CARTILAGE

Cartilage is a form of connective tissue composed of cells called chondrocytes and a highly specialized extracellular matrix. Types of CARTILAGE: HYALINE CARTILAGE is characterized by a homogeneous amorphous matrix ELASTIC CARTILAGE, whose matrix contains elastic fibers and elastic lamellae FIBROCARTILAGE, whose matrix contains large bundles of type 1 collagen

STRUCTURAL PLAN OF CARTILAGE PERICHONDRIUM outer fibrous layer inner cell layer (chondrogenic cells + chondroblasts) CHONDROCYTES (isogenous groups of cells located in lacunas) with integrin (anchoring glycoprotein of plasma membrane) CARTILAGE MATRIX type II collagen fibers or elastic fibers ground substance consisting - aggrecan (proteoglycan rich in hyaluronic acid + chondroitin sulfate + keratan sulfate) - chondronectin (anchoring glycoprotein)

LOCALIZATION OF DIFFERENT KINDS OF CARTILAGE HYALINE CARTILAGE is found as the structural framework for the larynx, trachea and bronchi; on the anterior ends of the ribs; on the surfaces of synovial joints. Hyaline cartilage constitutes much of the fetal skeleton. ELASTIC CARTILAGE is found in the auricle of the external ear, in the auditory tube, in the epiglottis, and in part of the larynx. FIBROCARTILAGE is found at the intervertebral discs, the symphysis pubis, and some joints.

BONE

BONES AND BONE (OSSEOUS) TISSUE Bone is a type of connective tissue characterized by a highly mineralized extracellular matrix (65% of calcium hydroxyapatite crystals) + 35% of type I collagen fibers. Non-calcified intercellular substance is called Osteoid Bone tissue is CLASSIFIED as: - Primary (Woven) bone - Secondary (Lamellar) bone - Compact (Dense) bone - Spongy (Cancellous) bone Bones are covered by Periosteum: a sheath of dense connective tissue Bone cavities are lined by Endosteum: a delicate layer of connective tissue cells and fibers

CELLS OF BONE TISSUE Osteoprogenitor cell is a resting cell that can transform into an osteoblast Osteoblast is the differentiated bone-forming cell that secretes bone matrix Osteocyte, the mature bone cell, residing in lacuna, is enclosed by bone matrix that is previously secreted by an osteoblast Osteoclast is a large multinucleated cell whose function is resorption of bone

Light micrograph of intramembranous ossification with different cell types

EM of bone-forming cells

Osteoclast structure and function (scheme)

STRUCTURE OF ADULT LONG BONE Anatomy: Diaphysis + 2 Epiphyses + 2 Metaphyses Units of diaphyseal bone structure are called OSTEONS. Each osteon includes: - concentric lamellae – collagen fibers arranged in parallel manner - Haversian canal with blood vessel, osteoblasts and osteoprogenitor cells inside - osteocytes located in lacunas forvarding their processes into the bony canaliculi Besides osteons diaphysis consists of: Interstitial lamellae Circumferential lamellae Perforating (Volkmann’s) canals Periosteum Endosteum

Primary (intramembranous) bone formation

STAGES OF ENDOCHONDRAL OSSIFICATION Formation of a hyaline cartilage template (model) Appearance of a bony collar around the cartilage model Calcification of cartilage matrix Migration of periosteal cells into the cavity with growing blood vessels Structure of epiphyseal cartilage throughout the growth period: Zone of reserve cartilage Zone of proliferation Zone of maturation and hypertrophy Zone of cartilage calcification Zone of ossification (cartilage resorption)

Anatomy of diarthrodial joint

Events in bone fracture repair