L15- Cartilage And Bone

Question 1

A) What are the 3 types of cartilage?

B) what do all 3 have in common?

Answer 1

A) Hyaline cartilage, Elastic cartilage and fibrous cartilage

B) all have Chondrocytes and all have a matrix containing proteoglycan and hyaluronic acid

Question 2

HYALINE CARTILAGE:

A) Composition: cells and matrix

B) Where where it found?

C) function

Answer 2

A)
Cells: Only contains chondrocytes that are present singly or in isogenous groups

Extracellular matrix: proteoglycan and hyaluronic acid bound to fine collagen matrix (type 2 fibres)

Isogenois= equal origin

B) Parts of articulating surface ( articulater joints) epiphyseal plate until growth ceases and parts of the rib cage, nose, trachea, bronchi and larynx

C) Endochondral ossification- hyaline cartilage is the precursor model of the bones that develop in this way

Question 3

A) Function of chondrocytes and where are they found?

B) what does the extracellular matrix in all cartilage consist of and its function?

Answer 3

A) Produce and maintain the extracellular matrix

• lie in a lacuna: a depression
• lay down extracellular matrix in vesicles in the cell and when they burst release the matrix

B) Proteoglycan and hyaluronic acid: brings h20 into tissue, assists resilience to the repeated application of pressure, good shock absorber- makes a stiff gel like substance

Question 4

How does hyaline cartilage grow?

Answer 4

• Grows from the perichondrium- contains fibroblast like cells that develop into chondroblasts and then into chondrocytes
• chondroblasts produce and maintain extracellular matrix

Can either grow just from the periphery: appositional growth OR from two sides: interstitial growth

Question 5

Why is the extracellular matrix so important in cartilage?

Answer 5

Hyaluronic acid brings water into tissues, water is non-compressible and so permits resilience to increase loads

Question 6

Outline the structure and function of cartilage in the tracheal wall

Answer 6

Tube formed by C-shaped hyaline cartilage ring

• reinforces trachea
• protect and maintain airway (prevents it from collapsing so gas change can occur)
• lined with pseudostratified ciliated epithelium

Question 7

ELASTIC CARTILAGE:

A) Composition: cells and matrix

B) Where where it found?

C) function

Answer 7

A)
Cells: only chondrocytes
Matrix: elastic fibres and elastic lamellae (layers)- confers elasticity

B) only in 3 places:

1. Pinna of the ear
2. Eustachian tube
3. Epiglottis

C) extra flexibility and support

Question 8

What would you see in a histology of the trachea?

Answer 8

1. Pseudostratified columnar ciliated epithelium and submucosa- glands and goblet cells
2. Perichondrium: connective tissue sheath that covers cartilage.
   Vascular. Contain fibroblast-like-cells that develop into chondroblasts then chondrocytes
3. Hyaline cartilage ring (c shaped: contain chondrocytes in a lacuna and extracellular matrix

Question 9

What would you see in a histology slide of the pinna of the ear?

Answer 9

1. Skeletal muscle- striated
2. Adipose tissue (white areas)
3. Fibrocollagenous tissue with chondroblasts on edge
4. Elastic cartilage: dark staining elastin fibres, sometimes holes where chondrocytes used to be
5. Dermis/epidermis
6. Keratinised material on surface

Question 10

FIBROCARTILAGE:

A) Composition: cells and matrix

B) Where where it found?

C) function

Answer 10

A)
Cells: chondrocytes AND fibroblasts

Only type of cartilage that contains type I and type II collagen (combination of dense regular connevgtive tissue and hyaline cartilage)

B) Intevertebral discs, articulate discs of sternoclavicular and temporomandibular joints and menisci of the knee joint and in the pubic symphysis

C) found in areas of directional stress, where resistance to compression, durability and tensile strength are needed

Resilience to act as a shock absorber and resist shearing forces

Question 11

Why does fibrocartilage not have any distinct perichondrium?

Answer 11

Because it blends with other tissues such as tendon or hyaline cartilage

Question 12

A) What is bone ossification?
B) what are the types?
C) what is the similarities and differences?

