Exemplar Problems
Question:
Classify and describe epithelial tissue on the basis of structural modifications of cells. Epithelial cells can be classified on the basis of shape, number, and specialized structure.
Answer:
I. On the basis of cell shape, epithelial cells are of the following types:
(i). Squamous Epithelium: Cells are flat and thin, resembling scales. They are suited for rapid diffusion and filtration. Found in the lining of blood vessels (endothelium) and air sacs of the lungs (alveoli).
(ii). Cuboidal Epithelium: Cells are cube-shaped with equal dimensions. They are involved in secretion and absorption. Found in kidney tubules and various glands.
(iii). Columnar Epithelium: Cells are tall and rectangular. They are involved in absorption and secretion. Can be found in the lining of the digestive tract (intestinal lining) and respiratory tract (bronchi).
II. On the basis of the number of cells, epithelial cells are of the following types:
(i). Simple epithelium: Consists of a single layer of cells. Provides minimal protection and is involved in absorption and secretion. They are present in the lining of the alveoli, blood vessels, and intestines.
(ii). Stratified Epithelium: It consists of multiple layers of cells. It provides more protection and is found in areas subjected to mechanical stress, such as the skin (epidermis) and the lining of the mouth (oral mucosa).
III. On the basis of specialized structures:
(i). Ciliated Epithelium: Found in the respiratory tract and female reproductive tract. Cells are columnar and have hair-like projections called cilia that move in coordinated waves to move mucus and particles.
(ii). Glandular epithelium: specialized for secretion. Glands can be unicellular (goblet cells) or multicellular (exocrine and endocrine glands). Exocrine glands release substances through ducts (e.g., sweat glands), while endocrine glands release hormones directly into the bloodstream (e.g., thyroid gland).
These different types of epithelial tissue have specific functions based on their structural modifications. They provide protection, absorption, secretion, diffusion, and sensory reception, depending on their location and characteristics. Epithelial tissue is often found covering and lining body surfaces and cavities, contributing to the overall structure and function of organs.
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