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What is tissue?
A tissue is a combination of similar cells performing a particular operation in a body.
There are four types of animal tissue and they are –
- Epithelial Tissue
- Connective Tissue
- Muscle Tissue
- Neural Tissue
Epithelial Tissues are flat, cuboidal or columnar in shape They spread the surface region of the body and lines the different body pits and inside organs, including the veins. A few examples are – skin layer, mouth nose lungs, stomach, etc.
The function of Epithelial Tissue
The main function of epithelial tissues are –
- Provide protection of the body from outside.
- Absorption and secretion of nutrients in the case of the intestine.
- They have sensory perception such as temperatures.
- There are four distinct classes of epithelial tissues by structure. Squamous epithelium, Stratified epithelium, and columnar epithelium
Squamous epithelium: It composed of a thin and flat cell. It also has prominent nuclei packed tightly. Example: A few examples are, – lymph and blood vessels. Lining the mouth and nasal cavities. It helps to protect from germs, harmful chemicals, and mechanical injury.
Stratified epithelium: It is made up of numbers of layers of the same or different kinds of epithelial cells. Mainly it is located at mouth and cornea.
Cuboidal epithelium: it is found in certain pieces of kidney tubules and in some glandular pipes, for example, those of salivary organs, pancreatic channel.
Columnar epithelium: It is generally found inside the surface of the stomach and intestines. It composed of cylindrical or brick-like cells that are arranged vertically to each other. The size of these cells is generally tall.
Three types of fibers strengthen and support most connective tissue, collagen, reticular and elastic. The fundamental characteristics of connective tissues are given bellow.
- It composed of the matrix, fewer cellular elements, and fibers.
- Connective tissues bind one tissue to another.
- They connect various organs.
- They help to bind and pack the organs.
- They provide support to cartilages and bones.
- They are divided into three subcategories, Connective tissue proper, Supportive connective tissue, and Fluid connective tissue
Connective tissue proper
Areolar or packing tissue: It found under the epidermis of the skin. It spread widely. Due to this tissue, the skin becomes elastic.
Adipose tissue: The main function of this tissue is to store fat. These tissues create padding beneath the skin, kidneys, and eyeballs. They work as insulation for retaining the heat of the body.
Fibrous connective tissue: It usually forms tendons that connect muscles and bone. It also creates ligaments that connect one bone to another.
Supportive connective tissue
There are two types of supportive connective tissues, one is Cartilage and another is Bone.
Cartilage: The matrix or intercellular substance is usually thick. It is nonporous. It is found at the external ears, top of the nose, trachea, etc. Cartilage is elastic and semi-transparent.
Bone: It consists of inorganic salts that make it hard and osteoblasts which is a living cell. Obviously, it is porous. A huge supply of blood vessels and nerves is present in it.
Fluid connective tissue:
Fluid connective tissue composed of two things one is blood and the other is lymph. Blood and Lymph both provide immunity to the body and transport nutrients, oxygen, carbon dioxide, etc.
Blood: The blood consists of two major things one is Plasma and the other is Lymph. Plasma is the liquid part and RBC (red blood corpuscles) WBC (white blood corpuscles) and platelets are the cellular part of blood.
Lymph: Lymph contains only white blood cells, not the red blood cells. It is essentially the blood plasma and fluid that surrounds the body cells.
- Muscle tissues are the building block of the body.
- It has special properties contraction and relaxation. That’s why the body can move.
- There are three kinds of muscles, striated, unstriated and heart or cardiac muscles.
- Made up of long fibres which have a nucleus.
- One can control these muscles by will. This means it moves only one want it to.
- It constitutes about 50 percent of the body weight.
- It founds in legs, arms, neck, etc..
- Made up of non-nucleated spindle-shaped tapering cells.
- No one can control these muscles by will.
- It found at the lining of blood vessels, urinary bladder, walls of the intestine. It helps to passage food in the intestine.
- Cardiac muscles are found only in the walls of the heart.
- They are involuntary in function.
- They do not get tired soon.
- They can contract and expand continuously without outside stimulation.
- The fibre of this muscle is striated, uninucleated and branched.
Neural Nervous Tissue
The main characteristics of neural nervous tissues are given bellow.
- They constitute the whole nervous system of a body.
- It consists of neurons that may be very long. It sometime may be about more than one meter. For an elephant, it is about 3 meters long.
- The top part consists of a nucleus and known as perikaryon or cyton.
- The rest elongated part consists of the axon and it may be very long.
- Numbers of axon creates a nerve. Nerve allows animals to sense the pain in the body. It also helps animals to make a response.
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