The human body is composed of 11 organ systems that work together to keep us alive. Each system is made up of major structures that carry out important functions. The organ systems include the circulatory system which transports blood throughout the body; the digestive system which breaks down food and absorbs nutrients; and the nervous system which controls the body's functions and senses the environment. Working in harmony, these 11 systems allow the human body to survive and thrive.

1. Human Body Systems

2. Human Body Organization
The Human Body
is composed of
Organ Systems
are composed of
Organs
are composed of
Tissues
are composed of
Cells

3. • Cell membrane----controls entry and exit
• Nucleus---DNA and function and structure
• Cytoplasm---hold organelles, for replication
• Tissues—
• 1 connective—support, structure
• epithelial---lining for cavities and organs,
secretion
• Muscle----cardiac, skeletal, smooth
• Nervous---sensation, stimulate muscle

4. Circulatory System
Major Structures
• heart, blood vessels,
blood, lymph nodes and
vessels, lymph
Functions
• transports nutrients,
wastes, hormones,
and gases

5. Interesting Facts…
• 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
make scabs.
• The four blood types are A, B, AB, and O.

6. Digestive System
Major Structures
• mouth, throat,
esophagus, stomach,
liver, pancreas, small and
large intestines
Functions
• extracts and absorbs
nutrients from food;
removes wastes;
maintains water and
chemical balances

7. Interesting Facts…
• Food takes 3 days to complete its journey through the
digestive system.
• 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
lifetime.
• 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.

8. Endocrine System
Major Structures
• hypothalamus, pituitary,
pancreas, pineal, adrenal,
thyroid, parathyroid,
testes, and ovaries
Functions
• regulates body
temperature, metabolism,
development, and
reproduction; maintains
homeostasis; regulates
other organ systems

9. Interesting Facts…
• 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.

10. Excretory System
Major Structures
• kidneys, urinary bladder,
ureters, urethra, skin,
lungs
Functions
• removes wastes from
blood; regulates
concentration of body
fluids

11. Interesting Facts…
• 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.

12. Immune System
Major Structures
• white blood cells, lymph
nodes and vessels, skin
Functions
• defends against
pathogens and diseases

13. Interesting Facts…
• 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.

14. Integumentary System
Major Structures
• skin, nails, hair
Functions
• protects against injury,
infection, and fluid loss;
helps regulate body
temperature

15. Interesting Facts…
• 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.

16. Muscular System
Major Structures
• skeletal, smooth, and
cardiac muscle tissues
Functions
• moves limbs and trunk;
moves substances
through body; provides
structure and support

17. Interesting Facts…
• 40% of body weight
• 85% of body heat from muscles
• 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).

18. Nervous System
Major Structures
• brain, spinal cord, nerves,
sense organs
Functions
• regulates behavior;
maintains homeostasis;
regulates other organ
systems; controls sensory
and motor functions

19. Interesting Facts…
• 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.

20. Reproductive System
Major Structures
• ovaries, uterus, and
breasts (in females);
testes and penis (in
males)
Functions
• produces gametes and
offspring

21. Interesting Facts…
• 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.
• Eggs is fertile for about 2 days then degenerates.

22. Respiratory System
Major Structures
• lungs, nose, mouth,
trachea
Functions
• moves air into and out of
lungs; controls gas
exchange between blood
and lungs

23. Interesting Facts…
• 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
the blood.
• A smoker’s lungs are dark gray and full of dirt and tar.

24. Skeletal System
Major Structures
• bones and joints
Functions
• protects and supports
the body and organs;
interacts with skeletal
muscles; produces red
blood cells, white blood
cells, and platelets

25. Interesting Facts…
• Osteoblast---makes bone
• Osteoclast---breaks down bone
• Osteocyte—mature bone cell
• Alendronate for osteoporis---no prone fro 30 minutes
A baby is born with 270 bones while an adult body has 206
bones.
• The hands and feet contain half of the bones in the human
body.
• 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).