Histology: The Study of Cells, Tissues, and Organs - Prof. Sankar, Study notes of Medicine

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Atlas of Human Histology

A Guide to Microscopic Structure of

Cells, Tissues and Organs

Robert L. Sorenson

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This atlas is a series of photographs ranging from low to high magnifications of the indi-

vidual tissue specimens. The low magnification images should be used for orientation,

while the higher magnification images show details of cells, tissues, and organs. Al-

though every effort has been made to faithfully reproduce the colors of the tissues, a full

appreciation of histological structure is best achieved by examining the original speci-

mens with a microscope. This atlas is a preview of what should be observed.

The photomicrographs found in this atlas come from the collection of microscope slide

used by medical, dental and undergraduate students of histology at the University of

Minnesota. Most of these slides were prepared by Anna-Mary Carpenter M.D., Ph.D.

during her tenure as Professor in the Department of Anatomy (University of Minnesota

Medical School).

Each tissue specimen, in its entirety, has been digitized with a high resolution 40X

or 60X lens to generate virtual microscope slides. The Virtual Microscope Collection

includes additional slides which complement and extend the core slide collection. Pro-

ducing the virtual slide collection and developing the web site for their presentation was

done with the very capable assistance of Todd C. Brelje Ph.D.

The drawings that appear in the atlas are the product of Jean E. Magney, who is ac-

complished both as an histologist and an artist. Her talented interpretation of biological

structure and its artistic rendering greatly facilitate the learning and comprehension of

histology. These drawings first appeared in “Color Atlas of Histology” Stanley L. Erland-

sen and Jean E. Magney, Mosby 1992.

Robert L. Sorenson, Ph.D.

First edition 2004

Second edition 2008

(second printing 2011)

Copyright © 2008 All Rights Reserved

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InTroduCTIon :

What is histology? Histology is the study of cells, tissues and organs as seen through the micro- scope. Although this atlas is a guide to biological structure that can be observed through the light microscope, histology also includes cellular detail down to the molecular level that can be observed using an electron microscope. The importance of histology is that it is the structural basis for cell, tissue and organ biology and function (physiology) and disease (pathology).

What is the plan for the study of cells, tissues and organs? Histology is organized into four basic types of tissues.

1. Epithelium
2. Connective tissue including

Cartilage and bone

Blood and blood formation

3. Muscle
4. Nervous tissue

Chapters 2-8 are concerned with the features of the four basic tissues. The remaining chapters focus on features of organs. Organs are typically made up of more than one type of tissue and cells with varying degrees of differentiation.

The light microscope, tissue preparation, limits and challenges.

The bright field light microscope is a two lens com- pound optical instrument. The two lenses are the objective and the oculars. The oculars have a 10 fold magnification and the objectives range from 10X, 20X, 40X to 100X. Thus the total magnifica- tion typically ranges from 100 fold to 1000 fold. In practice this means that while using the 10X objec- tive you have a wide field of view, but with low reso- lution. While using the 100X objective you have high resolution, but with a very small field of view. To use a metaphor what this means is that when using the low power objective you can see the for- est but not the trees and while using the high power objective you can see the leaves on the trees but not the forest. Therefore when examining a speci- men it is essential to start with the low power ob- jective to gain perspective and then work up to the highest power magnification as needed to observe the necessary detail.

Examination of tissues requires that they be pre- pared for viewing with a microscope. This is a multi-step process that includes fixation (preserves the tissue), embedment (stabilizes the tissue for sectioning), sectioning (cuts the specimen into thin slices of about 5 um) then placing the sections on a glass slide so they can be stained for viewing.

A note about resolution and detection. Resolu- tion refers to the ability to discriminate between two adjacent objects. For the light microscope with optimal lenses and sample preparation this approaches 0.2 um, which is the theoretical limit for light microscopes. [The eye can resolve about 250-500 um and the electron microscope can re- solve about 1 nm) Detection refers to the ability to detect something and this can be much smaller than the limit of resolution. For fluorescence mol- ecules this can be as little as a few molecules!

Structure Size Light Micro- scope Human ovum 120 um Most cells 10-30 um Red blood cell (RBC)

7 um

Mitochondium 0.4-1.0 um Cilium 0.3 um

Microvillus 100 nm Electron Micro- scope Microtubule 24 nm Myosin filaments 15 nm Intermediate fila- ments

10 nm

Plasma mem- brane

9 nm

Microfilaments (actin)

5 nm

There are several challenges in learning histol- ogy. The first being that the view observed through a microscope gives you a perspective that you are unlikely to have experienced previously. It is a complex data set – one with a broad range of shapes and sizes, with varying shades of red and blue. This complex image offers very few clues that are intuitive. Also, the tissue specimen is a two dimensional slice of a complex three dimensional

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10. Location

a. Example

i. Adjacent to similar cells

ii. Borders a lumen

iii. Surrounded by extensive extra- cellular matrix

iv. Etc.

11. Organization (cells, tissues and organs)

a. Arrangement of cells of similar and different types

b. Arrangement of cells with respect to extracellular material

12. Compare and contrast with similar/differ- ent cells.
13. Heterogeneity among homologous cells:

a. Cell development and differentiation

b. Cell Cycle

c. Active and resting cycles

d. Exposure to a concentration gradient of nutrients

i. Example

1. Skin cells
2. Liver hepatocytes

C. Include questions in the notes.

Carefully formulated questions can often reveal the answer.

D. Drawing (and taking notes) is a way of thinking, seeing and understanding.

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Chapter 1 Introduction & Cell 2

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Chapter 1 Introduction & Cell 3

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Chapter 1 Introduction & Cell 5

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Chapter 1 Introduction & Cell 6

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Chapter 1 Introduction & Cell 8

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Chapter 1 Introduction & Cell 9

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Chapter 1 Introduction & Cell 11

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Chapter 1 Introduction & Cell 12

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