This post is tied to the post I made about plant tissues.
Animal tissues are classified into a LOT of categories and sub-categories. I am not going to do that. This will cover the general types and will not divide that particular type’s constituents into sub-types of any kind. Well then, let’s start!
Classification of Animal Tissues
Epithelium Tissue
It’s the first type of animal tissue in most classifications. It’s a layer of cells on the entire body surface and acts a barrier to separate different body systems.
It’s a continuous sheet of tightly packed cells. The cells are attached with a non-cellular basement membrane which is composed of collagen protein.
Functions
- Protection
It protects the underlying cells from adverse environmental conditions such as dryness, injury and bacteria.
- Barrier As written before, epithelium forms an effective barrier and separates different body systems.
- Exchange of Material
The permeability of epithelium tissue plays an important role in the exchange of materials between the body and the external environment.
- Absorption
The epithelial tissue of alimentary canal helps in the absorption of water and nutrients.
- Secretion
Few epithelial tissues are capable of secreting various substances like sweat, saliva, enzymes etc.
- Nerve Conduction
Some epithelial cells help in nerve transmission, like taste buds on the tongue and the receptors present in the ear.
Types of Epithelium Tissues
1. Squamous Epithelial
- It’s made up of thin layers of flat cells.
- It consists of smooth but irregular cells.
- Each cell has a spherical nucleus at the center of the cytoplasm.
Location
It forms the delicate inner lining of :
- blood vessels
- the heart
- alveoli
- lungs
- food pipe
Functions
- acts as a protective lining
- acts as a selectively permeable surface
- secretes biologically important molecules
Note : The human skin is differently developed, which shows multiple layers of epithelial cells and called stratified squamous tissue.
2. Cuboidal Epithelium
This is the only epithelium with multiple layers. It consists of cube like cells, which appear polygonal in section. These cells have spherical and centrally located located nucleus.
Location
Cuboidal epithelium forms the inner linings of :
- kidney tubules
- duct of sweat gland
- duct of salivary gland
- alveoli
and inner layers of the ovary and thyroid.
Functions
- It’s a mechanical tissue so it provides structural strength.
- Helps in absorption, exchange of materials and secretion.
3. Columinar Epithelium
It consists of pillar-like cells, these cells are tall and thin giving them this appearence. These cells have an oval nucleus located at the base of the cell. The epithelium may have striated borders containing microvilli at the free end of the cell which increases the surface area.
Location
The columinar epithelium cells are present in the lining of :
- stomach
- intestine
- gall bladder
- oviduct.
Functions
The layer of columinar cells facilitate the movement of substance across itself.
Absorption
4. Gandular Epithelium
Consists of — columinar or specialized cuboidal — cells capable of releasing substances. These cells form
the glands
in the human body. The isolated glandular cells are known as unicellular glands while a cluster of such cells are known as multicellular glands.
The glands which secrete their synthesized substances directly into the bloodstream are called endocrine glands while the glands which secrete substances by way of a duct are called exocrine glands.
Location
It’s present in glands like :
- the pancreas
- adrenal glands
- mamary gland
Functions
- The exocrine glands secrete mucus, saliva, oil, milk and other enzymes.
- The endocrine gland secretes hormones which are responsible for carrying out different, vital body functions. An example would be the pituitary gland.
5. Ciliated Epithelium
Certain cuboidal or columinar cells bear numerous hair-like structures called cillia on their surface.
Location
They are present in :
- the ovidcut
- the sperm duct
- respiratory tract
etc.
Functions
The cillia of the epithelium tissue helps in moving particles in a specific direction by moving rythmically.