Tissues:
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Epithelial
tissue:
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The
epithelium is the lining, covering, and glandular tissue of the body. One
type makes up our skin. Epithelial functions include
protection, secretion, absorption, and filtration
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Epithelial
cells fit closely together to form continuous sheets. Cells are bound tightly
together at as many points as possible by both desmosomes and tight junctions
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The
membranes have one unattached surface or edge. This apical surface is exposed
to the body's exterior or the cavity which it lines. The exposed surface
may be slick and smooth, or rough, covered in villa
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The
lower surface of the membranes rests on a basement membrane, a structureless
material secreted by the cells
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Epithelial
tissues are avascular. That is, they do not have a blood suply of their
own. These cells depend on diffusion from the cappilaries in the underlying
conective tissue. If well-fed, the cells regenerate easily, or they are
mitotic
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The
simple epithelia are mostly concerned with absorption, secretion, and filtration.
Because they are thin, protection is not one of their strengths
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Simple
squamous epithelium is a single layer of thin squamous cells resting on
a basement membrane. They fit closely together, like floor tiles. Squamous
cells are flat. Side-on, they appear a slender rectangle. Simple squamous
epithelium usually forms membranes where filtration or exchanges by rapid
diffusion occur. This type of tissue is utilized in the lungs, and also
forms the serous membranes, or serosae. The serosae are the slick membranes
which line the ventral body cavity and cover the organs therein
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Simple
cuboidal epithelium is a single layer of cuboidal cells on a basement membrane.
Side-on, these cells' faces appear squarish, at least, ideally. This type
of epithelial tissue is common in glands and ducts. It also makes up the
walls of the kidneys and covers the surface of the ovaries
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Simple
columnar epithelium is a single layer of columnar cells, fitted closely
together. Goblet cells, which produce a lubricating mucus, are often seen
in this kind of epithelium. Simple columnar epithelium lines the entire
digestive tract. Any epithelial membrane which lines body cavities, open
to the bodies exterior, are called mucosae, or mucous membranes
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Pseudostratified
columnar epithelium rests on the basement membrane, and is made up of columnar
cells. However, the nuclei are not lined up, giving the false appearance
of stratification. Like the simple epithelium, these tissues are used for
absorption and secretion. A ciliated variety, precisely called pseudostratified
ciliated columnar epithelium, lines the respiratory tract. The mucus produced
by the goblet cells traps duct and other irritants, the cilia propel it
up and away from the lungs
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Stratified
epithelia consists of two or more layers of cells resting on the basement
membrane. Being stronger, their main, but not only, function is protection
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Stratified
squamous epithelia are the most common stratified epithelia in the human
body. It usually consists of several layers of cells: those near the free
edge are squamous, while those near the basement membrane are cuboidal
or columnar. Stratified squamous is found at sites which take a great deal
of abuse and friction, such as the esophagus, mouth, and outer skin, which
is keritinized, for the layer of keratin (waterproof, tough material) on
the surface
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Stratified
cuboidal epithelium usually has just two layers of cells with at least
the surface cells being cuboidal. The surface cells of columnar stratified
epithelium are columnar cells, but the basal cells vary in size and shape.
Both epithelia are fairly rare in the body, found mainly in ducts of large
glands
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Transitional
epithelia is a highly modified, stratified squamous epithelia the forms
the lining of only a few organs- the urinary bladder, the ureters, and
part of the urethra. All of these organs are part of the urinary system,
and are subject to a great deal of stretching. Cells of it's basal layer
are cuboidal or columnar, those it the surface are more varied. When not
stressed (stretched), the membrane many-layered and the superficial cells
are rounded and dome-like. When stressed, the epithelium thins, and surface
cells become flattened and squamous-like. The ability of transitional cells
to slide past one another and change shape allows the membrane to stretch,
and the urinary system to function
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A
gland consists of one or more cells that produce a secretion, typically
containing proteins in an aqueous fluid. Two major types of glands develop
from the epithelial sheets. The endocrine glands lose their connection
to the surface, and are thus called ductless. Examples would be the thyroid,
adrenals, and pituitary. The exocrine glands retain their ducts, and their
secretions empty through the ducts to the epithelial surface. The exocrine
glands, which include sweat and oil glands, the liver, and pancreas, are
both internal and external
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Connective
tissue:
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Connective
tissue is the most abundant in the human body. It is generally well vascularized,
though exceptions include tendons and ligaments. Cartilage is avascular.
Consequently, they heal very slowly
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Connective
tissues are made up of many differing kinds of cells, and a nonliving substance
known as the extracellular matrix. The matrix is produced and secreted
by the connective tissue cells. It may be gel-like, semisolid or very hard.
