Cartilage (Histology)

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What type of connective tissue surrounds Cartilage?

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Dense Connective Tissue

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Ground Substance Composition

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Gags, proteoglycans, glycoproteins, water

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Matrix Cartilage Composition

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Collagen fibers, elastic fibers, Ground substance ( gags, proteoglycans glycoproteins, water)

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Interstitial Growth

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mitotic division from preexisting chondroblasts

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Appositional Growth

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Differentiation of new chondroblasts from perichondrium

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Perichondrium

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sheath of dense connective tissue surrounding cartilage in most places except fibrocartilage

forms interface between cartilage and tissue supported by cartilage

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Embryonic development

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differentiation of cartilage from center outward

Central cells=chondrocytes

peripheral=chondroblasts

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Appearance if Hyaline

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homogenous and glassy

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Hyaline Collagen Type

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Type II

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Hyaline Location (adult)

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surfaces of movable joints

walls of large respiratory passages (nose, larynx, trachea, bronchi)

epiphyseal plate of long bone (Between the secondary centre and calcified matrix of the bone shaft)

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Hyaline Growth

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Perichondrium: inner layer=progenitor cells = chondroblasts (divide and differentiate) = chondrocytes

BUT NOT in articular surfaces/epiphyses of growing long bone

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Matrix

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collagen (Type II) - barely discernable

proteoglycans

basophilic

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Hyaline Cells

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chondrocytes:

Chondroblasts (young chondrocytes): deeper in the cartilage, round and may appear in groups of 8/less cells (originate from mitotic div. of single chondrocyte)=isogenous aggregates

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Elastic Cartilage Collage Type

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Collagen Type II

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Location of Elastic Collagen

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Visible part of ear

walls of external auditor canals

epiglottis

larynx

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Growth of Elastic Collagen

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Perichondrium (fibroblasts to fibrocytes)

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Fibrocartilage Location

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invertebral disks (act as lubricated cushions and shock absorbers)

Certain ligaments

pubic symphasis

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matrix of Fibrocartilage

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Type II and I (acidophilic)

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Growth of Fibrocartilage

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No perichondrium - mitotic division

chondrocytes occur singly in isogenous aggregate alignment

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Perichondrium

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provides nutrients to cartilage

forms interface between tissues being supported by cartilage and cartilage

-formed by superficial mesenchyme

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Cartilage formation

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Chondrogenesis: forms from embryonic mesenchyme and begins as round mesenchymal cells that retract and extend , multiple and become densely packed

Form chondroblasts and chondrocytes (divide )

Interstitial Growth

Appositional Growth

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Interstitial Growth of Cartilage

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Mitotic division of preexisting chondroblasts

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appositional growth

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differentiation of new chondroblasts from perichondrium

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Cells of Cartilage

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Chondrocytes embedded in lacunae surrounded by ECM

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Is cartilage vascularized?

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NO-difficult to repair and heal

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Fibrocartilage Histologically

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histologically consists of small chondrocytes in hyaline matrix with layers of bundled type I collagen with fibroblasts

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Function of Fibrocartilage

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tough strong support at tendon insertions and in invertebral discs and joints

replaces injured cartilage

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repair of cartilage

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slow and inefficient due in part to a vascularity and low metabolic rate

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endosteum

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CT, surrounds trabeculae around bone marrow cavity

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periosteum

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Dense CT, surrounding exterior

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Volkmann Canal

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Allows central canal of aversion system to communicate with marrow cavity and periosteum

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Bone function

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solid support for the body

protects vital organs

harbors cavities containing bone marrow (where blood cells form)

Reservoir for calcium, phosphate, and other ions

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Composition of bone

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bone matrix

Three major cells

osteocytes, osteoblasts, osteoclasts

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Osteoblast function

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synthesize and secrete organic composition of bone matrix

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Location of osteoblast

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surface of boney matrix usually side by side in layer resembling epithelium

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Histology of osteoblast

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individual lacunae

active: cuboidal columnar in shape and basophilic cytoplasm

inactive: flatten and reduced basiphilia

(bone lining cells in endosteum and periosteum)

polarized(secretes toward preexisting bone matrix

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Osteoblasts Differentiate into...

