RAD ANA BASIC TYPE OF TISSUES

Basic Types of Tissues

  • Epithelial Tissue

  • Nervous Tissue

  • Muscle Tissue

  • Connective Tissue

Objectives

  • Determine the four basic types of tissues that make up the human body.

  • State the characteristics of each type of tissue.

  • Determine the functions of each type of tissue.

Definition of Tissues

  • Tissues: A group of cells that have a common origin in an embryo and function together to carry out specialized activities.

  • Histology: The science that deals with the study of tissues.

  • Pathologist: A physician who examines cells and tissues to help others make accurate diagnoses.

Characteristics of the Four Basic Tissue Types

Epithelial Tissue

  • Covers body surfaces and lines hollow organs, cavities, and ducts.

  • Forms glands allowing interaction between internal and external environments.

Connective Tissue

  • Protects and supports body and its organs.

  • Binds organs together and stores energy reserves as fats.

  • Provides immunity from disease-causing organisms.

Muscular Tissue

  • Composed of cells specialized for contraction and generation of force.

  • Generates heat and warms the body.

Nervous Tissue

  • Detects changes in conditions inside and outside the body.

  • Responds by generating electrical signals (nerve impulses) to activate muscle contractions and glandular secretions.

Clinical Correlation

  • Biopsy: Removal of a sample of living tissue for microscopic examination.

    • Used to help diagnose disorders such as cancer, unexplained infections, and inflammation.

Cell Junctions

  • Contact points between the plasma membranes of tissue cells.

Types of Junctions

  • Tight Junctions

  • Hemidesmosomes

  • Adherens Junction

  • Gap Junctions

  • Desmosomes

Epithelial vs Connective Tissue Characteristics

Epithelial Tissue

  • Cell Density: Many cells tightly packed together.

  • Extracellular Matrix: Lesser.

Connective Tissue

  • Cell Density: Cells are widely scattered.

  • Extracellular Matrix: Large amount of extracellular materials.

Epithelial Tissue Structures

  • Arrangement of Cells

    • Forms continuous sheets, either single or multiple layers.

    • Little intracellular space exists between adjacent plasma membranes.

    • Forms coverings and linings throughout the body.

    • Not covered by other tissues, hence has a free surface.

Major Functions of Epithelial Tissue

  1. Selective Barrier: Limits and aids transfer of substances into and out of the body.

  2. Secretory Surface: Releases products produced by cells onto free surfaces.

  3. Protective Surface: Resists abrasive influences of the environment.

Surfaces of Epithelial Cells

  • Apical Surface: Faces open space, can have cilia or microvilli.

  • Lateral Surface: Faces adjacent cells, contains cell junctions.

  • Basal Surface: Opposite of apical, adheres to extracellular materials (basement membrane).

Basement Membrane in Epithelial Tissue

  • Thin extracellular layer consisting of two layers:

    1. Basal Lamina: Secreted by epithelial cells, includes laminin and collagen.

    2. Reticular Lamina: Secreted by connective tissue, contains collagen fibers.

Functions of Basement Membrane

  • Attaches and supports overlying epithelial tissues.

  • Forms a surface for epithelial cell migration during growth/wound healing.

  • Restricts passage of larger molecules between epithelium and connective tissue.

Epithelial Tissue Functional Features

  • Avascular (lack of blood vessels) but has a high rate of cell division for constant renewal.

  • Relies on diffusion from adjacent connective tissue for nutrient absorption and waste elimination.

Types of Epithelial Tissue

  1. Covering and Lining Epithelium

    • Outer covering of skin and internal organs.

    • Inner lining of blood vessels, ducts, body cavities, and various systems.

  2. Glandular Epithelium: Secreting portions of glands (e.g., thyroid, adrenal, sweat).

Classification Based on Layers

  • Simple Epithelium: Single layer; performs diffusion, osmosis, filtration, secretion, absorption.

  • Pseudostratified Epithelium: Appears multilayered, but all cells contact basement membrane.

  • Stratified Epithelium: Two or more layers; provides protection.

Cell Shape Classification

  • Squamous: Thin for rapid passage of substances.

  • Cuboidal: Shaped like cubes, involved in secretion/absorption.

  • Columnar: Column-shaped for protection; have microvilli or cilia for secretion/absorption.

  • Transitional: Changes shape, can be found in urinary bladder.

