Tissue- Definition Type of Tissue Epithelial tissue Types of epithelial tissue

1. Chapter: 2
The Tissues
Part 1: Introduction and Epithelial tissue and
its types
By: Bithika Baidya
Content:
• Tissue: Definition and basic classification
• Epithelial Tissue: Definition and characteristic
• Epithelial Tissue: Classification (Structure, location and function)

2. • Tissue: Definition
The word ‘Tissue’comes from an old French verb meaning ‘to weave’
• Definition:
✓ “Tissues are aggregates or groups of cells organized to perform one or more specific
functions.”
✓ “Tissues are a group of cell that have similar structure, act together to perform specific
function and have same origin.”
✓ “A tissue is a group of cells that usually have a common embryonic origin and function
together to carry out specialized activities.”

3. • Types of tissues
Body tissues can be classified into four basic types according to structure and
function:
1. Epithelial tissue covers body surfaces and lines hollow organs, body cavities,
and ducts. It also forms glands. (Origin Ectoderm)
2. Connective tissue protects and supports the body and its organs. Various types of
connective tissue bind organs together, store energy reserves as fat, and help
provide immunity to disease-causing organisms. (Origin Mesoderm)
3. Muscular tissue generates the physical force needed to make body structures
move and generates body heat. (origin )
4. Nervous tissue detects changes in a variety of conditions inside and outside the
body and responds by generating action potentials (nerve impulses) that activate
muscular contractions and glandular secretions. (Origin Ectoderm)

4. • Epithelial Tissue: Definition and characteristic
An epithelial tissue (ep-i-THE¯ -le¯-al) or epithelium (plural is epithelia) consists of cells arranged in continuous
sheets, in either single or multiple layers. Epithelial tissue forms coverings and linings throughout the body.
• Characteristic
✓ The cells are closely packed and are held tightly together by many cell junctions.
✓ There is little intercellular space between adjacent plasma membranes.
✓ It is never covered by another tissue, so it always has a free surface.
✓ There are various surfaces- Apical surface of the epithelium faces the body surface or body cavity and it may
contain cilia or microvilli. The lateral surfaces of an epithelial cell face the adjacent cells on either side. The
basal surface of an epithelial cell is opposite the apical surface, and the basal surfaces adhere to basement
membrane
✓ The basement membrane is a thin extracellular that functions as a point of attachment and support for the
overlying epithelial tissue.

5. • Types of epithelial tissue
• The bases for classifying epithelium tissue is
Cell shapes:
1. Squamous cells arranged like floor tiles and are
thin.
2. Cuboidal cells are shaped like cubes or hexagon
3. Columnar cells are much taller than they are wide,
like columns.
Arrangement of layers:
1. Simple:- single layer of cells present
2. Stratified:- multiple layers of cells are present

6. Combining the two characteristics (arrangements of layers
and cell shapes), the types of covering and lining epithelia
are as follows:
1. Simple epithelium
a) Simple squamous epithelium
b) Simple cuboidal epithelium
c) Simple columnar epithelium (nonciliated and ciliated)
d) Pseudostratified columnar epithelium (nonciliated and
ciliated)
2. Stratified epithelium
a) Stratified squamous epithelium
b) Stratified cuboidal epithelium
c) Stratified columnar epithelium
d) Transitional epithelium

7. 1. Simple epithelium
a) Simple squamous epithelium
Description: Single layer of flattened cells with disc-shaped centrally located nucleus and sparse cytoplasm; the simplest of the
epithelia.
Location: Lines heart, blood vessels, lymphatic vessels, air sacs of lungs, glomerular (Bowman’s) capsule of kidneys, and inner
surface of the tympanic membrane (eardrum); forms epithelial layer of serous membranes, such as the peritoneum, pericardium,
and pleura.
Function: Filtration, diffusion, osmosis, and secretion in serous membranes.
Nuclei of squamous
Epithelial cells
Air sacs of
lung tissue
Photomicrograph: Simple squamous epithelium
forming part of the alveolar (air sac) walls (125x).
Lungs

8. b) Simple cuboidal epithelium
Description: Single layer of cube-shaped cells; centrally located nucleus.
Location: Covers surface of ovary, lines anterior surface of capsule of the lens of the eye, forms the pigmented epithelium at
the posterior surface of the eye, lines kidney tubules and smaller ducts of many glands, and makes up the secreting portion of
some glands such as the thyroid gland and the ducts of some glands such as the pancreas.
Function: Secretion and absorption.
Simple cuboidal
Epithelial cells
Kidney tubules
Photomicrograph: Simple cuboidal
epithelium in kidney tubules (430x).

