Introduction to Histology

PULSEOctober 7, 2009

What is Histology?-THE STUDY OF TISSUES

-But, what does all this mean?-Put simply, it’s microanatomy!

But Why Do We Really Care?

NOT SO MUCH!

Because…structure correlates with function! In disease states,

normal tissue architecture changes.

If we understand the normal, then we understand the disease!

We can use this information to help us make a diagnosis and possibly even to guide treatment.

BORING!!!!!

Histology Basics

Cells are the basic structural and functional unit of the human body

All disease processes can be traced back to an underlying defect in the cell

BUT…We want the BIG PICTURE!!!!!! CellsTissuesOrgansOrgan Systems

What is a Tissue?

There are four basic types of tissues that come together to comprise organs: 1) Epithelium 2) Connective tissue 3) Muscle 4) Nervous tissue

Epithelium

EPITHELIUM IS A TYPE OF TISSUE THAT LINES THE SURFACES OF THE BODY AS WELL AS THE SURFACES OF BODY CAVITIES (E.G. THE GASTROINTESTINAL AND RESPIRATORY TRACTS)

IN ADDITION, MANY GLANDS (ENDOCRINE AND EXOCRINE) ARE ALSO FORMED FROM EPITHELIAL TISSUE.

Epithelium

Classification: By cell shape:

Squamous: Flat, “pancake-shaped” cells; flat nuclei

Cuboidal: Cube-shaped cells equal in width and height; circular nuclei

Columnar: Tall rectangular cells with a height greater than two times the width; stretched nuclei

Transitional: Complex! Not important…yet!

By the number of layers: Simple: One cell layer Stratified: Two or more cell layers

*The type of epithelium found in a given structure depends on the function of that structure!

Stratified Squamous

Simple Cuboidal

Simple Columnar

Connective Tissue

Connective tissue is important in support and strength

It consists of cells (mostly fibroblasts) and extracellular matrix (laid down by the connective tissue cells

Connective Tissue: Classification

1) Connective Tissue Proper A) Loose connective tissue B) Dense irregular connective tissue C) Dense regular connective tissue

2) Embryonic Connective Tissue 3) Specialized Connective Tissue

A)Blood B)Cartilage C)Bone

Loose Connective Tissue

A lot of cells; not a lot of extracellular matrix

Often found beneath epithelial surfaces, around glands It serves as a place

for immune cells to “wait” beneath the epithelial surfaces to attack invading microbes

Dense Irregular Connective Tissue

Dense: More extracellular matrix (mostly collagen), less cells

Irregular: Collagen fibers have no specific pattern; wavy

Function: Resists stretching (e.g. found in the deep layer of the skin)

Dense Regular Connective Tissue Dense: More

extracellular matrix (mostly collagen), less cells

Regular: Collagen fibers are laid down in rows

Function: STRENGTH! Found in tendons

and ligaments

Muscle

Three types 1) Skeletal 2) Cardiac 3) Smooth

Skeletal Muscle

Skeletal muscle is what you think about when you hear the term “muscle”

Features: Multiple nuclei per

cell Nuclei at the

periphery of the cell Striated

Cardiac Muscle

Cardiac muscle is the muscle found in the heart

Responsible for pumping blood!

Features: One nucleus per cell Nucleus is centrally-

located in the cell Striated Intercalated discs Branching pattern

Smooth Muscle

Smooth muscle is the muscle found in blood vessels, glands, and the components of the GI tract

This is “involuntary” muscle We can’t make it contract by

thinking about it like we can with our skeletal muscles

Features: One nucleus per cell Nucleus is centrally-located

within the cell Not striated “Spindle-shaped” cells and

nuclei

Nervous Tissue

Pretty complex! We won’t cover it today!

Microscope Etiquette-One more important thing before we start the laboratory exercise