH 
Target
Function
Regulation 
Other

Answer 10

From chief cells of PT glands

Bone (osteoblasts) and kidney

Increase plasma Ca and decrease PO4

Decreased plasma increases PTH synthesis

Incrase plasma free Ca is negative feedback

Max response needs Vit D3

Question 11

Vit D3 synthesis

Answer 11

In skin, liver, kidney

Final in kdiney

Known as calcitrol

Question 12

Actions of PTH

Answer 12

Increase bone resoprtion and osteocytic osteolysis which increases serum Ca (and PO4)…needs Vit D3

In kdiney, increase Ca reabsorption and D3 synthesis, decrease PO4 reabsorption

Intestine - nothgin

Question 13

Vit D3 actions

Answer 13

Intestine- increase of Ca absorption totally by D3

Bone - permissive to PTH

Question 14

Estradiol and Testosterone

Answer 14

Pubertal grwoth spurt

Increase E2 in females
Increased T in males increases bone E3…mediated by estrogen in both sexes

High levels of E2 causesd epiphyseal closure

E2 protects bone throughout life

T will increas bone srength

Question 15

Ca 
Secretion
Regulation
Action
Uses

Answer 15

Secretion by thyroid C cells

Increased plasma Ca increases calcitonin

Decreases Ca by decreasing resorption..inhibits osteoclasts

Paget’s dz, severe osteoporosis, marker for medullary thyroid cancer

Question 16

Thyroid
Glucocoritcoids
GH

Answer 16

Thyroid - increase bone turnover…too hgih - osteoporosis

GC - at hhigh levels cause hypocalcemia via decreased INtenstinal and renal Ca reabsorptiojn and inhibit bone formation…can cause osteoporosis

GH - increased levels at puberty

Question 17

Age and bone loss

Answer 17

Due to decreased sex steroids

2 phases in women
1) rapid at menopause…2) slower (also in men)

Estrogen loss contributes to both men and wome n

Question 18

Type 1 diabetes, other endocrine abnormalities, drugs causing bone loss

Answer 18

Type 1 - high glucose activate osteoclasts

inadequate metab of Vit D can occur in liver or kidney dzz

GC or anticonvulstants can increase rate of conversion of D3 to inactive

Question 19

Hypocalcemia

Answer 19

Osteomalacia or rickets (if Vit D problem)

Increase NM activitiy

Hyperreflexia
Tetany

Question 20

Hypercalcemia

Answer 20

Kidney stones 
Decrease NM 
Anorexia, sontip, nausea
Neurpsych disorders
Bone weakness, pain, fractures
Ulcers (increase gastric secretion)
Calcifcation of soft tissue