Human Anatomy and Physiology - Human Tissues and Membranes
Histology - a branch of science that deals with the study of a tissue.
Tissue - is a group of similar cells and their intercellular substance that have a similar
embryological origin and function together to perform a specialized activity.
Four Classes of Tissue
Epithelial tissues
Epithelial tissues - cover body surface, lines body cavity and ducts, and form glands.
Covering & lining epithelium - It forms the outer covering of the external body surface and outer
covering of some internal organs.
It lines the body cavity, interior of respiratory & gastro intestinal tracts, blood vessels
and ducts and makes up along with the nervous tissue .
It is a tissue from which gametes (egg and sperm) develop.
Sub-classes of Covering & lining epithelium (according to arrangement of layers)
a. Simple epithelium - it is specialized for absorption, and filtration with minimal wear &
tears.
b. Stratified epithelium - it is many layered and found in an area with high degree of wear
and tears.
c. Pseudostratified epithelium - is a single layer but seems to have many layers.
Sub-classes of Covering & lining epithelium (according to cells shape)
a) Squamous: - flattened & scale like
b) Cuboidal: - cube shaped
c) Columnar: - tall and cylindrical
d) Transitional: - combination of cell shape found where there is a great degree of
distention or expansion, these may be cuboidal to columnar, cuboidal to polyhedral and
cuboidal to Squamous.
Sub-classes of Covering & lining epithelium (according to arrangement of layers and
cells shape)
I. Simple epithelium
a. Simple – Squamous epithelium, contain single layer of flat, scale like resemble tiled
floor. It is highly adapted to diffusion, osmosis & filtration. Thus, it lines the air sacs of
lung, in kidneys, blood vessels and lymph vessels.
, b. Simple – cuboidal epithelium, Flat polygon that covers the surface of ovary, lines the
anterior surface of lens of the eye, retina & tubules of kidney.
c. Simple – columnar epithelium, Similar to simple cuboidal. It is modified in several
ways depending on location & function. It lines the gastro-intestinal tract, gallbladder,
excretory ducts of many glands. It functions in secretions, absorption, protection &
lubrication.
II. Stratified epithelium
It is more durable, protects underlying tissues form external environment and from wear
and tears.
a. Stratified Squamous epithelium - In this type of epithelium, the outer cells are flat.
Stratified squamous epithelium is subdivided into two based on the presence of keratin.
1. Non-Keratinized stratified squamous epithelium - is found in wet surfaces that are
subjected to considerable wear and tear. e.g. mouth, tongue and vagina.
2. Keratinized stratified squamous epithelium - the surface cell of this type forms a tough
layer of material containing keratin. e.g. skin.
Keratin - is a waterproof protein, resists friction and bacterial invasion.
b. Stratified cuboidal epithelium - rare type of epithelium. It is found in sweat glands duct,
conjunctiva of eye, and cavernous urethra of the male urogenital system, pharynx and
epiglottis.
Its main function is secretion.
c. Stratified columnar epithelium - uncommon to the body, which is found in the milk duct
of mammary gland and anus layers.
It functions in protection and secretion.
d. Transitional epithelium - The distinction is that cells of the outer layer in transitional
epithelium tend to be large and rounded rather than flat, allowing the tissue to be
stretched without breakage.
It is found in the urinary bladder, part of Ureters and urethra.
III. Pseudo stratified epithelium
Pseudo stratified epithelium - lines the larger excretory ducts of many glands,
epididymis, parts of male urethra and auditory tubes.
Its main function is protection and secretion
Glandular Epithelium - main function is secretion.
A gland may consist of one cell or a group of highly specialized epithelial cells.
Histology - a branch of science that deals with the study of a tissue.
Tissue - is a group of similar cells and their intercellular substance that have a similar
embryological origin and function together to perform a specialized activity.
Four Classes of Tissue
Epithelial tissues
Epithelial tissues - cover body surface, lines body cavity and ducts, and form glands.
Covering & lining epithelium - It forms the outer covering of the external body surface and outer
covering of some internal organs.
It lines the body cavity, interior of respiratory & gastro intestinal tracts, blood vessels
and ducts and makes up along with the nervous tissue .
It is a tissue from which gametes (egg and sperm) develop.
Sub-classes of Covering & lining epithelium (according to arrangement of layers)
a. Simple epithelium - it is specialized for absorption, and filtration with minimal wear &
tears.
b. Stratified epithelium - it is many layered and found in an area with high degree of wear
and tears.
c. Pseudostratified epithelium - is a single layer but seems to have many layers.
Sub-classes of Covering & lining epithelium (according to cells shape)
a) Squamous: - flattened & scale like
b) Cuboidal: - cube shaped
c) Columnar: - tall and cylindrical
d) Transitional: - combination of cell shape found where there is a great degree of
distention or expansion, these may be cuboidal to columnar, cuboidal to polyhedral and
cuboidal to Squamous.
Sub-classes of Covering & lining epithelium (according to arrangement of layers and
cells shape)
I. Simple epithelium
a. Simple – Squamous epithelium, contain single layer of flat, scale like resemble tiled
floor. It is highly adapted to diffusion, osmosis & filtration. Thus, it lines the air sacs of
lung, in kidneys, blood vessels and lymph vessels.
, b. Simple – cuboidal epithelium, Flat polygon that covers the surface of ovary, lines the
anterior surface of lens of the eye, retina & tubules of kidney.
c. Simple – columnar epithelium, Similar to simple cuboidal. It is modified in several
ways depending on location & function. It lines the gastro-intestinal tract, gallbladder,
excretory ducts of many glands. It functions in secretions, absorption, protection &
lubrication.
II. Stratified epithelium
It is more durable, protects underlying tissues form external environment and from wear
and tears.
a. Stratified Squamous epithelium - In this type of epithelium, the outer cells are flat.
Stratified squamous epithelium is subdivided into two based on the presence of keratin.
1. Non-Keratinized stratified squamous epithelium - is found in wet surfaces that are
subjected to considerable wear and tear. e.g. mouth, tongue and vagina.
2. Keratinized stratified squamous epithelium - the surface cell of this type forms a tough
layer of material containing keratin. e.g. skin.
Keratin - is a waterproof protein, resists friction and bacterial invasion.
b. Stratified cuboidal epithelium - rare type of epithelium. It is found in sweat glands duct,
conjunctiva of eye, and cavernous urethra of the male urogenital system, pharynx and
epiglottis.
Its main function is secretion.
c. Stratified columnar epithelium - uncommon to the body, which is found in the milk duct
of mammary gland and anus layers.
It functions in protection and secretion.
d. Transitional epithelium - The distinction is that cells of the outer layer in transitional
epithelium tend to be large and rounded rather than flat, allowing the tissue to be
stretched without breakage.
It is found in the urinary bladder, part of Ureters and urethra.
III. Pseudo stratified epithelium
Pseudo stratified epithelium - lines the larger excretory ducts of many glands,
epididymis, parts of male urethra and auditory tubes.
Its main function is protection and secretion
Glandular Epithelium - main function is secretion.
A gland may consist of one cell or a group of highly specialized epithelial cells.
