Microanatomy of Bone, Cartilage, Tendon, Ligament and Joint

Flashcards about Microanatomy of Bone, Cartilage, Tendon, Ligament, and Joint.

Functions of Bone

Frame & body structure, protect, and support soft tissues (e.g. brain); Hematopoietic tissue production, store minerals.

Functions of Cartilage

Semi-rigid support to specific sites, acts as a shock absorber in menisci and intervertebral disks, protects the ends of bones.

Functions of Ligaments

Provide stability of joints; connect bones to bones.

Functions of Tendons

Provide strong, flexible connections between muscles and bones.

Functions of Joints

Spaces with fluid between bones; lubricated; provide varying degrees of movement and flexibility.

Osteoid

90% collagen and Inorganic (mineral) components – Hydroxyapatite [Ca10(PO4)6(OH)2]

Functions of Bones

Protect other organs (brain), produce hematopoietic cells, store minerals, provide structure and support for the body.

Trabecular Bone

Large surface area; contains bone marrow.

Cortical Bone

More dense than trabecular bone.

Mature Lamellar Bone

Collagen in parallel layers resulting in strong mature bone; found in trabeculae and cortical bone.

Woven Bone

Collagen disorganized, weak, new bone formation; Locations = fracture repair, inflammation, neoplasia.

Lamellar Bone

Strong mature bone; collagen fibers in matrix arranged in layers (lamellae) resulting in strong mature bone (osteoid).

Woven Bone

Weak immature bone; disorganized arrangement of collagen fibers; present at sites of rapid bone formation (e.g., fracture repair, inflammation, neoplasia).

Osteon

Functional unit of lamellar bone; located in circles around the central canal (Haversian) and in the interstitial bone between the circles of bone; found in mature bone (lamellar) not woven bone.

Volkmann's Canals

Canals running in bone and connecting Haversian (central) canals.

Osteoblasts

Derived from osteoprogenitor cells.

Osteoclasts

Monocytic origin.

Osteoblasts

Produce osteoid (the organic component of bone matrix) and initiate its mineralization.

Osteocytes

Most abundant cells; reside in lacunae surrounded by mineralized matrix.

Parathyroid Hormone (PTH)

Stimulates activity; resides in shallow pits (Howship’s lacunae); acid demineralizes bone and enhances activity of acid hydrolases released from osteoclasts (extracellular digestion).

Bone Lining Cells

Flat, elongated cells that cover endosteal surfaces of inactive bone.

Parathyroid hormone (PTH)

Promotes bone resorption.

1,25-dihydroxyvitamin D3

Required for normal bone growth and mineralization; also stimulates bone resorption.

Calcitonin

Inhibits bone resorption.

Glucocorticoids

Inhibit formation and stimulate resorption.

Estrogen

Inhibits bone resorption.

Osteoid (organic component)

Type I collagen (~90%), osteonectin, osteocalcin, proteoglycans, growth factors, hydroxyapatite [Ca10(PO4)6(OH)2].

Intramembranous Ossification

Bone formed from mesenchymal tissue in periosteum; occurs in flat bones of skull and pelvis and on all periosteal surfaces throughout life; responsible for the growth of bones in width.

Endochondral Ossification

Bone formed from hyaline cartilage precursors in physes; most bones develop by this method (appendicular, axial and base of skull); at physes responsible for growth of bones in length.

Endochondral ossification

Occurs at ends of bones.

Growth Plate

The physis is white and made of cartilage.

Growth plate (Physis)

Where hyaline cartilage differentiates, matures, mineralizes, dies and is scaffold that osteoblasts reside on.

Growth Plate Zones

Zone of reserve/resting cells, zone of proliferation, zone of hypertrophic cells, primary spongiosa.

Cartilage

Semi-rigid support to specific sites: present in many locations between bones, joints, ligaments, respiratory tree, and intervertebral discs; acts as a shock absorber in menisci and intervertebral disks; protects the ends of bones.

