Transcript 06-med-shunu-biol-2013.ppt

Topic 6
Epithelial Tissue
Literature
• http://www.lab.anhb.uwa.edu.au/mb140/
(notes)
• http://www.anatomyatlases.org/Microscopic
Anatomy/MicroscopicAnatomy.shtml
Epithelial Tissue
The layer of cells that covers the outer, and lines the inner, body
surfaces.
Cells have a free surface, which is actually or potentially exposed to the
external environment (skin, and the respiratory tract), or to a moist
environment continuous with the external environment (digestive,
reproductive, and urinary tracts). Other epithelial cells, comprising
glands found in underlying connective tissue, are in continuity with the
surface epithelium by epithelial duct cells. The glandular epithelium
secretes diverse products, which are carried to the external surface. The
products of these glands include sweat, bile, urine, reproductive cells
and associated glandular secretions, mucus, milk, digestive enzymes,
hydrochloric acid, and so on. Some epithelial cells have migrated away
and have lost contact with the free surface. These cells form distinctive
cellular masses, which are termed endocrine glands. The secretory
products of these cellular masses are delivered into the vascular system
to be carried to their specific sites of activity by the blood stream.
Basal membrane membrāna
Reticular lamina –fibroblasts
Basal lamina –epiteliocytes
• Lamina lucida 50 nm,
• Intermediate layer 50 nm, (tumšs)
• Lamina densa 10 nm,
http://synapses.bu.edu/atlas/3_5.stm
Classification
1) morphologic;
2) development – ectodermal, entodermal,
mesodermal;
3) function – covering epithelium, glandular
epithelia;
4) tissues – skin, kidney, a.o.
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 described according to their height as
squamous (scale- or plate-like), cuboidal or columnar.
Functions of Epithelial Tissue
Protection
Epithelial cells from the skin protect underlying tissue from mechanical
injury, harmful chemicals, invading bacteria and from excessive loss of
water.
Sensation
Sensory stimuli penetrate specialised epithelial cells. Specialised
epithelial tissue containing sensory nerve endings is found in the skin,
eyes, ears, nose and on the tongue.
Secretion
In glands, epithelial tissue is specialised to secrete specific chemical
substances such as enzymes, hormones and lubricating fluids.
Absorption
Certain epithelial cells lining the small intestine absorb nutrients from
the digestion of food.
Excretion
Epithelial tissues in the kidney excrete waste products from the body
and reabsorb needed materials from the urine. Sweat is also excreted
from the body by epithelial cells in the sweat glands.
Diffusion
Simple epithelium promotes the diffusion of gases, liquids and
nutrients. Because they form such a thin lining, they are ideal for the
diffusion of gases (eg. walls of capillaries and lungs).
Cleaning
Ciliated epithelium assists in removing dust particles and foreign
bodies which have entered the air passages.
Reduces Friction
The smooth, tightly-interlocking, epithelial cells that line the entire
circulatory system reduce friction between the blood and the walls of
the blood vessels.
Simple squamous epithelium
This type is composed of a single layer of flattened,
scale- or plate-like cells.
The large body cavities and heart, blood vessels and
lymph vessels are typically lined by a simple squamous
epithelium.
The nuclei of the epithelial cells are often flattened or
ovoid, i.e. egg-shaped, and they are located close to the
centre of the cells.
•P. Apinis. Cilvēks. Anatomija, fizioloģija, anatomijas pamati. SIA Nacionālais Medicīnas apgāds un
SIA Jāņa Sēta. Rīga. 1999.
•P. Apinis. Cilvēks. Anatomija, fizioloģija, anatomijas pamati. SIA Nacionālais Medicīnas apgāds un
SIA Jāņa Sēta. Rīga. 1999.
As their name implies, cuboidal cells are roughly square or
cuboidal in shape. Each cell has a spherical nucleus in the
centre. Cuboidal epithelium is found in glands and in the lining
of the kidney tubules as well as in the ducts of the glands. They
also constitute the germinal epithelium which produces the egg
cells in the female ovary and the sperm cells in the male testes.
