- The covering or protective tissue in animal body are epithelial tissue, covering most organs and cavities it forms a barrier to keep different body systems separate.
- The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are made up of epithelial tissue.
- Cells of epithelial tissue are tightly packed and form a continuous sheet having small amount of cementing material between them and almost no inter-cellular spaces.
- All epithelium are separated from the underlying tissue by an extracellular fibrous basement membrane.
Epithelial tissue Classification
i) Squamous epithelial tissue
- Squamous epithelial tissue consists of a layer of thin flat cells.
- It is present in the linings of blood vessels, lungs, mouth, oesophagus etc.
- The skin has several layers of epithelial cells. This tissue is called Stratified squamous tissue.
ii) Columnar epithelial tissue :-
- Columnar epithelial tissue consists of tall pillar like cells.
- It is present in the walls of the intestine.
- The columnar epithelial tissue in the respiratory tract has hair like projections called cilia.
- This tissue is called Ciliated columnar epithelial tissue.
iii) Cuboidal epithelial tissue :-
- Cuboidal epithelial tissue consists of cone shape cells having a basement membrane.
- It forms the lining of kidney, tubules and ducts of salivary glands and provide mechanical support.
iv) Glandular epithelial tissue :-
- Sometimes epithelial tissue folds inwards and forms a multicellular gland which secretes substances.
- This tissue is called Glandular epithelial tissue.
- The cells of a connective tissue are loosely packed and embedded in inter cellular matrix, this matrix may be jelly like, fluid, dense or rigid.
- Blood is a type of connective tissue.
i) Blood :-
- Blood contains a fluid matrix called plasma which contains red blood cells (RBC), white blood cells (WBC) and platelets.
- The blood transports gases, digested food, hormones, waste materials etc.
ii) Bone :-
- Bone is a hard and strong tissue
- It consists of cells which are embedded in a hard matrix containing calcium and phosphorus compounds.
- Bone forms the framework of the body and supports the body and the main organs.
iii) Ligaments :-
- Ligaments are flexible tissues which joins bones together and helps in movements.
iv) Tendons :-
- Tendons are fibrous tissues which joins muscles to bones and helps in movements.
v) Areolar tissues :-
- It fills the space between skin and muscles, inside the organs, around blood vessels etc.
- It helps to repair the tissues.
vi) Adipose tissue :-
- Adipose Tissue is found below the skin and between internal organs.
- It contains fats and helps to store fats.
- Muscular tissue contains elongated cells are called muscle fibres and is responsible for movement in our body.
- Muscular tissue contains special proteins called contractile proteins which can contract and relax.
- Muscles that move by our conscious will are called voluntary muscles for example muscles present in our limbs and are also called skeletal muscles .
- Muscles which do not move under our will are called involuntary muscles.
i) Striated muscles :-
- Striated muscles are voluntary muscles having light and dark striations.
- The cells are long, cylindrical and are multinucleated.
- They are also called skeletal muscles because they are attached to bones.
- They help in voluntary movements of the body.
ii) Unstriated muscles ( Smooth muscles) :-
- Unstriated muscles are involuntary muscles having no striations.
- The cells are long and spindle shaped and are uninucleated.
- They are present in alimentary canal, blood vessels, bronchi of lungs, iris of eye etc.
- They help in involuntary movements.
iii) Cardiac muscles :-
- Cardiac muscles are involuntary muscles having faint striations.
- The cells are long, cylindrical, branched and multinucleated.
- They are present in the heart and helps in the contraction and relaxation of the heart.
- Nervous tissue is highly specialized for responding and transmitting stimulus very rapidly.
- Nervous tissue have cells called neurons containing a cell body with a nucleus and cytoplasm
- Each neuron has single long part called axon and many short branched part called dendrites.
- The combination of functions of nerves and muscle tissue is fundamental to animals.