View Full Version : Epithelial tissue

26-05-09, 05:57 PM
I. Definition:
Epithelial tissue covers the whole surface of the body. It is made up of cells closely packed and ranged in one or more layers.
Epithelial tissue that occurs on surfaces on the interior of the body is known as endothelium.
Epithelial cells are packed tightly together, with almost no intercellular spaces and only a small amount of intercellular substance.
Epithelial tissue is usually separated from the underlying tissue by a thin sheet of connective tissue; basement membrane.
The basement membrane:
(i) provides structural support for the epithelium
(ii) binds it to neighbouring structures.
II. Functions of epithelial tissue:
- Protection.
- Sensation: Consist of sensory nerve ending in skin, eyes, ears, nose and on the tongue
- Secretion: Enzymes, hormones and lubricating fluids.
- Absorption: In small intestine : nutrients from the digestion of food.
- Excretion: Epithelial tissues in the kidney and in the sweat glands
- Diffusion: Walls of capillaries and lungs.
- Cleaning: Ciliated epithelium removes dust which have entered the air passages.
- Reduce friction: The smooth epithelial cells that line the entire circulatory system reduce friction between the blood and the walls of the blood vessels.
III. Type:
Epithelial cell can be divided into 2 groups depend on the number of layer of epithelium
(i) Simple epithelium: one layer
2 types by shape and function
(a) Squamous epithelium:
- Thin, flat plates
- Position : Form the lining of cavities such as the mouth, blood vessels, heart and lungs and make up the outer layers of the skin.
(b) Simple cuboidal epithelium
- square or cuboidal.
- spherical nucleus in the centre.
- Position :
+) Glands, duct of glands, kidney tubules
+) Constitute germinal epithelium
(c) Simple columnar epithelium
- Elongated and column-shaped
- Position:
(+) Lining of the stomach and intestines
(+) Sensory reception: nose, ears and the taste buds of the tongue.
- Secrete: mucus or slime
(d) Ciliated Columnar Epithelium
- Like simple columnar epithelium but they posses cilia (hair-like) on free surfaces.
- Cause the movement of the mucus in one direction.
- Position:
(+) Air passage: nose
(+) Uterus and Fallopian tubes.
(e) Glandular Epithelium:
- Consist of columnar epithelium and goblet cells
- Synthethising and secreting many subtances such as : enzymes, hormones, milk, mucus, sweat, wax and saliva.
- Position: in most glands of the body.
(ii) Stratified epithelium (compound): two or more layers
- Composed of severals layer of cell
- The top cells may be:
(+) Keratinised: in mammalian skin
(+) Unkeratinised: The lining of the mouth cavity

26-05-09, 05:59 PM
Glandular epithelium:
@Admin: I want to post more than 4 pictures in a topic.