Tissue: Epithelial Connective, Nervous, and Muscle
The different types of epithelia are classified based on two major characteristics:
(1) the number of cell layers present, and (2) the shape of the outermost layer of cells
Epidermis
(an epithelium) of the skin separates the inside of the body from air, water and other external components.
Tissue
(tissu = woven)
In a desmosome
, the space between the lateral plasma membranes of two adjoined cells is filled with cell adhesion molecules which act like mortar between bricks.
Epithelial Tissue
Epithe = laid on, covering
Avascularity
Epithelia lack blood vessels
Four Major Types of tissues
Epithelial (Covering & secretion) Connective (Support) Muscle (Movement) Nervous (Control)
unicellular glands
Glands made up of a single cell
Four Shared Characteristics of Epithelia
Polarity Attachment Avascularity Regeneration
Epithelia form boundaries
between different environments.
Epithelia are characterized
by having a large supply of sensory receptors and nerves.
internal epithelia
can also send signals regarding the status of our internal organs
A gland
can consist of one or more cells that make a secretory product that is exported to another location.
Desmosomes
cell adhesion molecules, filaments and cytoskeleton make the tissue able to withstand twisting, stretching, and compression. Skin cells.
The term, tissue
comes from a root word meaning woven because the four major kinds of tissues interweave together to form organs.
The simple squamous epithelium
comprise the serosae or serous membranes that line internal body cavities and the viscera is referred to as mesothelium
Gap Junctions
connexons form channels between cells for the rapid and coordinated passage of small molecules and ions. Cardiac muscle, smooth muscle.
Simple cuboidal epithelia
consist of a single layer of cube-shaped cells with large, centrally located spherical nuclei. Simple cuboidal epithelia are found where secretion and absorption are important.
The typical basement membrane
consists of a basal lamina
simple squamous epithelium
consists of a single layer of flattened cells. It is a very thin epithelium and therefore is found where diffusion or filtration of materials must occur.
A single layer of columnar cells
constitutes a simple columnar epithelium. this type of epithelium may function in absorption and/or secretion. It may also be ciliated and function to propel materials along its surface. Simple columnar epithelium has a wide distribution and forms the lining of many different organs.
The structure of Epithelium
depends on its primary function and its location in the body
Nutrients of the correct size and type
must enter through transporters on the apical plasma membrane, whereas unwanted materials are prevented from gaining access to the body because adjacent cells are held together so tightly.
the microvilli
are folds of the apical plasma membrane. This arrangement increases surface area for transport of materials without increasing the amount of physical space occupied by the cell or epithelium
Stratified squamous epithelia
are found in regions of the body that are subject to friction or abrasion
Tight junctions
are found on the lateral borders of adjacent cells close to the apical surface. These junctions are like a series of spot welds that rivet the membranes of the two cells together. The rivets or welds are actually interlocking junctional proteins.
Simple epithelia
are generally found where absorption, secretion, exchange of respiratory gases, or filtration occur and protection is NOT of primary importance.
Tissue
are groups of cells that are similar in structure and perform a common or related function. Some types of tissues are organized together to form membranes which represent the simplest of organs. Typically, the four major kinds of tissues are knitted together in varying proportions to form the organs of the body.
Simple cuboidal epithelia
are located in kidney tubules, ducts and secretory portions of small glands, Ovary surface.
A single layer of columnar cells
are located in noncilliated type lines, most of the digestive tract, gallbladder and excretory ducts of some glands, some regions of the uterus.
Desmosomes
are more complex and are specialized in epithelia that are subject to stretching, compression and twisting
Gap junctions
are not typically found in epithelia, but are present in excitable tissues such as cardiac muscle in the heart, and smooth muscle in the walls of hollow organs where they help to synchronize the flow of ions used for electrical signals.
Epithelia
are nourished by diffusion of materials from the blood vessels that are located in the underlying connective tissue
Columnar cells
are taller than they are wide and have elongated basally located nuclei.
pseudostratified epithelia
are technically a simple epithelium. Pseudostratified epithelia can have modifications based on their location. The most common form is called ciliated pseudostratified columnar epithelium with mucous secreting goblet cells.
The only important unicellular gland
are the mucous-secreting goblet cells that are found in epithelia that line the respiratory and digestive passageways.
Stratified epithelia
are usually common to areas where protection is important, such as the skin or lining of the oral cavity (mouth).
Epithelia Act
as Interfaces.
The epithelium lining the uterine tubes or oviducts
beat to move a female gamete (oocyte) from the ovary to the uterus.
Epithelia control permeability
because any substance entering or leaving the body must cross an epithelium, and therefore is subject to regulation and selection by the plasma membranes of all the cells comprising the epithelium.
