Four Tissues of the Body

Introduction

• The human body consists of 30 trillion cells.
• Approximately 200 different cell types exist.
• Cells are grouped into four main types of tissues based on their function:
  1. Nervous Tissue
  2. Muscle Tissue
  3. Epithelial Tissue
  4. Connective Tissue

Nervous Tissue

• Function: Communication within the nervous system.
• Components:
  • Neurons: Main cells responsible for communication.
  • Glia (Supporting Cells): Includes various types such as:
    • Oligodendrocytes
    • Schwann cells
    • Ependymal cells
    • Astrocytes
• Structures Formed:
  • Brain
  • Brainstem
  • Spinal Cord
  • Cranial and Spinal Nerves
• Cranial Nerves: 12 pairs of nerves that connect to the brain.

Muscle Tissue

• Function: Facilitates movement.
• Types of Muscle Tissue:
  1. Cardiac Muscle: Forms the heart muscle.
  2. Skeletal Muscle: Attached to bones, enabling skeleton movement.
  3. Smooth Muscle: Lines hollow organs (e.g., GI tract, urinary system).
     • Enables processes like peristalsis (movement of food and fecal matter in the GI tract).

Epithelial Tissue

• Function: Forms boundaries between different environments.
• Locations:
  • Skin
  • Kidneys
  • Lungs
• Types and Features:
  • Simple Squamous: Single layer, thin, allows diffusion (e.g., in lungs).
  • Stratified Squamous: Multiple layers, protective, found in skin.
  • Simple Cuboidal: Cube-shaped, involved in secretion.
  • Simple Columnar: Column-shaped, involved in secretion.
  • Pseudostratified: Appears multi-layered but is single-layered.
  • Transitional: Can change from one type to another.
• Functions of Shape:
  • Thin layers allow exchange; multiple layers provide protection.
  • Larger cells (cuboidal, columnar) usually involved in secretion, e.g., glandular functions.

Connective Tissue

• Function: Supports, protects, and binds other tissues.
• Types of Connective Tissue:
  • Bone
  • Tendons
  • Fat (adipose tissue)
  • Blood
• Characteristics:
  • Can be solid, semi-solid, or liquid.
  • Composed of gels and fibers.
  • Gels: Act as the embedding medium (like concrete).
  • Fibers: Added to gels to alter consistency.
    • Elastic fibers make it bendy.
    • Rigid fibers add strength.
• Examples: Variations in gels and fibers result in different tissue types like bone versus blood.