Animal Tissues
Breathing is one of the most vital activity for humans. When we breathe, we can, in fact, feel the movement of our lungs and diaphragm. For breathing, we have specialized cells in our bodies, called muscle cells. The contraction and relaxation of these muscle cells result in movement.
During breathing we inhale oxygen and it goes to our two lungs and then it transported to all cells of our body through the blood. Mitochondria present in each and every cell of our body, utilises oxygen to generate energy in the form of ATP molecules. These ATP molecules provide energy for all sorts of activities performed by our body cells.
Blood is a fluid connective tissue. It flows and connect different parts of body. It carries oxygen and food to all cells and in return collects metabolic wastes (e.g., carbon dioxide) from them.
Blood and muscles are both examples of tissues found in our body. On the basis of the functions they perform in the body of multicellular animals, the animal tissues are classified as 1. Epithelial tissue 2. Muscle or muscular tissue 3. Connective tissue 4. Nervous tissue.
- Epithelial Tissue:-Epithelial tissue is the simplest tissue. It is a protective tissue of the animal body. The cells of this tissue are tightly packed and they form a continuous sheet. Cells of epithelial contain very little or no intercellular matrix. The tissues covers most organs and cavities within the body. It also forms barrier to keep different body systems separate. The skin and lining of buccal cavity, blood vessels, alveoli and kidneys tubules are made of epithelial tissue. Epithelial cells lie on a delicate non-cellular basement membrane which contains a special form of matrix protein, called collagen.
Functions of Epithelial tissue:-
- The cells of the body surface form the outer layer skin. These protect the underlying cells from drying, injury, and chemical effects. They also protect the body from viral or bacterial infection.
- Inside the body, epithelial cells form lining of mouth and alimentary canal and protect these organs.
- Epithelial tissues help in absorption of water and nutrients.
- Epithelial tissues help in elimination of waste products.
- Some epithelial tissues perform secretory function. They secrete a variety of substances such as sweat, saliva, enzymes, etc.
There are four types of epithelial tissue:-
- Squamous epithelial
- Cuboidal epithelial
- Columnar epithelial
- Glandular epithelial
- Ciliated epithelial
- Squamous epithelial:- Squamous epithelial cells are extremely thin and flat and form a delicate lining. The oesophagus and the lining of the mouth are also covered with squamous epithelium. The skin, which protects the body, is also made of squamous epithelium.
- Cuboidal epithelial:- It consists of cube-like cells which are square in section but the free surface appear hexagonal. It is found in kidney tubules, thyroid vesicles and in glands (e.g., salivary glands, sweat glands and exocrine pancreas). It forms germinal epithelium of gonads (tastes and ovaries). It helps in absorption, excretion and secretion. It also provides mechanical support.
- Columnar epithelial:- The columnar epithelial consists of cells which are taller than broader (i.e., pillar-like). The nuclei are towards the base and sometimes the free ends of cells have a brush border containing microvilli. It forms the lining of stomach, small intestine and colon, forming mucous membrane. It also forms lining of gall bladder and oviducts and facilitates movement across the cells. Its main functions include absorption (e.g., stomach, intestine ) and secretion (e.g., mucus by goblet cells or mucus membrane).
- Glandular epithelial:- The columnar epithelial is often modified to form glands which secrete chemicals.
- Ciliated epithelial:-Ciliated cuboidal epithelial is found in the sperm ducts. The ciliated columnar epithelium lines the trachea (wind-pipe), bronchi (lungs), kidney tubules and oviducts (Fallopian tubes). The rhythmic, concerted beating of the cilia moves solid particles (e.g., mucus) in one direction through the ducts.
