1. Introduction to Histological Tissues
Elena Stark, MD, PhD
Stephen Schettler, PhD
Department of Pathology & Laboratory Medicine David Geffen School of Medicine at UCLA   Contributor: Paul Frank, DGSOM Class of 2014
THIS FILE HAS COPYRIGHTED MATERIAL. IT IS INTENDED FOR YOUR USE ONLY. DO NOT DISTRIBUTE OR SHARE IT.
Non-graphical content and organization Copyright 2012 M.E. Stark, MD, PhD. 1

2. Main Menu
3 1. Introduction to Histological Tissues – Basic Cell Histology
4 2. Microscopy – Introduction
Microscopy – Light Microscopy Tissue Preparation
Microscopy – Light Microscopy Tissue Preparation – Slicing
Microscopy – Light Microscopy Tissue Preparation – Staining
Microscopy – Light Microscopy Tissue Preparation – Frozen Sections
13 3. Tissue Types
Tissue Types – Muscular
Tissue Types – Nervous
Tissue Types – Connective
Tissue Types – Epithelial
Tissue Types – Summary
19 4. Image Sources
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3. 1. Introduction to Histological Tissues – Basic Cell Histology
Please review the fundamentals of the cell on your own. Before you proceed with this module make sure you are familiar with the terms listed below. We recommend the following textbooks to learn the basics of the cell:
Young B, et al. Wheater's Functional Histology. 5th ed. Churchill Livingstone, Elsevier Limited; March 14, 2006.
Mescher AL. Junqueira’s Basic Histology. 12th ed. McGraw-Hill Medical; August 28, 2009.
Nucleus
Nucleolus
Chromatin
Plasma membrane
Cytoplasm
Cytosol
Cytoskeleton
Mitochondria
Ribosome
Endoplasmic reticulum
Golgi complex
Lysosomes
Peroxisomes
Secretory granule
Inclusions 3

4. 2. Microscopy – Introduction
In the next several slides, we will provide a brief introduction to the subject of microscopy (including the concepts of slicing tissue and staining tissue). Please do not memorize this information, just read through it, it’s only FYI.
There are 3 main modalities of microscopy used to study tissues:
1- Light microscopy (LM) that includes several types, such as bright-field, fluorescence, phase-contrast, and confocal and polarizing microscopy (however, we do NOT expect you to know the difference between these subtypes).
2- Electron microscopy (EM) that includes transmission electron microscopy (TEM) and scanning electron microscopy (SEM).
3- Scanning probe microscopy.
Note: our modules use images taken with the light microscope (LM) and the electron microscope (EM), so we will focus on these types in general (1 and 2 above). 4

5. 2. Microscopy – Introduction
The main difference between light microscopy (LM) and electron microscopy (EM) is their capacity to reveal detail.
LM can magnify up to 1000 times (x1000); while EM can magnify up to 100,000 times
(x ).
Electron microscopy (EM) includes 2 subtypes
Transmission electron microscopy (TEM), also referred to simply as EM,
is an electron beam that goes through the structure to form an image.
This requires ultrathin slices of the structure that is under observation.
The result is a two-dimensional (2-D) image.
Scanning electron microscopy (SEM) produces three-dimensional (3-D) images
of a structure’s surface.
Ignore the i.ds in the images.
SEM image of villi in the intestinal wall (x100).
TEM image of the surface of a villus in the intestinal wall (x56 000).
LM image of 2 villi in the intestinal wall (x150).
© Elsevier. Young et al. Wheater’s Functional Histology 5e – 5

6. 2.1 Microscopy – Light Microscopy Tissue Preparation
Since we will use LM images most often, our focus will be on sample preparation for LM.
For study through LM, samples of tissues are obtained. Biopsies (small pieces of tissue) are taken from organs. The sample must be sliced and stained.
The biopsy is immediately placed in a tissue cartridge (also called a cassette); which is then immersed in a fixative, such as formaldehyde or glutaraldehyde.
The fixative helps:
– Arrest cell metabolism
– Prevent enzymatic degradation
– Harden the tissue
Tissue cartridges/tissue cassettes. 6

