Lectures 3 & 4
Histology: The Study of
Tissues
4-1
Tissues and Histology
• What is a Tissue?
– A collection of similar cells and noncellular
substances (extracellular matrix) secreted by the
cells
• Tissue Level of Organization
–
–
–
–
Epithelial
Connective
Muscle
Nervous
• Histology: Microscopic Study of Tissues
4-2
Epithelium Characteristics
Fig. 4.1
1. Consists almost
entirely of cells
2. Covers body
surfaces and forms
glands
3. Has free and basal
surface
4. Avascular
5. Undergoes mitosis
4-3
Classification of Epithelium:
How to Make Sense of It All?
There are 2 basic features (or criteria) for classification
of epithelium:
1. Number of cell layers
•
•
Simple
– Single layer
Stratified
– More than 1 layer
Exceptions?
•
•
Pseudostratified
– Single layer; only some cells reach free surface
Transitional
– Number of cell layers decreases as it is stretched
Fig. 4.2
4-4
Classification of Epithelium
2. Shape of cells
• Squamous (=scaly)
–
•
Cells flattened
Cuboidal
–
•
Cells cube-shaped
Columnar
–
Cells are taller than wide
Fig. 4.2
4-5
Types of Epithelium
• Name of epithelium is combination of: number of
cell layers and shape of cell (Table 4.2)
• 3 types of simple: simple squamous epithelium,
simple cuboidal epithelium and simple columnar
epithelium
• 3 types of stratified: stratified squamous
epithelium, stratified cuboidal epithelium and
stratified columnar epithelium
• Pseudostratified columnar epithelium
• + Transitional epithelium: Cuboidal to columnar when
not stretched and squamous-like when stretched
4-6
Review Question
Which of the following statements about epithelial tissue is
correct?
(a) All cells of pseudostratified columnar epithelial tissue
have a free surface.
(b) You would predict simple squamous epithelium lining
the inside of an organ that absorbs substances.
(c) Transitional epithelium has multiple layers of cells that
can change shape.
(d) The epithelium of your skin is a simple squamous
epithelium.
(e) Cuboidal or columnar cell shapes are optimal for
diffusion.
4-7
Glands
•
•
Secretory organs made mostly of epithelium
Form as invaginations (ingrowths) of outer layer
of epithelium in embryo
• Two basic types:
1. Exocrine:
– Have ducts lined with
epithelium
2. Endocrine
– Have no ducts
– Examples include pituitary gland, pancreas,
thyroid gland
Fig. 4.4
4-8
Connective Tissue
• Abundant and diverse
• Consists of cells separated by extracellular
matrix
• Specialized cells produce the extracellular
matrix
– Suffixes
• -blasts: create the matrix
• -cytes: maintain the matrix
• -clasts: break the matrix down for remodeling
• Performs variety of important functions
4-9
Connective Tissue Categories
• Embryonic or
mesenchyme
• Adult
– Loose
– Areolar
– Adipose
– Dense
– Cartilage
– Bone
– Blood
Table 4.6
4-10
Loose Connective Tissue
Table 4.9
Areolar tissue
• Loose packing material of most organs and tissues
• Attaches skin to underlying tissues
• Contains collagen, reticular, elastic fibers and variety of
cells
4-11
Loose Connective Tissue
Adipose Tissue
• Consists of adipocytes
– Types
• Yellow (white)
– most abundant,
white at birth and
yellows with age
• Brown
– found only in
specific areas of
body as axillae, neck
and near kidneys
Table 4.9
4-12
Dense Regular Connective Tissue
Has abundant collagen fibers
• Tendons: Connect muscles to bones
• Ligaments: Connect bones to bones
Table 4.10
4-13
Dense Irregular Connective Tissue
• Forms most of dermis of the skin
Table 4.10
4-14
Elastic Connective Tissue
• Ligaments in vocal folds
• In walls of elastic arteries
Table 4.10
4-15
Review Question
In which of the following locations would you expect to find
dense irregular connective tissue?
(a) Nuchal ligament
(b) Dermis of skin
(c) Vocal cords
(d) Large arteries
(e) Tendon
4-16
Points to Remember
• Two basic components to a tissue:
– Similar cells specialized for a function
– Non-cellular matrix secreted by the cells
• Epithelial tissue is typically a covering or
lining
• Connective tissue is diverse and extremely
abundant
4-17
Questions?
4-18