Calcium homeostasis and Bone metabolism Flashcards
Calcium in the bone is seen in which form/complex
Calcium-phosphate complexes
What are the 3 hormones that primarily regulate bone metabolism and serum calcium levels
1) Parathyroid hormones (most important regulator)
2) Vitamin D
3) Calcitonin (from thyroid gland)
PVC
Functions of PTH
1) Bone resorption (breakdown)
2) Regulation of Vitamin D levels
3) Opposing the actions of calcitonin
catabolic
Functions of vitamin D
1) Increases calcium absorption from the gut
2) Increases bone deposition of calcium
Anabolic
Functions of calcitonin
1) Stimulates bone deposition
2) Inhibits bone resorption this decreasing serum calcium levels
What diseases arise from abnormalities in bone metabolism
1) Osteoporosis
2) Osteomalacia and rickets
3) Pagets disease
4) Hypo- or Hypercalcemia
5) Hypo- or Hyperparathyroidism
Which cells are responsible for bone breakdown?
OSTEOCLASTS (they contain numerous lysosomes and mitochondria)
Which calls are the bone forming cells?
OSTEOBLASTS (they secrete organic matrix rich in collagen)
What are the 5 steps in bone remodeling?
Activation
Resorption
Reversal
Formation
Termination
What is the most attendant mineral in the body?
Calcium (8.5-10.5mg/dl)
Which protein is needed for the absorption of calcium from the gut and what stimulates its synthesis?
Calbindin is synthesis is stimulated by vitamin D
List the functions of calcium
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
What are the 3 forms that calcium can exist
Free form
Ionized form
Bound (bound to albumin)
How does calcium exist intercellularly?
1) Bound to intercellular protein Calmodulin
2) Sequestrated within endoplasmic reticulum
What’s the formula for calculating corrected calcium?
(Total calcium) + 0.8(4 - serum albumin)
Which organs does the PTH act and what do they do in each?
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
What is the rate limiting step for calcium absorption from the intestine?
Calbindin levels
Which organs does vitamin D act and what do they do?
BONES
Stimulate osteoblastic active
GIT
Promotes absorption of calcium
KIDNEYS
Increases calcium reabsorption
List other functions of vitamin D
1) Immune function and inflammation
2) Glucose and cholesterol metabolism
3) Inhibition of angiogenesis
4) Cell signaling, growth, proliferation etc
What is the half life of 25-hydroxy vit D3
2-3 weeks
Say is the half life of 1,25-dihydroxy vitD3
4-6 hours
What is the primary circulating form of vitamin D in the body?
25-hydroxycholecalciferol
Which cells produce calcitonin
C cells in the thyroid gland
What are the functions of calcitonin
BONES
Inhibit osteoclasts
Stimulate osteoblasts (mild effect)
KIDNEYS
Reduce calcium reabsorption
Reduce phosphate reabsorption