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osteocytes

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Osteocyte function

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maintain bony, calcified matrix

regulation of bone remodeling

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Osteocyte: Way of receiving Nutrients

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microvasculature in central canals via canaliculi

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Production of Osteocyte

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generated from osteoblasts

cells extend many long dendritic processes which become surrounded by calcifying matrix

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Communication of Osteocyte

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via gap junctions

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Osteocytes HIstologically

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flat, cigar shaped

less RER smaller golgi

more condensed nuclear chromatin

enclosed individually in lacunae

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Osteoclasts function

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matrix resorption during bone growth and remodeling

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Origin of Osteoclasts

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bone marrow

(monocytes in bone)

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Production

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-osteoprogenitor cells differentiate and cover surface of existing bone matrix to create osteoid

(collagen type I) secreted by osteoblast

-calcification hardens and traps osteobblasts

-differentiation into osteoclast (trapped in lacunae)

-osteoclasts reside on bony surfaces and erode matrix during remodeling

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Howship Lacunae

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osteoclasts lie within these cavities in matrix when active

-surface of cell against bone matrix is folded by cytoplasmic zone (actin filaments=adhesion matrix)

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Ruffled Border

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contact point of matrix: surface against bone matrix folded into irregular projections

-surrounded by cytoplasmic zone (rich in actin filaments)

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Periosteum

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outer layer:

dense Ct

blood vessels

collagen bundles

fibroblasts

Inner layer:

bone lining cells

osteoblasts

mesenchymal cells (osteoprogenitor)

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Sharpey fibers

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fibers penetrate the bone matrix binding the periosteum to bone

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function of periosteum

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nourish bone tissue and provide supply of osteoblasts for appositional bone growth

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Endosteum

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covers small tabeculae of bony matrix (project into marrow cavity)

thin

contains osteoprogenitor, osteoblasts, bone lining cells

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Type of bone

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compact

cancellous

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cementing line

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outer boundary of osteon, collagen rich

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Interstitial lamellae

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irregularly shaped group of lamellae

in inactive oseons

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compact bone

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lamellar bone

dense area near surface

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spongy/cancellous bone

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lamellar bone

covered by thin layer of compact bone

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lamellar bone

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compact or spongy/cancellous

mature

type I collagen-alligned in parallel successive changing lamellae

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Woven bone

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immature primary

embryo and bone repair

interlacing collagen bundles

abundant

lots of minerals

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diaphysis

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compact bon

thin region of cancellous bone on inner surface around central marrow cavity

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Type of Bones Cells

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OSteoblast

Osteoclast

Osteocytes

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osteoblast

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differentiate from osteoprgenitor cells (stem cells) and secrete primary matrix (osteoid) that allows mineralization to occur

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Osteoclast

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large cells formed by fusion of several blood monocytes which locally erode bone matrix during osteogenesis

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Osteocytes

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differentiate further from osteoblasts when enclosed in lacunae and act to maintain matrix and detect mechanical stresses

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Periostem

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layer of dense CT, outer surface of bone

bound to bone matrix by bundles of collagen type 1 fibers

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Sharpey fibers

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type 1 collagen fibers that attach periosteum to bone matrix

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Appositional Growth of Bone

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Periosteum next to bone are rich in osteprogenitor cells and osteoblasts that increases in bone thickness

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endosteum

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thin layer of active and inactive osteoblasts

lines all internal surfaces within bone

osteoclasts required for bone growth

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Long bones

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Bulbous ends=epiphyses

intervening shaft =diaphyses

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woven bone

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formed during osteogenesis or repair and has calcified matrix with random arrangement of collagen fibers

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Lamellar bone

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Soft and Cancellous/spongy

acting of osteoclasts and osteoblasts, woven bone is remodeled into lamellar bone with new matrix deposited in distinct layers with parallel Collagen bundles

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difference between woven and lamellar bone

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Woven has randomly arranged collagen

lamellar bone has organized collagen fiber in parallel form

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intramembranous Osteogenesis

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origin: CT, osteoblasts differentiate directly from progenitor cells/mesenchymal cells from perichondrium

Flat bones: skull and jaw

differentiate into osteoblasts

secretion of osteid>spicules ad trabeculae>osteocytes>fusion of spicules/trabeculae>bone

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endochondral osteogenesis

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thickening of perichondrium

bone collar formed

perichondrium->periosteum

Chondrocyte death->calcification>blood vessels grow through periosteum of diaphyses=Primary ossification center>osteogenic cells(basophilic)

osteoclasts resorb calcified cartilage>

osteblasts lay down osteoid(eosiniophilic)

Secondary ossification center: invasion of blood vessels>bone matrix on calcified cartilage

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Growing Plates 1-2

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From epiphyses to Diaphyses:

(Ryan Please Hype Calcium Orelse)

Zone of RESTING cartilage (white) : hyaline cartilage reserve

Zone of PROLIFERATING Cartilage (basophilic): proliferating chondroblasts aligned as axial aggregates in lacunae cartilage with proliferating chondroblasts (long dark stacks)

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Growing plates 3-5

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Zone of HYPERTROPHIC cartilage(less basophilic):degenerating cartilage in which aligned cells are hypertrophic and have condensed matrix (white cells not a lot of dark space)

ZOne of CALCIFIED cartilage(white) : chondrocytes disappeared matrix is undergoing calcification

Zone of Ossification (acidophilic) blood vessels and osteoblasts invade lacunae of old cartilage

=marrow cavities and osteoid for new bone