Fibers that make up the matrix include collagen, which is white, elastic,
colored yellow, and reticular, or fine collagen fibers. The main functions
of connective tissue are protecting, supporting and connecting
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Bone,
sometimes called osseous tissue, consists of bone cells in cavities called
lacunae, surrounded by layers of herd matrix material containing calcium
salts
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Hyaline
cartilage is rubbery and smooth. The matrix is somewhat hard. Found only
in a few places, it's main function is support. Fetal skeletons are made
up of hyaline cartilage, but is replaced by birth with osseous tissue.
Though hyaline is the most common of cartilages, there are others. Elastic
cartilage supports where elasticity is desired, such as the outer ear.
Highly compressed fibrocartilage forms the cushion-like discs between the
vertebrae
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Dense
fibrous tissue has collagen fibers as it's matrix material. Crowded between
the collagen fibers are rows of fibroblasts. The dense fibrous tissue forms
long, rope-like structures, ligaments and tendons. Tendons attach skeletal
muscle to bone, ligaments connect bone to bone. The latter is the most
elastic of the two. Dense fibrous tissue also makes up the lower levels
of the dermis, or skin
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Areolar
tissue is the most widely distributed connective tissue in the body. It
is soft, pliable, cushions and protects the body of the organ. It functions
as the universal packing tissue and the connective tissue glue that helps
hold the internal organs together and in proper position. A soft layer
of areolar tissue, named the lamina propria, underscores all mucosae. The
fluid matrix is a combination of matrix materials which form a loose network
of fibers. When viewed, it is airy and delicate in appearance. Because
of it's loose and fluid nature, areolar connective tissue provides a storage
for water and salts, mainly for use by the surrounding cells. When the
tissue soaks up excess fluid and becomes puffy and swollen, the condition
is called edema. Many kinds of phagocytes wander through the tissue and
scavenge for bacteria, dead cells, and other debris
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Adipose
tissue is fat. Basically, it's areolar tissue in which fat cells are predominant.
Most of the cells volume is taken up by a vacuole which houses a fat droplet,
forcing the nucleus off to on side. These cells ore sometimes called signet
rings cells for their appearance. Adipose tissue insulates and protects
the body from impact. It also protects some individual organs, such as
the kidneys, which are surrounded by a capsule of fat. Adipose tissue cushions
the eyes in their sockets, and is stored in the hips and breasts for energy
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Reticular
connective tissue consists of a delicate network of interwoven reticular
fibers and associated reticular cells, which resemble fibroblasts. It forms
the stroma, or internal supporting framework that can support many free
blood cells, largely lymphocytes, in lymphatic organs such as lymph nodes,
the spleen, and bone marrow
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Blood,
or vascular tissue, is considered to be a connective tissue. It consists
of a matrix-- plasma-- and blood cells suspended within it. The fibers
of the blood only become visible when the blood clots. The platelets break
down and form the fibers
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Nervous
tissue is made up of cells called neurons.
Two main functional characteristics are irritability and conductivity.
The structure of the neuron is unique: a cell body is covered in small,
tree-like arms called dendrites. One extends beyond, to the next cells
in the chain, called an axon. At the synapses, the cells do not physically
touch. Instead, the impulse causes a chemical reaction which, in turn,
passed the electrical message along. Axons can reach up to three feet in
length. They are, in "white matter", sheathed in myelin cells, which insulate
it and increase the impulse speed. Theses cells make up the brain, spinal
cord, and all nerves. The myelin cells are really just specialized fat
cells
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Muscle
tissue:
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Muscle
tissues are highly specialized to contract. They are made up of muscle
fibers. they support, move, and heat the body
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Skeletal
muscle is packaged by connective tissue into skeletal muscles. These muscle
are voluntary, letting us lift our arm, walk, and stick out our tongue
at an offending anatomy teacher. The cells are long, multinucleated, and
cylindrical. They also have obvious striation, or bands that run across
them, which show areas of differing contractile proteins
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Cardiac
muscle is found only in the heart. As it contracts, it propels blood out
of the heart and into the arteries. The cells are also striated, but branch
and join each other at junctions called intercalated disks. They can be
either mono- or multinucleated
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Smooth,
or visceral, muscle is not striated. The cells are mononucleated, and spindle-like
in appearance. Smooth muscle is involuntary in nature, and can constrict
or dilate a body cavity, or organ. This muscle moves food through the digestive
tract, blood through the blood vessels, and so one. The wavelike motion
of the contractions is called peristalsis
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When
tissue injury occurs, the body has several ways to defend itself. Inflammation
is a nonspecific response to help protect against further injury. The immune
response is highly specific, to fight bacterial or viral invaders. There
are two major ways for a tissue to heal; regeneration and fibrosis. Regeneration
is the replacement of destroyed cells. Fibrosis is the repair of the damage
by fibrous connective tissue, which causes scarring. When the surface of
the skin is broken, clotting occurs, and then granulation tissue forms.
The granulation tissue is mostly made up of capillaries, phagocytes which
dispose of the scab, and fibroblasts which synthesize collagen fibers (forming
the scar). Scar tissue is strong, but lacks flexibility
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