Week 6: Cartilage Structure and Function

Question 1

What is cartilage?

Answer 1

Cartilage is a specialised support CT, that provides firm and rigid support. It creates a smooth surface, is resilient and shock absorbing = joints. It is essential for growth of long bones.

Question 2

What cells are in cartilage?

Answer 2

chondrocytes

Question 3

Describe the cells that make up cartilage.

Answer 3

Chondrocytes make up cartilage. They form from differentiation of mesenchymal stem cells (MSCs). They synthesise and secrete matrix that surrounds cells. They form clusters known as isogenous groups when dividing in lacunae (single or multiple chondrocytes per lacunae). They undergo cell division, and have spherical nuclei.

Question 4

Describe the matrix of cartilage.

Answer 4

Matrix consists of fibres and ground substance.
Mainly collagen (type II) in a firm hydrated gel of proteoglycans (have many associated water molecules) and structural glycoproteins. Also provides strength to cartilage.
Amorphous ground substance provides firmness to cartilage.
Matrix is strong, almost rigid, which allows it to resist compression.
No blood vessels or nerves in cartilage and matrix.
Acts as a medium for diffusion of nutrients to cartilage cells.
Chondrocytes within lacunae give rise to matrix. Matrix allows cells to divide

Question 5

What is the periochondrium?

Answer 5

Sheath of dense CT, surround cartilage, except for articular cartilage or joints of fibrocartilage.

Question 6

Why is the perichondrium needed?

Answer 6

Needed for growth and maintenance, vascular supply, nerves and lymph.

Question 7

What comprises the perichondrium?

Answer 7

Fibrous layer: outer sheath of dense CT provides protection, attachment to adjacent structures.
Chromogenic layer: inner cellular layer within chondrogenic cells.
Capillaries: source of nutrients

Question 8

Give examples of types of cartilage.

Answer 8

hyaline, elastic and fibrocartilage

Question 9

Where is hyaline cartilage found?

Answer 9

Most common type - found in larger respiratory passages: cartilage keeps large airways open, ventral ends of ribs: allows expansion of thoracic cavity during inspiration, end of long bone, growth of bones, nose, larynx, trachea

Question 10

What is the structure of hyaline cartilage?

Answer 10

Firm but flexible matrix composed mainly of collagen fibres embedded in AGS rich in proteoglycans.

Question 11

What is the function of hyaline cartilage?

Answer 11

Provides structural support, reduces friction between articulating bones and absorbs shock in joints. Forms a smooth surface for easy movement and flexibility.

Question 12

What is the structure of elastic cartilage?

Answer 12

Elastic fibres and collagen fibres within its matrix

Question 13

Where is elastic cartilage found?

Answer 13

In structures that require both support and flexibility - ear, epiglottis, larynx

Question 14

What is the function of elastic cartilage?

Answer 14

Provides strength, support and elasticity to maintain the shape and structure of these body parts (ear, epiglottis, larynx)

Question 15

What is the structure of fibrocartilage?

Answer 15

Dense arrangement of collagen fibres within tis matrix, giving it a strong and fibrous appearance. Less uniform structure compared to hyaline and elastic cartilage.

Question 16

Where is fibrocartilage found?

Answer 16

In areas subjected to heavy mechanical stress or where there is a need for strong support, e.g., intervertebral discs, joint capsules, ligament

Question 17

What is the function of fibrocartilage?

Answer 17

Provides strength, shock absorption and resistance to compression in areas where stability and support are crucial. Helps distribute forces and maintain the integrity of the structures it is part of.

Question 18

What do most bones first appear as?

Answer 18

Most bones first appear in the foetus as hyaline cartilage that grows and is then systematically replaced by bony tissue, during endochondral ossification.

Question 19

By what process do bones arise?

Answer 19

Endochondral ossification: hyaline cartilage in the foetus systematically replaced by bony tissue

Question 20

Role of epiphyseal plate in bone growth.

Answer 20

Bones increase in length by the growth of epiphyseal cartilage and then replaced by bone.

Question 21

What is articular cartilage? What are its features?

Answer 21

• Hyaline cartilage at end of long bones
• Has no perichondrium: coats surfaces of bones in a joint
• Provides a smooth, slippery surface, shock absorbing function

Question 22

What modes of growth are there for hyaline cartilage?

