1. Classify the animal tissues.
On the basis of the function they perform, animal tissues are classified into four different types. They are:
i) Epithelial tissue
ii) Connective tissue
iii) Muscular tissue
iv) Nervous tissue
2. What are epithelial tissues? What are the characteristic features of these tissues?
The covering or protective tissues in the animal body are called epithelial tissues. They also perform the functions of secretion and absorption other than protection.
i) It is the simplest tissue made up of a single layer of cells, compactly arranged without any intercellular spaces.
ii) It forms a protective covering and lines most of the organs and cavities within the body.
iii) They form a barrier to keep the different body systems separate
iv) All epithelial tissues are separated from the underlying connective tissues by an extracellular fibrous basement membrane.
v) Blood vessels are absent in epithelial tissues.
3. What are the functions of epithelial tissues?
Epithelial tissues perform the following functions:
i) Protection: they protect the underlying tissues from drying, injury, infections and from harmful chemicals. Epithelium also produces exoskeletal structures like hair, nails, hoofs, horns, scales etc
ii) Absorption: they form the lining of the intestine and absorb digested food and nutrients and water.
iii) Excretion: they form the lining of kidney tubules and help in the elimination of nitrogenous waste products.
iv) Secretion: epithelial lining of digestive glands and endocrine glands secrete useful enzymes for digestion and other biological processes in our body.
v) Respiration: epithelial cells lining the blood vessels and the alveoli in lungs allow the diffusion of gases between blood and inhaled air.
4. Describe the different types of epithelial tissues.
Based on the shape and function of the cells, the epithelial tissue is of different types. They are:
1. Simple squamous epithelium
2. Cuboidal epithelium
3. Columnar epithelium
4. Glandular epithelium
5. Ciliated epithelium
6. Stratified squamous epethelium
i) Simple squamous epithelium: it consists of an extremely thin layer of flattened cells forming a delicate lining. It lines the blood vessels, oesophagus, lining of mouth, alveoli of lungs etc. It is protective in nature. It protects the underlying tissue from drying, mechanical injury, entry of germs and chemicals.
ii) Cuboidal epithelium: is made up of cup shaped cells, more or less square shaped with a prominent nucleus in the center. It forms the lining of kidney tubules, ducts of the salivary glands, it also lines the sweat and thyroid glands. It provides mechanical strength. It also helps in secretion, absorption and excretory functions.
iii) Columnar epithelium: it consists of tall, pillar like cells with dense cytoplasm and a prominent nucleus at the base. It is present in the inner lining of the intestine, gall bladder and stomach. They perform the function of secretion and absorption.
iv) Glandular epithelium: the columnar and cuboidal epithelial cells intersperse to form the glandular epithelium. The goblet cells are cuboidal and secretory in function. They secrete mucous and certain chemicals. They are found lining the stomach, intestine, glands such as salivary glands, gastric glands. They secrete mucous to protect the inner lining of cells of the stomach.
v) Ciliated columnar epithelium: it is columnar epithelium with cytoplasmic extensions at the free end called cilia. They are found in the respiratory tract like trachea, lungs; these cilia create a wave like motion, helps in the movement of ovum in the oviduct, sperms in the spermduct, filters dust particles in the upper nasal passage, secretes mucous and helps in the removal of certain solid particles by its movement....
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