94 - Histology of Bones and Joints

Question 1

Most common type of cartilage

Answer 1

Hyaline

Question 2

Components of hyaline cartilage ECM

1-4

Answer 2

– Collagen type II (mainly)
– aggrecans (large GAGs including chondroitin
sulphate and heparan sulphate)
– hyaluronic acid
– chondronectin (glycoprotein, binds collagen, aggrecans and integrins)

Surrounded by perichondrium

Question 3

Cellular component of hyaline cartilage

Answer 3

Chondrocytes

Question 4

Components of elastic cartilage

Answer 4

Hyaline cartilage with elastin.

Surrounded by perichondrium.

Question 5

Where is elastic cartilage found?

Answer 5

In the ear, ear canals, epiglottis, larynx.

Question 6

Role of fibrocartilage

Answer 6

Binds solid joints, forms menisci and IV discs

Question 7

Composition of fibrocartilage

Answer 7

Mixture of dense connective tissue and isolated islands of cartilage

Question 8

Location of fibrocartilage

Answer 8

In joints, in the form of menisci, in IV discs, where bones fuse

Question 9

Composition of fibrocartilage

Answer 9

No perichondrium.
Type 1 collagen
Chondrocytes (that have differentiated from fibroblasts)

Question 10

Composition of IV discs

Answer 10

External ring of fibrocartilage (annulus fibrosis)
Nucleus pulposis (form gelatinous centre with collagen type II, replaced with fibrocartilage around age 20)

Question 11

Structure of cortical bone

Answer 11

Concentric layers (cylindrical modules of bone, concentrically surrounding artery). These are called Haversian systems.

Outermost part of bone is made up of layers of cortical bone, not Haversian systems

Question 12

Structure of trabecular bone

1-4

Answer 12

1) Open structure braces joints
2) Spaces are continuous and full of marrow and blood vessels
3) Made up of lamellae
4) Osteocytes are in contract with the marrow cavity and vessels via their processes

Question 13

Differences between yellow and red marrow

Answer 13

Yellow marrow is mostly fat cells, red marrow is mostly haemopoietic cells.
In early life, red marrow predominates, in later life yellow marrow predominates.
Yellow marrow retains some haemopoietic cells, can become actively haemopoietic if required.

Question 14

Blood supply in bone marrow that is unusual

Answer 14

Blood vessels include sinusoids (large, open capillaries with pores in the walls).

Question 15

Periosteum

Answer 15

Thin layer of connective tissue that surrounds bony surface

Question 16

Layers of periosteum
1
2

Answer 16

Outer layer is fibrous (fibroblasts, blood vessels, more collagen)
Inner layer is more cellular (osteoprogenitor cells, which can give rise to osteoblasts)

Question 17

Components of endosteum

Answer 17

Bone lining inner marrow cavity covered by endosteum

thinner than periosteum, still contains osteoprogenitor cells

Question 18

Components of where tendons and ligaments attach to bone

Answer 18

Collagen is parallel to surface of compact bone.
At tendon connection, bone collagen is continuous with collagen of ligament or tendon.
Collagen fibres penetrate bone surface (these are Sharpey’s fibres)

Question 19

Blood supply to bone

1-4

Answer 19

1) Arteries supply bones at discrete points
2) Branch in marrow cavity
3) Arteries supply shaft (diaphysis) and ends (epiphysis_ separately
4) Periosteum is separately supplied

Question 20

How are bones innervated?

Answer 20

Nerves follow blood vessels

Question 21

Components of articular cartilage

Answer 21

Hyaline cartilage
Slippery, smooth, resistant to compression
No perichondrium in joints

Question 22

Problems with having no perichondrium in articular cartilage

Answer 22

Perichondrium contains cells to repair cartilage, so lacking it makes articular cartilage repair very slowly.

Question 23

Type of surface that synovial membrane is

Answer 23

A connective tissue structure that is very porous (it is not epithelium)

Question 24

Structure of synovial membrane

1-4

Answer 24

1) Not epithelial
2) Surface layer (intima) is two-three cells thick, a mix of fibroblast-like cells and macrophage-like cells
3) Sub-intimal layer is fibrous connective tissue
4) Synovial fluid is an ultrafiltrate of synovial blood vessels plus proteoglycans

Question 25

Cells embedded in Haversian systems

Answer 25

Osteocytes.

