Histology
the study of
TISSUE
A groups of cells with similar structure that function
together as a unit
Click on title
Types of Cell to Cell Junctions
• Tight junctions provide seals to prevent leaking
across the free epithelial surface.
– Ex. epithelia in the digestive tract that prevents attack of
the wall by acids and enzymes.
• Adhesion junctions (AKA Desmosomes) are like
"spot welds" that cement cells together and prevents
them from pulling apart so that they function as a
unit. Ex. Skin
• Gap junctions contain hollow cylinders (connexons)
that allow chemical cell to cell communication
Ex. heart cells and embryonic cells
Before we start:
Interstitial fluid (ISF):
• The fluid found in the spaces between cells
• Composed of water, amino acids, sugars, fatty
acids, coenzymes, hormones, salts and cellular
products.
• It bathes and surrounds the cells of the body,
and provides a means of delivering materials
To be discussed further when we discuss
the lymphatic system.
1. Epithelial Tissue
• AKA: Epithelium (epi- upon)
Functions
– Protection, secretion, absorption, excretion
– Mitosis is frequent to replace damaged cells
Epithelial Tissue
Characteristics
– Closely packed flat cells
(little intercellular material)
– Avascular (lacking blood vessels)
needs are meet through diffusion from
neighboring cells
Epithelial
Location
• Coverings or linings of organs
• Upper surface of the epithelium is exposed to the
outside of the body OR to an internal cavity
1. Classifying Epithelium
A. Cell shape
• Squamous (squashed): cells are flat, nucleus
near surface of cell, looks like “fried egg”
1. Classifying Epithelium
cell shape
• Cuboidal (cube): cells square shaped with a
central nucleus
1. Classifying Epithelium
cell shape
• Columnar (column): enlongated cell, nucleus
near the bottom, some have microvilli (finger-
like projections that increase surface area),
some have cilia (tiny “hair-like” structures that
help move materials along)
1. Classifying Epithelium
cell shape
• Transitional: flat and/or tall, can extend and
compress
1. Classifying Epithelium
B. Number of cell layers
• Simple: single layer
• Statified: (strat- layer) multiple layers
• Psuedostratified: (pseudo- false) seems to
appear as if it is layered, however, it is one
layer of cells that are differing in size
Other terms to know:
• Apical surface: surface of epithelial tissue
that is exposed to open space or the outside
of the body
• Basal surface: surface of the epithelial tissue
that is the furthest from the apical surface
• Basement membrane: extracellular substance
secreted by epithelial cells, found on the basal
surface of tissue
Practice Looks
• Epithelia Page
• 1. Simple Squamous
2. Simple Squamous
3. Simple Cuboidal
4. Simple Cuboidal
5. Simple Columnar
6. Simple Columnar
7. Pseudostratified Columnnar
8. Pseudostratified Columnnar (Ciliated)
9. Transitional
10. Transitional
11. Stratified Squamous
12. Stratified Squamous
13. Stratified Squamous
14. Stratified Squamous (Keratinized)
15. Stratified Squamous (Keratinized
16. Stratified (High) Cuboidal
17. Stratified Cuboidal