histology epithelial endothelial mesothelial

1. Epithelial
Dr. Sami

2.  The organs in your body are composed of four basic types of tissue, including:
 Epithelial.
 Connective.
 Muscular.
 Nervous.

3. Definition:
 The epithelium is a type of body tissue that forms the covering on all
internal and external surfaces of your body, lines body cavities and hollow
organs and is the major tissue in glands.
 Epithelial tissue has a variety of functions depending on where it’s located in
your body, including protection, secretion and absorption.

4. Difference between epithelium,
endothelium and mesothelium
 Epithelium, endothelium and mesothelium are three types of epithelial cell layers
that line your internal organs, body cavities and form the outer layer of your skin.
 Epithelium generally lines pathways that are open to the external environment,
such as your respiratory tract and digestive system.
 In general, endothelium lines
 fully internal pathways, such as your vascular system (i.e. blood vessels) and
cornea.
 Mesothelium lines your major body cavities, such as the peritoneum
(abdomen cavity), pleura (lung cavity) and pericardium (heart cavity).
Mesothelium secretes a lubricant film called serous fluid.

5. Epithelial Cell:
 A cell has three main parts:
 The cell membrane: The cell membrane surrounds the cell and controls the
substances that go into and out of the cell.
 The nucleus: The nucleus is a structure inside the cell that contains most of
the cell’s DNA (genetic material).
 The cytoplasm: The cytoplasm is the fluid inside the cell. It contains other
cell parts that have certain functions.
 epithelial cells, have characteristics on the surface of the cell that help them
perform certain functions, including:

6. Microvilli:
 Microvilli are non-motile (they don’t move) finger-like structures on the
surface of epithelial cells that function to increase the cell’s surface area
 They are involved in a wide variety of functions, including absorption,
secretion, cellular adhesion,
 The epithelial cells that line your small intestine have thousands of microvilli
that absorb nutrients from the food you eat and protect your body from
intestinal bacteria.

8. Cilia:
 Cilia are tiny, hair-like, motile (they can move) structures on the surface of
the cell that help move entire cells or can move substances along the outer
surface of the cell.
 Ciliated cells usually have hundreds of cilia on their surfaces.
 Epithelial cells lining your respiratory tract have cilia that trap dust and
other substances you breathe in and move them toward your nostrils so
that they don’t go into your lungs.
 Another example of cells with cilia are the epithelial cells that line the
fallopian tubes that help move an egg from an ovary to the uterus.

11. Stereocilia:
 Stereocilia: Stereocilia are specialized microvilli that resemble cilia and
project from the surface of certain epithelial cells. Stereocilia are needed
on the epithelial tissue in your inner ear for hearing and balance.
 They convert physical force from sound, head movement or gravity into an
electrical signal

13. Function:
 Protection:
 Epithelial tissue protects several aspects of your body.
 For example, your skin is made up of epithelial tissue and protects the
tissues deeper in your body, such as blood vessels, muscle and internal
organs.
 The cilia on the epithelial cells that line your intestines protect the rest of
your body from intestinal bacteria.

14.  Secretion:
 Epithelial tissue in your glands (glandular epithelium) can secrete (release)
enzymes, hormones and fluids.
 Absorption:
 The epithelial lining of your internal organs, such as your liver and lungs,
can allow the absorption of certain substances. For example, the internal
epithelial lining of your intestines absorbs nutrients from the food you eat.

15.  Excretion:
 Excretion is the removal of waste from your body. The epithelial tissue in
your kidneys excrete waste, and the epithelial tissue in your sweat glands
excrete sweat.
 Filtration:
 The epithelium of your respiratory tract filters out dirt and particles and
cleans the air that you breathe in. Epithelial tissue in your kidneys filters
your blood.

16.  Diffusion:
 In biology, diffusion is the passive movement of molecules or particles
from regions of higher concentrations to regions of lower concentration.
Simple squamous epithelial cells form a membrane that allows selective
diffusion of materials to pass through. Diffusion helps with filtration,
absorption and secretion functions.

17.  Sensory reception:
 Sensory nerve endings that are embedded in epithelial tissue allow your
body to receive outside sensory stimuli.
 As an example, the stereocilia on the surface of the epithelial tissue in your
ear are essential for hearing and balance.
 In addition, your taste buds are embedded in the stratified squamous
epithelium of your tongue.

