Session3 Dr. Maria Zahiri - PowerPoint Presentation

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Session3

Dr. Maria Zahiri

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Lecture outline

Overview ( special connective tissue)

Cartilage:

morphology

Type

Histogenesis

Bone:

morphology

Type

Histogenesis

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Cartilage

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Cartilage

:

is a flexible connective tissue in animals, including the joints between bones, the rib cage, the ear, the nose,

the bronchial

tubes and the intervertebral discs. 

 It is not as hard and rigid as bone, but it is stiffer and less flexible than 

muscle.

Important for:

- support to softer tissues

- formation and growth of long bones

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Because of its rigidity, cartilage often serves the purpose of

holding

tubes open in an animal's body

.

Example:

 rings of the trachea, such as the cricoid cartilage and 

carina

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cartilage

Consists of:

Cells

ECM

-

collagen and/or elastin fibers

- proteoglycans

- water

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Cells:

CHONDROBLAST

Progenitor of chondrocytes

Lines border between

perichondrium

and matrix

Secretes type II collagen and other ECM components

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Chondrocytes

 Chondrocytes are

chondroblasts

which are surrounded by matrix and are quiescent

They

produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans

.

Mature cartilage cell

Reside in a space called the

lacuna

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ECM:

Collagen provides tensile strength and durability

papain

For example, if you inject

papain

(an enzyme that digests the protein cores of

proteoglycans

) into the ears of a rabbit, after a few hours the ears will loose their stiffness and droop.

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The combined properties of collagens and

aggrecan in articular cartilage

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More Features of Cartilage

Cartilage is an

avascular

tissue and relies on diffusion of nutrients and waste through the matrix

The vasculature located in adjacent

perichondrium

and in absence of

perichondrium

, synovial fluid

nurishes

the cartilage

Cartilage has no

innervation

, and no lymphatic vessels

Chondrocytes

have low metabolic activity

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Perichondrium

Perichondrium

is a vascular sheath of dense irregular connective tissue surrounding cartilage

(type I collagen)

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perichondrium

perichondrium has

2 layer:

inner

cellular layer

outer

fibrous layer

The cellular layer of the perichondrium contains

chondrogenic

cells that undergo division and differentiate into

chondroblasts

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In embryo it serves as skeleton until replacement by bones, and form template for many bones

It is also exist in epiphyseal plate, nose, bronchi, ends of ribs adjacent to sternum

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More Features of

hyallin

Cartilage

Cells:

Outer chondrocytes are elliptical with long axis parallel to surface

Deeper ones are round, may be in groups of up to 8 -

isogenous

group

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Isogenous

groups of

chondrocytes

:

are the result of mitotic divisions of the cells during interstitial growth, several

chondrocytes

occupy a single

lacuna

.

In

epiphyseal

plate

chondrocytes

located in rows

They are often shrunken in histological sections

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Amorphous ground substance

Territorial matrix:

adjacent to

chondrocytes

stains darker than non-territorial matrix, because

matrix around lacuna is poor in collagen but rich in

chondroitin

sulfate

Interterritorial

matrix:

which is the bulk of cartilage is richer in type II collage

Pericellular

capsule:

just around the lacuna is made of fine meshwork of collagen fibers and basal lamina like substances which protects the

chondrocytes

from mechanical stress

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Matrix of Hyaline Cartilage

Fiber:

collagen type II



, IX, X, and XI

Proteoglycan

:

Aggrecan

GAGs of

Aggrecan

is

chondroitin

4-sulfate,

chondroitin

6-sulfate, and

heparan

sulfate

Glycoprotein:

Chondronectin

water

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Cartilage Growth

Interstitial growth:

Existing

chondrocytes

Isogenous

groups

(enlarging cartilage from within)

Appositional growth:

Chondrogenic

cells new

chondroblasts

(from inner layer of

perichondrium

)

(That adding matrix to periphery of cartilage)

mitotic division

differentiation

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More Features of Elastic Cartilage

It is similar to hyaline cartilage, but with many branching elastic fibers

Yellow in

colour

Chondrocytes

are more abundant and larger but matrix is less than hyaline cartilage

Perichondrium

is also rich in elastic fibers

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Fibrocartilage

Usually merges with adjacent dense connective tissue

Chondrocytes

in rows or groups with thick bundles of collagen between them

matrix is scant (rich in

chondroitin

and

dermatan

sulfate), and exhibit bundles of type I collagen which stain acidophilic

It has no

perichondrium

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Intervertebral

Disks

It is located between vertebrae

Each disk has two components;

