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 H 2 O –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 - categories 1. Simple cuboidal

Epithelial tissue - categories 2. Simple columnar

Epithelial tissue - categories 3. 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 basement membrane

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