Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
Types of Tissues
A tissue is composed of similarly specialized cells that perform
a common function in the body. The tissues of the human body can be
categorized into four major types:
epithelial tissue, which covers body surfaces and lines body cavities;
connective tissue, which binds and supports body parts
; muscular tissue, which moves body parts;
nervous tissue, which receives stimuli and conducts impulses
from one body part to another
Epithelial Tissue
Epithelial tissue, also called epithelium, consists of tightly
packed cells that form a continuous layer or sheet lining the
entire body surface and most of the body’s inner cavities. On the external
surface, it protects the body from injury, drying out, and possible
pathogen (virus and bacterium) invasion.
On internal surfaces, epithelial tissue may be specialized for other
functions in addition to protection. For example, epithelial tissue secretes
mucus along the digestive tract and sweeps up impurities from the lungs
by means of cilia (sing.,cilium). It efficiently absorbs molecules from
kidney tubules and from the intestine because of minute cellular
extensions called microvilli.There are various types of epithelial tissue
Squamous epithelium is composed of flattened cells and is
found lining the lungs and blood vessels. Cuboidal epithelium
contains cube-shaped cells and is found lining the
kidney tubules. Columnar epithelium has cells resembling rectangular
pillars or columns, and nuclei are usually located near the bottom of each
Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
cell. This epithelium is found lining the digestive tract. Ciliated columnar
epithelium is found lining the oviducts, where it propels the egg toward
the uterus.
An epithelium can be simple or stratified. Simple means the tissue has a
single layer of cells, and stratified means the tissue has layers of cells
piled one on top of the other. The walls of the smallest blood vessels,
called capillaries,are composed of a single layer of epithelial cells. The
permeability of capillaries allows exchange of substances between the
blood and tissue cells. The nose, mouth, esophagus,anal canal, and vagina
are all lined by stratified squamous epitheliumthe outer layer of skin is
also stratified squamous epithelium, but the cells have been reinforced by
keratin, a protein that provides strength Pseudostratified epithelium
appears to be layered; however,true layers do not exist because each cell
touches the baseline. The lining of trachea, is called pseudostratified
ciliated columnar epithelium. A secreted covering of mucus traps foreign
particles, and the upward motion of the cilia carries the mucus to the back
of the throat, where it may either be swallowed or expectorated.Smoking
can cause a change in mucus secretion and inhibit ciliary action, and the
result is a chronic inflammatory condition called bronchitis.
basement membrane often joins an epithelium to underlying
connective tissue. We now know that the basement membrane is
glycoprotein, reinforced by fibers that are supplied by connective tissue.
An epithelium sometimes secretes a product, in which case it is described
as glandular. A gland can be a single epithelial cell, as in the case of
mucus-secreting goblet cells found within the columnar epithelium lining
the digestive tract, or a gland can contain many cells. Glands that secrete
their product into ducts are called exocrine glands, and those that secrete
their product directly into the bloodstream are called endocrine glands.
The pancreas is both an exocrine gland, because it secretes digestive
juices into the small intestine via ducts, and an endocrine gland, because
it secretes insulin into the bloodstream
Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
Connective Tissue
Connective tissue binds organs together, provides support and
protection, fills spaces, produces blood cells, and stores fat. As a rule,
connective tissue cells are widely separated by a matrix, consisting of a
noncellular material that varies in consistency from solid to semifluid
to fluid. The matrix may have fibers of three possible types: white
collagen fibers contain collagen, a protein that gives them flexibility and
strength. Reticular fibers are very thin collagen fibers that are highly
branched and form delicate supporting networks.Yellow elastic fibers
contain elastin, a protein that is not as strong as collagen but is more
elastic Loose Fibrous and Dense Fibrous Tissues Both loose fibrous and
dense fibrous connective tissues have cells called fibroblasts that are
located some distance from one another and are separated by a jellylike
matrix containing white collagen fibers and yellow elastic fibers.
Loose fibrous connective tissue supports epithelium and also many
internal organs Its presence inlungs, arteries, and the urinary bladder
allows these organs to expand. It forms a protective covering enclosing
many internal organs, such as muscles, blood vessels, and nerves
Dense fibrous connective tissue contains many collagen fibers that are
packed together. This type of tissue has more specific functions than does
loose connective tissue. For example, dense fibrous connective tissue is
found in tendons, which connect muscles to bones, and in ligaments,
which connect bones to other bones at joints.
