Tissue and Other Levels of Organization: Animal and Epithelial Tissues (For CBSE, ICSE, IAS, NET, NRA 2022)

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Animals are various types which perform different functions and are types as under.

Image Showing Types of Animal Tissues

Epithelial Tissue

  • Location: continuous layer over the free surfaces of many other tissues and it covers the external surfaces of the animal body and the internal surfaces of visceral organs, body cavities and blood vessels.
  • Structure: consists variously shaped cells, arranged in single or multilayered sheets, are closely packed with no intercellular space in between and arise from a non-cellular basement membrane. Epithelial cells possess the power of division and regeneration, blood vessels are absent, and the free surface of cells may be smooth or may have fine hair-like cilia, stereocilia and microvilli.
  • Function: Protects the underlying or overlying tissues from the mechanical injury, entry of germs, drying up and harmful chemicals and also help in absorption, secrete and also bear protoplasmic projections such as the Cilia.

Types of Epithelial Tissue

Types of Epithlial Tissue
Squamous EpitheliumThin, flattened and contain little cytoplasm enclosing centrally placed disc nuclei and margins of cells are tessellated (irregular)Lining of lungs alveoli, blood vessels and Bowman՚s capsule of the kidneyDiffusion of material or exchange of gases O2 and CO2
Cuboidal EpitheliumCells are cube-shaped and possess a central spherical nucleus. Cells are either pentagonal or hexagonal (polygonal)Lining of many ducts such as salivary, pancreatic and collecting ducts of the kidneySecretion, excretion and absorption
Brush-bordered cuboidal epitheliumCells of cuboidal epithelium in absorptive surfaces bear microvilli on their free ends and gives a brush like appearance to their border, so it known as this nameProximal convoluted tubules of nephronMicrovilli greatly increase the area of the free surface of the cells and thereby absorption
Ciliated cuboidal epitheliumCilia on the free surface, associated with secretory goblet cells.Parts of the nephronFlow of nephric filtrate
Ciliated EpitheliumBear numerous cilia at their free surfacesLining of the hollow organs such as ovi-ducts, ventricles of the brain, the spinal canal and the respiratory passagesTo move particles, free cells in a specific direction over the epithelial surface
Columnar epitheliumCells are tall and quite narrow, nucleus is usually located at the baseLining of stomach, intestine, and gall-bladder, also present in gastric and intestinal glandsSecretion or absorption
Ciliated Columnar EpitheliumCilia at free end. Mucus secreting goblet cells in betweenRespiratory passage (bronchioles) , oviducts and spinal canalFlow of fluids in a particular direction
Brush bordered Columnar EpitheliumMicrovilli at the free endsIntestinal mucosaIncrease surface area for nutrition
Pseudo-stratified epitheliumMade up of single layer of columnar cells, appears two layered because shorter cells have their nuclei at a different level, shorter cells lack cilia while longer cells are ciliatedLining of urinary tract, the trachea, other respiratory passages and as component of olfactory mucosaSecretes mucus which traps bacteria and particles on the epithelial surface. The ciliary beat expels the bacteria and particles in the outward direction
Image Showing Types of Epithelium

If the epithelial cells are in a single layer, they form simple epithelium. If the epithelial cells are arranged in many layers, they form compound epithelium. Compound epithelium have little role in secretion and absorption and provides protection to underlying tissues against mechanical, chemical, thermal or osmotic stresses. Compound epithelium may be stratified and transitional.

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