Human Body Systems
Human Body Organization
The Human Body
is composed of
are composed of
are composed of
are composed of
• heart, blood vessels,
blood, lymph nodes and
• transports nutrients,
• The heart is a muscle about the size of a fist.
• Each blood cell takes around 20 seconds to make its
deliveries and travel back to the heart.
• The heart works by contracting and relaxing.
• The heart has flapping valves that allow blood to flow in one
direction. The flaps create a “lub-dup” sound.
• A heart attack is caused by a blood vessel blocked by a clot.
• The average person has about 5 liters of blood.
• The body can replace blood within a few weeks after loss.
• Platelets in the blood help it to clot, or stick together, to
• The four blood types are A, B, AB, and O.
• mouth, throat,
liver, pancreas, small and
• extracts and absorbs
nutrients from food;
maintains water and
• Food takes 3 days to complete its journey through the
• An adult digestive system is about 30 feet long.
• An average person takes in about 4.4 pounds of food and
drink every day, consuming over 110,000 pounds in a
• Gravity and bands of muscles help food travel down the
esophagus to the stomach, making it possible to eat lying
down or even upside down.
• The stomach is lined with a slimy mucus and releases an
acid called gastric juice to help dissolve food.
• Stomach noises are caused by food and air sloshing around.
• Water makes up about 70% of the body.
• hypothalamus, pituitary,
pancreas, pineal, adrenal,
testes, and ovaries
• regulates body
other organ systems
• Endocrine glands release hormones, chemicals that act as
signals telling different parts of the body what to do.
• The body makes over 20 hormones, each with a different
job to do.
• The blood carries hormones around the body until reaching
the target organ, the body part needing it.
• Hormones can affect the way a person feels.
• As a person ages, the body makes less of some hormones.
• kidneys, urinary bladder,
ureters, urethra, skin,
• removes wastes from
concentration of body
• Leftover waste in the large intestine is called fiber. Fiber
sweeps the digestive system clean as it moves along.
• The large intestine contains millions of bacteria that feed
on the leftovers in the bowel.
• Kidneys are located in the middle of the back.
• Each kidney contains up to a million tiny units called
nephrons that filter all of the blood in the body.
• People with failing kidneys have their blood cleaned by a
dialysis machine or have a new kidney transplanted.
• white blood cells, lymph
nodes and vessels, skin
• defends against
pathogens and diseases
• The immune system is constantly on guard to keep
germs, bugs, and poisons out the body.
• The skin is the immune system’s first line of defense.
• There are germ-killing chemicals in saliva, tears, ear
wax, and mucus.
• White blood cells destroy germs that enter through cuts.
• Sticky yellow pus is made of bodies of white blood cells
that die in the battle against germs.
• An allergy is the immune system making a mistake.
• Some white blood cells make antibodies which can
protect against bacteria, viruses, and poisons.
• skin, nails, hair
• protects against injury,
infection, and fluid loss;
helps regulate body
• Skin cells are made of a tough protein called keratin.
• About 40 million dead skin cells are lost each day.
• The average adult skin spread out would take up about 2.2
square yards and would weigh around 15 pounds.
• The skin is waterproof. It keeps water out so the body is
not a sponge and holds in moisture so it does not dry out.
• Skin expands to fit the body.
• Skin forms bumps when cold and releases sweat when hot.
• The skin repairs itself forming scabs and scars.
• Skin absorbs sunlight to make vitamin D. Too much sun
can lead to sunburn and can even cause skin cancer.
• skeletal, smooth, and
cardiac muscle tissues
• moves limbs and trunk;
through body; provides
structure and support
• There are nearly 600 skeletal muscles that make up
nearly half of the total body weight in the human.
• Muscles can only pull – they cannot push.
• Energy is stored in the muscles in a chemical called ATP.
• Lactic acid is released when the muscles are overworked
and lack O2, making the muscles hurt or ache.
• Muscles are attached to bones by tendons.
• The biggest muscles in the body are the gluteus maximus
muscles (buttocks), but the muscle that can exert the
most force is the masseter (jaw muscle).
• brain, spinal cord, nerves,
• regulates behavior;
regulates other organ
systems; controls sensory
and motor functions
• The left half of the brain controls the right half of the
body and vice-versa.
• The human brain is more powerful and complicated than
the world’s biggest computer. It can store millions of
memories and do billions of calculations every day.
• The human body has over 100 billion neurons in all.
• The brain can receive over 100,000 signals per second.
• Messages whiz through the nerves at up to 270 mph.
• Neurons reaching from the spinal cord to the toes are
the longest cells in the human body, measuring up to 4
feet in length.
• ovaries, uterus, and
breasts (in females);
testes and penis (in
• produces gametes and
• A person grows over 5 million times bigger changing
from a single cell to a newborn human being.
• Humans grow for about 20 years, changing from a child
to an adult.
• Male reproductive cells are called sperm, and female
reproductive cells are called eggs.
• Sperm and eggs have only 23 chromosomes each.
• When joined together, sperm and egg make a whole cell
called a fertilized egg which can grow into a baby.
• lungs, nose, mouth,
• moves air into and out of
lungs; controls gas
exchange between blood
• The lungs fill up most of the chest cavity.
• The left lung is slightly smaller than the right lung,
because it must allow enough space for the heart.
• Inside each lung is a network of thousands of tunnels
called the bronchial tree which branch into bronchioles
containing six million tiny bags (air sacs) called alveoli.
• The lungs take millions of O2 molecules out of the air
and put them into the blood to be delivered to the cells.
• Simultaneously, the lungs also take waste gases out of
• A smoker’s lungs are dark gray and full of dirt and tar.
• bones and joints
• protects and supports
the body and organs;
interacts with skeletal
muscles; produces red
blood cells, white blood
cells, and platelets
• A baby is born with 270 bones while an adult body has
• The hands and feet contain half of the bones in the
• Bones are made of the hard mineral calcium, living cells,
blood vessels and nerves.
• Bones are made of several layers – periosteum,
compact bone, and spongy bone.
• A joint is where two bones meet.
• Joints can be cartilagenous (spine), ball-and-socket
(shoulders and hips), pivot (neck), gliding (wrists), and
hinged (fingers, elbows, and knees).