Adipose Tissue
In adipose tissue the fibroblasts enlarge and store fat. The body uses
this stored fat for energy, insulation, and organ protection. Adipose tissue
is found beneath the skin,around the kidneys, and on the surface of the
heart.
Reticular Connective Tissue Reticular connective tissue forms the
supporting meshwork of lymphoid tissue present in lymph nodes, the
Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
spleen, the thymus,and the bone marrow. All types of blood cells are
produced in red bone marrow, but a certain type of lymphocyte (T
lymphocyte) completes its development in the thymus.The lymph nodes
store lymphocytes.
Specialized connective tissue
Cartilage
In cartilage, the cells lie in small chambers called lacunae (sing.,
lacuna), separated by a matrix that is solid yet flexible.Unfortunately,
because this tissue lacks a direct blood supply, it heals very slowly. There
are three types of cartilage,distinguished by the type of fiber in the
matrix.
1-Hyaline cartilage the most common type of
cartilage, contains only very fine collagen fibers. The matrix has a white,
translucent appearance. Hyaline cartilage is found in the nose and at the
ends of the long bones and the ribs, and it forms rings in the walls of
respiratory passages.The fetal skeleton also is made of this type of
cartilage. Later,the cartilaginous fetal skeleton is replaced by bone
Elastic cartilage has more elastic fi bers than hyaline
cartilage. For this reason, it is more fl exible and is found, for
example, in the framework of the outer ear.
Fibrocartilage has a matrix containing strong collagen
fi bers. Fibrocartilage is found in structures that withstand
tension and pressure, such as the disks between the vertebrae
2-Bone
Bone is the most rigid connective tissue. It consists of an extremely hard
matrix of inorganic salts, notably calcium salts.These salts are deposited
around protein fi bers, especially collagen fi bers. The inorganic salts give
bone rigidity. The protein fi bers provide elasticity and strength, much as
steel rods do in reinforced concrete. Cells called osteoblasts and
osteoclasts are responsible for forming the matrix in bone tissue.
Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
a-Compact bone makes up the shaft of a long bone It consists of
cylindrical structural units called osteons
The central canal of each osteon is surrounded by rings of hard matrix.
Bone cells are located in lacunae between the rings of matrix. In the
central canal, nerve fi bers carry nerve impulses,and blood vessels carry
nutrients that allow bone to renew itself. Thin extensions of bone cells
within canaliculi (minute canals) connect the cells to each other and to the
central canal.
b-The ends of the long bones are composed of spongy bone covered by
compact bone. Spongy bone also surrounds the bone marrow cavity. This,
in turn, is covered by compact bone forming a “sandwich“ structure.
Spongy bone appears as an open, bony latticework with numerous bony
bars and plates. These are separated by irregular spaces. Although lighter
than compact bone, spongy bone is still designed for strength. Just as
braces are used for support in buildings, the solid portions of spongy bone
follow lines of stress
3-Blood
Blood represents a fl uid connective tissue. Blood, which consists of
formed elements and plasma, is located in blood vessels. Blood transports
nutrients and oxygen to tissue fl uid. Tissue fl uid bathes the body’s cells
and removes carbon dioxide and other wastes. Blood helps distribute heat
and also plays a role in fl uid, ion, and pH balance. The systems
of the body help keep blood composition and chemistry
within normal limits.
4-Lymph
Lymph is also a fl uid connective tissue. Lymph is a clear (sometimes
faintly yellow) fl uid derived from the fl uids surrounding the tissues. It
contains white blood cells. Lymphatic vessels absorb excess tissue fl uid
and various dissolved solutes in the tissues. They transport lymph to
particular vessels of the cardiovascular system. Lymphatic vessels absorb
fat molecules from the small intestine. Lymph nodes, composed
of fi brous connective tissue, occur along the length of lymphatic vessels.
Lymph is cleansed as it passes through lymph nodes, in particular,
because white blood cells congregate there. Lymph nodes enlarge when
you have an infection..
Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
Muscular Tissue
Muscular (contractile) tissue is composed of cells called
muscle fi bers. Muscle fi bers contain fi laments made of proteins
called actin and myosin. The interaction of actin and
myosin accounts for movement. The three types of vertebrate
muscular tissue are skeletal, smooth, and cardiac
1-Skeletal muscle is also called voluntary muscle
It is attached by tendons to the bones of the skeleton. When it contracts,
body parts move. Contraction of skeletal muscle is under voluntary
control. Skeletal muscle fi bers are cylindrical and long—sometimes they
run the length of the muscle. The nuclei are located at the
periphery of the cell, just inside the plasma membrane. The
fi bers have alternating light and dark bands that give them a striated, or
striped, appearance. These bands are due to the placement of actin fi
laments and myosin filaments in the cell.
