TISSUES
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Description and Location
In biology, tissue is a cellular organizational level between cells and a
complete organ. A tissue is an ensemble of similar cells and their extracellular
matrix from the same origin that together carry out a specific function. Organs are
then formed by the functional grouping together of multiple tissues.
Structure
Function
Human body tissue makes up organs and other body parts. There are four
main types of tissue: muscle, epithelial, connective and nervous. Each is made of
specialized cells that are grouped together according to structure and function.
EPITHELIAL TISSUES
DID YOU KNOW
Most epithelial tissue is described with two names. The first name describes
the number of cell layers present and the second describes the shape of the cells.
For example, simple squamous epithelial tissue describes a single layer of cells that
are flat and scale-like in shape.
Description
identified by both the number of layers and the shape of the cells in the
upper layers. There are eight basic types of epithelium: six of them are identified
based on both the number of cells and their shape; two of them are named by the
type of cell (squamous) found in them. Epithelial tissue is classified based on the
number of cells, the shape of those cells, and the types of those cells.
Structure
Location
Epithelia tissue forms boundaries between different environments, and nearly
all substances must pass through the epithelium.
Function
Protection for the underlying tissues from radiation, desiccation, toxins, and
physical trauma.
Absorption of substances in the digestive tract lining with distinct
modifications.
Regulation and excretion of chemicals between the underlying tissues and
the body cavity.
The secretion of hormones into the blood vascular system. The secretion of
sweat, mucus, enzymes, and other products that are delivered by ducts come from
the glandular epithelium.
The detection of sensation.
Simple squamous epithelium
Description
Simple squamous epithelium cells are flat in shape and arranged in a single
layer. This single layer is thin enough to form a membrane that compounds can
move through via passive diffusion.
Structure
Location
Air sacs of the lungs and the lining of the heart, blood vessels and lymphatic
vessels
Function
Allows materials to pass through by diffusion and filtration, and secretes
lubricating substances
Simple cuboidal epithelium
Description
Simple cuboidal epithelium consists of a single layer cells that are as tall as
they are wide. The important functions of the simple cuboidal epithelium are
secretion and absorption.
Structure
Location
In ducts and secretory portions of small glands and in kidney tubules
Function
Secretes and absorbs
Simple columnar epithelium
Description
Simple columnar epithelium is a single row of tall, closely packed cells,
aligned in a row. They possess cellular extensions (e.g., microvilli in the small
intestine, or the cilia found almost exclusively in the female reproductive tract).
Structure
Location
Ciliated tissues including the bronchi, uterine tubes, and uterus; smooth
(nonciliated tissues) are in the digestive tract bladder
Function
Absorbs; it also secretes mucous and enzymes.
Pseudostratified columnar epithelium
Description
These are simple columnar epithelial cells whose nuclei appear at different
heights, giving the misleading (hence pseudo) impression that the epithelium is
stratified when the cells are viewed in cross section.
Pseudostratified epithelium can also possess fine hair-like extensions of their
apical (luminal) membrane called cilia. In this case, the epithelium is described as
ciliated pseudostratified epithelium.
Structure
Location
Ciliated tissue lines the trachea and much of the upper respiratory tract
Function
Secrete mucous; ciliated tissue moves mucous
Stratified squamous epithelium
Description
consists of squamous (flattened) epithelial cells arranged in layers upon a
basal membrane. Only one layer is in contact with the basement membrane; the
other layers adhere to one another to maintain structural integrity.
Structure
Location
Lines the esophagus, mouth, and vagina
Function
Protects against abrasion
Stratified cuboidal epithelium
Description
is a type of epithelial tissue composed of multiple layers of cube-shaped cells.
Only the most superficial layer is made up of cuboidal cells, and the other layers
can be cells of other types.
Structure
Location
Sweat glands, salivary glands, and mammary glands
Function
Protective tissue
Stratified columnar epithelium
Description
is a rare type of epithelial tissue composed of column shaped cells arranged
in multiple layers. Stratified columnar epithelia are found in the conjunctiva of the
eye, in parts of the pharynx, anus, the uterus, and the male urethra and vas
deferens.
Structure
Location
The male urethra and the ducts of some glands.
Function
Secretes and protects
Transitional epithelium
Description
Transitional epithelia are found in tissues that stretch and it can appear to be
stratified cuboidal when the tissue is not stretched, or stratified squamous when the
organ is distended and the tissue stretches.
Structure
Location
Lines the bladder, urethra and ureters
Function
Allows the urinary organs to expand and stretch
MUSCULAR TISSUES
Description and Location
Muscle is a soft tissue that is highly specialized for the production of tension
which results in the generation of force. Muscle cells, or myocytes, contain
myofibrils comprised of actin and myosin myofilaments which slide past each other
producing tension that changes the shape of the myocyte. Numerous myocytes
make up muscle tissue and the controlled production of tension in these cells can
generate significant force.
Structure
Function
Muscle tissue can be classified functionally, voluntary or involuntary and
morphologically striated or non-striated. Voluntary refers to whether the muscle is
under conscious control, striation refers to the presence of visible banding within
myocytes which occurs due to organization of myofibrils to produce a constant
direction of tension.
