Bone and cartilage

Question 1

What are the three types of cartilage?

Answer 1

Hyaline
Elastic cartilage
Fibrocartilage
These all have cells and extracellular matrix.

Question 2

Where is cartilage found?

Answer 2

On the articular surfaces of all synovial joints.
Forming the cartilaginous model of most developing bones and their epiphyseal growth plate.

Question 3

Where is flexible cartilage found?

Answer 3

Forming the flexible skeleton of the nose, larynx, pinna of the ear and costal cartilages of the ribs.
In its structural role in the intervertebral disc allowing flexibility to the spine.

Question 4

What is perichondrium?

Answer 4

Found on peripheries of hyaline and elastic tissue.
The outer layer is dense vascular connective tissue.
The inner layer is chondrogenic.
It’s function is protection, nutrition and repair from stem cells.

Question 5

What are the cells in cartilage?

Answer 5

Chondroblasts - immature, form all structures of cartilage
Chondrocytes - mature, maintain the cartilage.

Question 6

What is the role of cartilage?

Answer 6

The highly hydrated nature of cartilage means that it can withstand significant compressive forces.
It also provides an almost frictionless surface across which other cartilages can move.

Question 7

What are the components of ECM?

Answer 7

Organic components - ground substance and fibres
Inorganic components - water, electrolytes, minerals, vitamins and gases

Question 8

What are the components of ground substance in cartilage?

Answer 8

Proteoglycan - versican
GAGs: Chondroitin sulphate and dermatan sulphate

Question 9

What is hyaline cartilage?

Answer 9

Contains glycosaminoglycans and type II collagen fibres.
Located in isogenous groups.
Avascular (poor blood supply) - doesn’t repair itself well.
Predominant in lining articulating surfaces of synovial joints and respiratory tract.

Question 10

What is the function of hyaline cartilage?

Answer 10

The type II collagen fibres give it good strength, which is needed to provide a friction-surface and act as a shock absorber.

Question 11

What does hyaline cartilage look like?

Answer 11

Has a white glassy appearance
c = chondrocytes
P = perichondrium
M = matrix
see image

Question 12

Why does hyaline cartilage look glassy?

Answer 12

Because of the highly hydrated nature of the ground substance which consists of three types of glycosaminoglycans:
hyaluronic acid, chondroitin sulphate and keratin sulphate, all of which trap water.

Question 13

What is elastic cartilage?

Answer 13

Has type II collagen fibres.
It is more flexible than hyaline cartilage.
Located in the auricle of the ear.
Auditory tubes, epiglottis.

Question 14

What does elastic cartilage look like?

Answer 14

Histologically it resembles hyaline cartilage, but contains an abundance of elastic fibres which allow to to deform and return to it’s original shape.
see image
Dark lines are elastic fibres.

Question 15

What is fibrocartilage?

Answer 15

A mixture of hyaline cartilage and dense connective tisuse - type I and II collagen.
Found in intervertebral discs, pubic symphysis and discs of knee joints.

Question 16

What is the function of fibrocartilage?

Answer 16

Provides strong connections and stability - so contains many collagen fibres.

Question 17

What does fibrocartilage look like?

Answer 17

see image

Question 18

How does cartilage survive?

Answer 18

Because cartilage is avascular, it is dependent on diffusion of nutrients and metabolites thorugh the matrix.
The main source of nutrients is from the synovial fluid in the tissue and joint spaces, but there is some diffusion from blood vessels in the bones.

Question 19

What are the types of bone?

Answer 19

Compact bone - on the outside
Spongy bone - on the inside

Question 20

What is periosteum?

Answer 20

Bones are enclosed in periosteum except at their articulating surfaces which are covered by cartilage.
It is formed from two fibrocollagenous membranes, contains osteoblasts which are capable of proliferation, and are especially important in healing fractures.
Also has osteoclasts which are bone destroying cells.

Question 21

What is the structure of periosteum?

Answer 21

The outer layer is fibrous made of dense connective tissue.
The inner layer is cellular osteogenic and contains stem cells - osteoprogenitor cells.
It is secured to the bone by Sharpey’s fibres.

Question 22

What is endosteum?

Answer 22

Covers the internal bone surface.
Osteogenic - forms bones.

Question 23

What is the structure of compact bone?

