Allison Gong

• Histology• Microscopy• Development

I. Histology

Histology

• Histology = study of tissues• Tissue = group of cells with similar structure

and function• Four types of human tissues:

– Nervous tissue– Muscle– Connective tissue– Epithelial tissue

Connective tissue

• Provides support (physical + metabolic) for other tissues

• Surrounds all other tissues– Provides structural framework

• Types of connective tissue:– Bone– Blood– Cartilage– Adipose tissue– Tendons, ligaments

Connective tissue

• Combination of:– Cells (type varies)– Extracellular materials; matrix

• Cells far apart• Matrix holds H2O

– Resists compression– Nutrients/wastes pass through

(interstitial fluid)

• Stretchy and strong

Epithelial tissue

• Covers surfaces, lines tubes, forms glands• Cells tightly packed, form sheets• Functions:

– Protection (e.g., skin)– Absorption (e.g., gut)– Secretion (e.g., gut, exocrine/endocrine glands)

Epithelial tissue

• Gland - group of epithelial cells, specialized to secrete specific substance(s)

• Types of glands:– Exocrine gland - ducts; to outside of body

• e.g., sweat gland

– Endocrine gland - ductless; hormones distributed via bloodstream

• e.g., thyroid, pancreas

Epithelial tissue

Epithelial tissues are categorized by number and type (shape) of cells

Epithelial tissue

• 3 cell types:– Cuboidal– Columnar– Squamous

• Number of cells:– 1 layer thick - simple

• Good for absorption (e.g., intestinal epithelium)

– > 1 layer thick - stratified• Good for protection (e.g., skin)

Epithelial tissue - categories1. Simple cuboidal

Epithelial tissue - categories2. Simple columnar

Epithelial tissue - categories3. Simple squamous

Epithelial tissue -stratified epithelia

Stratified cuboidal - sweat gland

Epithelial tissue -stratified epithelia

Stratified columnar - duct

Epithelial tissue -stratified epithelia

Stratified squamous - esophagus

The basement membrane

• Not usually visible with light microscope• Functions:

– “glue” - holds tissues together– Template for cell migration during development

• Separates epithelial and connective tissues:

connective tissue

basementmembrane

II. Microscopy

Parts of a light compound microscope

Requirements for a clear image

1. Magnification - make the image larger than life-size

2. Resolution - ability to distinguish two objects in close proximity

3. Contrast - make the image stand out against background

1. Magnification

• Our scopes have four objective lenses:– 4X– 10X– 40X– 100X (oil immersion only)

• Ocular lenses are 10X• Total magnification = (objective)(ocular)

e.g., if using the 40X objective,total magnification = (40)(10) = 400X

2. Resolution

i.e., How close can two objects be and still be seen as two objects?

well resolved

poorly resolved

**Note: Increasing magnification does not help problems of resolution!!

3. Contrast

• i.e., How well can you see the image against the background?

• Living cells have little contrast• Use stains

– Dyes that bind to certain functional groups in cells– Examples: hematoxylin, eosin

• But, most stains kill cells– Use phase contrast lighting instead