Physiology of Bone and Calcium Homeostasis Flashcards Preview

Hugh's Locomotor > Physiology of Bone and Calcium Homeostasis > Flashcards

Flashcards in Physiology of Bone and Calcium Homeostasis Deck (30):
1

What is osteoid?

A collagen and protein mix produced by osteoblasts to which hydroxyapatite binds

1

What are the major preventable risk factors for osteoporosis?

Low dietary Ca

Lack of exercise

Smoking

2

Which cells release calcitonin?

C cells of the thyroid

2

How does PTH cause increased activation of Vitamin D3

Activating kidney enzymes required for activation of D3

3

When is calcitonin released?

Only in extreme hypercalaemia

4

What are the progenitor cells to osteoblasts?

Fibroblasts

4

The effect of PTH on Ca levels that is seen within minutes is due to what?

The increase in reabsorption in the kidneys

5

What are chondrocytes?

Collagen producing cells of the cartilage

5

What are the effect of PTH hyposecretion?

Hypocalcaemia

Hyperphosphataemia

Rare by often fatal

6

What are the effects of calcitonin?

Decrease Ca and phosphates by: 

Decreasing bone resorption

Increase Ca excretion

7

Through which organ systems is the effect of PTH mediated?

Bone

Kidneys

Small intestines

8

Explain the process by which chondrocytes lengthen bones

Chondrocytes replicate in vertical lines 

Old chondrocytes at the end of those columns die leaving space

New bone is laid down by osteoblasts in the space left by chondrocytes

8

Why do you get hypophosphataemia in a PTH hypersecretion state?

Because PTH blocks phosphate reabsorption (despite increase bone resorption that provides phosphate

9

Does calcitonin have an effect on the small intestine?

No

10

What percentage of total body Ca is extracellular?

0.1%

11

What is osteocalcin and osteonectin?

Proteins produced by osteoblasts that aid bone deposition

12

What are the main controllers of Ca reabsorption in the kidneys?

PTH = stimulates reabsorption

Calcitonin = downregulates reabsorption

14

What makes up the major non-cellular component of bone?

Calcium phosphate (most commonly hydroxyapatite) crystalising on a collagen matrix

16

What do osteoclasts produce to dissolve bone matrix?

H+ and enzymes

17

Where in the kidney is phosphate reabsorbed?

Proximal tubule

19

On which aspect of a bone is new bone depositied?

The outer aspect

20

Is PTH or vitamin D3 the mediator of increased Ca absorption in the gut?

Vitamin D3 - but PTH helps activate vitamin D3

21

What effect does PTH have on phosphate levels?

Decreases plasma phosphate

23

What are the major signals for Ca acquisition from bone?

PTH

Calcitriol

Cortisol

24

What effect does PTH have on Ca absorption in the small intestine?

Increase indirectly increases it via activating vitamin D3

25

What is PTH secreted in response to?

Low Calcium

26

Calcitriol is another name for what?

Vitamin D3

27

Describe the appearance of osteoclasts

Large, multinucleated, mobile cells

29

Why isn't blood Ca low in vitamin D deficiency?

Because Ca levels are maintained by PTH stimulated resorption of bones - therefore you get bone demineralisation

30

What are the main functions of Ca?

Intracellular signalling

Structural support

Cofactor in blood coagulation

Required for normal nerve excitability and function