Histology Guide virtual histology laboratory

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Histology Guide

Chapter 1 - Introduction

Ultrastructure is the architecture of cells that is visible at higher magnifications than found on a standard optical light microscope. Electron microscopes are used to investigate the ultrastructure of biological specimens.

This chapter demonstrates the potential of electron microscopy in understanding histology.

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Fig 002 Microscopes

Transmission Electron Microscopy (TEM)

TEM produces two-dimensional images of a specimen by imaging a thin section with a beam of electrons. Ultrathin tissue sections are stained with heavy metals (such as osmium tetroxide, uranium or lead salts). The images are colorless and have a resolution of ~0.1 nm (or ~1000x greater than a light microscope).

Example micrographs of cells imaged with TEM.

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EM 006 Fibroblast

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EM 017 Small Intestine

Schematic comparison of a cell imaged by TEM and light microscopy.

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Fig 007 Cell Structure

Ultrastructure of cells as seen by TEM.

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EM 001 Cell Structures

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EM 007 Nucleus

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EM 004 Cell Structures

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EM 008 Golgi Apparatus

EM 026 Endoplasmic Reticulum

Figures

Schematic representations of a simple columnar cell from images acquired by TEM, SEM, and freeze fracture.

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Fig 009 Cell Structure

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Fig 010 Nucleus

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Fig 014 Mitochondria

Scanning Electron Microscopy (SEM)

Scanning electron microscope (SEM) produces three-dimensional images of a speciment by measuring the relative differences in the reflection of a focused beam of electrons scanned across a specimen. Biological specimens are usually coated with a thin layer of metal (such as platinum) to form a replica that is then imaged. This allows the surface structures of organelles, cells, and tissues to be visualized. The images are colorless and have a resolution of ~10 nm (or ~100x greater than a light microscope).

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EM 206 Red Blood Cells

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EM 195 Podocytes

Freeze Fracture

Freeze fracture reveals the internal structure of biological specimens. Frozen specimens are physically broke apart (fracturing) and the exposed surface is coated with evaporated platinum. This replica is then imaged by TEM.

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Fig 011 Freeze Fracture

Freeze fracture forms enface views of membrane-bound compartments that give striking three-dimensional representations.

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EM 009 Freeze Fracture

Comparison of Ultrathin Sections and Freeze Fracture

Micrographs of a mast cell as seen by ultrathin sections and freeze fracture.

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EM 014 Mast Cell (TEM)

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EM 015 Mast Cell (Freeze Fracture)

Examples of Freeze Fracture

The interior structure of cells and organelles as seen by freeze fracture.

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EM 011 Nuclear Envelope

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EM 295 Plasma Membranes

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EM 010 Plasma Membrane

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EM 013 Endoplasmic Reticulum

Mitosis

Cells undergoing mitosis as seen by transmission electron microscopy (TEM).

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EM 207 Mitosis

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EM 115 Mitosis