Physiology of Bone & Calcium Homeostasis

Question 1

3 main hormonal controllers of Ca+2

Answer 1

Parathyroid Hormone (PTH)
Vitamin D3 (calcitrol)
Calcitonin

Question 2

main hormones involved in growth

Answer 2

Growth Hormone and IGFs
Thyroid hormone (permissive role in growth, direct contribution for nervous system development)
Insulin
Sex Steroid

Question 3

main histological constituents of bone

Answer 3

Cells (osteoclasts, osteoblasts, osteocytes, osteoprogenitor cells)
Extracellular Matrix (Collagen, Calcium Phosphate)
[most common Hydroxyapatite]

Question 4

main constituents of bone macroscopically

Answer 4

Cortical bone
Trabecular Bone
Bone Marrow

Question 5

Main cell type on which bone growth depends

Answer 5

Osteoblasts

Question 6

main product of the osteoblast

Answer 6

Enzymes + Osteoid [collagen+protein mix]

Question 7

main site of bone growth

Answer 7

epiphyseal plate

Question 8

3 main divisions of bone

Answer 8

epiphysis
metaphysis
diaphysis

Question 9

where in the bone are the chondrocytes localised

Answer 9

epiphysis

Question 10

once they have laid down the osteoid osteoblasts become

Answer 10

osteocytes

Question 11

osteoclasts are

Answer 11

large, mobile, multinucleate cells

Question 12

osteoclasts and osteoblast are derived from the same cell lineage

Answer 12

F.
osteoclasts are derived from Haematopoietic Stem Cells
osteoblasts mesenchymal stem cells

Question 13

what are the main products of osteoclasts

Answer 13

acid and proteases

Question 14

name some of the functions of calcium

Answer 14

intracellular signal
structural functions (cement of the tight junction)
cofactor in blood coagulation
normal excitability of neurone and muscle

Question 15

what are the main 3 pools of calcium within the body

Answer 15

bone matrix (99%)
extracellular (0.1%)
intracellular (0.9%)

Question 16

what are the main target sites for calcium regulation

Answer 16

small intestine
bone
Kidney

Question 17

how much of Daily calcium intake is absorbed by the intestine?

Answer 17

1/3

Question 18

main regulators of calcium uptake from the intestine

Answer 18

PTH

Calcitrol

Question 19

how is most calcium lost in the body

Answer 19

via urine

Question 20

what is the main signal for the release of parathyroid hormone PTH? what type of hormone is it?

Answer 20

low plasma (extracellular) calcium
peptic hormone, little stored

Question 21

main results after the release of PTH?

Answer 21

increasing plasma calcium and decreasing plasma phosphate levels

Question 22

actions of PTH on bone are by directly stimulating osteoclasts

Answer 22

F
osteoclast do not have receptors for PTH. PTH actions are mediated by binding to osteoblasts and inhibiting the production of osteoprotegin (OPG) and increasing RANKL

Question 23

where is the parathyroid?

Answer 23

4 small glands that sit behind the thyroid

Question 24

in order of time, what are the main results PTH at different targets?

Answer 24

Kidneys min
Bone hours
Intestine days

Question 25

what is the main function of PTH on the intestine?

Answer 25

indirectly increases ca+2 absorption by increasing the synthesis of calcitrol

Question 26

what is the main function of PTH on the kidneys?

Answer 26

increase reabsorption of calcium and decrease reabsorption of phosphate

Question 27

where is the main site for calcitonin secretion?

Answer 27

C cells of the thyroid

Question 28

what is the main stimulus for the release of calcitonin?

Answer 28

high Ca+2 levels

Question 29

actions of calcitonin

Answer 29

lowering plasma calcium and phosphate

Question 30

just as PTH calcitonin has a homeostatic role

Answer 30

F, only secreted in extreme hypercalcaemia | may have a role protecting the bone during lactation and pregnancy

Question 31

main target sites and functions of calcitonin?

Answer 31

kidney increase excretion of both calcium and phosphate | increase bone deposition

Question 32

what is the main vitamin D precursor obtained from the diet and also produced in the body when exposed to direct sunlight?

Answer 32

Vitamin D3 (17-dehydrocholesterol)

Question 33

in order to obtain the active form of vitamin D, calcitrol, adding of 2 hydroxyl groups are required this is done sequentially in ---1---- and ---2--- being the site of action of PTH

Answer 33

Liver | Kidney

Question 34

Vitamin D travels bound to plasma proteins? and what is the name of the main active form?

Answer 34

T | 1.25-Dihydroxycholecalciferol --> Vitamin D3 ---> calcitriol

Question 35

what are the main outcomes of vitamin D deficiency?

Answer 35

Children --> rickets | Adults --> osteomalacia

Question 36

main function of oestrogen in bone?

Answer 36

increases deposition of bone and | decreases reabsorption

Question 37

risk factors for osteoporosis?

Answer 37

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