Lecture 4: Bone Tissue and its Microscopic Structure (Bone II)

Question 1

What is bone?

Answer 1

Bone is a living tissue. It has cells, as well as calcifies cellular matrix.

Question 2

What do bone cells respond to?

Answer 2

Bone cells respond to external forces and trauma (to unite broken parts)

Question 3

What does bone tissue consist of?

Answer 3

• Connective tissue: Supports other tissues/organs + maintain form
• 2 extracellular components: Organic component + inorganic component

Question 4

What does the organic part of the extracellular component consist of?

Answer 4

33% of bone is organic: Collagen (protein) + ground substance (proteoglycans)

Question 5

What is the function of the organic bit of the extracellular components?

Answer 5

To resist tension

Question 6

What does the inorganic bit of the extracellular component consist of?

Answer 6

67% of bone matrix is inorganic: Hydroxyapatite + other calcium minerals (mineral salts)

Question 7

What is the function of the inorganic bit of the extracellular component?

Answer 7

To make bone hard and resistant to compression (due to the mineral component)

Question 8

What does the cellular component of bone consist of?

Answer 8

4 types of cells:
• Osteogenic ces
• Osteoblasts
• Osteocytes
• Osteclasts

Question 9

Together, what do these cells do and how?

Answer 9

Maintain bone homeostasis, by balancing bone destruction and formation (means amount of bone stays the same)

Question 10

What percentages of the cellular and extracellular component make up bone weight?

Answer 10

• 2% cellular
• 98% extracellular

Question 11

What do the 4 types of cells, of the cellular component of the bone, do?

Answer 11

1. Osteogenic cells: Stem cells that produce osteoblasts
2. Osteoblasts (makers): produce new bone matrix
3. Osteocytes (maintainers and communicators): Recycle protein and minerals from matrix + control activity of osteo (blasts/clasts)
4. Osteoclasts (destroyers): Remove bone matrix

Question 12

What are the 2 types of bone tissue?

Answer 12

• Compact
• Cancellous

Question 13

What are the 2 types of bone tissue made of?

Answer 13

Both bone tissue types are made id the same things (ECM + cells).

Question 14

How are the 2 bone tissue types structured?

Answer 14

They are structured differently.
• Compact bone tissue: Osteon structure
• Cancellous bone: Trabecular structure

Question 15

What does compact bone look like macroscopically?

Answer 15

• Outer surfaces seem dense and impenetrable (periosteum)
• Foramina (holes) for blood supply

Question 16

What does compact bone look like microscopically?

Answer 16

Made up of circumferential lamellae and units called osteons

Question 17

What are osteons and what is its function?

Answer 17

Osteons are longitudinal (lengthwise) units within a compact bone. It provides a pathway for nutrients to get to cells in the ECM.

Question 18

What dies a central canal contain?

Answer 18

Blood vessels and nerves

Question 19

What is a lamellae?

Answer 19

A series of cylinders, formed of ECM, around the central canal.
• Forma the shape of the osteons
• Collagen fibres within lamellae resist forces

Question 20

What is a lacunae?

Answer 20

A lake for osteocytes

Question 21

Whats is a canaliculi?

Answer 21

A channel for nutrients through ECM

Question 22

What is a trabeculae?

Answer 22

A strut if lamella bone

Question 23

What does cancellous bone consist of?

Answer 23

• Trabeculae
• Marriw fills the cavities between trabeculae
• Osteocytes housed in lacunae (in between lamellae / on surface)

Question 24

Why are trabeculae oriented certain ways?

Answer 24

• Organisation of trabeculae resists force from multiple directions
• Directs force from body weight in single direction down shaft
• Spreads force distally

Question 25

How is force distributed through the pelvic girdle?

Answer 25

Trabeculae channel weight around the ilia into the femora

Question 26

What is the purpose of bone remodelling?

Answer 26

To allow bones to grow (appositional growth)
• Osteoblasts add bone matrix in lamellae to bone surface
• Osteoclasts remove bone from the medullary cavity

Question 27

How does bone maintain homeostasis?

Answer 27

• Balance of OB and OC activity
• Bone is constantly being formed and destroyed (allows body to mobilise calcium, phosphate and other minerals from the bone matrix)
• Process called remodelling (allows bine to respond plastically) + (shape change possible through life to resist strain, etc)

Question 28

What happens if bone homeostasis isn’t maintained?

Answer 28

The body has requirements to maintain homeostasis, e.g. adequate calcium in diet, moderate exercise, etc.

Without these, we can get an imbalance in osteoblastic / osteoclastic activity.

Question 29

What happens if there is an imbalance in OB / OC activity?

Answer 29

Osteoporosis and osteopenia = OC > OC activity

Question 30

What is osteoporosis?

Answer 30

When the trabeculae becomes thinner in cancellous bone.

Question 31

Why do only some people get osteoporosis?

Answer 31

Depends on lifestyle factors and when the start point was.

Women are more at risk of osteoporosis (due to loss of oestrogen and post-menopause).