Cartilage and Bone

Question 1

Functions of Cartilage

Answer 1

1. Support of soft tissues
2. Forms articular surface of long bones
3. Growth in length of long bones

Question 2

Cartilage ECM

Answer 2

Type II collagen maintains shape and provides tensile strength

Proteoglycan aggregates (between layers of collagen) provide resilience

Composition permits cartilage to bear mechanical stress without permanent distortion

GAGs: chondroitin sulfate 4, chondroitin sulfate 6, keratin sulfate

Question 3

How to make a proteoglycan aggregate

Answer 3

1. Begin with core proteins
2. Add GAGs (creates proteoglycans)
3. Bind proteoglycans to core of hyaluronic acid with link proteins

Question 4

Morphological features of Chondrocytes

Answer 4

The only cells found in healthy cartilage

Round diffuse nucleus with prominent nucleolus

Cytoplasm rich in RER, well-developed Golgi and mitochondria (basophlic)

Question 5

Identify

Answer 5

Hyaline cartilage (most common form) surrounded by perichondrium

Located on joint surfaces, tracheal rings, ventral end of ribs, nose, larynx, trachea, bronchi, epiphyseal plate

ECM: Type II collagen, basophilic

Chondrocytes live within lacunae - spaces in matrix.

Rich in sulfated GAGs in cytoplasm - makes ECM basophilic (blue)

Question 6

Consequences of cartilage lacking blood vessels (avascular)

Answer 6

1. Size limitation
2. Low metabolic rate
3. Poor potential for repair (except in young children)
4. Systemic drug treatment is difficult (medically relevant)

Question 7

Identify

Answer 7

Elastic cartilage (arrow to elastic fibers): located where flexible support is needed - external ear, epiglottis, eustachian tube, larynx

ECM: more flexible than hyaline, less homogenous, numberous elastic fibers (stain with orcein dyes)

Chondrocytes look identical to those in hyaline

Less susceptible to deneration/age change sthan hyaline

Question 8

Identify

Answer 8

Fibrocartilage: Intervertebral discs (annulus fibrosus), pubic symphasis, menisci, some tendons

ECM : eosiniphilic (pink) ground substance reduced, collagen increased (type I predominates)

Chondrocytes look the same as those in elastic and hyaline

No perichondrium

Distinguish from dense regular CT: has irregular fiber distribution, fewer cells per unit area and rounder chondrocytes

Question 9

Medical Conditions Assoicated with Cartilage

Answer 9

1. Calcification of the matrix: hyaline cartilage is most susceptible, occurs with aging
2. Osteoarthritis: loss/change in physical properties of articular cartilage, occurs with aging
3. Chondroma: benign tumors
4. Chondrosarcoma: slow growing malignant tumors

Question 10

Functions of bone

Answer 10

1. Supports fleshy structures
2. Protects vital organs
3. Harbors bone marrow
4. Reservoir of calcium, phosphate, etc.
5. Involved in body movement

Question 11

Similarities between cartilage and bone

Answer 11

1. Both supportive CT
2. Bone consists mostly of ECM
3. Osteocytes reside within lacunae
4. Bone is surrounded by periosteum (specialized CT)
5. Bone can grow by means of appositional growth

Question 12

Differences between cartilage and bone

Answer 12

1. Interstitial growth does not occur in bone
2. Bone has a more regular arrangment of cells and fibers
3. Bone is vascularized and has nerves
4. Calcification of ECM is a normal process in bone

Question 13

General structure of long bone

Answer 13

Diaphysis: cylindrical part, thick outer layer of compact (aka cortical) bone with thin marrow cavity containing spongy bone (aka cancellous or trabecular)

Epiphysis: bulbous ends, spongy bone covered by thin layer of compact bone

Question 14

Canaliculi

Answer 14

In compact bone, small channels that radiate in all directions thru the ECM from each lacuna.

Connect (gap junctions) with canaliculi of adjacent lacunae for communication

Nutrients from intersitital fluid (in contact with capillaries)

Red squiggles in picture

Question 15

Lamellae

Answer 15

Concentric layers of compact bone in an osteon that surround a central canal (Haversian Canal)

Question 16

Osteocytes

Answer 16

Reside in lacunae, have processes that extend into canaliculi.

Adjacent osteocytes are in contact with one another via gap junctions - allows exchange of ions and small molecules (can provide nourishment for a chain of about 10 cells)

Question 17

Types of Lamellar Organization (compact bone)

Answer 17

1. Haversian Canals: parallel to long axis of bone, have small blood vessels, loose CT, and nerves

Haversian system = osteon

2. Volksman Canals: oblique angles to long axis of bone, connect Haversian canals to each other and to the free surface, not completely surrounded by concentric lamellae
3. Interstitial lamellae: wedge-shaped regions between osteons, fragments of previous Haversian systems (continually made and destroyed)
4. Inner circumferential lamellae: beneath endosteum
5. Outer circumferential lamellae: beneath periosteum

(4 and 5 observed at external and internal surfaces)

Question 18

ECM of Bone: Organic Matrix (osteoid)

