HISTOLOGY

The study of tissues

Levels of organization in the biosphere

What is a tissue?

Groups of cells with a common structure and function– Structure is suited to its function

General types of tissues

Epithelial tissue

Connective tissue

Nervous tissue

Muscle tissue

Epithelial tissue

Covers outside of body and lines organs and cavities inside the body– Functions as a protective barrier

• Protects against injury• Protects against invasion by bacteria, etc.

Epithelial Tissue

Classified by number of cell layers and shape of cells

Remember: form reflects function!

Epithelial Tissue

By Layers:– Simple epithelium

• Single layer of cells

– Stratified epithelium• Multiple layers of cells

– Pseudostratified epithelium• Single layer of cells that appears to be multi-

layered

Epithelial Tissue

By shape:– Cuboidal– Columnar– squamous

Epithelial Tissue

Epithelial Tissue: Examples

Simple cuboidal epithelium

Epithelial Tissue: Examples

Simple columnar epithelium

Epithelial Tissue: Examples

Simple squamous epithelium

Epithelial Tissue: Examples

Stratified squamous epithelium

Epithelial Tissue: Examples

Stratified squamous epithelium with layer of keratin

Epithelial Tissue: Examples

Pseudostratified columnar epithelium

Connective Tissue

Functions to bind and support other tissues– Few cells scattered in a matrix of various

substances

Connective tissue fibers

Collagenous

Elastic

reticular

Collagenous fibers

Made of collagen

Non-elastic

Elastic fibers

Long threads made of elastin

Rubbery

Reticular fibers

Thin

Branched

Composed of collagen

Form tightly woven fabric

Main types of connective tissue

Loose connective tissue

Adipose tissue

Fibrous connective tissue

Cartilage

Bone

blood

Loose connective tissue

Most commonHas all 3 fiber types (collagenous, elastic, reticular)Binds epithelia to underlying tissues, holds organs in placeFibroblasts and macrophages scattered in the meshAlso called “areolar” connective tissue

Loose connective tissue

Adipose tissue

Specialized form of loose connective tissue

Stores fat

Act as insulation and fuel

Adipose tissue

Fibrous connective tissue

Large numbers of collagen fibers– Arranged in parallel bundles– Strong– Found in tendons (join muscle to bone)

and ligaments (join bone to bone)

Fibrous connective tissue

Cartilage

Collagen fibers embedded in a rubbery matrix of chondroitin sulfate– Strong, yet flexible– In human ears, nose, rings of trachea

• Flexible support

– Chondrocytes secrete chondroitin and collagen

Cartilage

Bone

Mineralized connective tissue--hard

Osteoblasts = bone-forming cells

May be compact or spongy (cancellous)

Repeating units are called osteons (Haversian systems)

Bone

Blood

Matrix = plasma– Made of salt, water, dissolved proteins

Types of cells:– Erythrocytes = RBC’s– Leukocytes = WBC’s– platelets

General types of tissues

Epithelial

Connective

Nervous

Muscle

Nervous Tissue

Functional unit = neuron– Transmit nerve impulses

Structure:– Cell body, dendrites, axons

• Dendrites transmit impulses from tips toward the neuron cell body

• Axons transmit impulses toward another neuron or a muscle cell

Neuron

Muscle Tissue

Fibers are capable of contraction

Made of proteins, actin and myosin

3 types– Skeletal– Cardiac– smooth

Skeletal Muscle tissue

Attached to bones by tendons

Responsible for voluntary movement

Striated appearance

Cardiac Muscle

In heart

Striated, but cells are branched

Smooth Muscle

Lacks striations

Spindle-shaped

Responsible for involuntary movements

Lines digestive tract, bladder, arteries

Types of Muscle tissue