CONNECTIVE

Chapter 4: Epithelial & Connective Tissues

Introduction to Tissues

• Definition of Tissue: A group of cells with similar structure and function, along with the extracellular substance surrounding them.

• Histology: The study of tissues.

• Four Tissue Types in Human Body: Epithelial, connective, muscle, and nervous tissues.

Epithelial Tissue (ET) Functions and Characteristics

• Functions of Epithelial Tissue:

  • Physical protection.

  • Control of permeability (selective absorption and secretion).

  • Diffusion and filtration.

  • Provides sensation.

  • Produces secretions (forms glands).

• General Characteristics:

  1. Mostly composed of cells.

  2. Covers body surfaces and lines cavities.

  3. Has an exposed surface (apical surface).

  4. Attaches at the basal surface to the basement membrane.

  5. Specialized cell connections (junctions) and matrix attachments.

  6. Avascular (no blood vessels).

  7. Capable of regeneration (continues to divide).

Epithelial Tissue Classification

Classification Based on Number of Layers:

• Simple: Single layer of cells.

• Stratified: Multiple layers of cells.

Classification Based on Shape of Cells:

• Squamous: Flat cells.

• Cuboidal: Cube-shaped cells.

• Columnar: Taller, column-like cells.

Types of Simple Epithelium

Simple Squamous Epithelium

• Structure: Single layer of flat cells; hexagonal in shape.

• Function: Diffusion and filtration; some secretion and protection against friction.

• Location: Blood vessels, heart, lymphatic vessels, alveoli, kidney tubules, serous membranes.

Simple Cuboidal Epithelium

• Structure: Single layer of cube-shaped cells; some have microvilli or cilia.

• Function: Secretion and absorption (especially in kidney tubules); movement of particles in mucus.

• Location: Kidney tubules, glands, and duct linings.

Simple Columnar Epithelium

• Structure: Single layer of tall, narrow cells; may have cilia or microvilli.

• Function: Movement of particles, secretion, absorption.

• Location: Uterine tubes, stomach, intestines, and gallbladder.

Types of Stratified Epithelium

Pseudostratified Columnar Epithelium

• Structure: Appears stratified but is a single layer of varying height; often ciliated with goblet cells.

• Function: Mucus secretion and movement of particles.

• Location: Respiratory tract (nasal cavity, trachea, bronchi).

Stratified Squamous Epithelium

• Structure: Several layers; cuboidal at the base, progressively flattened at the surface; can be keratinized or nonkeratinized.

• Function: Protects against abrasion and infection; reduces water loss.

• Location: Skin (keratinized) and moist areas (nonkeratinized) like the mouth and vagina.

Transitional Epithelium

• Structure: Stratified cells that change shape (cuboidal to squamous) when stretched.

• Function: Accommodates fluctuations in fluid volume.

• Location: Lining of the urinary bladder and ureters.

Connective Tissue Overview

• Definition: Comprised of cells, protein fibers, and extracellular matrix.

• Components:

  • Ground substance: Gel-like substance primarily composed of proteoglycans.

  • Protein Fibers: Three types—collagen, reticular, and elastic fibers.

• Functions:

  1. Enclosure and separation of tissues.

  2. Connecting tissues.

  3. Supporting body structure.

  4. Storage of compounds.

  5. Cushioning and insulating.

  6. Transporting (blood).

  7. Protecting from pathogens.

Types of Connective Tissue

Loose Connective Tissue: Areolar

• Structure: Network of collagen and elastic fibers; contains fibroblasts, macrophages.

• Function: Support and nourishes structures.

• Location: Widely distributed; underlies epithelial tissue.

Loose Connective Tissue: Adipose

• Structure: Sparse matrix, large adipocytes (fat cells).

• Function: Insulation, energy storage, protective cushioning.

• Location: Subcutaneous areas, around organs.

Loose Connective Tissue: Reticular

• Structure: Fine network of reticular fibers.

• Function: Provides support for lymphatic and hemopoietic tissues.

• Location: Lymph nodes, spleen, bone marrow.

Dense Connective Tissue: Dense Regular

• Structure: Collagen fibers oriented in one direction.

• Function: Resists pulling forces.

• Location: Tendons, ligaments, dermis.

Dense Connective Tissue: Elastic

• Structure: Contains collagen and elastin fibers.

• Function: Allows stretching and recoiling.

• Location: Elastic ligaments, blood vessels.

Supporting Connective Tissues

Cartilage: Hyaline

• Structure: Collagen fibers dispersed in a firm matrix; chondrocytes in lacunae.

• Function: Provides support and allows growth of long bones.

• Location: Respiratory system, embryonic skeleton.

Cartilage: Fibrocartilage

• Structure: More collagen fibers arranged in thick bundles.

• Function: Provides flexibility and withstands pressure.

• Location: Intervertebral disks, cartilage in joints.

Cartilage: Elastic

• Structure: Similar to hyaline but has elastic fibers.

• Function: Offers rigidity with flexibility.

• Location: External ears, epiglottis.

Bone

• Structure: Hard matrix with osteocytes in lacunae and layers of lamellae.

• Function: Provides strength and support; protects organs.

• Location: All bones, includes compact and spongy bone.

Fluid Connective Tissue: Blood

• Structure: Formed elements in a fluid matrix (plasma).

• Function: Transports substances, protects against infections.

• Location: Throughout blood vessels.