7. 2.1 Microscopy – Light Microscopy Tissue Preparation
Once the sample is fixed, it is then infiltrated with an embedding medium**
(usually paraffin wax or plastic resin) in order to be cut into very thin sections,
and then mounted onto glass slides.
**Most tissues must be dehydrated between fixation and embedding.
This example shows paraffin-embedded tumor blocks:
portions of a tumor have been enclosed in paraffin wax.
This can be done with any tissue, NOT just tumor tissue. 7

8. 2.1 Microscopy – Light Microscopy Tissue Preparation
So far, here are the steps of tissue preparation for LM:
Fixation
Dehydration (needed in most cases)
Embedding
(4.) Now, the sample is ready to be sectioned into very thin slices.
(5.) Next, the slices are stained to visualize the tissue components.
The process is as follows:
Fixation > Dehydration > Embedding > Sectioning > Staining > Microscope ready
These steps sometimes result in some distortions in the cell structure or the architecture of the tissue sample. We will see examples of this during the course.
In the next slides, we will present more information on those last 2 very important steps: sectioning and staining. 8

9. 2.1.1 Microscopy – Light Microscopy Tissue Preparation – Slicing
These figures will help you visualize the way three-dimensional (3-D) structures (that have been sliced) appear in two-dimensional (2-D) histological slides.
This is a very simple concept, but essential in understanding histology.
Note: we will look at slides during lab to review this concept. 9

10. Reference: medscape.com
Microscopy – Light Microscopy Tissue Preparation – Staining A
After being sliced, tissues are stained in order to visualize their components.
There are several stains for observation with the light microscope (LM)
that are commonly used:
H&E (hematoxylin and eosin) (image A, at the top)
Stains acidic structures purple/blue (nuclei, ribosomes, and RER).
Stains basic structures pink (most cytoplasmic proteins).
Masson’s trichrome (image B, in the middle)
Stains extracellular structures blue (e.g. collagen).
Giemsa (image C, at the bottom)
Stains blood cells – nuclei stain blue/violet, cytoplasm stains light bluish, red cells stain pale pink.
There are many other types of stains like these that we will discuss throughout the course.
However, in tissue preparation for observation with an electron microscope (EM), there are NO common colored stains (like the ones listed above). Instead, the appearance is black and white with shades of gray (refer to the example shown on slide # 5, “2. Microscopy – Introduction”). Other techniques are applied to prepare tissue for EM (see next slide). B C
Reference: medscape.com 10

11. 2.1.2 Microscopy – Light Microscopy Tissue Preparation – Staining
Histochemical techniques are applied to stain specific components of cells and tissues.
In sample preparation for both LM and EM.
Particularly helpful in understanding tissue
function – often used for diagnosis of
pathological tissues.
Periodic acid–Schiff reaction (PAS) is an example where complex carbohydrates, mucus, and glycogen stain in deep red/magenta color (image A, at the top).
Immunohistological techniques are applied for the identification of specific cell structures – by conjugating antibodies to a fluorescent stain that binds to specific antigens (image B, at the bottom).
Important for diagnosis and research. A
Reference: B
Again, these descriptions are very simplistic.
We will elaborate on staining techniques as the course progresses.
Reference: 11

12. Thin sections are then cut in a refrigerated chamber
Microscopy – Light Microscopy Tissue Preparation – Frozen Sections
In situations where an urgent diagnosis is needed (e.g. when the patient is undergoing surgery and a biopsy has been taken, the surgeon needs to know the results right away in order to proceed), the tissue is biopsied and then rapidly frozen to -150ºC to -170ºC by immersion in liquid nitrogen.
Thin sections are then cut in a refrigerated chamber
(called a cryostat) and stained without previous fixation, dehydration, or embedding.
This way of tissue preservation is NOT as good as when using the regular method (previously described).
Frozen sections are usually stained with H&E,
but can also be treated with histochemical and
immunohistological techniques.
Nonfrozen section.
Frozen section. 12

