ToB: Bone and Cartilage

Question 1

Name 6 functions of bone

Answer 1

locomotion, strength, protection, enables forceful muscle contractions, bone density adapts to mechanical demands, mineral storage, hematopoiesis in bone marrow

Question 2

Name 3 differences between compact and spongy bone, and the role of these differences

Answer 2

Compact:

1: Has periosteum: Layer of dense vascular CT that envelops bones
2. Haversian and Volkmann’s canals: carries blood vessels, lymphatics and nerves
3. Spongy bone is lighter: provides space for yellow and red bone marrow (has stem cells that form blood and immune cells)

Question 3

Where are osteocytes found in compact bone and what do they originate from?

Answer 3

Metabolically active and embedded in the lacuna, mature osteoblasts

Question 4

What is the surface area of spongy bone lined with?

Answer 4

Osteoblasts (smaller) and larger osteoclasts

Question 5

Name the unit of bone and what it’s typically comprised of

Answer 5

Lamellae, matrix and Haversian canals (in compact)

Question 6

What makes the organic component of bone?

Answer 6

Type I collagen: the osteoid; calcifies and mineralizes bone (needs an inorganic component to embed within collagen fibres)
Provides flexibility and stress resistance

Question 7

What makes the inorganic component of bone?

Answer 7

Calcium hydroxyapatite crystals: stores Ca2+ and phosphate which embeds in the organic component that gives bone hardness and compression ability

Question 8

Name the 4 stages of bone repair after fracture

Answer 8

1. Hematoma
2. Soft fibrocartilage callus: clot removed by macrophages and replaced by procallus tissue, collagen and fibroblasts
3. Hard bony callus: fibrocartilage turns into woven bone *invaded by blood vessels and osteolasts
4. Bone remodelling; aided by cutting cones

Question 9

Which bones are developed by Endochondral ossification and is its overall process?

Answer 9

All bones below the skull EXCEPT the clavicle:
Begins in utero from a hyaline cartilage template, bone collar develops and primary ossification centre (angiogenesis and osteoprogenitor invasion), at birth the secondary ossification centre develops on the other side of the epiphyseal growth plate.

The plate continually fuses and pushes for bone elongation until the end of puberty

Question 10

If the epiphyseal growth plate fuses at puberty, how are bones capable of appositional growth?

Answer 10

The periosteum keeps a reservoir of osteoblasts

Question 11

What are 2 core differences between endochondral ossification and intramembranous?

Answer 11

Intramembranous forms flat bones (like in skull) and instead of using a hyaline cartilage template, osteoblasts differentiate from local mesenchymal tissue

Question 12

What happens to bone growth if there are insufficient/excessive sex hormones?

Answer 12

Insufficient: bone growth continues longer than normal and person is taller (no sex hormones to close the growth plate)

Excessive: growth plate fuses early

Question 13

What are the effects of insufficient/excessive growth hormone on bones?
What is the name of the growth hormone and where is it synthesized?

Answer 13

Somatotrophin: synthesized in the anterior pituitary

Insufficient: pituitary dwarfism
Excessive: gigantism

Question 14

Name two bone diseases caused by a calcium deficiency/significant lack of Vitamin D and their common symptoms

Answer 14

Adult version: Osteomalacia: bone pain, back-ache, muscle weakness, increased risk of fracture

Child version: Rickets: long bones soft/malformed, bow legs, bossing, enlargement of costochondral rib junction

Question 15

What kind of mutation occurs in osteogenesis imperfecta? What are the two types?

Answer 15

Autosomal dominant mutation of type I collagen: COL1A1 or COL1A2

Type 1: frequent fractures after walking, bones thin and curved, shorter, blue sclera, progressive hearing loss

Type 2: lethal perinatal disease

Question 16

Name a bone disease with a genetic basis other than OI

Answer 16

Achondroplasia: Short limbed dwarfism
Autosomal dominant mutation of the fibroblast growth factor so FGFR3 promotes early growth plate closure, leading to fewer chondrocytes to generate the matrix

Question 17

Osteoporosis:
Name 3 common sites
How it can be diagnosed and treated (and why)
And the two types and their cellular activity

Answer 17

Common sites: wrist, hip and spine

Detected with DEXA scan that measures bone mineral density, treated with bisphosphonates that bind to the calcium hydroxyapatite crystals protecting them from osteoclasts

Type 1: post-menopausal women: less estrogen and increased osteoclast activity

Type 2: Elderly, reduced osteoblast activity

Question 18

Name 4 modifiable and non-modifiable risk factors for Osteoporosis

Answer 18

Modifiable: smoking, alcohol, exercise, Ca2+ intake

Non modifiable: age, gender, previous fractures, other diseases like rheumatoid

Question 19

Name 3 general features of cartilage

Answer 19

Not innervated, non-vascularized and slow turnover

Question 20

What do chondroblasts do and how do they become chondrocytes?

Answer 20

Chondroblasts secrete ECM and divide into the perichondrium. They form small groups of cells called isogenous groups that become separated and continue to produce matrix.

When a chondroblast is fully embedded in the matrix it becomes a chondrocyte - they are the only cells found in healthy cartilage

Question 21

What is the perichondrium?

Answer 21

CT that envelops cartilage where it’s not a joint

Question 22

Where is hyaline cartilage commonly found and what is it composed of?

Answer 22

Trachea, end of long bones, articulate cartilage found at joints, larynx, connects ribs to sternum

Composed of ECM: type II collagen, water and GAGS (proteoglycans attached to hyaluronic acid (keeps it hydrated)

Question 23

Name 3 features of hyaline cartilage

and why they appear that way if needed

Answer 23

Glassy: fibrils in Type II collagen don’t form fibres
Provides smooth surface for articulation
A large ratio of GAGs to collagen facilitate diffusion of substances between chondrocytes and blood vessels

Question 24

What types of cartilage don’t have a perichondrium?

Answer 24

Articulate cartilage (hyaline) and fibrocartilage

Question 25

Name where fibrocartilage is commonly found, what it’s composed of and 3 features

Answer 25

Menisci of knee, pubic symphysis and IV discs

Type I collagen, regular CT and hyaline cartilage

Tough, inflexible and shock absorbing

Question 26

Name 2 common sites for elastic cartilage, what it’s composed of and its main role

*Bonus! what doesn’t elastic cartilage do with age?

Answer 26

Epiglottis and external ear
Type II collagen, elastic network
Flexible and allows for recoil

Elastic cartilage doesn’t calcify with ageing

Question 27

What’s the main pathology of osteoarthritis?

Name 2 risk factors

Answer 27

Wear and tear of articulate cartilage combined with a lack of stem cells means cartilage doesn’t heal after damage; joint and soft tissue around joint are affected

Age and weight gain

Question 28

What is the cause of meniscal damage (think simple)

Answer 28

Wear and tear of meniscal fibrocartilage

Question 29

Name the disease caused by excess GH secreted from the pituitary stimulating appositional growth?

Answer 29

Acromegaly