Histology is the study of tissues.
Tissues: a group of cells that are similar in structure and function
Tissues are studied in thin sections. Microscopic observation reveals that the cells in a
tissue share morphological features and are arranged in an orderly pattern that
achieves the tissue’s functions.
The many types of cells in the human body are organized into four types of tissues:
1. Epithelial,
2. connective,
3. muscle,
4. nervous.
1
Epithelial tissue (epithelium): sheets of cells that cover exterior surfaces of the body,
line internal cavities and passageways, and form certain glands.
This type of tissue can be classified according to the shape of the cells and number of
the cell layers formed as shown in the pictures.
Simple=1 layer
Stratified= 2 or more layers of cells
Cell shapes: squamous (flattened and thin), cuboidal (cube shaped), or columnar
(rectangular, taller than it is wide).
The bottom of the cells are attached to a basement (basal) membrane. The top of the
cells are called the apical surface
2
The layers and shapes can be combined to describe the specific type of epithelium
under observation. For example, simple squamous epithelium, simple columnar
epithelium, stratifed cuboidal epithelium etc.
3
For each tissue type note the description, function, location and annotations on
micrographs.
Images of tissues do not look identical but they have traits in common. To train your
eye to recognize and differentiate between tissue types, compare the images on
these slides to those in your eBook, Connect Anatomy & Physiology Revealed (APR)
as well as online.
4
5
6
7
8
Transitional epithelium is named for the gradual changes in the shapes of the apical
cells as the bladder fills with urine. It is found only in the urinary system, specifically
the ureters and urinary bladder so it is also known as urothelium
9
Muscle tissue is characterized by properties that allow movement. There are 3 types
of muscle tissue. Note that skeletal muscle is the only one that we have
voluntary/conscious control over.
10
In lecture, you will learn more about what forms the striations
11
To distinguish cardiac muscle from skeletal muscle look for the intercalated discs.
Cardiac muscle cells (cardiomyocytes) are typically have a single centrally located
nucleus, whereas skeletal muscle cells have multiple nuclei per cell and the nuclei
tend to be pushed up against the cell membrane.
12
13
Nervous tissue is characterized as being excitable and capable of sending and
receiving electrochemical signals that provide the body with information.
14
This micrograph is stained yellow. You will also see images of nervous tissue stained
blue or red so look at a variety of pictures.
15
Connective tissue connects other tissues and organs. It is the most diverse of the 4
main tissue types. Whereas epithelial tissue has cells closely packed with little to no
extracellular space in between, connective tissue cells are often dispersed in
extracellular space also known as matrix. You will consider the 5 main types of
connective tissue listed here.
16
There are 2 types of loose connective tissue (CT). This one shows areolar CT. The inset
on the left shows epithelium tissue attached to a sheet of connective tissue named
the lamina propria.
Three main types of fibers are found in the matrix:
•Elastic fibers - often look like strands of hair.
•Collagen fibers - are thick and straighter than reticular fibers
•Retiocular fibers – similar in composition to collagen but are narrower and tend to
branch
17
The 2nd type of loose CT is reticular, named for the abundance of reticular fiber. This
somewhat resembled a bunch of grapes. They may look like something else to you;
use whatever analogy helps you as a memory aid.
18
There are 3 types of dense CT: regular, irregular and elastic.
Dense regular can sometimes look like smooth muscle to the untrained eye. Notice
however that the nuclei are not as prominent as in smooth muscle.
19
The fibers of dense irregular tissue run in random directions. You will see this tissue
again when you examine the dermis of the skin.
20
Elastic tissue has lots of stringy hair-like elastic fibers
21
You’ll notice that adipose tissue is here classified as loose CT. Some textbooks groups
it as such, others list it as a separate category. One of the identifying features is that it
looks like soap bubbles, or chicken wire.
22
Bone (osseous) tissue is the hardest of the CT. The histology of transverse tissue from
long bone looks like a cross section of tree rings. The pattern is a result of concentric
circles of osteocytes (bone cells) with a central canal. You will examine more details
of bone structure in future modules.
23
The 3 types of cartilage (hyaline, elastic, fibrocartilage) can be distinguished by the
appearance of the matrix and the size of lacunae (chambers that house the cells).
Hyaline is the most common type of cartilage in the body. Under the microscope,
tissue samples appear clear, almost glassy. The surface of hyaline cartilage is smooth.
24
The matrix of elastic cartilage is characterized by elastic fibers therefore the cartilage
isn’t clear like hyaline. The lacunae are often larger in appearance.
25
Fibrocartilage has thick bundles of collagen fibers dispersed through its matrix.
Remember that different stains may be used in different preparations so don’t rely on
color.
26
Blood is complex and is considered an organ by some biologists. Here we’ll classify it
as a tissue. It is liquid connective tissue. You will learn more about the different
components of blood in A&P II; for now you should be able to recognize an image of
it from the tiny pink donut-like red blood cells, and the various white blood cells with
their colored nuclei.
27
28