4 Types of Tissues in Human Body and its Functions
Human body has 4 different types of tissues.
A “tissue” in simple terms is a bunch of cells.
They are formed by a combination of similar cells so as to have same physiological function in body.
Specific type of tissue has the same function in almost all of the higher animals.
These tissues together form the organs in the body.
They serve many purposes in the body and are differentiated to carry out special physiological functions.
Based on their physical structure and function, tissues of the body are differentiated as
Types of tissues
- Epithelial tissue
- Connective tissue
- Muscular tissue
- Nervous tissue.
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Epithelial tissue: This tissue is an upper most tissue covering all the organs or body. This tissue based on need is of different types as simple epithelium, squamous epithelium, columnar epithelium etc.
This is further classified as
- Simple epithelium
- Stratified epithelium.
Simple epithelium is one which has a single layer of epithelial cells. It is present at sites where filtration or diffusion of substances is necessary. It is found in the nephron of kidney for filtration of blood, for diffusion of oxygen from lungs to blood. This type of single layer of epithelium is so thin and offers least resistance for transfer of molecules from one side to another.
Based on the shape of cells in this layer, it is further differentiated as simple squamous epithelium, simple cuboidal epithelium and simple columnar epithelium.
Stratified epithelium is a multi layered epithelium. This is differentiated based on the upper most layer and also the shape of cells in bottom layers.
The upper layer cells might be keratinised, dehydrated to protect from heat, microbes, wear and tear, chemicals etc. This type of layer is seen in skin.
In most other types of stratified epithelium, the upper layer is non-keratinised.
Based on the shape of lower layer cells, the epithelium is again differentiated as stratified squamous epithelium, stratified cuboidal epithelium, columnar stratified epithelium and psuedostratified columnar epithelium.
There is another type called transitional epithelium. This type of tissue is present in urinary bladder. The Cells are cuboidal or columnar in relaxed state. But when there is load, they stretch and become flat to accommodate the substance (urine).
There is one more type of epithelium i.e. is glandular epithelium which are present in glands.
Types of simple epithelium tissues:
- Simple squamous epithelium: As the name indicates, this is a single layer of squamous shaped epithelium cells.
2. Simple cuboidal epithelium has single layer of cuboid shaped cells.
3. Simple columnar epithelium has single layer of long column shaped cells
Types of Stratified epithelium tissues:
1. Stratified squamous epithelium: This has squamous shaped cells arranged in multiple layers.
2. Stratified cuboidal epithelium has cuboidal cells in multiple layers
3. Stratified columnar epithelium with column shaped cells in layers
4. Psuedo-stratified columnar epithelium: Single layer of columnar shaped cells arranged in such a way to give false impression of multiplayer.
Connective tissue: This tissues as the name indicates, is in connecting position in between tissues. This is many types like adipose tissues, reticular tissue etc.
This connective tissue is divided as
- Loose connective tissue. (Areolar tissue, adipose tissue)
- Dense connective tissue.
- Cartilage tissue
- Bone tissue
- Liquid connective tissue (examples of tissue is blood, W.B.C’s, lymph)
The connective tissue has different types of cells supporting specialized tissue. These cells include fibroblasts, fat cells, mast cells and also white blood cells like the macrophages, plasma cells etc.
Loose areolar connective tissue: It is widely distributed connective tissue. It is made of fibroblasts, mast cells, macrophages and fat cells. It provides elasticity and tensile strength to almost all the parts of the body. It supports and also connects other tissues like below the skin, between the muscles in the digestive tract etc.
Adipose tissue: This tissue consists of fat cells, fat globules in the matrix of areolar tissue. This tissue is of two types as
a) White adipose tissue
b) Brown adipose tissue
White adipose tissue makes upto 25% of body weight in healthy adults. It acts as thermal insulator and also energy store.
Brown adipose tissue is found in newborns and in very small amounts in adults. When metabolized, it produces more heat than the other fat.
Lymphoid tissue: This tissue is found in lymph nodes and organs of the lymphatic system. It is semisoild in nature and consists of reticular cells, monocytes and lymphocytes.
Dense connective tissue: Unlike the loose connective tissue, this has more of fibers and less number of cells. This is further differentiated as
a) Fibrous tissue
b) Elastic tissue
Cartilage: It is harder and stronger than prior tissue types. It is made up of cells called chondrocytes which are embedded in a matrix of collagen and elastic fibers. This cartilage is of three types as
a) Hyaline cartilage
b) Elastic cartilage
Bone tissue: This is formed by osteocytes (bone cells) along wth collagen fibersm inorganic salts like phosphate and calcium.
Muscular tissue: As the name indicates, this tissues makes muscles of the body. This tissue is of 3 types as
a) Skeletal muscle tissue
b) Cardiac tissue
C) Smooth muscle tissue
Striated muscles: This tissue is present attached to the body skeletal system, especially long bones. They also have bands or striation along the length. They are voluntary i.e. they are under the control of our will. They help in movement from one place to another.
Cardiac muscles: As the name indicates, these are present in the heart. They like skeletal muscles have striations in them. But the difference is, they have branches. This muscle helps to pump blood by the heart.
Smooth muscles are spindle or cone shaped in structure. They help in contraction and relaxation of man organs like lungs, stomach, uterus etc.
They help in movement, contraction and other physiological activities. They are involuntary in nature. They are controlled by brain.
Nervous tissue: This tissue is mostly present in the entire nervous system including brain and spinal cord. It has two types of tissue as nervous cell and neuroglia.
The nerve cells are the longest cells in the body. They can be up to few meters. They transmit impulses from brain to other body parts and vice-verse. This tissue controls the whole body by conduction of impulses across the body. The tissue operates by use of bio-molecular chemical substances called as neurotransmitters.
Neuroglial tissue is a binding tissue around the neurons. It helps to protect the nerve cell from damage. Unlike other cells, these cells does not multiply. They are formed during birth and last till death. If there is any damage to them in between, it can lead to loss of their function for ever.
Reference: Principles of Anatomy and Physiology.