10. Animal Tissue - part 01 - Simple epithelial tissue

 

10. Animal Tissue - part 01 - Simple epithelial tissue


Introduction :
  • A group of cells having same embryonic origin, structure and function. 
  • Various tissues combine together in an orderly manner to form large functional unit called organs. 
  • These organs combine together and form organ-system. 
  • The cells are of two typess - 
  1. somatic cells and 
  2. germ cells. 
somatic cells :
  • The word somatic is derived from the Greek word 'soma' means 'body'. 
  • All body cells of an organism except sperm and ova are somatic cells. 
germ cells
  • The sperm and ova are germ cells. 
  • They belong to reproductive system.


Cells → Tissues → Organs → Organ systems →Body

Histology : 

  • The study of the structure coelom, etc. and arrangement of tissue is called histology.
  • There are four types of tissues present in animals namely -  
  1. epithelial
  2. connective
  3. muscular and
  4. nervous. 


know the scientists

  • Marie Francois Xavier Bichat (1771- 1802), French anatomist and pathologist discovered tissue. He was known as ‘Father of Histology’.


Epithelial tissue (epi : above, thelium : layer of cells)

  • Epithelial tissue forms a covering on inner and outer surface of body and organs.
  • Cells are compactly arranged with little intercellular matrix. 
  • Cells rest on non-cellular basement membrane.
  • Cells are polygonal, cuboidal or columnar in shape. 
  • Single nucleus is present at the centre or at the base. 
  • This tissue is avascular. 
  • Has good capacity of regeneration.
  • Major function is protection and it also helps in absorption, transport, filtration and secretion.

Classfication of Epithelial tissue :

  1. Simple epithelium and 
  2. Compound epithelium.

Simple epithelium is made up of single layer of cells.
Compound epithelium is made up of two or more layers of cells. Lowermost layer lies on basement membrane.


A. Simple epithelial tissue :

1. Squamous epithelial tissue : 


  • Cells of this tissue are flat, thin, polygonal with serrated margin. 
  • Cells of this tissue fit together like tiles of footpath. Hence it is called pavement epithelium. 
  • Prominent spherical or oval nucleus is present at the centre of the cell. 
Function : Protection, absorption, transport, filtration, secretion. 

  • It is found in blood vessels, alveoli, coelom, etc.



2. Cuboidal epithelial tissue : 


  • In this tissue, the cells are cuboidal in shape with a spherical nucleus at the centre. 
Function :  Absorption, secretion. 

  • It is found in lining of pancreatic duct, salivary duct, proximal and distal convoluted tubules of nephron.


3. Columnar epithelium : 


  • Columnar epithelial cells are tall, pillar like. 
  • Inner ends of the cells are narrow while free ends are broad and flat.
  • Free surface shows large number of microvilli.
  • Nucleus is oval and is present in the lower half of the cell. 
Function :  Secretion, absorption.

  • It is found in inner lining of intestine, gall bladder, gastric glands, intestinal glands, etc.



4. Ciliated epithelium : 


  • Cells of this tissue are cuboidal or columnar. 
  • Free ends of cells are broad while narrow ends rest on a basement membrane. 
  • Free ends show hair like cilia.
  • Nucleus is oval and placed at basal end of cell.

Function : To create a movement of materials in contact in a specific direction and thus able to prevent entry of foreign particles in the trachea, push the ovum through oviduct.

  • It is found in inner lining of buccal cavity of frog, nasal cavity, trachea, oviduct of vertebrates, etc.



5. Glandular epithelium : 


  • Here, the cells may be columnar, cuboidal or pyramidal in shape.
  • Nucleus is large and situated towards the base. 
  • Secretory granules are present in the cytoplasm.
  • The glands may be unicellular (globlet cells of intestine) or multicellular (salivary gland) depending on the number of cells.
  • Depending on mode of secretion, multicellular glands can be classified as - 
  1. duct bearing glands (exocrine glands) 
  2. and ductless glands (endocrine glands).
Exocrine glands -
  • pour their secretions at a specific sites e.g. Salivary gland, sweat glands etc. 
Endocrine glands 
  • release their secretions directly into blood stream. e.g. thyroid gland, pituitary gland, etc. 
Function : 
  • Secrete the musus that trap the dust particles, lubricates the inner surface of respiratory and digestive tracts, secretion of enzymes and hormones.


6. Sensory epithelial tissue : 


  • It is composed of modified form of columnar cells and elongated neurosensory cells. 
  • Sensory hairs are present at the free end of the cell. 
Function : It perceive external as well as internal stimuli.

  • These are found in nose (Olfactory) Ear (Auditory hair cells) Eye (photoreceptors).



7. Germinal epithelial tissue : 

  • Cells of this epithelium divide meiotically to produce haploid gamets. 
  • Ex. : Lining of seminiferous tubules, inner lining of ovary.

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