Epithelial Tissue Lecture

Question 1

Human Body = 4 Basic Tissue Types

Answer 1

A) Epithelial
B) Connective
C) Muscular
D) Nervous

Question 2

Characteristics of Epithelial Tissues (4 details)

Answer 2

A.) Generally very closely aggregated polyhedral cells with very little intercellular substance.
-with the exception of a thin layer of glycoproteins glycocalyx covering the cells, no interstitial space can be observed with light microscope – This is in strong contrast to most other types of tissue in the body.
B.) Adhesion between cells is strong.
C.) Usually found covering the body’s surfaces and lining its cavities, or forming glands
D.) Cell shapes vary from tall columnar to low and flat squamous

Question 3

Functions of Epithelial Tissues:

Answer 3

(1) Covering and lining surfaces
a. Protection
b. Separation

(2) Absorption (intestine)
(3) Secretion (glands)
(4) Sensory (neuroepithelium)
(5) Contractile (myoepithelium)

Question 4

Tissue - is what?

Answer 4

• collections of cells with similar morphologic characteristics and specific functions.

Question 5

All epithelial tissues have their basal surface in contact with… what?

Answer 5

connective tissue

Question 6

Basal lamina (Def. and 3 Details)

Answer 6

a thin granular deposit made of very fine fibrils

1. this is composed of amorphous protein-polysaccharide complexes and collagen (also a protein).
2. basal lamina may be formed either from the connective tissue or the epithelium or both (probably epithelium).
3. it does not present a barrier to the diffusion of most substances - this is necessary because epithelial tissues are avascular and depend on adjacent tissue for nutrient and waste exchange.

Question 7

Lamina Propria (Def. and 3 Details)

Answer 7

Connective tissue adjacent to epithelial tissue

• This serves to:
  1. support the epithelium
  2. bind it to neighboring structures
  3. provide it with nutrients (i.e. no blood vessels actually penetrate epithelium). Nutrients and wastes must diffuse through the lamina propria to and from epithelial tissues

Question 8

Epithelial Cohesion - epithelial cells are very cohesive * this is due to: (5 things)

Answer 8

(A) Glycocalyx
(B) Desmosomes - these are believed to be points of attachment between adjacent membranes. These are distributed in “patches” on the membrane – they do not prevent circulation of fluid between epithelial cells.
(C) Junctional Complex - especially important in columnar epithelium
1. actually made up of 3 kinds of different attachments.
2. junctional complex is important not only in the adhesion of cells, but also in the formation of a barrier that prevents free passage of substances between cells
(D) Simple interdigitations – cells interlock with each other
(E) Gap Junction - believed to function more for communication than adhesion.

Question 9

Glandular Epithelium form glands. Details? (3)

Answer 9

1. Specialized in producing a fluid secretion differing in composition from blood or intercellular fluid.
2. Glands may be “unicellular glands” (i.e. goblet cell), or multicellular glands made up of clusters of cells. (Most glands are multicellular)
3. Glands may be Exocrine (with ducts) or Endocrine (ductless) (Secrete into blood stream)

Question 10

Exocrine Glands - May be classified by method of secretion. (3 types)

Answer 10

1) Merocrine glands – secretion granules leave the cell with no loss of cellular material (e.g. the salivary glands)
2) Holocrine glands – the product of secretion is shed with the whole cell-thus resulting in destruction of secreting cell (i.e. sebaceous glands)
3) Apocrine gland – Secretory product is discharged together with parts of apical cycloplasm, but the cell survives and repeats the process. (e.g.mammary)

Question 11

What does Epithelium cover? Types? *Prefixes (5)

Answer 11

usually cover surfaces or line cavities. Classified by shape and number of cell layers.

1. Simple = one cell layer
2. Stratified = more than one cell layer
   - classified according to the shape of the most superficial layer.
3. Squamous = flat - like fried egg
4. Cuboid = cube like
5. Columnar = column like

Question 12

Examples of Epithelium (5/6 Types)

Answer 12

1. Simple squamous–Blood vessel endothelium, mesothelium
2. Simple cuboidal–surface of ovary, lining of ducts
3. Simple columnar–intestinal lining
4. Stratified squamous–skin surface
5. Stratified cuboidal and stratified columnar–very rare - may find in some ducts or glands.

Question 13

Additional Epithelial Types in the body (4)

Answer 13

1. Transitional–lines urinary bladder, ureter, upper urethra
2. Pseudostratified Columnar–nuclei on various levels, but all cells are in contact with basal lamina
3. Neuroepithelia–cells of epithelial origin, specialized for sensory function (e.g. taste buds, olfactory epith.)
4. Myoepithelia–epithelial cells specialized for contractions (e.g. in sweat, mammary, and salivary glands)

Question 14

Renewal of Epithelium (Def. and 3 Details)

Answer 14

this is constantly occuring via mitosis
A. Occurs at different rates depending on the tissue.
B. In stratified tissues - dividing cells located near basal lamina.
C. Metaplasia–under certain physiologic conditions (or pathological) A single type of epithelial tissue may undergo a series of transformations into another type. Example: In heavy cigarette smoking the pseudostratified
epithelium lining bronchi can be transformed into stratified squamous ep.