Lecture 6 Tissue Level of Organisation

Overview

Four main types of tissues are identified in the body, each playing specific roles crucial for maintaining life: Epithelial, Connective, Muscle, and Nervous Tissue. These tissues work together to form organs and systems critical for the body's function and security.

Epithelial Tissue

Overview:

Epithelial tissue is primarily composed of large sheets of tightly packed cells with minimal extracellular matrix. It is important to note that epithelial tissues are avascular, meaning they lack blood vessels, and receive nutrients through diffusion. This tissue type has a high capacity for regeneration and can rapidly replace damaged cells, which is essential for protecting underlying structures.

Functions:

• Protection: Acts as a barrier against mechanical and chemical injury.

• Absorption: Facilitates uptake of nutrients, such as in the intestinal lining.

• Secretion: Produces substances like enzymes and hormones.

• Lubrication: Provides moisture to surfaces to reduce friction.

Characteristics:

• Polarity:

  • Apical End: Exposed side of the epithelial layer, facing the exterior or an internal cavity.

  • Basal End: Attached to the basal lamina, which supports the epithelium and anchors it to underlying tissues.

Classification by Layering:

• Simple Epithelia:

  • One layer of cells, allowing for efficient absorption, diffusion, secretion, and filtration.

• Stratified Epithelia:

  • Composed of multiple layers, mainly serving protective functions.

• Pseudostratified Epithelia:

  • Appears stratified but is a single layer with varying cell heights, involved in protection and secretion.

Classification by Shape:

• Squamous:

  • Flattened cells, ideal for absorption, diffusion, and filtration.

• Cuboidal:

  • Box-like cells that are efficient for secretion and absorption.

• Columnar:

  • Rectangular cells, often involved in secretion, absorption, and lubrication; may possess microvilli.

• Transitional:

  • Cells that can change shape, lining structures like the urinary bladder that undergo stretching.

Types of Epithelial Tissue:

1. Simple Squamous:

   • Location: Lung alveoli, kidney glomeruli.

   • Function: Facilitates filtration, diffusion, and absorption.

2. Stratified Squamous:

   • Location: Skin, mouth, esophagus.

   • Function: Provides protection; epidermal cells contain keratin for waterproofing.

3. Simple Cuboidal:

   • Location: Kidney tubules, small glands.

   • Function: Governs secretion and absorption.

4. Simple Columnar:

   • Location: Lumen of the intestines, ducts of glands.

   • Function: Involved in absorption and secretion; often features microvilli to enhance surface area.

5. Ciliated Simple Columnar:

   • Location: Upper respiratory tract.

   • Function: Moves mucus and trapped particles using cilia.

6. Pseudostratified Columnar:

   • Location: Upper respiratory tract.

   • Function: Facilitates secretion and movement of mucus, containing Goblet cells that produce mucus.

7. Stratified Cuboidal:

   • Location: Sweat glands, salivary glands.

   • Function: Mainly provides protection.

8. Transitional Epithelium:

   • Location: Urinary bladder.

   • Function: Allows for stretching and recoiling as the bladder fills and empties.

Connective Tissue

Overview:

Connective tissue serves multiple functions, including support, binding, and connecting various tissues and organs within the body. These tissues are characterized by cells that are dispersed within an extracellular matrix, which consists of protein fibers like collagen and elastin, along with ground substance which could include water, minerals, and other organic compounds.

Classification of Connective Tissues:

1. Connective Tissue Proper:

   • Loose: Includes areolar tissue (provides elasticity and support), adipose tissue (energy storage and insulation), and reticular tissue.

   • Dense: Comprises regular (representative of tendons) and irregular (found in the dermis of the skin) connective tissues.

2. Supportive Connective Tissue:

   • Bone: Provides structure, support, and protection for various organs while serving as a reservoir for minerals.

   • Cartilage: Supports and cushions joints; types include hyaline (most common), elastic (provides flexibility), and fibrocartilage (high tensile strength