W5 Aatomy And Histology Of Bone Cartilage And Ossification

Question 1

What is cartilage?

Answer 1

Avascular connective tissue

Consists of cells and extracellular matrix (fibres and ground substance)

Question 2

What does avascular mean for the cartilage?

Answer 2

It has no nerve supply or lymphatic drainage. Nutrition is by diffusion.

Question 3

What is cartilage surrounded by?

Answer 3

Perichondrium (except articular cartilage and fibrocartilage)

Question 4

What is the function of cartilage?

Answer 4

Tensile strength to provide a firm structural support for soft tissues, allowing flexibility without distortion and is resilient to compression.

Question 5

What are the 3 types of cartilage?

Answer 5

Hyaline
Elastic
Fibrous

Question 6

Where is hyaline cartilage found?

Answer 6

Covers articular surfaces, synovial joints, nasal septum, trachea, larynx etc

Question 7

Describe hyaline cartilage

Answer 7

Collagen type II
Many chondrocytes
Perichondrium

Question 8

Why are there no fibres in the hyaline cartilage?

Answer 8

The matrix is homogeneous. The matrix and fibres have the same retractive index so do not appear separate, leaving a glassy appearance.

Question 9

Describe elastic cartilage

Answer 9

Has many chondrocytes
Has a perichondrium
ECM has fine elastic fibres

Question 10

Where can elastic cartilage be found?

Answer 10

External ear, epiglottis

Question 11

Describe fibrocartilage

Answer 11

Type I collagen fibres
Few chondrocytes
No perichondrium

Question 12

Where is fibrocartikage found?

Answer 12

TMJ, intervertebral disc

Question 13

Describe the outer and inner layer of the perichondrium

Answer 13

Outer layer - dense vascular connective tissue

Inner layer - chondrogenic = stem cells which give rise to new chondroblasts

Question 14

Function of the perichondrium

Answer 14

Protection, nutrition, repair

Question 15

Which cartilages have perichondrium and which don’t?

Answer 15

Articular cartilage and fibrocartilage are not lined by perichondrium but hyaline and elastic are.

Question 16

What types of cells are found in cartilage?

Answer 16

Chondroblasts - synthesis the matrix. Enlarge the cartilage by both interstitial and appositional growth.
Chondrocytes - mature cartilage cells, enclosed in lacunae (maintain the matrix)

Question 17

What does the matrix of cartilage contain?

Answer 17

Glycosaminoglycans (chonrdoitin sulfate) and fibres (collagen or elastic)

Question 18

What is the function of the matrix of cartilage?

Answer 18

Allows diffusion and acts as a semirigid shock absorber.

Question 19

What are the roles of bone?

Answer 19

Haemopoiesis, reservoir for calcium and minerals

Question 20

What is the bone covered by?

Answer 20

Periosteum except articular surfaces.

Question 21

Why is the bone matrix highly vascularised?

Answer 21

To aid diffusion in the calcified matrix

Question 22

What do the organic and inorganic components of the bone matrix do?

Answer 22

Organic components resist tension

Mineral components resist compression

Question 23

What are the 4 types of bone cell?

Answer 23

Osteoblasts, osteogenic, osteoclasts, osteocyte

Question 24

What is the initial bone matrix called and what secretes it?

Answer 24

Osteoblasts secrete components of the initial matrix = osteoid (before it becomes mature, consists of the inorganic component)

Question 25

What are the osteoid components?

Answer 25

Type I collagen, osteocalcin (a protein), which then vines calcium and phosphate ions forming hydroxyapatite crystals

Question 26

What do osteocytes do?

Answer 26

They are enclosed within lacunae and maintain the matrix. They detect mechanical stresses on bone. They maintain communication with adjacent cells via a network of long dendritic processes (pass through canaliculi radiating from each lacuna.

Question 27

How does bone grow?

Answer 27

Interstitial growth: bone grows in length and height - important in growing age Apositional: growth in bone girth/width - important in fractures and repairs New bone is deposited and old bone is degraded

Question 28

How is bone repaired, e.g., after fracture? (Min 37 zoom)

Answer 28

1. Hematoma - accumulation of blood 2. Hematoma replaced by a fibrocartilaginous (soft) callus forms and blood vessels start to revascularise 3. A hard (bony) callus forms (woven bone) after a few days 4. Eventually the bone is remodelled to lamellar bone

Question 29

What do PTH and calcitonin do?

Answer 29

PTH decreases blood calcium levels and calcitonin increases blood calcium levels.