Answer 12

A) the process of bone formation
B) Intramembranous and endochondral
C) Both of them begin with a mesenchymal tissue precursor
- Intramembranous: the formation of bone from clusters of mesenchymal stem cells in the centre of the bone- forms the flat bones of the skull, clavicle and most of cranial bones
- Endochondral: begins with mesenchymal tissue transforming into a cartilage intermediate. Uses cartilage as a template which is later replaced by bone and forms remainder of axial skeleton and long bones

Question 13

Outline the structure of long bones

• include the structure if it was a growing bone

Answer 13

Two parts:

1. Diaphysis: tubular shaft in the middle. Hollow region: medullary cavity (yellow marrow) and walls: compact bone

MEDULLARY CAVITY:

• inside lining called endosteum (growth and remodelling)
• Fibrous membrane surface called periosteum (blood vessels, nerves that nourish bone)

2. Epiphysis: wider section at each end of the bone, filled with spongy bone with red marrow
   - covered with articular cartilage that reduces friction

If a growing bone:
Would have an epiphyseal plate (growth plate with a layer of hyaline cartilage)

If adult hood:
Epiphyseal plate replaced by epiphyseal line

Question 14

Outline the process of endochondral ossification

Answer 14

Developing long bones e.g. femur
Hyaline cartilage model

Begins in fetal development:

1. Mesenchymal cells —> chondrocytes (proliferate and secrete ex cell matrix to form hyaline cartilage and perichondrium)
2. collar of periosteal/ compact bone appears in the shaft
3. Primary ossification centre formed: central cartilage calcifies
   - nutrient artery penetrates, supplying bone depositing osteogenic cells

Post natal:
4. Medulla becomes cancellous bone. Cartilage form Epiphyseal growth plates.
Secondary ossification centres develop in the epiphyseal region
5. Epiphyses ossify and growth plates continue to move apart, lengthening the bone.
6. Epiphyseal growth plate replaced by bone but the hyaline ARTICULAR cartilage stays.

Question 15

What happens to the epiphyseal growth plate of adults?

Answer 15

It disappears after the cessation of growth.

Question 16

A) Composition of bone matrix?

B) composition of bone cells?

Answer 16

A)

1. 65 percent inorganic: calcium hydroxyapatite (ca, po4, carbonate, cl) and magnesium salts
2. 35 percent organic:
   - collagen 1
   - GAGS and proteoglycans
   - non- collagenous proteins

B)
1. Osteoprogenitor: undifferentiated stem cell, produce osteoblasts.
Found in inner layer (endosteum) and outer layer (periosteum)

2. Osteoblasts: intermediate cells: immature bone cell that secretes organic components of matrix (divide into osteocytes). When trapped becomes osteocyte
3. Osteocytes: mature bone cell that maintains the bone matrix (trapped within osteon/ matrix)
4. Osteoclasts: huge cells that are fused monocytes (multinucleate) Secrete acids and enzymes to dissolve bone matrix. Reabsorption of existing bone

Question 17

Outline the process of Intramembranous ossification

Answer 17

1. MSC aggegrate (form tight cluster)
2. MSC differentiate into osteoprogenitor cells and then osteoblasts
3. osteoblasts group form an ossification centre- begin secreting osteoid (unmineralised collagen-proteoglycan matrix that can bind calcium)
4. Osteoid mineralises- crystals of calcium form in and around it to form rudimentary bone tissue spicules (surrounded by osteoblasts and contain osteocytes)
5. leads to entrapment of osteoblasts- formation of osteoblasts to osteocytes
6. Spicules join to form trabeculae which merge to spongy bone
7. trabeculae replaced by lamellae of mature compact bone

Question 18

Outline the microstructure of Compact/cortical bone

Answer 18

• Functional unit: Osteon (cylinders): layers of compact mineralised collagen which has a central canal called the Haversian canal
• Matrix (mineralised collagen) traps osteoblasts (produce bone) and then form osteocytes
• Between the layers of collagen the osteocytes are located in lacunae
• Haversian canal: contain blood vessels that are parallel (vertical) to long bone
• the volkmanns canal (horizontal) connect the blood vessels
• Osteoclasts are found on the edges (periosteum and endosteum) and not in cortical bone

Question 19

How do osteocytes communicate?

