L12 Biochemistry of Bone

Question 1

what is bone?

Answer 1

-complex
-highly organised
-specalized type of CT

Question 2

what do bones consists of?

Answer 2

-cells
-intercellular matrix

Question 3

what are the functions of bone?

Answer 3

-mechanical support for locomotion
-protecting vital organs
-regulates mineral homeostasis

Question 4

what are the biochemical components of bone ( by weight )?

Answer 4

-organic components ( 30%)
-inorganic components ( 60% )
-water ( 10%)

Question 5

what do the organic components of bone consists of?

Answer 5

-Type I collagen (90%)
-30 Non-collagenous proteins (10%) (eg: proteoglycans, glycoproteins )

Question 6

what do the inorganic components of bone consists of?

Answer 6

-Apatite ( Hydroxyapatite )
-Minerals (eg: sodium, magnesium, fluoride)

Question 7

Type I Collagen

Answer 7

A triple-helical molecule containing 3 polypeptide chains, found in skin & bones

Question 8

Magnesium metabolism

Answer 8

-strength and firmness of bones
-absorption and metabolism of calcium

Question 9

Distribution of Mg in body

Answer 9

60% bone
20% skeletal muscle
19% soft tissues
<1% extracellular fluid

Question 10

Mg balance in body is controlled by:

Answer 10

-intestinal absorption ( passive & active transcelullar )
-bone exchange
-renal excretion

Question 11

Regulations of serum magnesium concentrations by renal Mg absorptions:

Answer 11

-Proximal tubule 20%
-Cortical thick ascending limb 60%
-Distal convoluted tubule 5-10%

Question 12

Renal conservation of Mg is controlled by:

Answer 12

PTH- increases Mg absorption
Aldosterone- increases Mg ( and K ) clearance and excretion, promotes Na retention

Question 13

Ca and phosphate is stored:

Answer 13

in bone as hydroxyapatite

Question 14

Components of calcium in the serum:

Answer 14

45% free ionized form
40% bound to proteins
15% complexed w organic/ inorganic anions

Question 15

Components of phosphate in serum:

Answer 15

-Phospholipids
-Inorganic phosphate

Question 16

Where is calcium and phosphate homeostasis required?

Answer 16

-bone
-intestine
-kidney

Question 17

Factors affecting calcium & phosphate homeostasis in blood:

Answer 17

-Hormones ( PTH, Calcitonin, Calcitriol)
-Local factors

Question 18

When blood calcium is below normal
( Calcium ( +P) homeostasis ), PTH acts on?

Answer 18

Kidneys
-stimulate conversion of vitamin D into its active form
-rapidly decreases urinary Ca excretion BUT increases urinary P excretion
Bones
-stimulate bone resorption ( resulting in the release of Ca & phosphate )

Question 19

Increase in calcitriol acts on:

Answer 19

Intestine
-triggers absorption of both Ca & phosphate
Bone
-Stimulate the release of calcium from bone by activating osteoclasts

Question 20

when blood calcium rises to normal ( Calcium homeostasis ):

Answer 20

-Parathyroid glands stops secreting PTH
-Stimulates the production and secretion of calcitonin

Question 21

what does calcitonin do?

Answer 21

-Inhibits PTH secretion
-Decreases both bone resorption & intestinal calcium absorption
-Increases urinary calcium excretion

Question 22

where is calcium excreted?

Answer 22

-urine
-bile
-sweat
-digestive secretions
70%-90% - in the feces

Question 23

Where is phosphorus excreted?

Answer 23

-primarily thru the urine
-feces in non absorbed form

Question 24

Hypercalcemia:

Answer 24

Elevated serum calcium level up to 12-15mg/dl

Question 25

Conditions leading up to hypercalcemia:

Answer 25

-acute osteoporosis -hyperparathyroidism -Vitamin D intoxication

Question 26

Symptoms of hypercalcemia:

Answer 26

-dehydration -depression -fatigue -vomiting -anorexia

Question 27

Hypocalcemia:

Answer 27

Decreased level of calcium in the blood (<4mg/dl)

Question 28

Conditions leading up to hypocalcemia:

Answer 28

-insufficient vitamin D -hypoparathyroidism -increase in calcitonin levels

Question 29

Symptoms of hypocalcemia:

Answer 29

-muscle spasms & cramps -numbness in hands, feet -weak & brittle nails -easy fracturing of the bones -hallucinations