Nucleus

pulposus

and Annulus

fibrosus

)

Nucleus

pulposus

:

is a gel-like matrix rich in

hyaluronic

acid and cells

Annulus

fibrosus

:

is made of

fibrocartilage

in overlapping layers

Herniation

: results from rupture of annulus

fibrosus

and expulsion of nucleus

pulposus

which can compress spinal cord or nerves

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Bone

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Bone is a specialized connective tissue of:

calcified bone matrix

3 cell types:

Osteocytes

that are located in lacunae

Osteoblasts

that make new matrix and maintain old matrix

Osteoclasts

are multinucleated giant cells that

phagocytose

bone matrix in remodeling bone

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Osteoblasts

Synthesize and maintain matrix (collagen,

proteoglycans

, and

glycoproteins

)

bone forming cells

typically rounded or

cuboidal

in shape

Osteoblasts

are basophilic as a result of abundance of rough endoplasmic reticulum

Become

osteocyte

when surrounded by matrix

Osteoid

is newly made

uncalcified

matrix that separates

osteoblasts

and

osteocytes

from the calcified matrix

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Osteocyte

mature bone cells

are connect to other

osteocytes

by long processes via gap junctions

Narrow

canaliculi

house

cytoplasmic

processes of

osteocytes

Canaliculi

also contain extracellular fluid that carrying nutrients and metabolites

Osteocytes

maintain bone matrix

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Osteocyte

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Osteoclasts

Large, multinucleated, and motile cells

responsible for

resorbing

bone

Their precursor located in bone marrow in common with

monocytes

Acidophilic cytoplasm, many

lysosomes

, many mitochondria

Secrete organic acids,

collagenase

and other proteases that break down the matrix

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Osteoclasts

They occupy shallow depressions that is called

resorption

bay

(

Howship’s

lacunae)

ruffled membrane:

The region of the

osteoclastic

cytoplasm adjacent to the bone matrix which is being resorbed

This is an area of numerous microvilli closely applied to the bone that is being hydrolyzed by the enzymes secreted by the osteoclast

CO2+H2O

H2CO3

H

⁺

+ HCO3

⁻

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Bone Matrix

Inorganic part

calcium and phosphate (

Hydroxy

apatite crystals [Ca10(Po4)6(OH)2])

Organic part

Fiber

: type I collagen bundles

Glycoproteins

: (

Osteonectin

,

osteopontin

)

Proteoglycans

:

keratan

sulfate and

chondroitin

sulfate bind to

hyaluronic

acid and form

aggrecan

composites

Bone

sialoprotein

is another matrix protein that has binding site for

integrins

of bone cells and matrix components

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Periosteum

dense irregular connective tissue that covers outer surface of bone

Sharpey’s

fiber

inserting

periosteum

to the bone

Outer fibrous layer:

contains collagen bundles and fibroblasts of

periosteum

,

distribute blood vessels and nerves to bone

Inner cellular layer:

has

osteoprogenitor

cells and

osteoblasts

Osteoprogenitor

cells can form new

osteoblasts

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Endosteum

lines all internal bone surfaces

It is a

specialised

thin connective tissue composed a single layer of

osteoblasts

,

osteoclasts

, and

osteoprogenitor

cells

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Types of Bone

There is two different kind of mature bone

Compact bone (no cavities)

Cancellous

(spongy bone)

Long bones

have ends (epiphyses) of spongy bone covered by a thin layer of compact bone;

shaft (

diaphysis

) is mostly compact bone with small amount of spongy bone around marrow cavity

Short bones

have core of spongy bone surrounded by compact bone

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Spongy bone

Spongy bone is composed of branching bone

trabeculae

and

spicules

Spongy bone is lamellar but there is not any

haversian

system

It is extended from inner circumferential system of compact bone into marrow cavity

Lamellae are arranged in irregular manner

Spaces between lamellae contain bone marrow

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bone marrow

Red bone marrow:

where active

hemopoiesis

is taking place

contains stem cells

Yellow bone marrow:

is inactive in

hemopoiesis

but acts as a reserve tissue

It contains many

unilocular

adipocytes

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