13. 3. Tissue Types Cells in the human body are organized into tissues.
In the next few slides, we will mention the 4 basic types of tissue that are present in the human body. We will elaborate on these tissues throughout the year.
It is important that you understand the basic differences between tissues.
If you find this introduction too simplistic, please refer to these 2 textbooks:
Junqueira's Basic Histology by Mescher AL. 12th edition
Wheater's Functional Histology by Young B, et al. 5th edition
Cells in the human body are organized into tissues.
There are 4 types of tissues:
1. Muscular
2. Nervous
3. Connective
4. Epithelial
Tissues have CELLS and EXTRACELLULAR MATRIX or material (ECM) surrounding the cells.
The proportion of these 2 components varies depending on the type of tissue:
– Muscular tissue has a high cell density;
– Nervous tissue is formed almost exclusively of cells and has virtually NO extracellular material;
– Connective tissue is very rich in extracellular material and has a low proportion of cells;
– Epithelial tissue has a very high proportion of cells and very limited amount of extracellular material. 13

14. 3.1 Tissue Types – Muscular
There are 3 types of muscle tissue:
1. Skeletal (image A, at the top)
2. Smooth (image B, in the middle)
3. Cardiac (image C, at the bottom)
Muscle cells specialize in contraction.
Muscle tissues have high cell density and little ECM.
Muscle cell (1 in each type of muscle)
ECM in muscle tissue
Note: we will talk more about muscle in Block 2, where we cover the heart (cardiac muscle) and blood vessels (smooth muscle); and also in Block 4, where we cover skeletal or voluntary muscle (muscles we can contract at will). B
ORIENT YOURSELF: Images A, B, and C are histological slides of muscular tissue that have all been stained for LM observation at medium magnification.
Image A: thin slices of voluntary muscle
Image B: thin slices of the wall of an organ
Image C: thin slices of the heart
(To train your eye to the differences between tissues, we will practice with
many slides in lab.) For now, focus on the general concepts. C 14

15. An organ showing several types of cells and tissues.
3.2 Tissue Types – Nervous
Nervous cells specialize in generation and conduction of electrical impulses.
(We will cover nervous tissue in detail in Block 5.)
Nervous tissue has abundant cells of different types and virtually NO ECM.
For our purposes (before Block 5), we will identify nerves in terms of the structure highlighted below. This is a small peripheral nerve showing the long neuronal axons, as they appear in a cross-section. It looks like a bundle of cross-sected wires.
In this particular section, some of the axons are running obliquely – appearing oval in shape (vs. perfect circles).
An organ showing several types of cells and tissues.
The purpose of this slide is to start becoming familiar with the appearance of a cross-sected peripheral nerve in an organ. 15

16. 3.3 Tissue Types – Connective
Connective tissue has much ECM and few cells Thus, connective tissues are good “supporters” (since ECM is usually stronger than cells). They are found mainly forming the framework of organs or supporting other tissues.
This week’s lab will cover connective tissue in detail. 16

17. 3.4 Tissue Types – Epithelial
Epithelia have many cells and little ECM .
Epithelia are found mainly covering and lining organs.
This week’s lab will cover epithelia in detail.
Ignore the i.ds in the image. 17

18. Extracellular matrix (ECM)
3.5 Tissue Types – Summary
Tissue type
Cells
Extracellular matrix (ECM)
Function
Muscular
Contractile cells
Very small
amount
Movement of body (skeletal)
Involuntary movement (smooth)
Beating of heart (cardiac)
Nervous
Neurons containing long processes, called axons and dendrites
Supporting cells
Virtually NONE
Conduction of nerve impulses
Connective
Fibroblasts
Other cells
Large amount
Support of organs
Protection of organs
Epithelial
Tightly-packed cells with mostly flat edges
Very small amount
Lining and covering surfaces of body and body cavities
Glands: secretion (to be discussed in the next module: “Epithelial Tissue”) 18

19. UCLA David Geffen School of Medicine, Integrative Anatomy.
4. Image Sources
Young B, et al. Wheater's Functional Histology. 5th ed Churchill Livingstone, Elsevier Limited; March 14, 2006.
Mescher AL. Junqueira’s Basic Histology. 12th ed McGraw-Hill Medical; August 28, 2009.
UCLA David Geffen School of Medicine, Integrative Anatomy. 19