•P. Apinis. Cilvēks. Anatomija, fizioloģija, anatomijas pamati. SIA Nacionālais Medicīnas apgāds un
SIA Jāņa Sēta. Rīga. 1999.
Columnar epithelial cells occur in one or more layers. The cells
are elongated and column-shaped. The nuclei are elongated and
are usually located near the base of the cells. Columnar
epithelium forms the lining of the stomach and intestines. Some
columnar cells are specialised for sensory reception such as in
the nose, ears and the taste buds of the tongue. Goblet cells
(unicellular glands) are found between the columnar epithelial
cells of the duodenum. They secrete mucus or slime, a
lubricating substance which keeps the surface smooth.
•P. Apinis. Cilvēks. Anatomija, fizioloģija, anatomijas
pamati. SIA Nacionālais Medicīnas apgāds un SIA
Jāņa Sēta. Rīga. 1999.
These are simple columnar
epithelial cells, but in addition, they
posses fine hair-like outgrowths,
cilia on their free surfaces. These
cilia are capable of rapid, rhythmic,
wavelike beatings in a certain
direction. This movement of the cilia
in a certain direction causes the
mucus, which is secreted by the
goblet cells, to move (flow or stream)
in that direction. Ciliated epithelium
is usually found in the air passages
like the nose. It is also found in the
uterus and Fallopian tubes of
females. The movement of the cilia
propel the ovum to the uterus.
Stratified Epithelium
•P. Apinis. Cilvēks. Anatomija, fizioloģija, anatomijas
pamati. SIA Nacionālais Medicīnas apgāds un SIA
Jāņa Sēta. Rīga. 1999.
Where body linings have to withstand wear and tear, the
epithelia are composed of several layers of cells and are
then called compound or stratified epithelium.
The top cells are flat and scaly and it may or may not be
keratinised (i.e. containing a tough, resistant protein called
keratin). The mammalian skin is an example of dry,
keratinised, stratified epithelium.
The lining of the mouth cavity is an example of an
unkeratinisied, stratified epithelium.
Differentiation.
are not common. A two-layered cuboidal epithelium is, for
example, seen in the ducts of the sweat glands. Stratified
columnar epithelia are found in the excretory ducts of the
mammary gland and the main excretory duct of the large
salivary glands.
•P. Apinis. Cilvēks. Anatomija, fizioloģija, anatomijas pamati. SIA Nacionālais Medicīnas apgāds un
SIA Jāņa Sēta. Rīga. 1999.
Pseudostratified columnar epithelium
All cells of this type of epithelium are in contact with the basement
membrane, but not all of them reach the surface of the epithelium.
Nuclei of the epithelial cells are typically located in the widest part of
the cell. Consequently, the nuclei of cells which do or do not reach
the surface of the epithelium are often located at different heights
within the epithelium and give the epithelium a stratified appearance.
The epithelium will look stratified but it is not - hence its name
"pseudostratified". Pseudostratified columnar epithelia are found in
the excretory ducts of many glands.
Transitional epithelium
Transitional epithelium is found exclusively in the excretory urinary
passages (the renal calyces and pelvis, the ureter, the urinary
bladder, and part of the urethra).
The shape of the cells in the surface layer of a transitional
epithelium varies with the degree of distension of the organs
whose lumen is lined by this type of epithelium. In the 'relaxed'
state of the epithelium, it seems to be formed by many cell layers.
The most basal cells have a cuboidal or columnar shape. There
are several layers of polyhedral cells, and, finally, a layer of
superficial cells, which have a convex, dome-shaped luminal
surface. In the distended state of the epithelium only one or two
layers of cuboidal cells are followed by a superficial layer of
large, low cuboidal or squamous cells. In the distended state the
epithelium will resemble a stratified squamous epithelium.
Glandular Epithelium
• Columnar epithelium with goblet cells is called glandular
epithelium. Some parts of the glandular epithelium consist of
such a large number of goblet cells that there are only a few
normal epithelial cells left.
• Columnar and cuboidal epithelial cells often become
specialised as gland cells which are capable of synthesising
and secreting certain substances such as enzymes, hormones,
milk, mucus, sweat, wax and saliva.
