Physiology of bone and calcium homeostasis

Question 1

Describe how soft tissue and bone growth are measured?

Answer 1

Soft tissue: measured by weight

Bone: measured by height

Question 2

What is required for tissue and bone growth?

Answer 2

GH and IGFs

Thyroid hormone

Insulin

Sex steroids

Bone growth: calcium and protein

Question 3

Describe the ECM of bone?

Answer 3

Calcium phosphate crystals (hydroxyapatite) precipitate and attach to collagen fibre lattice

Question 4

Describe the structure of bone?

Answer 4

Outer cortical bone: privdes strength

Inner trabecular bone: open, cell-filled spaces between calcified struts of lattice

Central bone marrow

Question 5

When does bone growth occur, in terms of the state of the matrix?

Answer 5

When the matrix is deposited faster than it is resorbed

Question 6

What are osteobalsts?

Answer 6

Bone-forming cells

Modified fibroblasts

Question 7

What do osteoblasts produce?

Answer 7

Produces enzymes and osteoid (collagen and protein mix) to which hydroxyapatite binds

Question 8

What does the epiphyseal plate signify in terms of bone growth?

Answer 8

Site of linear growth of long bone

Question 9

What are chondrocytes?

Where are they found?

Answer 9

Collagen-producing cells of cartilage

Found near epiphysis

Question 10

Describe the columns created by chondrocytes?

Answer 10

Continuously dividing columns of chondrocytes that increase in length

Collagen layer thickens and old chondrocytes disintegrate, leaving behind spaces which are filled with cartilage

Question 11

Describe the actions of osteoblasts?

Answer 11

Lay down bone on top of cartilage base, where old chondrocytes degenerated

Revert to less active osteocytes when work is complete

Question 12

Briefly describe the effect of osteoblast and osteoclast action on blood Ca levels?

Answer 12

Osteoblasts deposit calcium in bone > decrease blood Ca levels

Osteoclasts resorb bone and release Ca > increase blood Ca levels

Question 13

Describe the action of osteoclasts?

Answer 13

Secrete acid and protease enzymes to dissolve bone matrix

Cause Ca to enter blood

Question 14

Describe the morphology of osteoclasts?

Answer 14

Large

Mutlinucleate

Derived from haematopoietic stem cells

Question 15

Which organs/structures are involved in control of blood calcium?

Answer 15

Bone

Kidneys

Intestine

Question 16

Which hormones are involved in the maintenance of blood calcium levels?

Answer 16

Parathyroid hormone

Vitamin D3/Calcitriol

Calcitonin

Question 17

What are the three major pools of calcium in the body?

Answer 17

Bone matrix

Extracellular (ionised Ca)

Intracellular (free Ca)

Question 18

Which of the three pools of calcium can move to other locations?

Answer 18

ECF

Question 19

Briefly describe how calcium is transferred between ECF and ICF?

Answer 19

ECF > ICF: electrochemical gradient

ICF > ECF: active transport

Question 20

Briefly describe what stimulates Ca to move between ECF and bone matrix?

Answer 20

Calcitonin: ECF > bone

PTH: bone > ECF

Calictriol: bone > ECF

Question 21

Describe what stimulates Ca to move between ECF and the intestines?

Answer 21

PTH and calcitriol stimulate absorption

(1/3 absorbed)

Question 22

Describe how calcium moves between ECF and the kidneys?

Answer 22

ECF > kidneys: passive filtration

Kidneys > ECF: stimulated by PTH, inhibited by calcitonin

Question 23

Where in the kidneys does calcium reabsorption occur?

Answer 23

Distal nephron

Question 24

How is excess calcium removed from the body?

Answer 24

Most in urine

Some in faeces

Question 25

Where is PTH released from? When is it released?

Answer 25

Parathyroid glands Released in response to decreased blood calcium

Question 26

Describe the actions of PTH on bone, kidneys and intestine?

Answer 26

BONE: stimulates osteoclasts via RANKL \> bone resorption KIDNEYS: increase calcium reabsorption, decrease phosphate reabsorption INTESTINE: activates Vitamin D \> increases calcium and phosphate reabsorption

Question 27

Describe the onset of action for PTH?

Answer 27

2-3 hours for bone 1-2 days for intestinal absorption Minutes for kidney transport

Question 28

Where is calcitonin released from? When is it released?

Answer 28

Released from C cells of thyroid gland Released when plasma Ca is extremely high

Question 29

Describe the target tissues of calcitonin?

Answer 29

Bone and kidney (NOT intestines)

Question 30

Describe the effect of calcitonin release?

Answer 30

BONE: decrease bone resorption KIDNEY: increase calcium excretion

Question 31

Describe the role of the thyroid and parathyroid glands in control of plasma calcium?

Answer 31

Question 32

Describe how Vitamin D is activated?

Answer 32

Question 33

Describe the effect of PTH on Vitamin D activation?

Answer 33

PTH activates kidney enzymes to activate Vitamin D

Question 34

Describe how plamsa calcium and phosphate levels affect Vitamin D activation?

Answer 34

Low plasma calcium\> PTH release \> Vitamin D activation Low plasma phosphate \> Vitamin D activation

Question 35

Describe the effect of Vitamin D on plasma calcium and phosphate?

Answer 35

Promotes intestinal absorption of calcium and phosphate \> increase plasma calcium and phosphate

Question 36

Describe the body's response to a decrease in plasma calcium?

Answer 36

Question 37

Which conditions may cause PTH hypersecretion? Which may cause PTH hyposecretion?

Answer 37

Hypersecretion: tumour Hyposecretion: autoimmune attack of glands (rare)

Question 38

Describe the effects of PTH hypersecretion and hyposecretion?

Answer 38

Hypersecretion: hypercalcemia, hypophosphatemia Hyposecretion: hypocalcemia, hypophosphatemia, neuromuscular excitability

Question 39

Describe the effect of Vitamin D deficiency?

Answer 39

Impaired intestinal calcium absorption \> low blood caclium \> PTH release \> bone resorption \> continues \> bone demineralisation Rickets in children Osteomalcia in adults

Question 40

What is osteoporosis?

Answer 40

Long term imbalance in resorption and formation of bone Resorption \> formation Reduced bone architecture

Question 41

Describe the risk factors for osteoporosis?

Answer 41

Age \> 50 years Post-menopause (oestrogen withdrawal) Low dietary calcium Lack of exercise Smoking