Question 26

Cells of bone | 1-4

Answer 26

Make bone: Osteoprogenitor cells Osteoblasts Osteocytes Degrade bone: Osteoclasts

Question 27

Osteoprogenitor cell location

Answer 27

In periosteum, endosteum

Question 28

Features of osteoprogenitor cells | 1-3

Answer 28

Normally resting or quiescent Can give rise to new osteoblasts to grow or repair bone. Renewed from stem cells in bone marrow

Question 29

Features of osteoblasts 1 2 3

Answer 29

Works on bone surface to make bone. Makes osteoid (organic ECM of bone, which is type I and bone matrix proteins). Inactive osteoblasts are flattened cells that look like osteoprogenitor cells

Question 30

Markers of osteoblast activity

Answer 30

Osteocalcin (Ca2+ binding protein) and alkaline phosphatase

Question 31

Osteocyte location

Answer 31

Present within bony matrix (not on surface like osteoprogenitor cells and osteoblasts).

Question 32

Role of osteocytes

Answer 32

Maintain bone in response to loading. | Can destroy local bone to free Ca2+

Question 33

Effect of loss of osteocytes

Answer 33

Bone resorption

Question 34

Morphology of osteoclasrts

Answer 34

Giant multinuclear cells (different progenitors to osteoprogenitor cells/osteoblasts/osteocytes)

Question 35

Role of osteoclasts

Answer 35

Destroy bones in growth, repair and normal turnover.

Question 36

How do osteoclasts resorb bone?

Answer 36

Seals itself to bone around edge. Secretes HCl, to degrade mineral component. Secretes proteases to degrade organic component.

Question 37

Marker of osteoclast activity

Answer 37

Tartrate-resistance acid phosphatase

Question 38

Progenitors of osteoclasts

Answer 38

Related to granulocytes (macrophages, neutrophils, etc).

Question 39

What regulates osteoclast activity?

Answer 39

Parathyroid hormone increases activity, calcitonin (form thyroid) decreases activity.

Question 40

Bone development

Answer 40

During bone development, bone is laid down as either membrane bone or endochondral bone. Membrane bone forms directly from mesenchyme (EG: skull, flat bones of the face, mandible, clavicles form this way) Endochondral bone (EG: weight-bearing bones, bones of the extremities) forms in hyaline cartilage. A cartilage structure of skeleton is replaced by bone.

Question 41

How does endochondral bone form?

Answer 41

It is not cartilage converted to bone (calcified cartilage is a pathology). Bone first forms in diaphysis (shaft) of hyaline cartilage. Things can't diffuse across bone, so cartilage around bone is starved of nutrients and starts dying off. Bone forms where the cartilage dies off. Then bone starts forming within epiphyses. Growth plate is remnant of cartilage between diaphysis bone formation and epiphysis bone formations.

Question 42

Number of centres of ossification in endochondral bone

Answer 42

Three normally. | One in diaphysis, one in each epiphysis.

Question 43

When do growth plates in humans fuse?

Answer 43

Around 21-22 years

Question 44

``` Structure of growth plate 1 2 3 4 5 ```

Answer 44

Layers. Distally is normal hyaline cartilage (resting zone) Line of dividing chondrocytes (proliferation zone) Region of mature chondrocytes (maturation zone) Zone of hypertrophic (dying) chondrocytes (hypertrophy zone) Degenerating cartilage is degraded, bone is laid down on its surface

Question 45

Type of bone that is newly-made

Answer 45

Woven bone (a special type of bone).

Question 46

Features of woven bone | 1-4

Answer 46

No Haversian systems. More collagen. More cellular. Woven bone is soon remodelled by osteoblasts and osteoclasts.

Question 47

How is woven bone remodelled?

Answer 47

Osteoclasts focally degrade woven bone (form tunnels). Tunnels formed along stress axis of bone. Blood vessels and osteoprogenitor cells (endosteum) invade tunnels. These form Haversian systems

Question 48

Haversian system formation

Answer 48

Form in tunnels formed by osteoclasts in woven bone. Osteoblasts lay layers of bone with the collagen alternating in direction (one layer is clockwise, other is anticlockwise) Final layer leaves a final space for blood vessel.