Classification of Epithelium

ByDr.Alaa AlsahlanyDec 30th, 2020

Classification of epithelium

Example

Based on cell shape
Based on cell layer
• Endothelim ( lining of blood vessels)
• S. Squamous
• (1) SIMPLE (S.)
• One layer
Thyroid follicles
• S. Cuboidal

Stomach, Intestine

S. Columnar
(non-ciliated)


Uterine tube
Trachea
• S. Columnar (ciliated)

• Nasal cavity

• Pseudostratified columnar
• (2) PSEUDOSTRATIFIED
• (They appear stratified but in fact they are simple)

Example

Based on cell shape
Based on cell layer
• Mouth cavity
• Str. Squamous
• Non-keratinized
• (3) STRATIFIED (Str.)
• More than one layer
Skin
Str. Squamous
Keratinized


Sweat ducts
Str. Cuboidal

conjunctiva

Str. Columnar

Urinary bladder

Transitional (stratified
epithelium
with
characteristics that allow
it to Distend)

Cell death

(1) Necrosis

(2) Apoptosis

Necrosis

Death of the cells due to tissue injury

Necrotic cells swell and subsequently rupture resulting in formation of cell debris.

This induces an inflammatory response at the site of injury

Necrosis of myocardium due to ischemia

Apoptosis (Programmed Cell Death or Regulated Cell Suicide)

Apoptotic cells shrink.

Their plasma membranes undergo blebbing without any loss (i.e. they are intact).

Their nuclei fragment forming apoptotic bodies.

Since the plasma membrane is intact, their intracellular contents are not released into the extracellular environment, so no inflammation

Apoptosis is a central mechanism controlling development in regulating the number of cells that mediate a particular activity (e.g. separation of the developing fingers and toes during embryogenesis).

Adipose tissue

General Features
A special type of connective tissue formed by aggregation of fat cells (adipocytes). It constitutes 15–20% of body weight in men and 20–25% in women.

Two types

(1)Parietal : It is found subcutaneously (under the skin) throughout the body
(2)Visceral: around viscera

Function

(1) Is a reservoir of energy.

(2) Gives shape to the body

(3) Gives thermal insulation to the body because it is a bad conductor of heat

Histological types of fat

Brown adipose tissue(embryonic type)
Yellow adipose tissue(adult type)
Multilocular (contain many lipid droplets)
Unilocular (contain single lipid droplet)
Small polygonal with central nucleus
Big round with peripheral nucleus
Found in fetus and newborn
Found in adult
Production of heat that protect the fetus against cold
Store house of energy

Lipid droplets

Abnormal fat

Obesity

Lipodystrophy

Glands

Exocrine glands secrete their products onto a surface directly or through ducts that are connected to a surface e.g. sweat glands


Endocrine glands lack a duct system. They secrete their products into the connective tissue, from which the products enter the bloodstream to reach their target cells. They produce hormones e.g. thyroid