Answer 22

Interstitial growth: expands from within via division of chondrocytes within ECM and hence production of more matrix
Appositional growth: addition of new cartilage at surface (functional significance)

Question 23

Describe regression of skeletal hyaline cartilage.

Answer 23

• Programmed to grow by interstitial growth and then degenerate
• Enlarged space in developing bone is replaced with bony tissue

Question 24

Describe the ability of hyaline cartilage to repair.

Answer 24

• Limited ability to repair
• Avascularity of cartilage
• Immobility of chondrocytes (can’t divide as easily)
• Limited ability of mature chondrocytes to proliferate

Question 25

What is the intervertebral disc? What are its components?

Answer 25

Lies between adjacent vertebrae in the vertebral column
Central nucleus pulposus: semi-liquid hyaluronic acid
Outer annulus fibrosus: several layers of fibrocartilage

Question 26

What is the functional significance of the intervertebral disc?

Answer 26

• Volume of liquid remains the same independent of pressure
• Inner pool of liquid confined by circular arrangement of collagen fibres in the fibrocartilage
• Vertebrae kept together by fibrocartilage, limited flexibility
• Vertebrae have certain distance between them that allows nerves to enter and leave spinal cord

Question 27

What can cause changes in the thickness of the intervertebral disc? What is the significance?

Answer 27

The intervertebral disc can undergo changes in thickness from early morning to late at night, due to weight bearing and with age. This causes the vertebral column to become shorter, causing slight differences in the height of an individual.

Question 28

What causes a herniated (slipped) disc?

Answer 28

A herniated (slipped) disc affects lumbar vertebrae.
Strain tears collagen layers of annulus fibrosis. Fluid moves to area of least resistance. Displaced disc contents impinge on spinal nerve.

Question 29

How can joints be classified?

Answer 29

Functionally: by their freedom of movement
Structurally: by how adjacent bones are joined (tissue type)

Question 30

Give examples of functional classifications of joints.

Answer 30

Diarthrosis: these are freely movable
Amphiathrosis: these are slightly movable
Synarthrosis: these have little to no movement

Question 31

Give examples of structural classifications of joints.

Answer 31

Fibrous tissue
Cartilaginous, bony tissue
Synovial joints (space)

Question 32

What are fibrous joints? What are their features?

Answer 32

• Bone held together by fibrous CT, rich in collagen
• No synovial cavity
• No (or limited) movement between bones

Question 33

What are the three types of fibrous joints?

Answer 33

Synarthrodial (sutures between bones in skull)
Syndesmoses (distal tibiofibular joint - slightly moveable) (desmos, a band or ligament)
Gomphoses (e.g., dentoalveolar joint, tooth in jaw, articulation of root of teeth with sockets) (immovable, dense CT = periodontal ligament)

Question 34

What are cartilaginous joints? What are their features? Give examples of where it is found.

Answer 34

• Lacks synovial cavity
• Little or no movement (more movement than fibrous, less than synovial joints)
• Bones connected by hyaline cartilage or fibrocartilage
• Epiphyseal plates in growing bones (synchondrosis - primary), joined by hyaline cartilage
• Intervertebral disc: vertebrae joined by fibrocartilage (symphyses - secondary)

Question 35

What are synovial joints? What are their features?

Answer 35

• Joint in which two bones are separated by a space called a joint cavity
• Most are freely movable
• Fibrous capsule (lined by synovial membrane, continuous with periosteum)
• Synovial (joint) cavity filled with synovial fluid (viscous, slippery fluid rich in albumin and hyaluronic acid. Lubrication, nutrient supply)

Question 36

Where are synovial joints found?

Answer 36

Found in articular cartilage and synovial membrane

Question 37

What is the temporomandibular joint? Describe its makeup.

Answer 37

• Bilateral synovial articulation connecting mandible to temporal bone of skull (complex synovial joint)
• Articular disc: dense fibrocartilaginous tissue between head of mandibular condyle and glenoid fossa of temporal bone

Question 38

Why is the TMJ important?

Answer 38

Important for movement of jaw, chewing, swallowing, breathing, talking