Download SYSTEMS OF THE HUMAN BODY

SYSTEMS OF THE HUMAN BODY
reflect
Think about all of the things you do in a single
day. You eat, travel to school, study for tests,
communicate with your family members and
classmates, and more. All of these activities are
possible thanks to the amazing human body!
The human body is made of many parts working
together to perform important life functions. What are
these different parts? What role do they play in your
body, and how do they work together to maintain life?
Organization in the Human Body
The smallest unit of life is the cell. The human body
is made of up trillions of cells. There are one million
millions in just one trillion! Each cell performs certain
functions necessary for keeping the body healthy.
Together, cells form tissues, which are groups of cells
that perform the same function. The human body is
composed of muscle tissue, nervous tissue, and skin
tissue. The different kinds of tissues group together
to form an organ. The heart and brain are examples
of organs. Finally, organs function together to form an
organ system. Organ systems are groups of organs that
work together to perform all the major functions the body
needs to stay alive.
Different organ systems serve different functions. From
moving blood around the body to deliver nutrients and
remove wastes to providing support, protection, and movement, the systems of the body
keep us alive. That’s why it’s important to keep the body systems healthy and strong.
Organ Systems
The duties of maintaining life are divided among the organ systems. Let’s look closer at the
systems and the important roles they play in a human body.
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SYSTEMS OF THE HUMAN BODY
Circulatory System: The circulatory system includes the
heart, blood vessels, and blood. The heart is an organ made
up of four different chambers (left and right atria and ventricles)
that work together to pump blood throughout the body. Blood
circulates to all the different parts of the body, delivering oxygen
and important nutrients to cells. The circulatory system also
picks up carbon dioxide from the cells and carries it to the
lungs where it is exhaled. Oxygen-rich blood (blood that carries
oxygen molecules) leaves the heart through blood vessels called
arteries. Oxygen is delivered to the body through vessels called
capillaries that are so thin, the oxygen molecules pass right
through their walls and into cells. Oxygen-poor blood (blood
that contains a lot of carbon dioxide waste) returns to the heart
through veins. Blood also contains white blood cells important for
fighting infections.
Respiratory System: When blood returns to the heart from the cells, it is pumped to the
lungs. The lungs are part of the respiratory system, which serves the main purpose of
supplying the blood with oxygen. The lungs include two branches called bronchi, narrower
tubes called bronchioles, and tiny air sacs called alveoli. The respiratory system also
includes the nose, pharynx (throat), and trachea. When a
person inhales, oxygen and other gases enter the mouth
trachea: tube connecting
and nose and pass through the pharynx and trachea.
the nose and mouth to the
The gases then branch into the left and right bronchi of
entrance to the lungs; also
the lungs. At the end of the bronchioles, alveoli are the
called the windpipe
sites of gas exchange in the lungs. Oxygen moves across
the membranes of the alveoli and into the capillaries of
the body. The respiratory system also removes carbon dioxide
from the body, which is waste produced by cells. Carbon dioxide
passes through capillary walls of the body and into the alveoli. It
then moves out of the body through the nose and mouth when a
person exhales.
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SYSTEMS OF THE HUMAN BODY
Skeletal System: The skeletal system includes bones and joints. (A joint
is an area in which two or more bones make contact.) Bones provide
the human body with structure and support. They also protect important
organs. The skull is like a helmet that protects the brain. Ribs keep the
heart and other nearby organs safe. Bones also store important minerals
such as calcium and produce new blood cells.
Muscular System: The muscular system, as you might have guessed,
includes muscles! It also includes tendons and ligaments. Tendons are
tissues that attach bones to muscles. Ligaments are tissues that attach
bones to other bones. Tendons and ligaments help the body move.
There are three types of muscles in the muscular
system: skeletal, smooth, and cardiac. Skeletal
muscles are voluntary—people have the ability to consciously control
them and work with bones to provide movement such as walking,
jumping, or even just raising a hand to answer a question in class.
