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The Human Body
Transcript of The Human Body
(made up of
skin, hair and nails
), serves as the body's
first defense against infection and injury, helps to regulate body temperature, removes waste products from the body, and provides protection against ultraviolet (UV) radiation from the sun.
The skin is made up of two main layers:
1.) the epidermis
2.) the dermis
Beneath the dermis is a layer of fat (the
) and loose connective tissue that helps
insulate the body
the largest organ in the human body.
It also has an acidic pH value (anywhere between 4.5-7) to
help prevent bacteria and foreign material from growing on it
. Babies have a pH skin value closer to 7, but it decreases as you get older.
is made up of
, and constantly go through constant rapid cell division. This produces
push older cells to the surface of the skin
and creates a
tough, flexible, waterproof covering on the surface of the skin.
The epidermis also contains
dark brown pigment.
protect the skin from damage by absorbing UV rays
from the sun. Although most people have roughly
the same number of melanocytes
in their skin, differences in skin color are caused by the
different amount of melanin the melanocytes produce
, and where these cells are distributed.
you have in your skin, the
you look. People with fair skin have less melanin in their skin to begin with, but
some of their melanocytes make more melanin when exposed to the sun
. So instead of easily getting an even suntan, they sometimes get
the epidermis, and contains
blood vessels, nerve endings, sensory receptors, smooth muscle, sweat glands, and hair fibers.
The skin interacts with other body parts to maintain
(internal stability) by helping to regulate body temperature.
When the body needs to
on a cold day, the blood vessels in the dermis
, helping them lower heat loss.
On hot days, the blood vessels
bringing heat from the
body's core to the skin
and increasing heat loss.
Hair covers almost every exposed surface of the body. Hair on the head protects the scalp from
UV light from the sun and provides insulation from the cold.
Eyelashes, and hairs in the nostrils and outer ear canals prevent
dirt and other particles from entering
Nails cover and protect fingers and toes, and are made from the
same thing as hair
to their more frequent use, fingernails
4 times faster
Despite what some horror movies may say, a skeleton cannot move on its own.
is the function of the
of the mass of the average human body is
Muscle tissue is found
everywhere in the body
, not just beneath the skin. There are
of muscle tissue:
Each type of muscle is
for specific function in the body
1.) Skeletal Muscle
are usually attached to
(hence their name).
They are responsible for
, like typing on a keyboard, dancing, or winking.
When viewed under a microscope, skeletal muscle has alternating
light and dark bands called striations.
This is why skeletal muscles are also called
Skeletal muscle cells are
vary in length
2.) Smooth Muscle
not under voluntary control.
spindle shaped, have only one nucleus
, and are
move food through your digestive tract,
control the way
blood flows through your circulatory system,
and decrease the size of the
pupils of your eyes in bright light.
3.) Cardiac Muscle
is found in only one place:
Cardiac muscle is
striated like skeletal muscle
, but its cells are
similar to smooth muscle
because it is also
not under voluntary control.
When one muscle
in skeletal muscles are made up of
Each myofibril is made up of
filaments contain a protein called
filaments are made up mainly of a protein called
in the muscle fiber
slide over the thick filaments.
or pulling on body parts.
Individual muscles can only pull in
(no, not these guys -->) but yet we can manage to bend and extend things like our legs. How?
Skeletal muscles are joined to bones by tough
. Tendons are attached in such a way that they
pull on the bones
and make them work like levers.
Our body is kept together through hugs!
To retain their shape, all organisms need some type of
The human skeleton is composed of a type of
connective tissue called bone.
and other connective tissues, such as cartilage and ligaments,
form the skeletal system.
supports the body, protects internal organs, provides for movement, stores mineral reserves,
and provides a site for
blood cell formation.
It easy to think of bones as non-living. After all, many of the mass of bone is made of mineral salts. However,
bones are living tissue.
Bones are a solid network
living cells and protein fibers
that are surrounded by deposits of
Structure of bones
Bones are surrounded by a
tough layer of connective tissue
Blood vessels that
the periosteum carry
to the bone.
Beneath the periosteum is a thick layer of
. Although compact bone is dense,
it is not solid.
