Biology Today - February 2018

Simple cuboidal

epithelium

Consists of short, cube-shaped cells.

Nuclei are located in the centre of the cell.

The cells of cuboidal epithelium often form

microvilli on their free surface which

gives a brush-like appearance to their free

border, hence, also called brush bordered

cuboidal epithelium. Microvilli increase

absorptive surface area also.

Present in the small salivary and

pancreatic ducts, thyroid vesicles, parts

of membranous labyrinth, proximal

and distal convoluted tubules of

the nephrons of kidneys, ovaries,

seminiferous tubules, ciliary bodies,

choroid and iris of eyes. Other sites are

the inner surface of the lens, the pigment

cell layer of the retina and sweat glands.

Protection, secretion,

absorption, excretion

and gamete

formation.

Simple columnar

epithelium

Elongated cells are placed side by side like

column. The outer free surface of each cell

is slightly broader. The nuclei are somewhat

elongated along the axis of the cells. Nuclei lie

near the bases of the cells. Certain cells of this

epithelium contain mucus (a slimy substance)

and are called goblet (or mucous) cells.

The epithelium containing mucus secreting

cells, along with the underlying supporting

connective tissue is called mucosa or

mucous membrane.

Found in the lining of the stomach,

intestine, gall bladder and bile duct. It

also forms the gastric glands, intestinal

glands and pancreatic lobules where

it has secretory role and is called

glandular epithelium.

Intestinal mucosa have microvilli to

increase absorptive surface area, it is

called brush bordered columnar

epithelium.

Protection, secretion

and absorption.

Simple ciliated epithelium

Numerous delicate hair-like outgrowths, the

cilia are found on their apical surfaces. Mucus

secreting goblet cells also occur in the ciliated

epithelium. It is of two types:

(i) Ciliated columnar epithelium :

Columnar cells that have cilia on the free

surface.

(ii) Ciliated cuboidal epithelium :

Cubical cells that have cilia on the free

surface.

Lines most of the respiratory tract and

Fallopian tubes (oviducts), ventricles

of brain and central canal of spinal

cord, tympanic cavity of middle ear and

auditory tube (Eustachian tube).

Occurs in certain parts of nephrons of

the kidneys.

Maintenance as well

as movement of

mucus, urine, eggs and

cerebrospinal fluid in

particular direction. In

nephrons of kidneys,

the cilia helps in the

movement of urine.

Pseudostratified

epithelium

Cells are columnar, but unequal in size.

Long cells extend up to free surface while

short cells do not reach the outer free surface.

Long cells have oval nuclei, and short cells

have rounded nuclei. Mucus secreting goblet

cells are also present in this epithelium.

Epithelium is one cell thick, but it appears to

be multilayered which is due to the fact that

the nuclei lie at different levels in different cells.

Hence, it is called pseudostratified epithelium. It

is of two types: (i) Pseudostratified columnar

epithelium; (ii) Pseudostratified columnar

ciliated epithelium.

Pseudostratified columnar epithelium

occurs in the large ducts of parotid

salivary glands, the urethra of the human

male and in the olfactory mucosa.

Pseudostratified columnar ciliated

epithelium occurs in the trachea and

large bronchi. The movements of the cilia

propel the mucus and foreign particles

towards the larynx.

Protection, secretion,

movement of secre-

tions from glands,

urine and semen in

male urethra and

mucus loaded with

dust particles and

bacteria from the

trachea towards the

larynx.