Smooth muscle is involuntary—it moves or contracts without conscious
control—and lines the inside of many organs such as the stomach and
blood vessels. One important function of smooth muscle is to help move
food through the body via muscle contractions in various organs like
the stomach. Smooth muscle also moves blood through veins. Cardiac
muscle is also involuntary and is found in the walls of the heart and aids
in the contraction of the heart in order to pump blood.
Digestive System: Food provides energy for
all of the organ systems, but it must be broken
down before it can be used. This is the function of the digestive
system. This system includes the mouth, esophagus, stomach,
intestines, and anus. Digestion begins in the mouth where it is
broken down into smaller pieces by the teeth and saliva. The
physical breaking down of food by teeth is called mechanical
digestion. Saliva contains substances that also break down the
food. This is the start of chemical digestion.
Food then travels down a tube called the esophagus and enters the
stomach where further chemical digestion occurs. Strong chemicals
and churning by stomach muscles break the smaller food particles
down into even smaller molecules. The liver and pancreas are
organs that also contribute chemicals that help break down food.
From the stomach, food moves into the small intestine where nutrients are absorbed into
the bloodstream. Materials that are not absorbed travel to the large intestine where any
remaining water is absorbed. The rest of the material leaves the body as waste through
the anus.
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SYSTEMS OF THE HUMAN BODY
Excretory System: Removing waste from the body is important to
maintaining health. The kidneys, bladder, and liver are the parts of
the excretory system that collect and dispose of waste produced by
cells. As already stated in the lesson, the lungs remove carbon dioxide
waste. The liver and kidneys filter the blood and remove toxins, excess
water, and other waste. The wastes are then stored in the bladder as
urine until they are released from the body during urination.
Getting Technical: Waste Removal in Space
Astronauts who live in space for long periods of time do not have
access to clean, fresh water piped into their faucets every day. Transporting water to space
is heavy and expensive. The best option is to recycle the water they have—every bit of it!
NASA developed a machine that filters water produced by the astronauts, including water
produced in their urine. The machine uses three steps to filter out toxins from the urine.
The first step removes particles and debris. The second step filters out impurities, and the
third step kills bacteria and viruses. NASA scientist Layne Carter says the water purified
through the machine in space is cleaner than water from a faucet on Earth. This is because
their process of water treatment is more aggressive than the processes used by water
treatment facilities on Earth. How would you feel about drinking a glass of water that came
from your own urine?
Reproductive System: The continuation of the human species
depends on reproduction, or producing offspring. Humans reproduce
sexually. A sperm from a male fertilizes
an ovum, or egg, from a female. In
sperm: male sex cell
males, the reproductive organs that
produce sperm are the testes. The sperm
ovum: female sex
are delivered to the female through the
cell; also called egg
penis. The female reproductive system
is much more complex than the male’s.
Ovaries produce and store eggs. Each month, the ovaries release
one egg. The egg travels to one of two fallopian tubes. Under normal
circumstances, the sperm fertilizes the egg in the fallopian tube.
The fertilized egg then travels to, and implants in, the uterus. The uterus is an organ that
protects and nurtures the egg as it grows into a baby. If an egg is not fertilized, it is released
from the body at the end of the menstrual cycle.
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SYSTEMS OF THE HUMAN BODY
Integumentary System: The integumentary system contains the
largest organ in the human body—the skin. Along with hair, nails, and
glands, the skin protects the body’s
internal organs from exposure to
glands: organs that
the outside environment. Skin is the
release hormones
body’s first line of defense against
illness and injury. This system also
excretes waste through sweat, helps maintain body temperature, and
produces vitamin D. The integumentary system plays an important role
in the body’s interactions with its surroundings. Special nerves in the
skin pick up stimuli from the environment and send messages to the
brain. For example, when skin touches something cold, nerves in the skin send a message
to the brain that the item is cold.
Nervous System: All of the organ systems are controlled by the nervous
system because it contains the brain, spinal cord, and nerves. Stimuli
from both outside and inside the body travel over the system of nerves as
electrical impulses to the brain in fractions of a second. The brain sends
messages back to parts of the body just as quickly, directing the body
parts on how to react. The lightening fast communication system allows
the nervous system to control all parts of the human body at once.
