Lecture on Histology and Tissues

Introduction to Histology

• Histology: Study of tissues.
• Tissues are made up of cells.

Four Major Types of Tissues

1. Epithelial Tissue
   • Covers and lines structures in the body.
   • Forms glands.
2. Connective Tissue
   • Binding and supportive tissue.
   • Most abundant tissue, acts as the body's support system.
3. Muscular Tissue
   • Responsible for movement, including elongation and shortening.
4. Nervous Tissue
   • Sends electrical signals (impulses).
   • Helps maintain homeostasis (along with the endocrine system).

Characteristics of Organisms

• Hierarchical organization: Atoms, molecules, cells, tissues, organs, organ systems, organisms.
• Metabolism
  • Sum of all chemical reactions in cells: Building (anabolism) and breaking down (catabolism).
  • Anabolism: Builds larger molecules (polymers) from smaller ones (monomers).
  • Catabolism: Breaks down larger molecules into smaller ones, releasing energy.
• Differentiation
  • Stem cells change (differentiate) into specialized cells (e.g., epithelial, muscle, nervous, connective tissues).
• Growth through Hyperplasia and Hypertrophy
  • Hyperplasia: Increase in number of cells (cell multiplication).
  • Hypertrophy: Increase in cell size.

Epithelial Tissue Overview

• Lines and covers surfaces.
• Characteristics:
  • Tightly packed cells
  • Free surface (apical surface): Top layer exposed to air or fluid.
  • Basement membrane: Sits on connective tissue.
  • Avascular: Lacks blood vessels but is innervated.

Layers and Shapes of Epithelial Cells

• Layers
  • Simple: One layer.
  • Stratified: Multiple layers.
  • Pseudostratified: Appears layered due to varying cell heights.
• Shapes
  • Squamous: Flat cells.
  • Cuboidal: Cube-shaped cells.
  • Columnar: Tall, column-like cells.

Specific Epithelial Tissues

1. Simple Squamous
   • Thin, allows for diffusion and filtration.
   • Locations: Lines blood vessels (endothelium), covers organs (mesothelium).
   • Forms serous membranes.
2. Simple Cuboidal
   • Cube-shaped, forms many glands.
   • Lines small ducts and tubules.
3. Simple Columnar
   • Tall, with goblet cells (mucus production).
   • Microvilli for absorption or cilia for movement.
4. Pseudostratified Ciliated Columnar
   • Cilia and goblet cells present, lines respiratory tract.
   • Produces mucus to trap particles.
5. Stratified Squamous
   • Keratinized (skin) or non-keratinized (mouth, esophagus).
   • Provides protection.
6. Transitional Epithelium
   • Stretches, lines urinary tract.

Gland Types

• Endocrine glands: Secrete hormones into the bloodstream.
• Exocrine glands: Secrete substances to a surface (e.g., sweat, saliva).

Membranes

• Mucous membranes: Line body cavities opening to the exterior (e.g., digestive, respiratory tracts).
• Serous membranes: Line closed internal body cavities (e.g., pericardial, pleural).
• Cutaneous membrane: Skin, covers the body surface.

Summary

• Understanding tissue types, their functions, and how they form membranes is crucial in anatomy and physiology.
• Each tissue type has unique features and roles in the body, contributing to overall organismal function.