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By
Dr.Pardeep Kumar
Definition: a group of closely associated
cells that perform related functions and
are similar in structure
 Between cells: nonliving extracellular
material
 Four basic types of tissue…function

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›
›
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Epithelium…covering
Connective tissue…support
Muscle tissue…movement
Nervous tissue…control
Epithelium: sheet of cells that covers a
body surface or lines a body cavity; also
form most of the body’s glands
 Roles: as interfaces and as boundaries
 Functions:

Protection
Absorption
Sensory reception
Ion transport
Secretion
Filtration
Formation of slippery surfaces for movement
Cellularity
 Specialized contacts
 Polarity

› Free upper (apical) surface
› Lower (basal) surface contributing basal lamina
to basement membrane
Support by connective tissue
 Avascular but innervated

› Without vessels
› With nerve endings

Regeneration
TISSUE
 Tissue is a group of cells, which have more or less similar origin,
structure and function.
Types: Four types:
 1. Epithelial tissue.
 2. Connective tissue.
 3. Muscular tissue.
 4. Nervous tissue.
Epithelial tissue:
 It is the tissue, which covers the free surfaces of the body as well
as inner surfaces of hollow organs.

It forms continuous layers

The cells are packed tightly

It has high regeneration capacity ranging from few days to one
month
Characteristics of epithelial tissue
 They are absolutely cellular, no fibre is present

Ground substance or matrix is scanty.

The cells are closely adherent to each other.

They rest on a basement membrane.(thin-non living layer)
They are avascular (i.e. devoid of blood supply),but get their
nutrition by osmosis and diffusion through basement membrane
from sub-epithelial blood vessels.
They are derived from all the embryonic layers (ectoderm,
endoderm and mesoderm).

Functions of epithelium
› The epithelium acts as a selective barrier, which is capable to
prevent or facilitate the passage of materials across the
surface.
› Protection of the underlying tissue.
› Secretions.
› Acts as sensory receptors
› Absorption
› Prevents reabsorption

According to thickness
› “simple” - one cell layer
› “stratified” – more than one layer of cells
(which are named according to the shape
of the cells in the apical layer)

According to shape
› “squamous” – wider than tall
› “cuboidal” – as tall as wide
› “columnar” - taller than wide
Epithelia are classified on the basis of the number of cell layers
and the shape of the cells in the surface layer.
 If there is only one layer of cells in the epithelium, it is
designated simple.
 If there are two or more layers of cells, it is termed stratified.
 Cells in the surface layer are, as a rule, described according
to their height as squamous , cuboidal or columnar.
Simple epithelium:
 It consists of a single layer of cells & is divided into 4 types.
 These being extremely thin
 It is more effective as secretory or as absorptive surface
Functions:They are designed to exchange materials such as the alveoli
exchange gases or the capillary walls exchange fluid and
nutrients with the interstitial tissues.

Simple pavement or squamous epithelium:
 The cells are flat, scale-like or plate-like arranged in a single
layer of one cell thickness.
 The edges of the cells are closely adherent.
 The nucleus situated in the centre.
 Shape of the nuclei is oval, spherical or bulging.
Types and examples:
 Lining of Lung Alveoli
 Lining of the Heart (Endocardium)
 Lining of Blood vessels, lymph vessels (Endothelium)
 Lining of Pleura, peritoneum, pericardium (Mesothelium)
Function:
 Protection
 Active & passive transport of water, electrolytes & other
substances


The outlines of individual epithelial cells are not always visible,
and it may be difficult to identify the shape of the cells.
It is often helpful to look at the shape, location and spacing
of the nuclei in the epithelium,
Simple cubical epithelium:
 The height and the width of the cells are almost equal
 The nucleus is spherical, central in position.
Example:
 Thyroid Follicles
 Salivary Glands
 Small excretory ducts of many gland
 Tubules of Kidney
 Lining of Ovary
Functions
 Protection
 Secretion
 Storage
Simple columnar epithelium:
 The cells are columnar in shape.
 Height greater than the breadth.
 Nucleus is oval in shape and lies near the base. (at the same
height)
Classified into
Apical surface may be striated or brush bordered or non-striated.
Non-Ciliated Columnar
Examples
 Stomach & Large Intestine
 Large Ducts of many glands
It helps in secretion & absorption
Ciliated Columnar
Examples
 Respiratory Tract to respiratory bronchiole
 Uterine tube (fallopian tube)
 Ventricles of Brian & Central canal of spinal cord
Columnar epithelium with microvilli (brush border)
Examples
 Small Intestine & gall bladder
 They help to increase the surface area for absorption of
nutrients.
Simple goblet cells:
 Goblet cells are glandular simple columnar epithelial cells whose
sole function is to secrete mucus.
 The majority of the cell's cytoplasm is occupied by mucinogen
granules, except at the bottom.
 Cell organelles are concentrated in the basal portion.
 Appear as large clear spaces here and there among the
columnar absorptive cells.
 When the secretion is out, the cell is rendered empty with a cup
shaped depression on the top.
Examples:
Trachea,
bronchi, small and large intestines.
Functions
Secretion
Protection
Lubrication
Pseudo-stratified columnar:
 They are simple epithelium but give a false impression of many
layers,
 The cells are of different heights. All cells touch the basement
membrane but all cells do not reach the surface.
 The cells which reach the surface touch the basement
membrane by their narrow processes in between basal cells.
 The basal cells are oval or spindle shaped.
 Due to different heights of the cells, the nuclei lie at different
levels and give it the appearance as if stratified. The cells may
be ciliated.
Compound epithelium
Stratified squamous epithelium:
 Superficial cells consist of multi-layered squamous cells and the
basal cells are columnar or cubical. Hence the name is
S.SquamousE.
 The deepest layer of cells rest on a basement membrane and
are columnar or cubical in shape.
 The middle layer of cells consists of large polyhedral or cubical
cells