Endocrine System: The endocrine system works with the nervous
system. Together, they are the body’s two systems for control and
communication. The main function of the
endocrine system is to maintain a stable internal
environment, or homeostasis. This system is
made up of glands that send messages through
hormones instead of electrical signals. Hormones
are chemical messengers that regulate
processes such as growth, reproduction, development, and energy
production. For example, testosterone is a hormone that is largely
responsible for the development of male reproductive organs.
Estrogen is a hormone that regulates the growth and development
of female reproductive characteristics.
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SYSTEMS OF THE HUMAN BODY
look out!
It is important to remember that body systems rarely function independent of one another.
Two or more body systems usually work together. For example, the digestive system
breaks down food, but the circulatory system moves the nutrients to different parts of the
body through the blood. The skeletal and muscular systems work together for movement.
The excretory system removes waste that the digestive and respiratory systems produce.
All of the organ systems communicate with the nervous system, and the nervous system
controls other systems through electrical impulses. Just like groups of cells make up tissues
and tissues make up organs, the organ systems together make up an organism.
cells
tissues
organs
organ systems
organisms
what do you think?
Which body systems work together to move your hand when you touch something hot?
Explain your reasoning.
What do you know?
Use what you have learned about the human body systems to complete the chart on the
next page. Fill in either the missing name of the system, the main parts of the body that
make up the system, or the system’s functions.
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SYSTEMS OF THE HUMAN BODY
System
Circulatory
Main Parts of System
Functions
Breaks down food into small
molecules, absorbs nutrients into
blood, removes food waste
Endocrine
Glands, hormones
Kidneys, bladder, liver
Protects inner organs from illness and
injury, regulates body temperature,
detects stimuli from surroundings
Muscles, ligaments, tendons
Nervous
Male: testes, penis
Female: ovaries, uterus,
fallopian tubes
Breathes in oxygen, breathes out
waste such as carbon dioxide
Skeletal
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SYSTEMS OF THE HUMAN BODY
connecting with your child
Human Body Systems at Home
To help students learn more about human
body systems, perform a simple dissection
at home. Buy a package of bone-in chicken
wings from a grocery store and have
students analyze the different structures
of the chicken that they can observe.
Carefully use a knife to cut away the skin
and help students identify the muscular
system (meat), the skeletal system
(bones), and the tendons that hold the
bones and muscles together. The tendons
look like thick silvery bands at the ends
of bones and are connected to the meat.
Have students manipulate the muscles to
demonstrate how they move the bones by
shortening and lengthening the muscles.
The bones should move up and down in
response.
Encourage students to look for structures
from other body systems including the
circulatory system (blood vessels can often
be found in raw meat) and the nervous
system (nerves look yellow and stringy).
Have them analyze the skin and identify
places where feathers were once attached.
If a hand lens is available, have students
look at the structures more closely to
see if they can observe more about the
body system parts. Discuss how all of the
structures you observe in the chicken wing
are similar to structures in the human body
systems.
Once the dissection is complete, be
sure students WASH THEIR HANDS
THOROUGHLY. Raw chicken may contain
food-borne illnesses such as Salmonella.
While eating their next meal, encourage
students to describe which of their body
systems are in action as they eat. Have
them describe which structures are
functioning and what tasks they perform. For
example, after a bite of food is swallowed,
students should explain that food has moved
into the stomach. The stomach uses smooth
muscle to churn the food. Chemicals from
the liver and pancreas help break the food
down into small molecules. Soon the small
intestine will absorb the food’s nutrients into
the bloodstream where the nutrients will
circulate to the cells.
Here are some questions to discuss with
students:
• What were some similarities between the
structures you observed in the chicken
wings and those found in the different
human body systems? What were some
differences?
• What are three main processes the body
systems do to keep a human healthy?
• What body system is working hard when
you do your homework? Play sports?
Lay out in the sun?
• Why is it necessary for body systems to
work together?
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