Download Systems of the Human Body

Systems of the Human Body
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 and nose and pass
through the pharynx and trachea. The gases then branch into the
trachea: tube connecting
left and right bronchi of the lungs. At the end of the bronchioles,
the nose and mouth to the
alveoli are the sites of gas exchange in the lungs. Oxygen moves
entrance to the lungs; also
across the membranes of the alveoli and into the capillaries of the
called the windpipe
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 males, the
reproductive organs that produce sperm are the
sperm: male sex cell
testes. The sperm are delivered to the female
through the penis. The female reproductive
system is much more complex than the male’s.
ovum: female sex
Ovaries produce and store eggs. Each month,
cell; also called egg
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 the outside environment.
glands: organs that
Skin is the body’s first line of defense
release hormones
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
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
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
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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