Cartilage and Bone

Cartilage

Avascular connective tissue

• Chondrocytes

• Abundant solid extracellular matrix

3 types:

• Hyaline cartilage

• Elastic cartilage

• Fibro cartilage

Chondrocytes

Basic cell type

Enclosed in lacunae, clustered in isogenous groups (recent division)

• Division / matrix formation determines spacing

Chondrocytes Isogenous Groups

Cell groups are farther, if matrix growth is more than cell division

Cell groups are closer, if matrix growth is less than cell division

Chondrocytes Lacunae

Chondrocytes

Cartilaginous Growth

Two processes:

Appositional growth: forms new cartilage at the surface of an existing cartilage

Interstitial growth: forms new cartilage within an existing cartilage mass.

Perichondrium

Dense irregular connective tissue

• Composed of Chondrogenic cells, appear like fibroblasts

Surrounds almost all forms of cartilage

Perichondrium

Hyaline Cartilage

Most common type of cartilage

• Collagen type II fiber

• Proteoglycans (creates ground substance)

• Glycoproteins (multi-adhesive)

Appears glassy

Function:

• Provides cushioning, low friction surface for joints

• Provides structural support in respiratory system

• Foundation for fetal skeleton development and endochondral bone formation

Fetal skeletal tissue, epiphyseal, synovial joints, costal, nasal cavity, larynx, trachea, bronchi

Endochondral ossification

During fetal development hyaline cartilage is the precursor for bone

Epiphyseal growth plates

Made of hyaline cartilage and is replaced by bone as the bone continues to grow length wise.

Articular cartilage

Hyaline cartilage that covers the articular surfaces of moveable joints

Do not have perichondrium

A remnant of the hyaline cartilage from the developing bone that persists throughout life

Elastic cartilage

Contains components of hyaline cartilage matrix, but also elastic fibers

• Surrounded by perichondrium

• Mostly elastic fibers, less collagen fibers

• Large Chondrocytes, Close isogenous groups

Function

• Provides flexible support for soft tissues

Pinna of external ear, external acoustic meatus, auditory tube, epiglottis

Elastic cartilage

Elastic cartilage

Elastic cartilage

Fibrocartilage

Combination of dense regular connective tissue and hyaline cartilage

• Mostly type I and II collagen

• Less cartilaginous matrix

• No surrounding perichondrium

Function

• Resists deformation under stress, shock absorber

Intervertebral discs, pubic symphysis, articular discs

Fibrocartilage

Fibrocartilage

Fibrocartilage

Bone

Specialized hard connective tissue w/ mineralized extracellular matrix

• Cells (contained in lacunae)

  • Osteoblasts, Osteoclasts, Osteocytes (have processes called canaliculi)

• Extracellular matrix is mineralized

  • Type I collagen, proteoglycans, glycoproteins, and Calcium

Function

• Support, protection, homeostatic regulation of blood calcium, blood cell formation and muscle attachment.

Bone tissue cells

Composed of 4 different cells:

• Osteoprogenitor

• Osteoblasts

• Osteocytes

• Osteoclasts

Osteoprogenitor Cells

Mesenchymal stem cells

• Flatened, elongated oval nuclei

• Found in periosteum, endosteum

Undergo mitosis, develop into many cell types (ex. osteoblasts)

Secrete bone matrix and has a vital role in growth and repair

Osteoblast

Found on bone surface

• Type 1 collage, proteoglycans and glycoproteins

Do not mitotically divide

May change to an osteocyte after matrix is secreted

Function:

• Bone calcification

• Form and maintain matrix

Osteoblast

Osteocytes

Located in lacunae

Do not secrete matrix material

Function:

• Extend cytoplasmic processes through canaliculi for nutrition

• Exchange of nutrients and waste with blood supply

• Death of osteocytes will lead to bone resorption

• Communicate by gap junctions

Osteocytes

Osteoclasts

Found on bone surface

Large, multinucleated, branched, motile cells

The surfacing matrix have projections > ruffled border

Contain many lysosomes, many mitochondria

Found in Howship’s lacunae

Phagocytic

Function:

• Involved with bone growth, maintenance, and bone repair

• Release lysosomes into extracellular space, phagocytic, remodeling

Osteoclasts

Osteoclasts

Bone Anatomy

Diaphysis : shaft of bone

Epiphysis: ends of bone

Epiphyseal Plate: Growth plate

Metaphysis: between epiphysis and diaphysis

Medullary cavity

Periosteum

Endosteum

Periosteum

Dense connective tissue covering bone

• Outer fibrous layer

• Inner cellular layer (osteoprogenitor cells)

• Collagen fibers extend directly into the bone

Nutrient foramina

Periosteum

Endosteum

Inner lining of compact and spongy bone facing medullary cavity.

Medullary Cavity

Hollow chamber in bone

Contains

• Red marrow produces blood cells – high activity

• Yellow marrow of adipose – low activity

Osteon

Compact Bone

Lacunae are connected to one another by canaliculi

Osteon contains:

• Central Canal (Haversian canal)

• Surrounding lamellae

• Lacunae

• Osteocytes

• Canaliculi

Volkmann’s Canal: horizontal canal that connects the central canals

Spongy Bone

Internal layer of bone, marrow cavity

Trabecular bone tissue forming a meshwork

Filled with red and yellow bone marrow

Osteocytes get nutrients directly from circulating blood