Eight Types of Epithelial Tissues

  1. Simple Squamous

  2. Simple Cuboidal

  3. Simple Columnar

  4. Transitional

  5. Stratified Squamous

  6. Stratified Cuboidal

  7. Stratified Columnar

  8. Pseudostratified Columnar

Example Locations of Epithelial Types

  • Simple Squamous: Alveoli

  • Simple Cuboidal: Kidney

  • Simple Columnar: Stomach

  • Transitional: Bladder

  • Stratified Squamous: Esophagus

  • Stratified Cuboidal: Sweat gland

  • Stratified Columnar: Salivary duct

  • Pseudostratified: Trachea

Glandular Epithelium

  • Function: Secretion

  • Glands: Group of cells that secrete substances either into ducts or onto surfaces, or directly into the bloodstream.

  • Endocrine Glands: Secrete hormones (e.g., thyroid, adrenal).

  • Exocrine Glands: Secretes products into ducts (e.g., sweat, salivary glands).

Functional Classification of Exocrine Glands

  • Merocrine: Secretions released via exocytosis (e.g., salivary glands).

  • Apocrine: Partial loss of secretory product during secretion (e.g., sweat glands).

  • Holocrine: Secretory product released with entire cell becoming a secretory product (e.g., sebaceous glands).

Connective Tissue Overview

  • Most abundant and widely distributed tissue types in the body.

  • Functions:

    • Binds, supports, and strengthens other tissues.

    • Protects and insulates organs.

    • Major transport system (blood).

    • Location for energy reserves (adipose tissue).

    • Main source of immune response.

Types of Connective Tissue Cells

  • Fibroblast: Immature cell in loose/dense connective tissue.

  • Chondroblast: Immature cells in cartilage.

  • Osteoblast: Immature cells in bone.

  • Adipocytes: Fat cells specializing in triglyceride storage.

  • Leukocytes: White blood cells involved in immune responses.

Classification of Connective Tissue

Embryonic Connective Tissue

  • Mesenchyme: Present in embryos, gives rise to other connective tissues.

  • Mucous Connective Tissue: Found in umbilical cord.

Mature Connective Tissue Categories

  1. Connective Tissue Proper: Loose and dense varieties.

  2. Supporting Connective Tissue: Cartilage and bone.

  3. Liquid Connective Tissue: Blood and lymph.

Connective Tissue Proper - Loose Connective Tissue

Areolar Connective Tissue

  • Widely distributed, provides strength and elasticity.

Adipose Tissue

  • Stores triglycerides, reduces heat loss, and serves as an energy reserve.

Reticular Connective Tissue

  • Forms stroma of organs and filters worn-out blood cells.

Dense Connective Tissue Types

Dense Regular Connective Tissue

  • Provides tensile strength and constructs tendons and ligaments.

Dense Irregular Connective Tissue

  • Provides strength in multiple directions; found in skin and organs.

Elastic Connective Tissue

  • Allows stretching, found in lungs and elastic arteries.

Supporting Connective Tissue

Cartilage Types

  • Hyaline: Most abundant, provides smooth surfaces for movement at joints.

  • Fibrocartilage: Strongest, found in intervertebral discs.

  • Elastic Cartilage: Provides strength and elasticity, found in the ear.

Bone Tissue

  • Composed of osteons; functions include storing minerals and housing marrow.

Types of Bone Tissue

  • Compact Bone: Dense and organized into osteons.

  • Spongy Bone: Lightweight and filled with red marrow.

Liquid Connective Tissue - Blood

  • Comprising blood plasma and formed elements like red blood cells, white blood cells, and platelets.

Muscle Tissue

  • Function: Produces movements, maintains posture, generates heat.

  • Types:

    • Skeletal Muscle

    • Cardiac Muscle

    • Smooth Muscle

Nervous Tissue

  • Components: Neurons and neuroglia

    • Neurons respond to stimuli and transmit impulses.

    • Neuroglia provides support and protection.

Tissue Repair

  • Replacement of worn-out or damaged cells.

    • Regeneration: Parenchymal cells facilitate repair.

    • Fibrosis: Formation of scar tissue through fibroblast activity.

    • Granulation Tissue: New tissue forming to support migrating epithelial cells.

    • Wound Dehiscence: Separation of sutured layers.