18. Epithelial cells based on specialized
functions:
 Transitional epithelium:
 also known as urothelium is a type of stratified epithelium.
 Transitional epithelium is a type of tissue that changes shape in response to
stretching (stretchable epithelium).
 The transitional epithelium usually appears cuboidal when relaxed and
squamous when stretched.
 It lines most of your urinary tract and allows your bladder to expand.

19.  Olfactory epithelium:
 The olfactory epithelium, located within your nasal cavity, contains
olfactory receptor cells, which have specialized cilia extensions. The cilia
trap odor molecules you breathe in as they pass across the epithelial surface.
Information about the molecules is then transmitted from the receptors to
the olfactory bulb in your brain, where your brain then interprets the smell.

20.  Glandular epithelium:
 Glandular epithelium, also known as glandular tissue, refers to a type of
epithelial tissue involved in the production and release of different
secretory products, such as sweat, saliva, breast milk, digestive enzymes,
and hormones, among many other substances.

21. Types:
 There are several different types of epithelial cells because epithelial
tissues have many different functions depending on where they are in
your body. Ex.
 Types of epithelial cells based on their shape
 Types of epithelial cells based on their arrangement

22. Types of epithelial cells based on their shape
 Squamous epithelium:
 Cuboidal epithelium:
 Columnar epithelium:

23. Squamous epithelium:
 Squamous epithelial cells are flat and sheet-like in appearance.
 Squamous, or flattened, epithelial cells, very thin and irregular in outline,
occur as the covering epithelium of the alveoli of the lung and of the
glomeruli and capsule of the kidney.

25. Cuboidal epithelium:
 Cuboidal epithelial cells are cube-like in appearance, meaning they have
equal width, height and depth.

27. Columnar epithelium:
 Columnar epithelial cells are column-like in appearance, meaning they are
taller than they are wide.
 Columnar epithelium covers the intestinal tract from the end of the
esophagus to the beginning of the rectum.

29. Types of epithelial cells based on their
arrangement:
 Simple:
 Stratified:
 Pseudostratified:

30. Simple epithelium
 A simple epithelium means that there’s only one layer of cells.

31. Stratified epithelium
A stratified epithelium is made up of more than one layer of cells.

32. Pseudostratified epithelium
A pseudostratified epithelium is made up of closely packed cells that appear to
be arranged in layers because they’re different sizes, but there’s actually just
one layer of cells.

33. Types of epithelial cells in your body
 Simple squamous epithelium: This type of epithelium typically lines blood
vessels and body cavities and regulates the passage of substances into the
underlying tissue. Allow diffusion and filteration.
 This type of epithelia lines the inner surface of all blood vessels
(endothelium), forms the wall of alveolar sacs in the lung and lines the body
cavities (mesothelium).

34.  Simple cuboidal epithelium: This type of epithelium is typically found in
glandular (secreting) tissue and kidney tubules.
 The simple cuboidal epithelium is mainly involved in secretion, absorption,
or excretion
 Simple cuboidal epithelium is found on the surface of ovaries, the lining of
nephrons, the walls of the renal tubules, parts of the eye and thyroid, and
in salivary glands.

35. Simple columnar epithelium:
 Simple columnar epithelium: This type of epithelium is often specialized for
absorption and usually has apical cilia or microvilli. These cells line your
stomach and intestines.
 Absorption and protection.

36. Stratified squamous epithelium:
 Function: This type of epithelium usually has protective functions, including
protection against microorganisms from invading underlying tissue and/or
protection against water loss.
 Location: Lines the esophagus, mouth, skin and vagina

37. Stratified cuboidal epithelium:
 Function: makes multiple membrane junctions between adjacent cells. In
effect, this creates an impermeable barrier between two distinct surfaces in
the body. This barrier acts like a filter, forcing nutrients and water to pass
through the cells.
 Location: Sweat glands, salivary glands, and mammary glands

38. Stratified columnar epithelium:
 Function: The primary function of stratified epithelium is protection. As the
epithelium has multiple layers, it protects the underlying tissues and
internal organs against several physical and microbial damages.
 Location: mucous membrane (conjunctiva) lining your eyelids, where it’s
both protective and mucus-secreting.

39. Pseudostratified columnar epithelium:
 Function: absorption and secretion of mucus, protection from foreign
particles (dust, pathogens, and allergens), and transport of materials such as
hormones and enzymes.
 Location: in the respiratory tract and inner ear.