epithelium

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Instructor Information

• Name: Joyce El-Haddad

• Affiliation: UNSW Sydney

• Contact: j.el-haddad@unsw.edu.au | Twitter: @orientatewithjoyce

Lecture Outline

• Topics Covered:

  • Cellular Structure Overview

  • Basic Tissues

  • Structure of Epithelium

  • Classification of Epithelium

  • Structure of Connective Tissue

  • Classification of Connective Tissue

• Learning Outcomes:

  1. Identify and describe the basic functions of cells and their organelles.

  2. Identify and describe different types of epithelia.

  3. Understand terms endothelium and mesothelium.

  4. Classify epithelia based on cell morphology and arrangement.

  5. Study surface specializations of some epithelial cells: cilia and microvilli.

Structural Organization of the Body

• Six Levels of Structural Organization (Reference: Tortora, 11th Edition):

  • 1. Chemical Level

  • 2. Cellular Level

  • 3. Tissue Level

  • 4. Organ Level

  • 5. System Level

  • 6. Organism Level

Basic Tissues

• Definition: A group of similar cells and cell products performing a special function; includes cells and extracellular matrix (liquid, semisolid, solid).

• Four Basic (Fundamental) Tissues:

  • Epithelial

  • Connective

  • Muscle

  • Nervous

Comparison of Basic Tissues

Epithelial Tissue Functions

• Functions of Epithelia:

  • Covering, lining, and protecting surfaces (e.g., skin and gut).

  • Secretion from glands.

  • Absorption (intestine).

  • Sensation through neuroepithelium.

  • Contractility via myoepithelial cells.

• Types of Epithelial Tissue:

  1. Surface Epithelia: Organized in layers covering external surfaces or lining cavities.

  2. Glandular Epithelia: Specialized for secretion.

Characteristics of Epithelial Tissues

• Consist of uninterrupted layers of tightly packed cells;

• Are polarized:

  • Apical Surface: Exposed side.

  • Basal Surface: Attached to underlying connective tissue.

• Have one or several layers of cells with a lamina propria layer of connective tissue underneath.

• Basement Membrane: Formed by secretions from both epithelial and connective tissue cells; acts as a selectively permeable filter.

• Epithelium is avascular; receives nutrients via diffusion from the lamina propria.

Surface Specializations

• Microvilli: Extensions of the plasma membrane that increase surface area for absorption.

• Cilia: Projections of the plasma membrane involved in locomotion.

Classification of Epithelium

• Based on Arrangement of Layers:

  1. Simple (one layer)

  2. Pseudostratified (fake layers)

  3. Stratified (multiple layers)

• Based on Cell Shape:

  1. Squamous (flat cells)

  2. Cuboidal (cube-shaped)

  3. Columnar (tall, column-like)

Types of Epithelial Tissue

1. Simple Squamous Epithelium:

   • Flat, irregularly shaped cells.

   • Functions: Diffusion and filtration.

   • Locations: Alveoli, blood vessels, serous membranes.

2. Simple Cuboidal Epithelium:

   • Cube-shaped cells.

   • Functions: Secretion, filtration, absorption.

   • Locations: Glands, kidney tubules.

3. Simple Columnar Epithelium:

   • Tall, tightly fitted cells, may have goblet cells.

   • Functions: Protection, lubrication, secretion, absorption.

   • Locations: Lining of intestines and uterine tubes.

4. Pseudostratified Epithelium:

   • Variable cell heights creating a false appearance of layers.

   • Functions: Protection, secretion, movement of particles (ciliated).

   • Locations: Trachea, bronchi, nasal cavity.

5. Stratified Squamous Epithelium:

   • Apical cells are squamous, underlying cells may be cuboidal or columnar.

   • Functions: Protection against abrasion.

   • Locations: Skin (keratinized) and mucous membranes (nonkeratinized).

6. Transitional Epithelium:

   • Cells change shape based on distension.

   • Functions: Protection, distensibility.

   • Locations: Urinary bladder, ureters.

Exocrine Glands

• Overview:

  • Exocrine glands release substances (sweat, saliva) through ducts to a body surface.

Types of Exocrine Secretion

1. Merocrine Secretion:

   • Exocytosis of secretory products; cells remain intact.

   • Examples: Sweat glands, salivary glands.

2. Apocrine Secretion:

   • Release of product with a portion of the cell; involves shedding.

   • Examples: Mammary glands during lactation.

3. Holocrine Secretion:

   • Full disintegration of glandular cell, releasing all contents.

   • Example: Sebaceous glands.

Endocrine Glands

• Ductless glands that release hormones directly into the bloodstream.

• Arranged in cords or clumps, close to capillaries for hormone transport.

• Exocrine glands connect to surfaces via ducts, while the epithelial component is parenchyma and supportive tissue is stroma.