Endothelium Notes

Introduction

• Lecture 2: Human Tissues

• Chapter 4 Overview

Types of Human Tissues

• Four primary tissue types classified by function:

  • Epithelial Tissue: Forms boundaries and covers surfaces.

  • Muscle Tissue: Facilitates contraction for movement.

  • Nervous Tissue: Responsible for communication and control within the body.

  • Connective Tissue: Offers support and connection between other tissues.

Epithelial Tissue

Functions

• Barrier Formation:

  • Separates the body from external environment and divides bodily compartments.

  • Examples:

    • Skin: Protects internal environment from external stimuli (e.g., chyme, air).

    • Endothelium of Blood Vessels: Acts as a barrier between blood and surrounding tissues.

    • Blood-Brain Barrier: Protects the central nervous system from external substances.

• Absorption:

  • Tissue capable of absorbing substances (e.g., nutrients).

• Secretion:

  • Produces and releases substances; includes two types of glands:

    • Exocrine Glands: Secrete substances (e.g., mucus, sweat) through ducts.

      • Examples: Salivary glands, sweat glands, mammary glands.

    • Endocrine Glands: Ductless, release hormones into the bloodstream.

      • Examples: Pituitary gland, adrenal gland.

• Sensation:

  • Contains sensory receptors that provide information about the environment.

Structural Features of Epithelial Tissue

Common Features

1. Cell Junctions: Enhance Structure

   • Tight Junctions: Seal spaces between cells, preventing passage of substances.

   • Adherens Junctions: Provide mechanical support by linking actin cytoskeletons.

   • Desmosomes: Link intermediate filaments for strength against stress.

   • Gap Junctions: Allow communication between cells through pores.

2. Avascular:

   • Lacks blood vessels, receives nutrients through diffusion from underlying tissues.

3. Polarity:

   • Epithelial cells exhibit polarity with varying surfaces:

     • Basal Surface: Attaches to the basement membrane.

     • Apical Surface: Faces the lumen or external environment.

     • Lateral Surface: Sides of the cell with junctions connecting to neighboring cells.

Examples of Epithelial Tissue Functions

Small Intestine

• Specialized epithelial cells aid in nutrient absorption:

  • Equipped with transport proteins for nutrient uptake.

  • Apical-basal polarity enhances function execution.

Gastric Gland

• Specialized cells generate and secrete acids:

  • Utilize carbonic anhydrase for CO2 processing.

  • Protons (H+) are pumped into the stomach lumen, while bicarbonate ions (HCO3-) are exchanged into the blood (Chloride Shift).

Endothelial Tissue (Blood Vessels)

• Simple squamous epithelium lines blood vessel walls:

  • Regulates vascular tone, immune cell trafficking, and blood clotting.

  • Acts as a selective barrier, enabling nutrient and gas exchange.

Types of Capillaries: Endothelial Tissue Functionality

• Continuous Capillaries: Tight junctions act as barriers (e.g., in brain).

• Fenestrated Capillaries: Small pores for increased permeability (e.g., kidneys).

• Sinusoidal Capillaries: Large gaps for larger molecule passage (e.g., liver).

Epithelial Tissue Classification & Naming

Classification Criteria

• Cell Layers:

  • Simple: One layer.

  • Stratified: More than one layer.

• Cell Shape:

  • Squamous: Flat cells.

  • Cuboidal: Cube-shaped cells.

  • Columnar: Column-shaped cells.

• Special Case:

  • Transitional Epithelium: Specialized epithelium that can expand and contract.