Underneath your skin, organs, muscles, nerves, and bones are hard at work. They keep you alive and healthy without you even realizing it. But how do these body systems work? Learn all about the main human body systems and how they function with helpful charts and descriptions.
Main Systems of the Human Body
The human body has many body systems. Its main systems are the nervous system, the circulatory system, the digestive system, the respiratory system, the urinary system, the muscular system, and the skeletal system. For more details, download the printable PDF human body for kids that provides labels for the main internal parts of the body.
The Nervous System
There are two main parts of the nervous system. The central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which branches out around the body. The brain sends and receives messages along nerves to various organs of the body, muscles and senses.
Body Part | Location | Function |
brain | inside the head (skull) | processing sensory signals provided by parts of the body; sending messages to the rest of the body; regulating automatic body functions (e.g. heartbeat, breathing, cell growth); storing memories; forming speech and behavior; facilitating movement |
nerves | spinal cord (central nervous system); everywhere in the body (peripheral nervous system) | transmitting signals to the brain from other parts of the body; transmitting signals from the brain to other parts of the body |
spinal cord | backbone (vertebrae) | connecting peripheral nerves to the brain; coordinating reflexes in the body |
The Circulatory System
The circulatory system is responsible for carrying nutrients around the body. One of its most important functions is to bring oxygen from the lungs to the body cells. People without healthy circulatory systems might have heart attacks or strokes.
Body Part | Location | Function |
heart | chest | pumping blood throughout the body |
arteries (blood vessels) | various places in the body | carrying blood away from the heart; distributing oxygen to different parts of the body |
veins (blood vessels) | various places in the body | bringing blood back to the heart; allowing deoxygenated blood to regain oxygen |
capillaries | everywhere in the body | connecting small arteries and veins; storing blood to be taken back to the heart |
blood | blood vessels | distributing oxygen and other nutrients across the body; removing carbon dioxide and other waste from cells |
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The Digestive System
In order for your body to have nutrients to distribute, it needs to digest food. When you chew food, it goes through a process called digestion. The body keeps nutrients that it needs and converts the rest into waste.
Body Part | Location | Function |
esophagus | neck, behind the larynx | carrying chewed food from the mouth to the stomach |
stomach | upper left side of abdomen | receiving chewed food from the esophagus; mixing food with stomach enzymes; holding food before it goes into the small intestine |
small intestine | middle of abdomen, between the stomach and large intestine | digesting food; absorbing nutrients from food |
liver | upper abdomen, above the stomach | filtering blood from the digestive tract; producing bile to take away waste |
pancreas | middle of abdomen, behind the stomach | creating enzymes to break down food; creating hormones that carry messages through the body |
gallbladder | right side of abdomen, under the liver | storing liver bile during digestion |
large intestine (colon, bowel) | along the backside of abdomen, between small intestine and rectum | moving waste to the rectum; absorbing water for the body; absorbing vitamins for the body |
rectum | at the end of the large intestine, between the large intestine and the anus | moving waste into the anus; absorbing vitamins for the body |
anus | between the buttocks, at the end of the rectum | pushing waste out of the body as a bowel movement |
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The Urinary System
Not all waste leaves the body through the digestive system. The urinary system, which is also called the renal system, balances the body by eliminating waste through urine. There are four main parts of the urinary system.
Body Part | Location | Function |
kidneys | rear back of abdomen | removing waste from the body; balancing fluids in the body; sending waste to the bladder |
ureters | tubes between kidneys and bladder | bringing urine to the bladder from the kidneys |
bladder | center of the pelvis | storing urine before urination |
urethra | end of the bladder to exterior of the body | bringing urine out of the body during urination |
The Respiratory System
A body can’t function without oxygen. The respiratory system receives oxygen through respiration, also known as breathing, and expels carbon dioxide from the body. These are the main parts of the body used for breathing.
Body Part | Location | Function |
nostrils | end of the nose | inhaling air during breathing; exhaling carbon dioxide |
nasal cavity | inside the nose | keeping foreign particles out of the respiratory tract (sneezing); making mucus to keep the nose moist |
oral cavity (mouth) | middle of the face | inhaling air during breathing; exhaling carbon dioxide |
throat | neck, behind the nose and mouth, above the trachea | connecting oral and nasal cavities to the trachea |
larynx (voice box) | neck, below the throat, in front of the esophagus | creating speech sounds; protecting the airway from choking; regulating airflow into the lungs |
trachea (windpipe) | bottom of neck, between the larynx and bronchial tubes | connecting larynx to bronchial tubes; passing air into the lungs |
bronchial tubes | chest, between the trachea and lungs | connecting trachea to lungs; bringing air into the lungs |
lungs | chest, behind rib cage | bringing oxygen into the body through blood vessels; taking carbon dioxide out of the body through exhalation (breathing out) |
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Parts of the Muscular System
The muscular system enables a body to move. When the brain sends a signal to a muscle in the body, neurotransmitters tell the muscle what to do. It creates the musculoskeletal system when combined with the skeletal system. The three major types of muscles are skeletal muscles, cardiac muscles and smooth muscles.
Body Part | Location | Function |
skeletal muscles | attached to bones, connected to tendons | voluntary movement; breathing (diaphragm) |
cardiac muscles | heart | keeping your heartbeat going (involuntary) |
smooth muscles | organ walls (intestines, stomach, bladder), eyes, skin | involuntary functions in organs |
Parts of the Skeletal System
When you think of a skeleton, you’re thinking of the skeletal system. Because humans are vertebrates, they have a skeletal frame built around a backbone. The skeletal system includes the body’s 206 bones, as well as connective tissue such as tendons, ligaments and cartilage.
Body Part | Location | Function |
teeth | inside mouth | chewing food |
skull | head | protecting the brain |
backbone (vertebrae) | back | protecting the spinal cord; stabilizing the body |
ribcage | chest | protecting the heart, lungs, and internal organs; stabilizing the body |
pelvis | between the hips, above the legs | supporting body weight; supporting abdominal organs; protecting digestive tract |
tendons | between muscles and other body structures | attaching muscles to bones; attaching muscles to organs |
ligaments | between bones | connecting bones to other bones; allowing joints to move and bend |
cartilage | joints, between bones | connecting bones to other bones; allowing joints to move fluidly; keeps bones from rubbing against each other |
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Body Systems Work Together
As you can see, none of these systems can exist without the others. If one organ fails, it can cause an entire system to stop functioning – which can affect the entire body. Learn more about the external parts of the body and how they work together to understand more about human body functions.