Cartilage

Avascular semi-rigid form of connective tissue characterized by absence of blood vessels, lymphatic vessels and nerves (adults); supports soft tissues; important for longitudinal bone growth – Endochondral ossification.

Isogenous Group

Cluster of chondrocytes formed through the division of a progenitor cell; found in hyaline cartilage, elastic cartilage, and fibrocartilage.

Hyaline Cartilage

Joints - articular cartilage; ribs, physes, nose.

Elastic Cartilage

Ear, epiglottis; flexibility needed.

Fibrocartilage

Menisci; discs; insertions of tendons & ligaments.

Locations of Hyaline Cartilage

Growth plates = physes, articular cartilage, costo-chondral junctions of the ribs, the nasal septum, larynx, tracheal rings, and bronchi.

Locations of Elastic Cartilage

Epiglottis; corniculate and cuneiform processes of the arytenoid cartilage, in the external auditory canal and in the ear pinna.

Locations of Fibrocartilage

Intervertebral discs (annulus fibrosus) menisci, insertions of tendons and ligaments, mandibular symphysis, pubic symphysis.

Perichondrium

Outer layer is composed of dense fibrous connective tissue. The inner layer is cellular and chondrogenic, contains cells with capacity to become chondroblasts.

Cartilage Matrix Components

Collagen, elastic fibers and proteoglycans (GAGs).

GAGs (Glycosaminoglycans)

Sulfated polysaccharide units.

Examples of GAGs

Chondroitin sulfate, keratan sulfate, dermatan sulfate, heparan sulfate and hyaluronan (hyaluronic acid in joint fluid).

GAGs bound to a protein core

Form macromolecules called proteoglycans that are responsible for the strong and flexible property of cartilage – shock absorption.

Function of Tendons and Ligaments

Attachments; flexibility

Tendon Composition

Approximately 85% collagen- 98% type I, 2% elastin, 1–5% proteoglycans.

Tendon

Mature tendon contains cells that have a limited ability to regenerate. Following injury, a tendon lays down type III collagen, or scar tissue, which is stronger than type I, but stiffer and less-elastic.

Fibrous Joints (Synarthroses)

Bones or cartilages are united by fibrous tissue.

Cartilaginous (Amphiarthrosis)

Bones or cartilages united by hyaline cartilage or fibrocartilage.

Synovial (Diarthrosis/True joints)

Unite two bone ends and are covered by articular cartilage and surrounded by a thick articular capsule.

Types of Fibrous Joints

Sutures (cranial suture), Syndesmosis (tibia-fibula), Gomphosis (i.e., a tooth socket).

Types of Cartilaginous Joints

Hyaline cartilage (i.e., costochondral joints) or fibrocartilage (i.e., pelvic and mandibular symphysis).

Synovial Joints Types

Synovial joints of appendicular skeleton and vertebral joints.

Morphologic Types of Joints

Fibrous (synarthrosis), Cartilaginous (amphiarthrosis), Synovial (diarthrosis).

Type A Cell of Synovial Membrane

Phagocytic function – remove debris.

Type B Cell of Synovial Membrane

Secrete hyaluronic acid, & protein complex (mucin) into synovial fluid = lubricant, protectant and nutrition to joints.

Articular Cartilage

Surface should be smooth; formed by Type II collagen and proteoglycans; lacks blood vessels and nerves (poor capacity for regeneration).

Articular Capsule

Thick sac of connective tissue that covers the entire joint and provides additional joint stability.

Synovial Membrane

Thin membrane with lots of villi superficially lined by a continuous layer of specialized cells (synoviocytes – type A are phagocytic; type B produce synovial fluid).

Synovial Fluid

Clear, viscous, colorless or slightly yellow fluid produced by synoviocytes (low cellularity and low protein content); function is to reduce friction; increases in many joint diseases (effusion).