Cartilage and Bone

What is the main function of cartilage?

Provides flexible support and resists compression while maintaining shape.

What cells produce cartilage?

Chondrocytes (within lacunae) and chondroblasts (precursors).

What is the composition of the cartilage matrix?

Proteoglycans, glycosaminoglycans (GAGs), and type II collagen fibers embedded in a hydrated ground substance.

Why can cartilage trap water?

The proteoglycans are highly charged, attracting and retaining water molecules.

Does cartilage have blood vessels?

No, it is avascular, nutrients diffuse through the matrix.

What surrounds most cartilage?

The perichondrium, a dense connective tissue layer containing fibroblasts and progenitor cells (except in articular cartilage).

What are the three types of cartilage?

Hyaline cartilage, elastic cartilage, and fibrocartilage.

Where is hyaline cartilage found?

Trachea, nasal septum, larynx, costal cartilages, and articular surfaces of joints.

What collagen type is found in hyaline cartilage?

Type II collagen.

What are the key features of hyaline cartilage?

Smooth, glassy matrix; chondrocytes in lacunae; surrounded by perichondrium (except at joints).

What is the perichondrium’s role in cartilage growth?

Contains chondrogenic cells that aid in appositional growth (growth at the surface).

What pathology arises from abnormal cartilage cell proliferation?

Chondroma (cartilage tumor).

Where is elastic cartilage found?

Epiglottis, external ear (auricle), and eustachian tube.

What collagen type and fibers are present?

Type II collagen and abundant elastic fibers.

Does elastic cartilage have a perichondrium?

Yes, it is present and contributes to growth and repair.

What feature distinguishes elastic cartilage histologically?

Dark staining elastic fibers interwoven in the matrix.

Where is fibrocartilage found?

Intervertebral discs, menisci, pubic symphysis, and temporomandibular joint.

What types of collagen are present in fibrocartilage?

Types I and II collagen.

What cells are present in fibrocartilage?

Both fibroblasts (produce type I collagen) and chondrocytes (produce type II collagen).

Does fibrocartilage have a perichondrium?

No, it lacks a perichondrium.

What is fibrocartilage specialized for?

High tensile strength and resistance to compression.

What are the two types of bone tissue?

Compact (dense) bone and spongy (cancellous) bone.

What is the composition of bone by weight?

~70% inorganic minerals (calcium phosphate, hydroxyapatite), 22% protein (mostly collagen type I), 8% water.

What are the layers of bone covering?

Periosteum (outer fibrous + inner osteogenic layer) and endosteum (inner lining).

What structures make up the osteon (Haversian system)?

Central (Haversian) canal, concentric lamellae, osteocytes in lacunae, and canaliculi.

What do canaliculi do?

Small channels that allow communication and nutrient exchange between osteocytes.

What are osteoblasts, osteocytes, and osteoclasts?

Osteoblasts: bone forming cells that secrete osteoid. Osteocytes: mature bone cells within lacunae maintaining matrix. Osteoclasts: large multinucleated cells that resorb bone.

What is the role of collagen in bone?

Provides tensile strength and flexibility.

What gives bone its hardness?

Mineral salts, primarily calcium phosphate crystals.

What are the two types of bone formation?

Intramembranous ossification and endochondral ossification.

Where does intramembranous ossification occur?

Flat bones of the skull, mandible, and clavicle.

What are the steps of intramembranous ossification?

1. Mesenchymal cells differentiate into osteoprogenitor cells. 2. Osteoblasts secrete osteoid (unmineralized matrix). 3. Osteoid becomes mineralized with calcium phosphate. 4. Osteocytes form within lacunae as osteoblasts become trapped.

Why are osteoclasts active on the inner surface of the skull?

To resorb bone and create space for the growing brain.

What is endochondral ossification?

Bone formation that replaces a cartilage model, used for long bones.

What are the steps of endochondral ossification?

1. Formation of cartilage model. 2. Primary ossification center forms in diaphysis during fetal development. 3. Secondary ossification centers form in epiphyses after birth. 4. Growth plate (epiphyseal plate) allows elongation until closure.

What signaling molecule stimulates endochondral ossification?

Bone Morphogenetic Proteins (BMPs).

What structures separate primary and secondary ossification centers?

Epiphyseal (growth) plates of cartilage.

What is the perichondrium?

Dense CT surrounding cartilage (except at joints), containing fibroblasts and chondroprogenitor cells.

What is the periosteum?

Dense CT layer surrounding bone; the perichondrium’s equivalent in bone.

Why do joints lack perichondrium?

To reduce friction and allow smooth movement at articular surfaces.