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.