• Unicellular glands consist of single, isolated glandular cells
such as the goblet cells. Sometimes a portion of the epithelial
tissue becomes invaginated and a multicellular gland is
formed. Multicellular glands are composed of clusters of cells.
Most glands are multicellular including the the salivary glands.
Glandulocytes
• Serocytes – water and proteins, stain with ar basal stains,
round nuclei.
• Mukocytes– mucus (polysaccharides), no stain (PAS
reakction), flattened nuclei at the bottomof the cell
• Sebocytes– lipīds, no stain (Sudāna III or IV), size of
nuclei depends on the location of the cell in the gland.
Merocrine secretion
• Merocrine is a term used to classify exocrine glands and
their secretions in the study of histology. A cell is classified
as merocrine if the secretions of that cell are excreted via
exocytosis from secretory cells into an epithelial-walled
duct or ducts and thence onto a bodily surface or into the
lumen.
• Merocrine is the most common manner of secretion. The
gland releases its product and no part of the gland is lost or
damaged (compare holocrine and apocrine).
• The term eccrine is specifically used to designate
merocrine secretions from sweat glands (eccrine sweat
glands).[1]
Apocrine secretion
• Apocrine is a term used to classify exocrine glands in the
study of histology. Cells which are classified as apocrine
bud their secretions off through the plasma membrane
producing membrane-bound vesicles in the lumen. This
method is also called decapitation secretion. The apical
portion of the secretory cell of the gland pinches off and
enters the lumen.
• Apocrine secretion is less damaging to the gland than
holocrine secretion (which destroys a cell) but more
damaging than merocrine secretion (exocytosis).
Holocrine secretion
• Holocrine is a term used to classify the mode of secretion
in exocrine glands in the study of histology. Holocrine
secretions are produced in the cytoplasm of the cell and
released by the rupture of the plasma membrane, which
destroys the cell and results in the secretion of the product
into the lumen.
• Holocrine secretion is the most damaging type of secretion,
with merocrine secretion being the least damaging and
apocrine secretion falling in between.
• Examples of holocrine glands include the sebaceous glands
of the skin and the meibomian glands of the eyelid. The
sebaceous gland is an example of a holocrine gland
because its product of secretion (sebum) is released with
remnants of dead cells.[1]
Endocrine and exocrine secretion
Exocrine
• Ekstraepitelial and
intraepitelial
• Unicellular and
multicellular.
• Simple glands and
compound glands
1) Inorganic substances
(water a.o.),
2) End products (CO2);
3) proteins,
4) mucus,
5) lipids
Endoocrine
• Unicellular and
multicellular..
• Simple glands and
compound glands
• Into blood or tissue
liquid
Hormons, cytokines,
neiromediators,
Intrakrine, autokrine,
jukstakrine, matikrine,
parakrine, endokrine
transportion.
Salivary gland
• water
• enzymes
• mucins
• alveolar
• tubular
• Tuboalveolar
Sweat gland
• Sweat glands (also known as sudoriferous or
sudoriparous glands, from Latin sudor, meaning
"sweat"),[6][7] are small tubular structures of the skin that
produce sweat. There are two main types of sweat glands:
• Eccrine sweat glands are distributed almost all over the
body, though their density varies from region to region.
Humans utilize eccrine sweat glands as a primary form of
cooling.[8]
• Apocrine sweat glands are larger, have a different secretion
mechanism, and are mostly limited to the axilla (armpits)
and perianal areas in humans.[8] Although apocrine glands
contribute little to cooling in humans, they are the only
effective sweat glands in hoofed animals such as the
camel, donkey, horse, and cattle.[9][10][11]
Sebaceous gland
• The sebaceous glands are microscopic glands in
the skin that secrete an oily/waxy matter, called
sebum, to lubricate and waterproof the skin and
hair of mammals.[1] In humans, they are found in
greatest abundance on the face and scalp, though
they are distributed throughout all skin sites
except the palms and soles.[2] In the eyelids,
meibomian sebaceous glands secrete a special type
of sebum into tears.
Pancreas
Islets of Langerhans
Merokrine secretion – exocytosis
α cells - glucagon
β cells - insulin
2.
1.