In the human body, tissues are groups of similar cells working together to perform specific functions. Every organ, bone, and muscle is made up of one or more of these tissues. Based on the structure and function of their cells, human tissues are classified into four main types:
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nervous tissue
1. Epithelial Tissue:
Epithelial tissue covers and protects the entire body, both inside and out. It forms the skin and the inner lining of organs like the stomach and intestines.
Functions of epithelial tissue:
- Rapid healing after injury (skin repair)
- Absorption of nutrients
- Secretion of hormones and enzymes
- Formation of sweat and saliva
Types of Epithelial Tissue:
Epithelial tissues are of two main types — Simple and Stratified.
A. Simple Epithelium
Made of a single layer of cells:
- Squamous Epithelium: Flat cells allowing diffusion; found in lungs, blood vessels, and heart.
- Cuboidal Epithelium: Cube-shaped cells; seen in kidney tubules and glands for secretion and absorption.
- Columnar Epithelium: Tall cells; absorb nutrients and secrete mucus (via goblet cells).
- Ciliated Epithelium: Has fine hair-like cilia that move substances, e.g., mucus in respiratory passages or ova in uterine tubes.
B. Stratified Epithelium
Made of multiple layers for protection.
- Stratified Squamous Epithelium: Found in skin, mouth, and esophagus; protects from friction.
- Transitional Epithelium: Stretchable tissue found in the urinary bladder.
2. Connective Tissue:
Connective tissue binds, supports, and protects body structures. It includes bones, cartilage, ligaments, tendons, fat, and blood.
Functions:
- Structural support
- Protection and cushioning
- Transport of substances
- Storage of fat (energy reserve)
Main Cells in Connective Tissue:
- Fibroblasts: Produce fibers like collagen and elastin
- Fat cells (Adipocytes): Store energy
- Macrophages: Destroy bacteria and foreign matter
- Leukocytes: White blood cells for defense
- Mast cells: Release histamine and heparin in allergic and immune reactions
Types of Connective Tissue:
- Loose connective tissue: Supports organs and tissues under the skin.
- Adipose tissue: Fat-storing tissue (white and brown types).
- Dense connective tissue: Forms ligaments, tendons, and fascia.
- Cartilage: Provides flexibility (hyaline, fibro, and elastic types).
- Bone: Hard, mineralized tissue for protection and movement.
- Blood and lymph: Fluid connective tissues for transport and immunity.
3. Muscle Tissue:
Muscle tissues help in movement and are specialized for contraction. They are of three types:
- Skeletal (Striated) Muscle:
- Voluntary control
- Attached to bones
- Helps in body movements
- Smooth (Non-striated) Muscle:
- Involuntary control
- Found in organs like the stomach, bladder, and blood vessels
- Helps in digestion and controlling vessel diameter
- Cardiac Muscle:
- Found only in the heart
- Involuntary and rhythmic contractions pump blood
- Contains intercalated discs for synchronized activity
4. Nervous Tissue:
Nervous tissue controls and coordinates body functions. It is made of neurons (nerve cells) and supporting cells.
Properties of neurons:
- Irritability: Ability to respond to stimuli
- Conductivity: Ability to transmit electrical impulses
Nervous tissue forms the brain, spinal cord, and nerves, enabling quick communication throughout the body.
Detailed Notes:
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