Simple epithelium

Simple epithelium only one layer of cells present on the basement membrane. It can be classified as simple squamous, simple columnar and simple cuboidal type.

Simple squamous epithelia

• The simple epithlia is also called as pavemental epithelia.
• Consists of flat scale like or plate like squamous cells separated by narrow intercellular spaces.
• The edges of the cells are usually serrated but may be smooth.
• The cells rest on connective tissue and their free surface shows delicate, cuticular border.
• The nucleus situated in the centre of the cells is spherical or oviod causing a bulging of cytoplasm.
• On surface view the cells appear as delicate mosaic which can be demonstrated well by precipitation of silver in the intercellular spaces.
• In profile the cells are spindle shaped, thin at the ends and thicker in the centre where the nucleus is situated.

Distribution 

• This epithelium lines the peritoneal, pleural and pericardial, cavities. Here it is called mesothelium.
• The mesothelium together with an underlying stratum of connective tissue, forms serous membranes viz. peritoneum, pleura and pericardium.
• It lines the heart and all blood vessels and lymph vessels; here it is called endothelium. It also lines the membranous labyrinth of the internal ear, Bowman’s capsule and tubules, alveoli of the lungs.

Simple cuboidal epithelia

• It consists of a single layer of more or less cubical cells, resting on a basement membrane.
• This is found in many parts of kidney tubules, thyroid gland acinar ducts of exocrine glands, mammary glands etc.

Simple columnar epithelium

• It consists of a single layer of tall prismatic cells resting on the basement membrane.
• The cells generally are wider at the free borders and narrow at the basal or attached ends and have oval nuclei, situated at the basal part of the cell.
• Pyramidal epithelium of many glands is a modification of the columnar epithelium.
• Simple columnar epithelium is found in the stomach, intestines interlobular and lobar ducts of many glands, in gall bladder, uterus, vas difference etc.
• The simple columnar epithelium of the small intestines shows certain special features. The free borders of cells show fine striations under EM which have been identified as micro villi.

Goblet cells

• They are the common variation of simple columnar epithelium found in the intestine and respiratory passages.
• They are unicellular mucous secreting glands.
• They become modified from the columnar cell by the deposition of mucous droplets.
• The cells swell up and the nucleus surrounded by a little cytoplasm is displaced by mucin. On further expansion, the cell membrane ruptures with escape of mucin.
• In ordinary H&E preparations mucin is unstained. The cell after rupture regenerates and the process is repeated.

Cilia

• The motile cytoplasmic processes present at the free surface columnar cells are called as cilia in certain locations.
• The length of cilia in different types of epithelium varies considerably.
• At the base of each cilium, in the superficial layer of protoplasm is a small thickening, the basal corpuscle, which stains back with iron haemotoxylin.
• The movement of the cilia consists of a rapid effective beat and a slow recovery stroke, always in one direction (usually towards the external opening of tube or passage which is lined by the ciliated epithelium). The ciliary movement occurs in regular waves.n some organs, the cells carry long non-motile cilia (stereo-cilia and these are supposed to help in elimination of secretion from the cells.