Sample for our assignment/learning topic help ! Epethilial tissue

EPETHILIAL TISSUE

Epethilial tissue covers the whole surface of the body.It covers body surfaces and lines hollow organs, body cavityies and ducts.It also forms glands

An epethilial tissue consist of cells arranged in continuos sheets, in either single or multiple layers.As cells are closely packed and are held tightly together by many cell junctions, there is little intercellular space between adjacent plasma memberanes.

Epethilial tissue may be divided inti two types :

1. Covering and lining epethilium : It forms the outer covering of skin and some internal organs.It also forms the inner lining of blood vessels, ducts and body cavities, and the interior of respiratory tract, digestive tract, urinary tract and reproductive tract. Epithelial tissue that occurs on surfaces on the interior of the body is known as endothelium 
2. Glandular epethilium : It makes up the secretin portion of the glands such as thyroid gland, adrenal gland and sweat gland.

The covering and lining epethilium tissue is further classified according to two characteristics like the arrangement of cells into layers and the shapes of the cells.

According to arrangement of cells into layers :

SIMPLE EPETHILIUM : Layer of cells that functions in diffussion, osmosis, filteration, secretion, absorption.It may be:

1. Simple squamous (pavement) epithelium

Description : Single layer of flat cells, Centrally located nucleus.

Location : Lines heart, Blood vessels,Lymphatic vessels, Air sacs of lungs. Glomerular (Bowman's capsule) of kidney, Inner surface of tympanic membrane( Ear drum),

Functions : Filtration, diffussion ,Osmosis and Secretion into serous memberanes

      2.  Simple Cuboidal Epithelium

Description : Single layer of cube shaped cells, Centrally located nucleus.

Location : Covers the surface of ovary, Lines anterior surface of capsule of lens of eye, Lines kidney tubules and smaller ducts of many glands, Makes up secretion portion of thyroid gland and duct of pancreas.

Functions : Secretion and Absorption.

      3   Simple Columnar Epithelium

Description : One or more layers, Elongated and Column-shaped and Elongated nuclei  located near the base of the cells.Goblet cells (unicellular glands) are found between the columnar epithelial cells of the duodenum. They secrete mucus or slime, a lubricating substance which keeps the surface smooth. 

Location : Lining of the stomach and intestines, Specialised for sensory reception such as in the nose, ears and the taste buds of the tongue.

Functions : Secretion and Absorption.

     4. Ciliated Columnar Epithelium

Description : simple columnar epithelial cells, in addition, they posses fine hair-like outgrowths, cilia on their free surfaces.

Location : Air passages like the nose,Uterus and Fallopian tubes of females

Functions : Capable of rapid, rhythmic, wavelike beatings in a certain direction

STRAITED EPETHILIUM

  

       1.   Stratified squamous epithelium.

Description : Several layers of cells cuboidal to columnar shape in deep layers.

Location : Keratinized variety forms superficial layer of skin, nonkeratinized variety lines wet surface such as lining of mouth , eosophagus.

Function : Protection.

       2. Straitified cuboidal epethilium

Description : Two or more layers of cells in which the cells in the apical layer is in cube shaped.

Location : Ducts of adult sweat glands and esophageal glands and part of male urethera.

Function : Protection, Limited secretion and Absorption.

         3. Straitified columnar epethilium

Description : Several layers of irregularly shaped cells, only the apical layer has columnar cells.

Location : Lines part of Urethra, Large excretory ducts of some glands such as esophagus glands, small areas of anal mucous membrane, and par of the conjunctiva of the eye.

Function : Protection

     4. Transitional epethilium

Description : Appearance is variable (transitional), shape of cells in apical layer ranges from sqamous (when stretched ) to cuboidal (when relaxed).

Location : Lines urinary bladder and portions of ureters and urethra.

Function : Permts distension.

GLANDULAR EPETHILIUM

     1.Endocrine glands

Description : Secretory products (hormones) diffuse into blood after passing through interstitial fluid.

Location : Pituitary glan at base of brain, Pineal gland in brain, Thyroid and Parathyroid gland near larynx, Adrenal glands superior of kidneys.

Function : Produce hormone that regulate various body activities.

    2. Exocrine glands

Description : Secretory products released into ducts.

Location : Sweat, Oil and Earwax glands of the skin, Digestive glands such as salivary glands and pancreas.

Function : Produce substance such as Sweat , Oil earwax , Saliva and Digestive enzymes.