The cells on the surface are squamous cells and may be alive,
nucleated and moist.
They are known as moist or non-cornified stratified squamous
cells.
Those which are non-nucleated, scaly and dead are known as
cornified or dead and dry stratified squamous epithelium
These are not very common
Stratified columnar:
 Composed of more than one layer of columar epithelium.
Examples:
Large glands and their ducts,( e.g. Pancreatic ducts)
Stratified cubical:
 Consists of more than one layer of cubical epithelium.
Example:
Ducts of Sweat glands & Mammary glands
Transitional Epithelium
 Consists of two or more layers of cells.
 The superficial cells show convexity towards the lumen,
 The middle cells are polyhydral or pear shaped.
 Basal cells are columnar or Cuboidal
 In the distended state the epithelium will resemble a stratified
squamous epithelium.
Examples:
Exclusively in the excretory urinary passages
 Renal pelvis, ureter, urinary bladder and upper part of urethra.
Functions of transitional epithelium:
 (I) Prevention of absorption
 (ii) Helps in stretching of mucosa.
Basement Membrane
 It is a thin layer of connective tissue onwhich the epithelial cells
rest upon. In multilayered the deepest cells lie on it
It has 2 layers
 Basal lamina- major components are glycoproteins and (usually
type IV) collagen.
 Reticular lamina- consists of reticular fibres embedded in ground
substance
Unless special stains are used, the basement membrane is rarely
visible
Function – support to epithelial cells
Lamina propria
 Epithelium with its basement membrane rests on a layer of
connective tissue is called LP
Mucous membrane
 Mucous membrane (Mucosa) is a moist sheet lining all
internal hollow organs
It consists of
 Lining epithelium
 Basement membrane
 Lamina propria
Glands
 Glands are group of cells whose function is secretion.
Classification
According to nature of secretion
› Mucous – viscous, slimy secretion
 Unicellular – e.g. goblet cells
 Multicellular – e.g. palatine glands
› Serous - secretion is watery e.g. Parotid gland, Pancreas.
› Mixed Contain both mucous & serous secreting cells &
secretion is of both types e.g. Sub mandibular gland,
Sublingual gland
According To the method of secretion transport
› Exocrine – Discharge their secretion by means of duct in
epithelial surface e.g. Parotid gland
› Endocrine : Release their secretion directly into blood or
lymph vessels e.g. Pituitary
 Both glands are developmentally derived from epithelia, which
form a down-growth into the underlying connective tissue.
 The cells then develop the special characteristics of the mature
gland.
 Exocrine glands maintain the connection with the surface
epithelium, whereas the connection is lost by endocrine glands.



Both glands are developmentally derived from epithelia, which
form a down-growth into the underlying connective tissue.
The cells then develop the special characteristics of the mature
gland.
Exocrine glands maintain the connection with the surface
epithelium, whereas the connection is lost by endocrine glands.

According to mode of secretion
› Holocrine : The entire cell disintegrates & is discharged as
secretions e.g. Sebaceous glands
› Apocrine: The luminal part of cell distintegrates with some loss
of apical part of cytoplasm e.g Mammary glands, apocrine
sweat glands .
› Merocrine: Only the secretory material is discharged e.g.
endocrine glands, digestive glands.
According to Development
› Ectodrerm – e.g. Parotid gland, Lacrimal gland
› Endoderm e.g. Thymus, Liver, Pancreas, thyroid
› Mesoderm e.g. Kidney, Spleen.
According to Structure
Summary