Wk 1 - Bone as a Tissue and Endocrine Control

Question 1

What are the organic and inorganic materials of bone matrix?

Answer 1

ORGANIC:
•Collagen (fibres)
•Proteoglycan - Glycosaminoglycan (Gels)

INORGANIC: the minerals
•Calcium and Phosphate
•Found as hydroxyapatite crystals [Ca10(PO4)OH)2]

Question 2

What is the functional unit of mature cortical bone?

Answer 2

The osteon

Question 3

What are the cells of bone tissue?

Answer 3

• Osteocytes (mature osteoblasts)
• Osteoblasts (building)
• Osteoclasts (crushing)
• Osteoprogenitor (creating - stem cells)

Question 4

What are osteocytes responsible for?

Answer 4

•Bone maintenance

Question 5

What are osteoblasts responsible for?

Answer 5

• Bone deposition
• Secretes osteoid (unmineralised matrix)
• Responsible for the mineralisation of osteoid by releasing alkaline phosphatase

Question 6

What are osteoclasts responsible for?

Answer 6

• Dissolving bone matrix

* Bone resorption (by releasing protons and therefore decreasing pH)

Question 7

What are osteoprogenitor cells responsible for?

Answer 7

•Precursors to osteoblasts

Question 8

Where is calcitonin secreted from?

Answer 8

The parafollicular cells of the thyroid gland

Question 9

What stimulates a secretion of calcitonin?

Answer 9

A high concentration of Ca2+ in the blood

Question 10

What is the function of calcitonin

Answer 10

• Inhibits osteoclast activity
• Lengthens lifespan of osteoblasts
• Decreases blood Ca2+ concentration

Question 11

Where is parathyroid hormone secreted from?

Answer 11

The parathyroid gland

Question 12

What stimulates the secretion of parathyroid hormone

Answer 12

A low concentration of Ca2+ in the blood

Question 13

What is the function of parathyroid hormone?

Answer 13

• Increase bone resorption
• Increases kidney absorption of Ca2+ (from filtrate)
• Increases tubular excretion of PO4 3-
• Increases enzymatic conversion of vitamin D to its active form
• Increases number (osteoclastogenesis) and activity of osteoclasts

Question 14

Where is oestrogen secreted?

Answer 14

Ovaries

Question 15

What is the function of oestrogen?

Answer 15

• Increases bone density

* Closes epiphyseal plates (physes)

Question 16

Where is testosterone secreted?

Answer 16

The testis

Question 17

What is the function of testosterone?

Answer 17

•Increase bone density

Question 18

What happens to osteoclastogenesis in the presence of oestrogen?

Answer 18

Osteoclastogenesis is inhibited

Question 19

Where is growth hormone secreted?

Answer 19

The anterior pituitary

Question 20

What is the function of growth hormone?

Answer 20

To stimulate longitudinal bone growth (both directly and indirectly)

Question 21

Where are glucocorticoids secreted from?

Answer 21

The adrenal cortex

Question 22

What is the most important glucocorticoid?

Answer 22

Cortisol

Question 23

What are the function of GC (cortisol)?

Answer 23

• Important in stress responses
• Inhibit bone matrix mineralisation
• Induce apoptosis of osteoblasts
• Inhibits osteoprotegerin (will increase number and activity of osteoclasts)

Question 24

What is the function of Vitamin D?

Answer 24

•Increase availability of Ca2+ and PO4 3- through increased intestinal absorption

Question 25

What is the purpose of both the central and perforating canals?

Answer 25

To carry neurovascular structures

Question 26

What is the functions of canaliculi?

Answer 26

• the exchange of nutrients between lamallae

* house dendritic processes from osteoctyes (for communication between adjacent osteocytes)