2-Smooth (visceral) muscle is so named because the cells lack striations
The spindle-shaped cells each have a single nucleus. These cells form
layers in which the thick middle portion of one cell is opposite the thin
ends of adjacent cells. Consequently, the nuclei form an irregular pattern
in the tissue. Smooth muscle is not under conscious or voluntary control.
Therefore, it is said to be involuntary. Smooth muscle is found in the
walls of viscera (intestine, bladder, and other internal organs) and blood
vessels..
.
Cardiac muscle is found only in the walls of the heart. Its contraction
pumps blood and accounts for the heartbeat. Cardiac muscle combines
features of both smooth and skeletal muscle. Like skeletal muscle, it has
striations, but the contraction of the heart is involuntary for the most part.
Cardiac muscle cells also differ from skeletal muscle cells in that they
usually have a single, centrally placed nucleus. The cells are branched
and seemingly fused, one with another. The heart . Cardiac muscle cells
are separate and individual, but they are bound end to end at intercalated
disks.
Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
Nervous tissue consists of nerve cells, called neurons, and
.neuroglia, the cells that support and nourish the neurons
First: Neurons
A neuron is a specialized cell that has three parts: dendrites, a
cell body, and an axon. A dendrite is an extension that receives signals
from sensory receptors or other neurons. The cell body contains most of
the cell’s cytoplasm and the nucleus An axon is an extension that
conducts nerve impulses. Long axons are covered by myelin, a white
fatty substance. The term fi ber1 is used here to refer to an axon along
،with its myelin sheath, if it has one. Outside the brain and spinal cord
.fi bers bound by connective tissue form nerves
The nervous system has three functions: sensory input
integration of data, and motor output. Nerves conduct signals from
sensory receptors to the spinal cord and the brain, where integration, or
processing, occurs.
Second : Neuroglia
In addition to neurons, nervous tissue contains neuroglia
Neuroglia are cells that outnumber neurons nine to one and
take up more than half the volume of the brain.
primary function of neuroglia is to support and nourish neurons,research
is being conducted to determine how much they directly contribute to
brain function. Neuroglia do not have long extensions (axons or
dendrites).
Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
neuroglia found in the brain are microglia, astrocytes, and
oligodendrocytes Microglia,in addition to supporting neurons, engulf
bacterial and cellular debris.
Astrocytes provide nutrients to neurons and produce a hormone known as
glial-derived neutrophic factor (GDNF). This growth factor is currently
undergoing clinical trials as a therapy for Parkinson disease and other
diseases caused by neuron degeneration.
Oligodendrocytes form the myelin sheaths around fi bers in the brain and
spinal cord. Outside the brain, Schwann cells are the type of neuroglia
that encircle long nerve fi bers and form a myelin sheath
Dr.Ihsan Raisan Al Rikabi /college of pharmacy /Al Qadisiya university
The skin
The skin has two regions: the epidermis and the dermis
The Epidermis The epidermis is made up of stratifi ed squamous
epithelium. New epidermal cells for the renewal of skin are derived from
stem (basal) cells. The importance of these stem cells is observed when
there is an injury to the skin. Two types of specialized cells are located
deep in the epidermis.
1- Langerhans cells are macrophages, white blood cells that
phagocytize infectious agents and then travel to lymphatic organs.
2-Melanocytes, lying deep in the epidermis,produce melanin. This is
the main pigment responsible for skin color. The number of melanocytes
is about the same in all individuals, so variation in skin color is due to the
amount of melanin produced and its distribution. When skin is
exposed to the sun, melanocytes produce more melanin. This protects the
skin from the damaging effects of the ultraviolet (UV) radiation in
sunlight
Dermis
The dermis is a region of dense fi brous connective tissue beneath the
epidermisThe dermis contains The dermis also contains blood vessels that
nourish the skin.collagen and elastic fi bers Blood vessels in the dermis
play a role in temperature regulation. If body temperature starts to rise the
blood vessels in the skin will dilate. As a result, more blood is brought to
the surface of the skin for cooling. If the outer temperature cools, the
blood vessels constrict, so less blood is brought to the skin’s surface The
sensory receptors—primarily in the dermis—are specialized for touch,
pressure, pain, hot, and cold. These receptors supply the central nervous
system with information about the external environment Nails, hair, and
glands are structures of epidermal origin, even though some parts of hair
and glands are largely found in the dermis