Bone And Skeletal Homeostasis

Question 1

What are some functions of calcium

Answer 1

Maintenance of healthy bones and teeth
Nerve impulse transmission
Muscle contraction
Cell division and transport
Blood clotting
Hormone secretion
Cell signalling

Question 2

What is the distribution of calcium in the body split into

Answer 2

99% in bone
1% in blood and body fluids

Question 3

What is the blood calcium distribution

Answer 3

35% non diffusible - 80% albumin bound, 20% globulin bound
65% diffusible - 80% ionized, 20% complexed (bicarbonate, citrate, phosphate)

Question 4

What is the concentration of calcium in the blood

Answer 4

9 - 11 mg/dL

Question 5

What are the 3 forms of calcium in plasma or serum

Answer 5

Protein bound calcium
Ionized or free calcium
Complexed or chelated calcium

Question 6

What is protein bound calcium

Answer 6

Cannot diffuse through membranes and thus is not usable by tissues

Question 7

What is ionized or free calcium

Answer 7

The physiologically active form

Question 8

What is complexed or chelated calcium

Answer 8

Bound to phosphate, bicarbonate, sulfate, citrate and lactate

Question 9

What happens if calcium levels rise above set point

Answer 9

Thyroid gland releases calcitonin- blood calcium level falls

Question 10

What happens if calcium levels fall below set point

Answer 10

Parathyroid glands release parathyroid hormone (PTH) - blood calcium rises

Question 11

What is the gut function of vitamin D

Answer 11

Stimulates transepithelial transport of calcium and phosphate in the small intestine (principally duodenum)

Question 12

What is the bone vitamin D function

Answer 12

Stimulates terminal differentiation of osteoclasts
Stimulates osteoblasts to stimulate osteoclasts to mobilise calcium

Question 13

What is the parathyroid function of vitamin D

Answer 13

Inhibit transcription of the PTH gene (feedback regulation)

Question 14

What does the parathyroid hormone do

Answer 14

Preserve normal blood calcium and phosphate
Stimulates bone resorption
Stimulates renal tubular reabsorption of calcium
Stimulates renal 1 alpha hydroxylation of 25(OH) vitamin D stimulating intestinal absorption of calcium

Question 15

What is calcitonin

Answer 15

Levels increased when serum Ca > 2.25mmol/L
Counteracts PTH
Bone - suppresses resorption
Kidney - increases excretion

Question 16

How does bone turnover affect calcium

Answer 16

Shift toward formation or resorption removes Ca from blood or puts Ca into blood and correspondingly affects bone mass

Question 17

When does skeletal mass in humans reach a peak

Answer 17

About age 30

Question 18

What happens as skeletal mass is increasing in humans

Answer 18

Bone formation exceeds bone resorption

Question 19

What happens at peak bone mass

Answer 19

The two processes are evenly matched/balanced
After the age of peak bone mass skeletal mass is lost for the rest of life

Question 20

What is bone formation mediated by

Answer 20

Osteoblasts

Question 21

What is bone resorption mediated by

Answer 21

Osteoclasts

Question 22

How do OPG and RANKL link to bone turnover

Answer 22

PTH stimulates the osteoblast to secrete RANKL, which then goes on to stimulate the osteoclast precursor to become active
OPG is a competitive inhibitor of RANKL and thus blocks it from activating the osteoclast

Question 23

In bone turnover what does OPG stand for

Answer 23

Osteoprotegerin

Question 24

What does RANKL stand for in bone turnover

Answer 24

Receptor activator of NF - kB (ligand)

Question 25

What effects does PTH have on the kidney

Answer 25

Stimulate activation of vitamin D
Promotes phosphate excretion
Reduces calcium resorption