A less dense tissue known as
is found inside the
of compact bone. Even though it is called spongy, it's actually
Within bones are
that contain a
is made up mostly of
red blood cells,
some kinds of
white blood cells,
The skeleton of an
is composed almost entirely of a type of connective tissue called
not contain blood vessels.
Because of this, it must rely on the
diffusion of nutrients
from the tiny blood vessels in surrounding tissues.
In adults, cartilage is found in parts of the body that are
such as the
tip of the nose, external ears, and where the ribs are attached to the sternum.
Types of Joints
A place where
one bone attaches to another
bone is called a
hold bones together
in a joint, and they are attached to the
that surround bones.
oxygen from the lungs
to the body's
(a waste product) in the
This is known as
and is the
main function of the respiratory system.
consists of the
nose, pharynx, larynx, trachea, bronchi, and lungs.
The air that makes it
past the nostrils
moves through the
to a tube at the back of the mouth called the
pharynx, or throat.
serves as a
air and food.
Then the air moves from the pharynx
into the trachea
flap of tissue
entrance to the trachea
allow air to
into some of the most
in the body.
To keep the lung tissue
air entering the respiratory system must be
warmed, moistened and filtered.
Large dust particles get
trapped by the hairs
lining the entrance to the
top of the trachea
highly elastic folds of tissue
known as the
pull the vocal cords together,
the air moving between them causes the cords to
produce sounds (such as words).
From the larynx, air passes into the lungs
through the trachea
, where it branches into
two large passageways
in the chest cavity called the
These then divide into
increasingly smaller branches
movement of air into and out of the lungs
. There are
connected to the lungs, instead, the force that drives air into the lungs is just ordinary
The lungs are
sealed in two sacs
inside the chest cavity. At the
of the cavity is a
large, flat muscle
known as the
breathe in (inhale)
, the diaphragm
and the rib cage
expands the volume of the chest cavity.
Most of the time,
breathing out (exhaling)
When the rib cage lowers and the
diaphragm muscle relaxes,
rushes out of the lungs.
Healthy lungs vs. smoker's lungs
The smallest bronchioles end in a
cluster of air sacs,
primary site for gas exchange
in the respiratory system.
Blood and the Lymphatic System
Just like the plumbing system in your home carries water through a series of pipes to different parts of a house,
the circulatory system carries blood through a series of blood vessels to different parts of the body
is a type of
dissolved substances and specialized cells.
oxygen from the lungs, nutrients from the digestive tract, and waste products from tissues.
The human body contains
4 to 6 liters of blood
, which is about
total body mass.
of the volume of
which are suspended in the
other 55%: a straw colored fluid
10% dissolved gases, salts, nutrients, enzymes, hormones, waste products and proteins.
of blood consists of
red blood cells, white blood cells, and platelets.
Red blood cells transport oxygen, white blood cells perform a variety of protective functions, and platelets help in the clotting process.
fragments of cells
derived from larger cells in
red bone marrow.
most numerous cells
in the blood are the
red blood cells.
, and get their color from
iron containing protein
that binds to
oxygen in the lungs
transports it to tissues
throughout the body.
Red blood cells
are shaped like disks that are thinner in the center than along the edges. They are
produced from cells in red bone marrow,
circulate for an average of 120 days
before they are
from squeezing through narrow capillaries.
White blood cells do not contain hemoglobin.
much less common than red cells
, which outnumber them almost
1000 to 1
. They can live for
days, months, or even years depending on health.
White blood cells
guard against infection, fight parasites and attack bacteria.
many different types
white blood cells,
and they perform a wide variety of important functions.
Some protect the body
by acting as
phagocytes, or "eating cells,"
engulf and digest bacteria
and other disease causing microbes.
Some react to foreign substances by
releasing chemicals known as histamines
. These chemicals
increase blood flow to the affected area
redness and swelling
that are often associated with
white blood cells
, known as
are involved in the
Blood is essential to life
, so when we hurt ourselves and lose this vital fluid it can be a problem. Luckily our body has a way to
slow bleeding and begin healing.
is made possible by
plasma proteins and cell fragments called platelets
that are formed from certain
large cells in red bone marrow
come into contact with the
edges of a broken blood vessel,
their surfaces become very
, and a
cluster of platelets
around the wound.
The Immune System
and Immune System Disorders
pathogens (disease causing agents)
all around us, it may seem like a miracle that you're not sick all the time. For that you can thank your
immune system, a series of defenses that guard against disease.
immune system recognizes, attacks, destroys, and "remembers" each type of pathogen that enters the body.
