Every cell in our body has a specific function. Similar cells form tissues, which are classified based on their structure and function. The human body has four main types of tissues: epithelial, connective, neural, and muscular.
What is Epithelial Tissue?
Epithelial tissue, or epithelium, forms the outer layer of the skin and lines body cavities. It covers the respiratory, digestive, reproductive, and excretory tracts and performs various functions such as absorption, protection, sensation, and secretion.
Structure of Epithelial Tissue
Epithelial tissue is a tightly packed layer of cells. One surface is exposed to the environment or body fluids, while the other is attached to tissue by a membrane made of fibers and polysaccharides. There is little space between cells, and specialized junctions connect them:
- Tight junctions: Prevent leakage
- Adhering junctions: Keep tissues together
- Gap junctions: Allow movement of ions and molecules
Epithelial cells form membranes consisting of epithelial and underlying connective tissue:
- Mucous membrane (mucosa): Contains goblet cells that secrete mucus for lubrication, protection, and movement. It lines cavities like the respiratory and digestive tracts.
- Serous membrane: Lines body cavities not opening outside, like the pleural cavity. Made of simple squamous epithelium, it secretes fluid inside the cavity.
Functions of Epithelial Tissue
- Protection: Acts as a barrier against injury, chemicals, fluid loss, and infections. Cilia trap dust particles in the respiratory tract.
- Absorption: Absorbs water and nutrients in the digestive tract.
- Exchange of substances: Regulates exchange between the body and external environment, and between internal body parts.
- Sensation: Contains sensory receptors in the nose, eyes, ears, and taste buds.
- Secretion: Glands secrete hormones, enzymes, saliva, mucus, and sweat.
Types of Epithelial Tissue
Epithelial cells differ in shape and function:
- Squamous Epithelium: Thin and flat cells.
- Cuboidal Epithelium: Short cylindrical cells appearing hexagonal in cross-section.
- Columnar Epithelium: Long cylindrical cells with nuclei at the base.
Epithelial tissue is also categorized by the number of cell layers:
- Simple Epithelium: Single layer, mainly for secretion or absorption.
- Compound (Stratified) Epithelium: Multiple layers, mainly for protection.
Glandular Epithelium
Specialized for secretion, made of cuboidal or columnar cells:
- Unicellular: Isolated glandular cells like goblet cells.
- Multicellular: Cluster of cells like salivary glands.
Ciliated epithelium, with cilia, helps move mucus in directions, found in places like fallopian tubes and bronchioles.
FAQs
Ciliated epithelium, with hair-like cilia, helps move mucus and other substances in specific directions, found in respiratory and reproductive tracts.
Glandular epithelial cells are specialized for secretion. They can be unicellular (single cells like goblet cells) or multicellular (clusters like salivary glands).
Mucous membranes line cavities opening outside and secrete mucus for protection and lubrication. Serous membranes line cavities not opening outside and secrete fluid to reduce friction.
Epithelial cells include squamous (thin and flat), cuboidal (short and cylindrical), and columnar (long and cylindrical). They can form simple (single layer) or compound (multiple layers) epithelium.
Epithelial tissue consists of tightly packed cells with specialized junctions, forming a continuous layer. One surface is exposed, and the other is attached to underlying tissue.
Epithelial tissue protects against injury and infection, absorbs nutrients and water, regulates substance exchange, senses stimuli, and secretes hormones and enzymes.
Epithelial tissue forms the outer layer of the skin and lines body cavities, covering organs and structures. It protects, absorbs, senses, and secretes.
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