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