TISSUES

Tissues

Definition: the group of cells called  it has Tissue

There are large number of cells which are present in our body in the form of tissue.

Tissue can be classified into 4 types according to the size, shape & function of these cells/.

1.      EPITHELIAL TISSUE

2.      CONNECTIVE TISSUE

3.      MUSCLE TISSUE

4.      NERVOUS TISSUE.

EPITHELIAL TISSUES: these are group of tissues is found covering the body & living cavities hollow organs & tubes.

It is also found in glands.

Functions of epithelial structures:-

1.      Protection of unerling structures.

Eg: dehydration chemical & mechanical Damage

2.      Secretion:

3.      Absorption

·         Epithelical cells are very closely packed & the intercellular substance called the matrix  is minimal.

·         The cells usually lie on a basement memberane

·         Epithetical tissue classified into

·         1. Simple-A single layer of cells

·         Stratified- several layers o cells.

SIMPLE EPITHELIUM:

Simple epithelium consists of a single layer of identical cells & devided int four types.

It is usually found on absorptive (or) secretory surfaces  where the single layer enhance these proceses & not usually on surfaces subject to stress.

The types are named according to the shape of thecells & functions

The more active the tissue, the taller the celles.

SQUAMOUS (PAVEMENT) EPITHELIUM:-

This is composed of a single layer of flattend cells.

The cells  fit closely together like flat stones forming a thin & very smooth membrane.

Diffusion takes place freely through this thin, smooth living of the following structure,

Heart

Blood vessels                         

Lymph vessels                         where it is known as ENDOTHELIUM

Alveoli of the lungs.

CUBOIDAL (CUBICAL  EPITHELIUM :-

-          These are CUBE shaped cells fitting closely together lying on a basement membrance

-          It forms the kidney tubles & is found in some glands.

-          cuboidal epithelium is actively involed in secretion, absorption & excertion.

COLUMNAR EPITHELIUM:-

-          This is formed be a single layer of cells rectangular in shape on a basement membrane.

-          It is found lining the organs of the alimentary tract & consist of a mixtures of cells some absorb the product of digestion & others secrets “ MUCUS”

-          MUCUS: it is a thick sticky substance secrated by specialized columnar cells called “ goblet cells”

CILIATED EPITHELIUM:-

-          Cilia are microscopic hair like processes on the free surface of columner epithelial cells lining certain passage ways,

Eg: uterine tubes & airways where their wave- like motion propels materials one-way.

The uterine tubes the cilia propels ova towards uterus & in the respiratory passages they propel muscus towards the through.

STRATIFIED EPITHELIA :-

-          Stratified epithelia consist of several layers of cells of various shapes:

-          The supertifical layers grow up from below.

-          Basement membranes are usually absent

-          The main function of stratified epithelium is to protect underlying structures from mechanical wear & tear.

It is divided into 2 types:

-          Stratified squamous

-          Transitional epithelium.

STRATIFIED SQUAMOUS EPITHELIUM:-

-          It is composed of a number of  layer of cells of different shapes representing newly formed & mature cells.

-          In the deepest layers the cells are mainly columnar & as they grow towards the surface they become flattened & are then shed.

NON-KERATINISED STRATIFIED EPITHELIUM”

-          It is found an wet surfaces subject to wear & tear but are protected from drying.

Eg:- the conjuctives of the eyes.

The lining of the month.

The pharynx, the oesphages & the vagina.

KERATINISED STRATIFIED EPITHELIUM:-

-          This is found on dry sufaces  subject to wear and tear I,e skin hair & nails.

-          The surface layer consists of dead epithelial  cells that contain the protein  called keratin.

-          This forms a though relatively water proof  protective layer that prevents drying of the live cells undermeath.

-          The surface layer of skin is rubbed of and replaced from below.

TRANSITIONAL EPITHELIUM:-

This is composed of several layers of pear shapes cells.

It is found living the urinary bladder & allows  for  stretching as the bladder fills.

STRATIFIED COLUMNAR EPITHELIUM :

 It provides protection along portion of the respiratory tract,GIT,Reproductive tracts.