Skeletal Muscle
Description
Skeletal muscle mainly attaches to the skeletal system via tendons to
maintain posture and control movement for example contraction of the biceps
muscle, attached to the scapula and radius, will raise the forearm. Some skeletal
muscle can attach directly to other muscles or the skin, as seen in the face where
numerous muscles control facial expression.
Structure
Location
Skeletal muscles and some epithelial tissue.
Function
Skeletal muscle is under voluntary control, although this can be subconscious
for example when maintaining posture or balance. Morphologically skeletal
myocytes are elongated and tubular and appear striated with multiple peripheral
nuclei
Cardiac Muscle Tissue
Description
As with skeletal muscle cardiac muscle is striated, however it is not
consciously controlled and so is involuntary. Cardiac muscle can be further
differentiated from skeletal muscle by the presence of intercalated discs which
control the synchronized contraction of cardiac tissues. Cardiac myocytes are
shorter than skeletal equivalents and contain only one or two centrally located
nuclei.
Structure
Location
Found only in the heart
Function
cardiac contractions pump blood throughout the body and maintain blood
pressure.
Smooth Muscle Tissue
Description
Smooth muscle is non-striated, although it contains the same myofilaments
they are just organized differently, and involuntary. Smooth muscle myocytes are
spindle shaped with a single centrally located nucleus.
Structure
Location
Smooth muscle tissue is found associated with numerous other organs and
tissue systems such as the digestive system or respiratory system.
Function
It plays an important role in the regulation of flow in such tissues for example
aiding the movement of food through the digestive system via peristalsis.
CONNECTIVE TISSUE
Description and Location
Connective tissue (CT) is a one of the four main classes of tissues. Although it
is the most abundant and widely distributed of the primary tissues, the amount of
connective tissue in a particular organ varies. Like to the timber framing of a house,
the connective tissue provides structure and support throughout the body.
3 Main Components
Ground substance
Fibers
Cells
Three types of fibers are found in connective tissue:
Collagen
Elastic fibers
Reticular fibers
Structure
Function
Connective tissue is incredibly diverse and contributes to energy storage, the
protection of organs, and the body’s structural integrity.
Binding and supporting.
Protecting.
Insulating.
Storing reserve fuel.
Transporting substances within the body.
Adipose Connective Tissue
Description
Structure
Location
Function
Dense Regular Connective Tissue
Description
This is loose connective tissue composed of adipocytes. It is technically
composed of roughly only 80% fat.
Structure
Location
The two types of adipose tissue are white adipose tissue (WAT) and brown
adipose tissue (BAT). Adipose tissue is found in specific locations, referred to as
adipose depots.
Function
Its main role is to store energy in the form of lipids, although it also cushions
and insulates the body.
Dense Irregular Connective Tissue
Description
This consists of closely packed bundles of collagen fibers running in the same
direction. These collagen fibers are slightly wavy and can stretch a little bit.
Structure
Location
With the tensile strength of collagen, this tissue forms tendons, aponeurosis
and ligaments.
Function
This tissue forms the fascia, which is a fibrous membrane that wraps around
the muscles, blood vessels, and nerves.
Hyaline Cartilage
Description
This is is the most abundant of all cartilage in the body. Its matrix appears
transparent or glassy when viewed under a microscope.
Structure
Location
It is a major part of the embryonic skeleton, the costal cartilages of the ribs,
and the cartilage of the nose, trachea, and larynx
Function
It provides strong support while providing pads for shock absorption.
Fluid Connective Tissue
Description
This is considered a specialized form of connective tissue. It is an atypical
connective tissue since it does not bind, connect, or network with any body cells. It
is made up of blood cells and is surrounded by a nonliving fluid called plasma.
Structure
Location
Blood
Function
Blood is a bodily fluid in animals that delivers necessary substances, such as
nutrients and oxygen, to the cells and transports metabolic waste products away
from those same cells.
NERVOUS TISSUE
Description and Location
Nervous tissue is the main component of the nervous system, which includes
the brain, spinal cord, and nerves. Nervous tissue is one of four major classes of
tissues. It is specialized tissue found in the central nervous system and the
peripheral nervous system. It consists of neurons and supporting cells called
neuroglia.
Structure
Function
The nervous system is responsible for the control of the body and the
communication among its parts. Nervous tissue contains two categories of cells—
neurons and neuroglia.
Neuroglia
Description
Neuroglia, also called glial cell or glia, any of several types of cell that
function primarily to support neurons. The term neuroglia means “nerve glue.”. For
instance, after high levels of neuronal activity neuroglial cells can take up and
spatially buffer potassium ions and thus maintain normal neuronal function.
(1) astrocytes, subdivided into fibrous and protoplasmic types, (2) oligodendrocytes,
subdivided into interfascicular and perineuronal types, (3) microglia, and (4)
ependymal cells.
Structure
Location
Neuroglia exceed the number of neurons in the nervous system by at least 10
to 1. Neuroglia exist in the nervous systems of invertebrates as well as vertebrates
Function
These cells that form myelin, protect, support, and maintain equilibrium in
your nervous system are called glial cells.
Neurons
Description
The core component of the nervous system in general, and the brain in
particular, is the neuron or nerve cell, the “brain cells” of popular language. A
neuron is an electrically excitable cell
Structure
Location
Nervous system CNS and PNS
Function
processes and transmits information by electro-chemical signalling.
