L8: Cartilage and Bone

HISTOPATHOLOGY I

HIS 1213

Types of cartilage

Types of boneTypes of bone

Cartilage

Cartilage is

a form of connective tissue composed of cells

called chrondrocytes and a highly specialized called chrondrocytes and a highly specialized

extra-cellular matrix.

Cartilage is an avascular tissue.

More than 95% of cartilage volume consists of

extracellular matrix.

Extracellular matrix is the functional element

of this tissue which is deposited by

chrondoblast.chrondoblast.

Eventually, the chondroblasts become

enclosed in spaces called lacunae (termed as

chondrocytes)

Major component of extracellular matrix:

proteoglycan (aggrecan)

Collagen molecules

multiadhesive glycoproteins multiadhesive glycoproteins

The extracellular matrix is solid firm and well

adapted to bear weight.

There are no vascular network within

cartilage (avascular), hence, extracellular

matrix is crucial to the survival of the

chrondrocytes.chrondrocytes.

Generally, there are three types of cartilage.

They differ in characteristic, appearance,

mechanical properties and are

distinguishable:

1. Hyaline cartilage

Matrix containing type II collagen fibers,

GAGs, proteoglycans, and multi-adhesive

glycoproteins.

Hyaline cartilage is an elastic, compressible

tissue located at the ends of bones and in

the nose.

C-shaped rings of hyaline cartilage keep

open the air passages of the respiratory

system (trachea, bronchi and larger

bronchiolesbronchioles

It also forms the skeleton of cartilaginous

fish (eg: sharks) and forms the embryonic

skeleton in bony vetebrates.

2. Elastic cartilage

characterized by elastic fibers and elastic

lamellae in addition to the material of

hyaline cartilage.

Elastic fibre is a dense network of

branching and anastomosing

The elastic material gives the elastic

properties to the elastic cartilage.

They confer greater elasticity and

flexibility than is found in hyaline cartilageflexibility than is found in hyaline cartilage

Besides, elastic fibres also permit tissue to

recover its shape quickly after distortion.

Eg: external ear, epiglottis.

3. Fibrocartilage

characterized by abundant type I collagen

fibers in addition to the matrix material of

hyaline cartilage.

This provides greater tensile strength than

hyaline cartilage and small degree of hyaline cartilage and small degree of

flexibility.

Note: Tensile strength is the maximum stress a

material subjected to a stretching load

can withstand without tearing.

Fibrous cartilage is located as discs

between vertebrae (intervertebral discs)

where it provides a cushioning effect.

It is also found in the symphysis pubis and

ligamentous capsules surrounding joints.ligamentous capsules surrounding joints.

Note : Symphysis pubis is the region between

two pubic bones of the pelvis

Perichondrium

It is a dense connective tissue.

Resemble capsule that surrounds glands

and many organs.

Was thought to serve as the source of new

chondroblast.chondroblast.

Versican

A proteoglycan monomer secreted by

fibroblast.

Fibroblast

Cell that produces fibre

Versican

A proteoglycan monomer secreted by

fibroblast.

Bone

Bone is the most abundant of all animal

skeletal materials, and provides support,

protection and some metabolic functions.

A bone consist of: A bone consist of:

Bone tissues Nerves

Connective tissues Blood vessels

Fat tissue

Calcium and phosphate stored in the bone can

be released into the blood (as needed), under

the influence of:

Parathormone (Parathyroid hormone)

Calcitonin

Base on the shape , bones can be classified

into four groups:

1. Long bones

(eg: tibia, femur, ulna, radius, humerus)

2. Short bones 2. Short bones

(eg: carpal bones, patella)

3. Flat bones

(eg: sternum, skull cap)

4. Irregular bones

(eg: vertebra)

If a bone is cut, two distinct structural

arrangement of bone tissue can be recognize:

Compact bone

(a compact, dense layer forms the outside

of the bone)of the bone)

Spongy bone

(a spongelike meshwork consisting of

trabeculae forms the interior of the bone)

COMPACT / DENSE BONE

Involved in the growth of long bones.

A transverse section of compact bone shows it

consist of numerous cylinders, each

surrounding a central Haversian canal.

One such cylinder plus its canal is termed a

Haversian system or osteon.

Each cylinder itself made up of a set of

concentric layers called lamellae which are

cylindrical.cylindrical.

Such arrangement of lamellae increases the

strength.

Between lamellae are numerous lacunae

(space).

Lacunae contains living bone cells called

osteoblast, which is capable of bone

deposition / making bone.

The cells are embedded in a firm, calcified The cells are embedded in a firm, calcified

matrix.

The matrix consist of 30% of organic material

(collagen) and 70% of inorganic bone salt

(hydropoxyapatite, sodium, magneisum, etc)

The combination of organic with inorganic

material produces a structure of great

strength.

As the osteoblasts mature, they are known

osteocytes.osteocytes.

Radiating from each lacuna are many fine

channels called canaliculi.

Canaliculi link up

Haversian canal

With other lacunae

Pass from one lamella to another

Such structure allows the passage of:

Nutrients

Respiratory gases

Metabolic waste

Covering the compact bone is a layer of dense

connective tissue called periosteum.

The inner region of periosteum has blood

vessels and forms a layer which contains cells

that can develop into osteoblasts.that can develop into osteoblasts.

SPONGY BONE

Consists of a meshwork of thin,

interconnecting bony struts called trabeculae.

Its matrix contaians less inorganic material

(60-65%) than compact bone.(60-65%) than compact bone.

The organic material is primarily composed of

collagen fibres.

The spaces between the trabeculae are filled

with soft marrow tissue.

The trabeculae are oriented in the direction in

which bone is stressed.

This enables the bone to withstand tension

and compression forces effectively.and compression forces effectively.