Answer 19

• maintain connections with each other through channels within bone called canaliculli.
• Osteocytes extend processes called filopodia
  through the canaliculli.
• Filopodia from adjacent cells contact each other and communicate via gap junctions.

Question 20

How could you identify the following cells in a histology slide?
A) Osteoblasts
B) osteoclasts
C) osteoid

Answer 20

A) they would be around the edge of the osteoid
B) multinucleated and are found in regions where bone appears to be carved out- they would be surrounded by blue osteoid
C) osteoid would be the blue matrix that entraps the cells

Question 21

What is the difference between osteoarthritis and rheumatoid arthritis?

Answer 21

Osteoarthritis:

• age related degeneration
• mechanical failure of the articular cartilage leading to narrowing of the joint space: bone rubs against bone
• growth of bony spurs causes inflammation and pain

Rheumatoid arthritis (RA)

• autoimmune disease
• osteoclasts will degrade the bone and macrophages will come in digest the bond sending signals to stimulate an immune response, T cells will create an autoimmune response damaging the cartilage
• fibroblasts lay down scar tissue
• extensive angiogenesis leads to more fluid and more inflammation

Inflammation of the synovial membrane and thickening of the joint capsule: bone and cartilage disintegrate

Question 22

Outline the microstructure of cancellous/spongy bone

Answer 22

• consists of trabeculae: lamellae that are arranged as rods or plates
• red bone marrow found between the trabeculae
• blood vessel within this tissue deliver nutrients to osteocytes and remove waste

Question 23

a) Outline the structure and function of hyaline articular cartilage
b) How would this look on histology?

Answer 23

a) covers articular surfaces of synovial joints
No perichondrium

Very flexible
Shock absorption
Chondrocytes are embedded in lacunae.

b) You would see the synovial fluid/joints

Question 24

How would you see elastic cartilage on histology slides?

Answer 24

CM contains a threadlike meshwork of elastic fibers.

Question 25

How can spongy bone be converted into compact bone

Answer 25

Bone remodelling

Question 26

In a histology slide how would you be able to tell a bone is arising from endochondral ossification or intramembranous ossification ?

Answer 26

Intramembranous: has osteocytes, osteons, haversian and volkmanns canals

Question 27

a) What is the perichondrium?
b) Where is it found and not found?
c) Function?

Answer 27

a) dense layer of fibrous connective tissue that covers cartilage in various parts of the body
b) elastic cartilage in parts of the ear, nose, hyaline cartilage in the larynx and trachea, epiglottis, area where the ribs connect to the sternum and area between the spinal vertebrae

-In adults, perichondrium tissue does not cover articular cartilage in the joint

c) Contain fibroblast-like-cells that develop into chondroblasts then chondrocytes
- it is vascular and its vessels supply nutrients to chondrocytes

Question 28

Difference between chondroblasts and chondrocytes

Answer 28

The extracellular matrix of cartilage is secreted by chondroblasts, (chondro = cartilage), which are found in the outer covering layer of cartilage. As the chondroblasts secrete matrix and fibres, they become trapped inside it, and mature into cells called chondrocytes

Question 29

What is osteoid?

Answer 29

unmineralised collagen-proteoglycan matrix that can bind calcium

Question 30

Difference in appositional and interstitial growth of cartilage?

Answer 30

1. Appositional: growth from the OUTSIDE/periphery
   - chondroblasts in perichondrium secrete matrix (on the edges), perichondrium then grows larger and then the chondroblasts become chondrocytes, grows in WIDTH
2. Interstitial: growth from within tissue
   - chondrocytes are in isogenic groups and secrete new matrix from within the lacunae and they spread apart, increases in LENGTH