It does this by
producing specialized cells
function of the immune system
fight infection through the production of cells that inactivate foreign substances or cells.
This process is called
The immune system includes
general categories of
guard against infections by
keeping most things out of the body.
between one threat and another .
most important nonspecific defense is the skin.
The importance of skin as a barrier against infection becomes obvious as soon as the skin is broken.
Pathogens can also enter your body through your
mouth and nose. Mucus in your nose and throat
these pathogens, and
cilia that line your nose and throat
push pathogens away
lungs. Stomach acid and digestive enzymes
pathogens that make their way to your stomach.
If pathogens do manage to enter your body, they may
multiply quickly, releasing toxins
into your tissues. When this happens, the
inflammatory response (a second line of defense)
If a pathogen is able to
the body's nonspecific defenses, the
immune response is to attack the particular disease causing agent.
A substance that
triggers this response
is known as an
. Viruses, bacteria, and other pathogens may serve as antigens.
of the immune system that recognize
specific antigens are B lymphocytes (B cells) and T lymphocytes (T cells).
provide immunity against antigens and pathogens
in the body fluids.
When a pathogen invades the body, its antigens are
by some of the
body's B cells
. These B cells
grow and divide rapidly,
producing large numbers of plasma cells.
Once the body has been
exposed to a pathogen,
millions of memory
B cells remain capable of producing antibodies specific to that pathogen
the chance that the disease could develop a second time.
Unfortunately they also make the acceptance of organ transplants difficult.
injection of a weakened form of a pathogen
is known as a
is the type of immunity produced by the body's reaction to a
Immune System Disorders
Although the immune system defends the body from a wide range of pathogens, sometimes disorders occur
in the immune system itself.
These disorders include:
2.) autoimmune diseases
3.) immunodeficiency diseases
most common overreactions
of the immune system to antigens are known as
Some allergic reactions can create a dangerous condition called asthma.
Asthma is a chronic respiratory disease
in which the
air passages become narrower than usual
; resulting in wheezing, coughing, and difficulty breathing.
When the immune system makes a mistake and
attacks the body's own cells
, it produces an
Some examples of autoimmune diseases include
Type 1 diabetes, rheumatoid arthritis, and multiple sclerosis (MS).
occur when either the
immune system fails to develop normally, or a viral infection destroys a normally healthy immune system.
An example of this second type of immunodeficiency disease
AIDS (acquired immune deficiency syndrome).
HIV (human immune deficiency virus) evades the defenses of the immune system, and attacks key cells in the immune system
which leaves the body with
against other pathogens.
Although HIV is a deadly disease, it is not easily transmitted and you
cannot catch it through casual contact.
HIV can only be transmitted through the exchange of:
3.) vaginal secretions
4.) breast milk
regulate internal environment factors,
. Also, components in blood help
, and can even
form clots to repair damaged blood vessels.
B lymphocytes produce antibodies. Antibodies
are essential to
to many diseases.
T lymphocytes help fight tumors and viruses.
Specific defenses track down harmful pathogens that have managed to break through the body's nonspecific defenses.
When that happens,
pathogens can enter your body
and multiply. As they grow, this can cause the
symptoms of an infection
caused by injury or infection
provide a defense against
abnormal cells and pathogens inside living cells (cell-mediated immunity).
They are also the body's way of fighting against its
when they have become
cancerous or infected.
Plasma cells release antibodies. Antibodies
are proteins that
recognize and bind to antigens
The antibodies are carried into the bloodstream to attack the pathogen that is causing the infection.
When allergy causing antigens enter the body, they
activate a particular type of cell called mast cells,
chemicals known as
The epidermis has two layers. The
outside of the epidermis
(the part that comes in contact with the environment) is made up of
...But sometimes we can't even see our freckles!
Smooth muscles are found in the
walls of hollow structures,
such as your
stomach, blood vessels, and intestines.
functions as a
the lever moves around.
Usually, there are
surrounding each joint that pull in
Depending on its type of movement, a joint is classified as
(like where your the bones in the skull meet),
(like the bones between our vertebrae), or
each kind of pathogen
, the immune system produces cells that are
to that pathogen.