Merocrine glands
secrete their products by conventional exocytosis. Examples include the salivary glands, pancreas, and the sweat glands used in thermoregulation of body temperature.
Multicellular exocrine glands
secrete their products in different ways
The mesothelium
secretes lubricating serous fluid which reduces friction in body cavities as organs move.
Epithelium lining the urinary bladder
separates urine from underlying internal components.
thyroid gland
showing epithelial cells surrounding pink spheres of the stored form of what will become active thyroid hormones.
There are two
simple squamous epithelia that have special names because of their location in the body.
Connective tissues
support and connect other organs
apocrine glands Slide 24
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Two major forms of Epithelium in the body
1.Covering and lining epithelium 2.Glandular epithelium
Epithelial Tissue: Characteristics
1.Polarity: Each cell in an epithelium has an: Apical (free) surface. Faces into a body cavity Lines the internal lumen (passage way) of an organ Basolateral (attached surface) Attaches the cell to underlying and adjacent cells Anchors cell to the basement membrane
Polarity
Cells have a top and bottom surface with different characteristics
simple
An epithelium consisting of a single layer of cells
cilia
Another common specialization of the apical surface is the presence of tiny hair-like projections. Cilia have the ability to "beat" in regular waves and they function to move materials along a surface
Attachment
Basement membrane attaches epithelia to underlying tissues
stratified
If an epithelium consists of more than one layer,
squamous
If the outermost (apical) cells and their nuclei are flat (squamous comes from a word meaning scale)
Glandular Epithelia
Sweat Oil Ear wax Hormones Thyroid hormones Sex hormones Insulin Adrenalin
this must be held together very snugly
The epithelia that function to line and cover surfaces and form interfaces between environments
Regeneration
Worn out or damaged cells are replaced quickly
basal surface
The opposite lower or attached surface of the cell. This surface is attached to underlying epithelial cells or to a basement membrane
endothelium.
The simple squamous epithelium that lines the inside of the heart, blood vessels and lymph vessels
Histology
The study of tissues
Pseudostratified columnar epithelium
This epithelium is called "pseudo" stratified because it looks like it is layered but it is not.
Example of epithelial controling permeability
absorption of nutrients by the epithelium lining the digestive tract, filtration of blood by the kidneys, and exchange of oxygen and carbon dioxide by the lungs.
exchange of oxygen and carbon dioxide between the lungs and blood stream occurs
across the simple squamous epithelium that lines the air sacs or alveoli.
Tight Junctions:
adhesion belt interlocks adjacent cells forming a barrier. Intestinal cells.
In a gap junction
adjacent plasma membranes are very close and are connected by hollow cylinders made up of transmembrane proteins called connexons
exocrine glands
all secrete their products onto the body surface or into a body cavity via tube-like ducts secretions include mucus, sweat, oil, saliva, digestive enzymes, bile, and many others.
Epithelial tissue
also called epithelium or epithelia when referring to more than one type, share four characteristics that distinguish it from other types of tissues. These are polarity, attachment, avascularity, and regeneration.
Cuboidal cells
are about as tall as they are wide, and typically have spherical, centrally located nuclei
Epithelia
are all avascular. (do not contain blood vessels) A in front of a word means without.
Cells in an epithelium
are also attached to each other on their lateral borders.
All epithelia
are attached to a basement membrane and supported by underlying connective tissue
the cells comprising epithelia
are both structurally and functionally polarized
adjacent plasma membranes
are connected in specific ways to prevent the cells from coming apart.
Endocrine glands
are ductless glands. Their products are chemical messengers called hormones. During development, endocrine glands became separated from the epithelial sheet from which they were derived. Because they have lost contact with the body surface or internal organ cavity, endocrine glands must secrete their products directly into the body fluid compartments, most commonly blood. This explains why endocrine glands are "bloody" or highly vascularized.
The connexons
form channels between the two adjacent cells which allow for selective passage of ions, simple sugars, amino acids and other small molecules
some types of epithelia
form glands
Muscle tissue
functions in creating movement
Epithelium
gets its name from a term that means laid on, or covering. This is because most epithelia form a sheet of cells that covers a body surface or lines a body cavity.
In addition to being uni-or multi-cellular
glands can be divided into endocrine or exocrine based on whether or not they have a duct to conduct their secretory product to a more distant location.
stratified squamous epithelium covering the outside of the body
has an outer layer of dead cells filled with a protein called keratin
The secretions from sweat glands
help to regulate our body temperature; oil from sebaceous glands lubricate our hair and skin, and tears keep our eyes clear of debris.
Avascularity
helps keep potentially dangerous environmental entities from gaining access to the blood stream.
