Biological Tissue Organisation

Biological Tissue Organisation

  • Instructor: Dr Josie Bradley, University of South Wales

Lecture Objectives

  • Types of Biological Tissue: Understand the four main types of biological tissue.
  • Embryological Origins: Know the embryological origins of each tissue type.
  • Tissue Sub-types and Properties: Distinguish between different sub-types of each tissue and describe their properties:
    • Epithelial Tissue: Includes glandular and non-glandular; simple and stratified; squamous, cuboidal, and columnar.
    • Connective Tissue: Includes loose CT, dense CT, cartilage (3 types), bone (2 types), liquid CT (2 types), and connective tissue membranes (4 types).
    • Muscle Tissue: Includes skeletal, smooth, and cardiac muscle.
    • Nervous Tissue: Understand the types of cells that make it up.
  • Function Relationship: Understand how the properties of each tissue relate to their functions.

Biological Organisation

  • Hierarchy of Biological Organisation:

    • Organism: e.g., human
    • Organ Systems
    • Organs
    • Tissues
    • Cells
    • Molecules

  • Molecular Composition:

    • Molecules (lipids, proteins, carbohydrates) are the building blocks of biological organisms.
    • Cells are constructed from various molecules (e.g., lipid membranes, proteins in nuclei).
    • Tissue consists of groups of similar cells working together.
    • Organs comprise various tissues (e.g., muscle and epithelial tissues in the stomach).
    • Organ systems consist of multiple organs working together (e.g., digestive system).

What is a Tissue?

  • Definition: A group of similar cells, usually with a similar embryological origin, specialised to perform a particular function.
  • Extracellular Matrix (ECM): Material between tissue cells influences structure and properties.

Extracellular Matrix Components

  • Key Role: Components of ECM influence tissue structure/function, including:
    • Arterial wall structure (including lumen and wall).

Four Principal Tissue Types

  • Epithelial Tissue: Covers body surfaces, lines hollow organs, and forms glands.
  • Muscle Tissue: Responsible for movement.
  • Connective Tissue: Supports and binds organs.
  • Nervous Tissue: Initiates and transmits action potentials.

Embryonic Origins of Tissues

  • Germ Layers: The three primary germ layers in the embryo are:
    • Endoderm: Provides Epithelial tissue.
    • Mesoderm: Gives rise to Connective and Muscle tissues.
    • Ectoderm: Forms Nervous tissue.

Epithelial Tissue

  • General Features:

    • Composed of closely packed cells with minimal extracellular material.
    • Avascular (no direct blood supply, relies on diffusion).
    • Innervated with good nerve supply.
    • Rapid cell division is characteristic.
    • Has a basement membrane, apical surface, and basal surface with various cell junctions.

  • Functions:

    • Protection, secretion, absorption, filtration, transportation, excretion, sensory reception, and reproduction.

  • Basement Membrane: Composed of two layers:

    • Basal Lamina: Secreted by epithelial cells, primarily collagen.
    • Reticular Lamina: Secreted by connective tissue cells, made of reticular fibers.
    • Functions to anchor cells and facilitate migration during development.

Types of Epithelial Tissue

  • Covering and Lining Epithelium: Non-glandular; involves skin, lining of blood vessels, and hollow organs.
  • Glandular Epithelium: Secreting parts of exocrine glands such as thyroid, pancreas, and sweat glands.
Epithelial Cell Types
  1. Squamous: Flat cells, facilitate diffusion.
  2. Cuboidal: Cube-shaped, involved in secretion and absorption.
  3. Columnar: Tall cells, typically in absorption and secretion roles.
  4. Pseudostratified: Appears stratified due to varying cell heights but is a single layer.
  5. Transitional: Lines urinary system, allows for stretch.

Glandular Epithelium

  • Exocrine Glands: Continuous with surface epithelium via ducts, e.g., goblet cells (unicellular), multicellular structures (tubular or acinar shapes).
  • Types of Secretions:
    • Merocrine: Secretion via exocytosis (e.g., saliva).
    • Apocrine: Secretion involves pinching off the apical part of the cell (e.g., smelly sweat).
    • Holocrine: Entire cell disintegrates to release product (e.g., sebaceous glands).

Connective Tissue Overview

  • Definition: Connects, supports, binds organs, highly abundant extracellular material derived from mesoderm (mesenchyme).
  • Cell Types: Fibroblasts, adipocytes, leukocytes, macrophages.
  • Extracellular Matrix: Contains collagen, reticular, and elastic fibers along with a ground substance (e.g., glycosaminoglycans).

Types of Connective Tissue

  1. Loose Connective Tissue: E.g., areolar tissue, mainly used for holding organs in place.
  2. Dense Connective Tissue: E.g., tendons, ligaments, closely packed fibers for strength.
  3. Cartilage: Types include hyaline (shock-absorbent), fibrocartilage (supportive but less flexible), and elastic cartilage (maintains shape).
  4. Bone: Compact (dense) and spongy (cancellous) with various functions from support to mineral storage.
  5. Liquid Connective Tissue: Blood and lymph, involved in transport and immunity.

Muscular Tissue

  • Types: Skeletal (voluntary, striated), Cardiac (involuntary, striated), and Smooth (involuntary, non-striated).
  • Functions: Movement, regulation, transport, and heat generation.

Nervous Tissue

  • Cell Types: Neurons (conducting signals) and Neuroglia (supporting cells).
  • Neurons: Responsive to stimuli and capable of transmitting nerve impulses.
  • Neuroglia: Provide structural and functional support, insulation, and nourishment to neurons.

Summary of Tissue Functions

  • Epithelial: Covers surfaces, lines cavities, forms glands.
  • Muscle: Movement generation and force.
  • Connective: Protects, supports, bonds organs, stores energy, provides immunity.
  • Nervous: Initiates and transmits impulses, coordinates body functions.

Recommended Reading

  • Tortora, Chapter 5: The Tissue Level of Organisation