human body systems. human body organization the human body is composed of organ systems are composed...

Human Body Systems

Human Body Organization

The Human Bodyis composed of

Organ Systemsare composed of

Organsare composed of

Tissuesare composed of

Cells

Circulatory System

Major Structures• heart, blood vessels,

blood, lymph nodes and vessels, lymph

Functions• transports nutrients,

wastes, hormones, and gases

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.

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

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.

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

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.

Excretory System

Major Structures• kidneys, urinary bladder,

ureters, urethra, skin, lungs

Functions• removes wastes from

blood; regulates concentration of body fluids


• 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.

Immune System

Major Structures• white blood cells, lymph

nodes and vessels, skin

Functions• 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.

Integumentary System

Major Structures• skin, nails, hair

Functions• protects against injury,

infection, and fluid loss; helps regulate body temperature


• 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.

Muscular System

Major Structures• skeletal, smooth, and

cardiac muscle tissues

Functions• moves limbs and trunk;

moves substances 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).

Nervous System

Major Structures• brain, spinal cord, nerves,

sense organs

Functions• regulates behavior;

maintains homeostasis; 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.

Reproductive System

Major Structures• ovaries, uterus, and

breasts (in females); testes and penis (in males)

Functions• produces gametes and

offspring


• 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.

Respiratory System

Major Structures• lungs, nose, mouth,

trachea

Functions• moves air into and out of

lungs; controls gas exchange between blood and lungs


• 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.

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


• 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).