9. b) Simple columnar epithelium
Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting
unicellular glands (goblet cells).
Location: (Ciliated) Covers surface of ovary, lines anterior surface of capsule of the lens of the eye, forms the pigmented
epithelium at the posterior surface of the eye, lines kidney tubules and smaller ducts of many glands, and makes up the
secreting portion of some glands such as the thyroid gland and the ducts of some glands such as the pancreas.
(Non-ciliated)Lines the gastrointestinal tract (from the stomach to the anus), ducts of many glands, and gallbladder
Function: Secretion and absorption
Photomicrograph: Simple columnar epithelium
of the stomach mucosa (860X).
Simple columnar
Epithelial cell
Basement
membrane
gastrointestinal tract

10. d) Pseudostratified columnar epithelium:
Description: Not a true stratified tissue; nuclei of cells are at different levels; all cells are attached to basement membrane,
but not all reach the apical surface.
Location: Pseudostratified ciliated columnar epithelium lines the airways of most of upper respiratory tract;
pseudostratified non-ciliated columnar epithelium lines larger ducts of many glands, epididymis, and part of male urethra.
Function: Secretion and movement of mucus by ciliary action.
Photomicrograph: pseudostratified
columnar epithelium lining the human trachea (570x).
Pseudostratified
Epithelial layer
Trachea cilia

11. 2. Stratified epithelium
a) Stratified squamous epithelium:
Description: Several layers of cells; cuboidal to columnar shape in deep layers; squamous cells form the apical layer and
several layers deep to it; cells from the basal layer replace surface cells as they are lost.
Location: Keratinized variety forms superficial layer of skin; non-keratinized variety lines wet surfaces, such as lining of the
mouth, esophagus, part of larynx, part of pharynx, and vagina, and covers the tongue.
Function: Protects underlying tissues in areas subjected to abrasion
Photomicrograph: Stratified squamous epithelium
lining the esophagus (285x).
Stratified
squamous
epithelium
Mouth, part of larynx,
pharynx

12. b) Stratified cuboidal epithelium (Rare)
Description: Two or more layers of cells in which the cells in the apical layer are cube-shaped.
Location: Ducts of adult sweat glands, salivary gland, mammary gland and part of male urethra.
Function: Protection and limited secretion and absorption.
Photomicrograph: Stratified cuboidal epithelium
Forming salivary gland duct
salivary gland
Stratified cuboidal
epithelium

13. c) Stratified columnar epithelium (Rare)
Description: Several layers of irregularly shaped cells; only the apical layer has columnar cells.
Location: Lines part of urethra, large excretory ducts of some glands, such as esophageal glands, small areas in anal
mucous membrane, and part of the conjunctiva of the eye.
Function: Protection and secretion
Photomicrograph: Stratified columnar epithelium
Lining male urethra
Stratified columnar
epithelium
male urethra

14. d) Transitional epithelium
Description: Appearance is variable (transitional); shape of cells in apical layer ranges from squamous
(when stretched) to cuboidal (when relaxed).
Location: Lines urinary bladder and portions of ureters and urethra.
Function: Stretches readily and permits distension of urinary organ
by contained urine.
urinary bladder Photomicrograph: Transitional epithelium lining
the urinary bladder, relaxed state (360X);
Transitional
epithelium

15. Questions:
1. Define Tissue
2. Enlist the basic types of tissue found in the body.
3. Define: Epithelium tissue
4. What are the characteristics of epithelial tissues?
5. Enlist the various function of epithelial tissue.
6. What is the function of the basement membrane?
7. Write a note on Simple Epithelial tissue and its types.
8. Write a note on Stratified Epithelial tissue and its types.
References:
Principles of Anatomy and Physiology - 12th Edition Gerard J. Tortora and Bryan Derrickson
Essentials of Anatomy and Physiology (Pictures credit)
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