Epithelial Tissue
is a sheet of cells that covers a body surface or lines a body cavity.
reticular lamina
is also a layer of extracellular material which contains fine interwoven collagen fibers produced by the underlying connective tissue
The intercellular space filled with adhesion molecules
is also reinforced by linker proteins that lock together like the teeth on a zipper
Deep to the basal lamina
is another non-living, proteinaceous layer called the reticular lamina.
basal lamina
is comprised of specific mixtures of glycoproteins, protein fibers and filaments
pseudostratified columnar epithelium
is confined to the respiratory passageways and so it is simply referred to as "respiratory epithelium". also located in non ciliated sperm carrying ducts and large glands.
The non-ciliated variety
is found in some ducts especially within the male reproductive system
The epithelial cells
secrete the basal lamina which functions to help strengthen the sheet of cells as well as aiding specificity by acting as a selective filter.
The non-keratinized squamous epithelium
is found lining many internal body passageways that are also subject to abrasion, but need to be kept moist. Examples include the lining of the oral cavity, esophagus, and vagina.
Transitional epithelium
is found lining urinary passageways and the bladder. It has the ability to change the shape of the epithelial cells and the apparent number of cell layers depending on whether it is stretched or contracted.
A tough plaque
is found on the cytoplasmic side of the plasma membranes in which are embedded intermediate filaments of the cytoskeleton
cell polarity
is functional as well as structural
the trachea
is lined with a ciliated epithelium which moves foreign debris captured in mucus away from the lungs where it could interfere with respiration
Example of covering/lining type of epithelium
is of the epithelium is the kind that lines the inside (or lumen) of blood vessels. This special epithelium keeps the blood in the circulation and prevents unregulated mixing of body fluids.
the epithelium as a whole
is polarized
The epithelium that lines the urinary bladder
is specialized for stretch and separates the urine containing waste products from the underlying internal components.
one of the most common specializations of the apical surface
is the existence of finger-like extensions of the plasma membrane called microvilli (microvillus singular)
Keratin
is the same protein that makes up your fingernails and hair. It is fairly impervious to water and chemicals.
major role of the covering/lining type of epithelium
is to form boundaries between different environments
role of tight junctions
is to prevent apical membrane proteins such as transporters, receptors, or channels from diffusing into the basal lateral regions of the plasma membrane (recall, plasma membranes are described by the fluid mosaic model, and have the consistency of olive oil so the phospholipids, cholesterol and proteins can move).
a major function of some types of epithelia
is to provide physical protection against abrasion, friction, dehydration and from potentially harmful chemicals and pathogenic organisms such as viruses and bacteria.
Epithelium lining blood vessels
keeps blood in the circulation.
epithelial tissues
line or cover the inside and outside of the body, or form glands that produce a secretory product.
Pseudo
means false, so it is falsely stratified.
Polarity
means that there are two different and opposite sides of an object. For example, we know that batteries have a negative end and a positive end, and that the Earth has a south pole and a north pole.
a gap
or communicating junction.
Example of covering/lining type of epithelium
our skin is made up of an outer layer called the epidermis which is a type of epithelium. The epidermis separates the delicately balanced internal environment of the body from the ever changing external environment we come in contact with.
in a simple squamous filtration membrane
part of the kidney where blood is filtered, materials pass across
The cells comprising glandular epithelia
produce a variety of secretory products
many glands
produce blood-borne chemical messengers called hormones which regulate homeostasis
Different types of glands
produce specialized secretory products such as saliva that moistens our food, or digestive enzymes that help to breakdown our food.
Surface epithelia
provide us with information such as touch, pressure, temperature and pain.
endothelium
provides a slick, friction-reducing lining so that blood (lymph) can flow without turbulence.
several other characteristics that are very common in epithelia , but are also found in other types of tissues
the presence of specialized contacts between cells support by connective tissue the presence of a rich supply of nerves
apical surface
the upper or outer surface of each cell is free. This side of the cell faces the exterior of the body, lines body cavities, or lines the internal cavity or lumen of hollow organs and blood vessels.
Covering/lining types of epithelia are usually subject to wear and tear
therefore have a high rate of turnover.
Although epithelia are avascular
they are supplied by nerves (innervated).
multicellular
those made up of many cells that formed from a sheet of epithelium
there are two major forms of epithelia
those that cover and line, and those that form glands.
nervous tissue
tissue controls the actions of the body's component parts.
The epithelial cells attach
to the basal lamina by junctions called hemidesmosomes (which structurally are like half a desmosome).
The intermediate filaments
traverse the width of the cell and attach to the plasma membrane on the opposite side forming a network of "guy wires" between the cells
The liver
which is the largest gland in the body, secretes bile which helps to breakdown dietary fats.