Answer 18

Responsible for toughness and resilience

1. Type 1 collagen
2. Non-collagenous proteins
3. Ground substance (GAGs and proteoglycans)

Question 19

ECM of Bone: Inorganic Matrix

Answer 19

Responsible for hardness

1. Calcium phosphate (hydroxyapatite): thin plates or crystals, associated with collagen fibers

Question 20

Identify

Answer 20

Osteoblasts

Question 21

Identify

Answer 21

Osteoprogenitor cells

Present in adults, have a low profile

Not actively making bone, but can be reactivated

Compact chromatin

Less basophilic cytoplasm

Question 22

Identify

Answer 22

1. Haversian canal (lined by endosteum)
2. Volksman canal
3. Bone marrow

Periosteum on outside

Question 23

Identify

Answer 23

1. Spongy bone
2. Marrow cavity
3. Compact bone

Question 24

Functional Adaptation (REMODELING)

Answer 24

• Both spongy and compact bone are destroyed and replaced in a constant process throughout life
• Involves relative activity of osteoblasts (make new bone) and osteoclasts (destroy bone). Need balanced activity to maintain skeletal integrity
• Bone adapts to mechanical load placed on it - osteocytes are mechanotransducers of local strain

Spongy bone more responsivle to changes in load than compact bone

Question 25

Objectives of Functional Adaptation

Answer 25

1. Provide maximal strength with minimal bone mass. Trabculae (aka spongy bone) follow lines of stress to do this. 2. Remove microdamage and replace with new bone

Question 26

Identify

Answer 26

Osteoclasts Large, multinucleated cells with eosinophilic (purple) cytoplasm and **ruffled borders.** Rich in mitochondria and lysosomes Attached to bone by podosomes that form a tight seal Fx: break down organix matrix (via cathepsins) and bone mineral (acidic env) Origin: fusion of monocytes

Question 27

Medical conditions associated with bone

Answer 27

1. Osteoporosis: osteoclast activity enhanced (break down exceeds formation). Causes fractures (vertebral, hip). Seen when estrogen levels fall in menopause and in men over 50. Treated with bisphosphonates 2. Osteopetrosis: defective osteoclasts, results in dense, heavy bone 3. Osteogenesis imperfecta: insufficient type 1 collagen production, leads to bone fragility 4. Rickets: abnormal calcification of bone matrix leads to soft bones, due to insufficient dietary Ca or lack of vitamin D in kids

Question 28

Location of cartilage in body

Answer 28

Nose Intervertebral discs Associated with ribs Articular surfae of bones Trachea, epiglottis, laynx, bronchi Pinna of ear Pubic symphysis

Question 29

Periosteum

Answer 29

Membrane covering outer surface of bone 1. Outer (fibrous) layer: dense irregular CT, few fibroblasts, blood vessels enter Volkman's canals, some collagen fibers anchor periosteum to bone 2. Deeper (cellular) layer: osteogenic potential, osteoblasts present in baby, osteoprogenitors in adults

Question 30

Function of chondrocytes

Answer 30

Produce and secrete extracellular matrix (ECM) Type II collagen determines tissue shape and produces tensile strength Proteoglycan aggregates give resilience to tissue ECM also has noncallagenous proteins

Question 31

Perichondrium

Answer 31

Dense irregular CT that surrounds hyaline and elastic cartilage (not articular cartilage) Outer fibrous layer (type I collagen, fibroblasts) Inner chondrogenic layer (more cellular, chondroblasts - retain ability to divide throughout fetal life) Formed from mesenchyme

Question 32

Growth of cartilage

Answer 32

1. Appositional: chondroblasts into chondrocytes, end up in lacunae. Add new cells and ECM to surface, latent in adults 2. Interstitial (from within): chondrocytes capable of mitosis for a while, produce isogenous groups (clusters of cells), diminished with age

Question 33

Compact bone

Answer 33

a. Composed mostly of ECM b. Lacunae form small cavities between lamellae (concentric patterns), each lacunae contains an osteocyte Canaliculi radiate in all directions from each lacuna

Question 34

Endosteum

Answer 34

Lines the inner surface of bone and surface of vascular channels More delicate, single layered structure Site where osteoclasts resorb bone

Question 35

Spongy bone | (Aka cancellus, trabecular bone)

Answer 35

Found at the end of long bone Lattice of branching bony trabeculae (functional unit) Lined by endosteum Filled with bone marrow - highly vascular Intercellular substance of trabeculae: not concentricaly arranged around a canal (no Haversian canals), not penetrated by blood vessels, nourished from surface by canaliculi Osteocytes idential to compact bone

Question 36

Identify

Answer 36

Pinna of ear Stratified squamous keratinized epithelium on outside Elastic cartilage in middle (S-shaped)

Question 37

Identify

Answer 37

Radius stained with thionine. The marrow cavity (mc): large open area containing trabeculae of spongy bone (sb) and bone marrow. Completely surrounded by a thin collar of compact bone (cb). Periosteum (p) covers the outside surface of the compact bone.

Question 38

Identify

Answer 38

Osteoclasts