Answer 23

Osteon pillars
Concentric lamellae - circular structures
Haversian system

Question 24

How is bone formed?

Answer 24

In developing bone, the collagen fibres are arranged in a random orientation - woven bone.
This is broken down by osteoclasts and remodelled to form cortical (compact) bone and spongey (cancellous) bone.
Bones can adapt slowly to environmental stresses.

Question 25

How is compact bone formed?

Answer 25

Osteoblasts have laid down the matrix in concentric rings known as osteons - Haversian systems. The osteons surround a central canal containing blood vessels, nerves and a lining of osteoblasts. Blood vessels enter each bone at nutrient foramina. Loss of blood supply to a bone causes avascular necrosis.

Question 26

What does an osteon look like?

Answer 26

see image

Question 27

What is a lacuna?

Answer 27

After forming bone, immature osteoblasts are trapped inside the concentric lamellae to form a space - lacuna. The osteoblasts then form mature osteocytes.

Question 28

What is spongey bone?

Answer 28

Has a sponge like appearance Trabeculae interlock with each other to form spaces where bone marrow are, and provides strength. Have few Haversian systems. Spaces contains haemotopoietic cells (red marrow) or fat (yellow).

Question 29

What are osteoblasts?

Answer 29

Derived from osteoprogenitor cells. Present in endosteum and periosteum. Lined up along the surface of bone matrix.

Question 30

What is the shape of osteoblasts?

Answer 30

They have a narrow spindle shape when inactive (osteoprogenitors). Large and broad spindle or cuboidal shape when active.

Question 31

What is the function of osteoblasts?

Answer 31

Synthesise osteoid and mediate mineralisation. Produce the organic bone matrix. Reponsible for deposition of inorganic component of matrix.

Question 32

What is bone matrix?

Answer 32

Or osteoid: Highly vascularised 70% is inorganic 30% is organic

Question 33

What is the inorganic material of bone matrix?

Answer 33

Calcium hydroxyapatie Bicarbonate Citrate Magnesium Potassium Na+

Question 34

What is the organic component of bone matrix?

Answer 34

Collagen type I Small proteoglycans Glycoproteins - osteonectin Osteocalcin and phosphatases promote calcification in the matrix.

Question 35

What are osteocytes?

Answer 35

Inactive osteoblasts that are trapped in matrix bound lacunae. When there is a need for more matrix the osteocytes are activated and secrete matrix.

Question 36

What are osteoclasts?

Answer 36

Phagocytic multinucleated cells. Essential for bone turnover and remodelling, this releases calcium into bloodstream. Ca is required for muscle contraction, so when in short supply, osteoclasts are activated to supply this. Excess calcium is absorbed back into the bone.

Question 37

How does the structure of osteoclasts link to function?

Answer 37

Has a ruffled border which secretes organic acids which dissolves the mineral component. Lysosomal proteolytic enzymes destroy the organic osteoid matrix. It is found in resorption lacunae.

Question 38

What is ossfication?

Answer 38

Turning into bone - intramembranous or endochondral.

Question 39

What is intramembranous ossification?

Answer 39

Bone forms directly from mesenchyme. Most skull bones and the clavicle.

Question 40

What is endochondral ossification?

Answer 40

It is modelled in hyaline cartilage, then replaced by bone tissue. This is how all other bones except the skull and clavicle are formed.

Question 41

How does endochonral ossification occur?

Answer 41

Perichondrium turns into periosteum. Chondrocytes stop getting nutrition and begin to die. The periosteum form osteoblasts which invade the cartilage and form a primary ossification centre, where bone matrix is released and replaces cartilage. Blood vessels then invade the primary ossification centre and bone is deposited into the middle.

Question 42

What is osteoporosis?

Answer 42

Bone disease caused by a reduction in bone density leading to fragile bones and higher risk of fractures. For women after menopause, there is less oestrogen, so less osteogenesis - uptake of matrix, and so increased risk in osteoporosis.

Question 43

What does a calcium deficiency do?

Answer 43

The bone matrix does not calcify normally and the epiphyseal plate is distorted. This causes bones to grow more slowly and become deformed - leading to rickets or osteomalacia. This can be due to lack of calcium in diet or lack of vitamin D which is needed for absorption.