Calcium homeostasis and Bone metabolism

Question 1

Calcium in the bone is seen in which form/complex

Answer 1

Calcium-phosphate complexes

Question 2

What are the 3 hormones that primarily regulate bone metabolism and serum calcium levels

Answer 2

1) Parathyroid hormones (most important regulator)
2) Vitamin D
3) Calcitonin (from thyroid gland)

PVC

Question 3

Functions of PTH

Answer 3

1) Bone resorption (breakdown)
2) Regulation of Vitamin D levels
3) Opposing the actions of calcitonin

catabolic

Question 4

Functions of vitamin D

Answer 4

1) Increases calcium absorption from the gut
2) Increases bone deposition of calcium

Anabolic

Question 5

Functions of calcitonin

Answer 5

1) Stimulates bone deposition
2) Inhibits bone resorption this decreasing serum calcium levels

Question 6

What diseases arise from abnormalities in bone metabolism

Answer 6

1) Osteoporosis
2) Osteomalacia and rickets
3) Pagets disease
4) Hypo- or Hypercalcemia
5) Hypo- or Hyperparathyroidism

Question 7

Which cells are responsible for bone breakdown?

Answer 7

OSTEOCLASTS (they contain numerous lysosomes and mitochondria)

Question 8

Which calls are the bone forming cells?

Answer 8

OSTEOBLASTS (they secrete organic matrix rich in collagen)

Question 9

What are the 5 steps in bone remodeling?

Answer 9

Activation
Resorption
Reversal
Formation
Termination

Question 10

What is the most attendant mineral in the body?

Answer 10

Calcium (8.5-10.5mg/dl)

Question 11

Which protein is needed for the absorption of calcium from the gut and what stimulates its synthesis?

Answer 11

Calbindin is synthesis is stimulated by vitamin D

Question 12

List the functions of calcium

Answer 12

1) Bone mineralization
2) Provides strength and form to the teeth
3) Muscle contraction
4) Regulation of heart rate
5) Assists in coagulation process
6) Regulation of nerve impulse conduction
7) Cell signaling

Question 13

What are the 3 forms that calcium can exist

Answer 13

Free form
Ionized form
Bound (bound to albumin)

Question 14

How does calcium exist intercellularly?

Answer 14

1) Bound to intercellular protein Calmodulin
2) Sequestrated within endoplasmic reticulum

Question 15

What’s the formula for calculating corrected calcium?

Answer 15

(Total calcium) + 0.8(4 - serum albumin)

Question 16

Which organs does the PTH act and what do they do in each?

Answer 16

BONES
1) Stimulate osteoclastic activities
2) Inhibits osteoblastic activities

KIDNEYS
1) Increases reabsorption of calcium
2) Increases excretion of phosphate so it doesn’t bind with calcium and deposit on bones
3) Hydroxylation of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol

GIT
1) Calcitriol promotes intestinal calcium absorption

Question 17

What is the rate limiting step for calcium absorption from the intestine?

Answer 17

Calbindin levels

Question 18

Which organs does vitamin D act and what do they do?

Answer 18

BONES
Stimulate osteoblastic active

GIT
Promotes absorption of calcium

KIDNEYS
Increases calcium reabsorption

Question 19

List other functions of vitamin D

Answer 19

1) Immune function and inflammation
2) Glucose and cholesterol metabolism
3) Inhibition of angiogenesis
4) Cell signaling, growth, proliferation etc

Question 20

What is the half life of 25-hydroxy vit D3

Answer 20

2-3 weeks

Question 21

Say is the half life of 1,25-dihydroxy vitD3

Answer 21

4-6 hours

Question 22

What is the primary circulating form of vitamin D in the body?

Answer 22

25-hydroxycholecalciferol

Question 23

Which cells produce calcitonin

Answer 23

C cells in the thyroid gland

Question 24

What are the functions of calcitonin

Answer 24

BONES
Inhibit osteoclasts
Stimulate osteoblasts (mild effect)

KIDNEYS
Reduce calcium reabsorption
Reduce phosphate reabsorption

Question 25

List other hormones that play a role in bone metabolism

Answer 25

1) Estrogen
2) Growth hormone
3) Glucocorticoids (promotes osteoclast survival and death of osteoblasts)
4) Thyroid hormone