Epithelial Tissue - Histology (L1)

Question 1

Epithelial tissue functions

Answer 1

Epithelial tissues function in protection and absorption, forming sheets covering a surface; in secretion, forming glands; and in excretion. Examples include skin (epidermis), glands, and the linings of the digestive tract and blood vessels.

The cells of epithelial tissues are tightly packed together, with very little intercellular materials or spaces.

Question 2

Epithelial cells

Answer 2

1. Flattened or squamous
2. Cube- shaped or cuboidal, (when viewed in a section perpendicular to the tissue surface), and
3. Columnar.

Epithelial tissue may be only one cell thick, in which case it is called simple epithelium, or it may be two or more cells thick and called stratified epithelium.

Question 3

Basement membrane

Answer 3

Epithelium, regardless of type, is usually separated from the underlying connective tissue by an extracellular basement membrane. The basement membrane is not penetrated by blood vessels; epithelia are thus dependent on the diffusion of oxygen and metabolites from underlying tissues. Both epithelial and connective tissue cells are thought to participate in the formation of the basement membrane.

Question 4

Toluidine blue

Answer 4

An acid loving dye, used to stain squamous epithelial cells from cheek

Question 5

Kinds of epithelium in the thin section of the kidney

Answer 5

1. Simple squamous

2. Simple cuboidal

Question 6

Glomerulus

Answer 6

Each simple squamous epithelium structure has a spherical capillary bed called a Glomerulus which is surrounded by a fluid space bound by a single layer of simple squamous epithelial cells called the Bowman’s Capsule.

Question 7

Bowman’s capsul

Answer 7

Single layer of simple squamous epithelial cells that surround the glomerulus.

Question 8

Lumen

Answer 8

Notice the capillary bed, the lumen (the clear space) around it and at the edge of the lumen is the simple squamous epithelium.

Question 9

Simple squamous epithelium

Answer 9

Only found in specific parts of the slide. Notice the capillary bed, the lumen (the clear space) around it and at the edge of the lumen is the simple squamous epithelium.

These cells act as barriers containing the fluid leaking from the capillaries, that will be subsequently be concentrated into urine by the simple cuboidal epithelium.

Question 10

Simple cuboidal epithelium

Answer 10

This tissue type is the majority of the tissue in the specimen. Simple cuboidal epithelial cells are approximately the same dimensions in each direction or roughly cube shaped, though in cross section the cells appear square to polygonal in shape.

Nuclei are usually round or circular in cross section.

The function of the cells you see here is concentration of urine.

Non-kidney examples of this tissue are found in salivary glands and pancreas. Simple cuboidal epithelium usually lines small ducts and tubules which may have excretory, secretory, or absorptive functions.

Question 11

Stratified squamous epithelium

Answer 11

The major function of this type of epithelium is protection against mechanical abrasion.

Cells closest to the basement membrane appear cuboidal, and here the tissue’s (adult type) stem cells are actively dividing. However the outermost layer of epithelia consists of squamous shaped cells, so this epithelium overall is named stratified squamous epithelium, even though the innermost cell layers are not squamous in shape.

This type of tissue is found in the oral cavity, pharynx, esophagus, anal canal and vagina.

Question 12

Simple columnar epithelial

Answer 12

Found in the cross-section of the duodenum.

At 10x magnification, search for an area of the slide that has finger-like projections surrounded by a lumen - these are the villi.

Switch to 40x. Cells are tall and columnar, at right angles to the basement membrane. The nuclei are elongated and may be arranged toward the base, the center or occasionally the apex.

Simple columnar epithelium is most often found on highly absorptive surfaces such as in the small intestine, although it may constitute the lining of highly secretory surfaces such as that of the stomach.

Question 13

Pseudostratified ciliated columnar epithelium

Answer 13

gives one the erroneous impression that there is more than one layer of cells. However, all the cells rest on the basement membrane (although not all cells extend to the luminal surface), so it is a simple epithelium.

The nuclei are disposed at different levels, thus creating the illusion of cellular stratification.

This type of tissue is almost exclusively confined to the larger airways of the respiratory system (i.e., trachea) and therefore often is referred to as respiratory epithelium.

Question 14

Stratified squamous keratinizing epithelium

Answer 14

This specialized form of epithelial tissue constitutes the surface layer of the skin and is adapted to withstand constant abrasion and desiccation; the outer cells of the skin have become engorged with the protein keratin, they lack nuclei, appear scale-like and are dead. Deeper in the tissue are cells of this tissue with lesser amounts of keratin. They have nuclei and were alive before sample harvesting. Thus the tough non-living surface of skin, is composed of the protein keratin and the remnants of degenerate epithelial cells. These dead cells are replaced by stem cells living in pockets close to the tissue’s basement membrane. The stem cells divide by mitosis, pushing the maturing epithelial cells out toward the surface.

Question 15

Keratin

Answer 15

Protein that engorges Stratified squamous keratinizing epithelium

Question 16

Transitional epithelium

Answer 16

Found in cross-section of ureter.

This form of stratified epithelium is observed mostly to the urinary tract in mammals (superior urethra, bladder, ureters, but also in the prostate in male mammals), where it is highly specialized to accommodate a great degree of stretch and to withstand the mild toxicity of urine.

Transitional epithelium is so-named because over time it exhibits cell shapes from cuboidal to squamous in shape, depending on the amount of pressure the lumen is experiencing. Under high pressure the lumen will expand and the cells flatten and stretch out into a squamous shape. In the relaxed state, as seen in most of the prepared ureter slides, this tissue appears to be stratified, approximately 4-5 cells thick. Basal cells are roughly cuboidal, intermediate cells are more polygonal, and the luminal surface cells may be large and rounded.

Notice that the plasma membranes of the surface cells are quite thick to provide a permeability barrier.

Notice the two layers of smooth muscle surrounding the epithelia; the inner layer is longitudinal and the outer layer is circular. The next layer of the section is loose connective tissue and the outermost layer is adipose tissue (fat cells).