20. 20

21. 3.1 Tissue Types – Muscular
BACK
3.1 Tissue Types – Muscular A
There are 3 types of muscle tissue:
1. Skeletal (image A, at the top)
2. Smooth (image B, in the middle)
3. Cardiac (image C, at the bottom)
Muscle cells specialize in contraction.
Muscle tissues have high cell density and little ECM.
Muscle cell (1 in each type of muscle)
ECM in muscle tissue
Note: we will talk more about muscle in Block 2, where we cover the heart (cardiac muscle) and blood vessels (smooth muscle); and also in Block 4, where we cover skeletal or voluntary muscle (muscles we can contract at will). B
ORIENT YOURSELF: Images A, B, and C are histological slides of muscular tissue that have all been stained for LM observation at medium magnification.
Image A: thin slices of voluntary muscle
Image B: thin slices of the wall of an organ
Image C: thin slices of the heart
(To train your eye to the differences between tissues, we will practice with
many slides in lab.) For now, focus on the general concepts. C 21

22. 3.1 Tissue Types – Muscular
BACK
3.1 Tissue Types – Muscular A
There are 3 types of muscle tissue:
1. Skeletal (image A, at the top)
2. Smooth (image B, in the middle)
3. Cardiac (image C, at the bottom)
Muscle cells specialize in contraction.
Muscle tissues have high cell density and little ECM.
Muscle cell (1 in each type of muscle)
ECM in muscle tissue
Note: we will talk more about muscle in Block 2, where we cover the heart (cardiac muscle) and blood vessels (smooth muscle); and also in Block 4, where we cover skeletal or voluntary muscle (muscles we can contract at will). B
ORIENT YOURSELF: Images A, B, and C are histological slides of muscular tissue that have all been stained for LM observation at medium magnification.
Image A: thin slices of voluntary muscle
Image B: thin slices of the wall of an organ
Image C: thin slices of the heart
(To train your eye to the differences between tissues, we will practice with
many slides in lab.) For now, focus on the general concepts. C 22

23. An organ showing several types of cells and tissues.
BACK
3.2 Tissue Types – Nervous
Nervous cells specialize in generation and conduction of electrical impulses.
(We will cover nervous tissue in detail in Block 5.)
Nervous tissue has abundant cells of different types and virtually NO ECM.
For our purposes (before Block 5), we will identify nerves in terms of the structure highlighted below. This is a small peripheral nerve showing the long neuronal axons, as they appear in a cross-section. It looks like a bundle of cross-sected wires.
In this particular section, some of the axons are running obliquely – appearing oval in shape (vs. perfect circles).
An organ showing several types of cells and tissues.
The purpose of this slide is to start becoming familiar with the appearance of a cross-sected peripheral nerve in an organ. 23

24. An organ showing several types of cells and tissues.
BACK
3.2 Tissue Types – Nervous
Nervous cells specialize in generation and conduction of electrical impulses.
(We will cover nervous tissue in detail in Block 5.)
Nervous tissue has abundant cells of different types and virtually NO ECM.
For our purposes (before Block 5), we will identify nerves in terms of the structure highlighted below. This is a small peripheral nerve showing the long neuronal axons, as they appear in a cross-section. It looks like a bundle of cross-sected wires.
In this particular section, some of the axons are running obliquely – appearing oval in shape (vs. perfect circles).
An organ showing several types of cells and tissues.
The purpose of this slide is to start becoming familiar with the appearance of a cross-sected peripheral nerve in an organ. 24

25. 3.3 Tissue Types – Connective
BACK
3.3 Tissue Types – Connective
Connective tissue has much ECM and few cells Thus, connective tissues are good “supporters” (since ECM is usually stronger than cells). They are found mainly forming the framework of organs or supporting other tissues.
This week’s lab will cover connective tissue in detail. 25

26. 3.3 Tissue Types – Connective
BACK
3.3 Tissue Types – Connective
Connective tissue has much ECM and few cells Thus, connective tissues are good “supporters” (since ECM is usually stronger than cells). They are found mainly forming the framework of organs or supporting other tissues.
This week’s lab will cover connective tissue in detail. 26

27. 3.4 Tissue Types – Epithelial
BACK
3.4 Tissue Types – Epithelial
Epithelia have many cells and little ECM .
Epithelia are found mainly covering and lining organs.
This week’s lab will cover epithelia in detail.
Ignore the i.ds in the image. 27

28. 3.4 Tissue Types – Epithelial
BACK
3.4 Tissue Types – Epithelial
Epithelia have many cells and little ECM .
Epithelia are found mainly covering and lining organs.
This week’s lab will cover epithelia in detail.
Ignore the i.ds in the image. 28