Calcium Homeostasis and Bones

Question 1

What is the function of soluble calcium

Answer 1

Excitable tissue, muscle, nerves

Cell adhesion

Question 2

What is the function of bone

Answer 2

Protect vital organs
Support muscle
Reservoir of calcium

Question 3

What is the function of the parathyroid gland

Answer 3

Regulate Ca & Phosphate levels

Secrete PTH in response to low Ca and high phosphate

Question 4

What does PTH do

Answer 4

Kidney: Increase Ca resorption in distal tubule
Inhibit phosphate resorption
Stimulate active form of Vit. D
Increase Ca released from bones

Question 5

What is the negative feedback mechanism for PTH

Answer 5

PTH transcription inhibited by 1,25 D3

PTH translation inhibited by increased serum Ca

Question 6

What is the active form of Vit. D

Answer 6

1,25 (OH)2 D3

Question 7

What is the source of Vit. D

Answer 7

UV radiation, eggs, fish

Question 8

Where is Vit. D metabolised

Answer 8

Skin and Kidney

Question 9

What is calcitonin

Answer 9

Produced by Thyroid C cells

Inhibits bone resorption via osteoclasts

Question 10

What is bone made of

Answer 10

Specialised connective tissue 
ECM 
Collagenous fibres 
Non-collagenous protein 
Cells

Question 11

What are the cells in bone

Answer 11

Osteocytes = long processes which contact osteocytes & osteoblasts 
Osteoblasts = bone forming cells = produce matrix constituents 
Osteoclasts = Produce acid the resorbs mineral and enzymes that resorb matrix. Multinucleated

Question 12

What is the difference between cortical bone and cancellous bone

Answer 12

Cortical = Hard outer layer 
Cancellous = Open cell porous network + Spongy

Question 13

What is the epiphyseal plate

Answer 13

Pushes epiphysis out

Eventually hard calcified plate

Question 14

What is hyperparathyroidism characterised by

Answer 14

High serum PTH

Question 15

What are the different types of hyperparathyroidism and their causes

Answer 15

Primary = parathyroid tumour: Loss of negative feedback
Secondary = Renal disease: Increase phosphate and decrease Vit. D activation 
Tertiary = Long standing secondary. Irreversible parathyroid hyperplasia despite correction of renal disease

Question 16

What is the difference between rickets and osteomalacia

Answer 16

Rickets = affects growing skeleton 
Osteomalacia = affects adult skeleton

Question 17

What is the cause of osteomalacia/rickets

Answer 17

Low Vit. D so lack of mineralisation of collagen and failure to absorb sufficient Ca from GIT

Question 18

What is renal osteodystrophy

Answer 18

Reduced renal mass leading to decrease in active Vit. D and increase serum phosphate

Question 19

What is osteoporosis

Answer 19

Loss of bone mass as mineral + osteoid decrease

Increased risk of fractures

Question 20

What are the causes of osteoporosis

Answer 20

Ageing

Oestrogen deficiency

Question 21

How do you treat osteoporosis

Answer 21

Oestrogen replacement

Bisphosphonates (osteoclast poisons)

Question 22

What is osteoid

Answer 22

Unmineralised, organic portion of bone matrix

If mineralised, become new bone tissue