The Human Body

Human Body Systems

The systems of the human body include the nervous, muscular, skeletal, circulatory, respiratory, digestive, integumentary (the skin), urinary, reproductive, immune and endocrine systems. All the systems work together to allow the human body to carry out its functions.

Nervous System

The nervous system includes the brain, spinal chord and nerves. It coordinates all the actions of the body by transmitting signals throughout the body through nerve cells. Information received by the senses travels through nerves to the brain, and information from the brain travels through nerves to the muscles to tell the body to move. The brain also tells muscles to move that you may not have to think about, such as those that control breathing and heartbeat.

Muscular System

The muscular system allows the body to move after receiving signals from the nervous system. Your muscles also work with the skeletal system to make movements and maintain posture

Skeletal System

The skeletal system is made up of bones. It provides support and protection for the body and gives your body shape. The joints in the skeleton assist in movement. Your bones are also responsible for producing blood.

Circulatory System

The circulatory system consists of the heart, blood and blood vessels. Your blood transports oxygen and nutrients throughout the body. The heart acts as a pump to move the blood through the blood vessels. The circulatory system works closely with the respiratory system, which brings oxygen into the body.

Endocrine System

The endocrine system consists of glands that produce enzymes and hormones that affect your body’s growth and response to certain information. The glands of the endocrine system also produce fluids used in digestion and reproduction.


Homeostasis describes the body when its systems are stable. The body maintains its body temperature and levels of chemicals in the blood, like pH, are maintained.


Nutrients are the chemicals organisms need to live. Some examples of nutrients may be oxygen, water, carbohydrates, fats, proteins, and other vitamins found in food. If the supply of nutrients in the environment changes, some organisms may not survive.


Nutrition is the ability for an organism’s body to get the nutrients it needs to live and be healthy. Food energy is measured in units of calories. Vitamins and minerals are other chemical compounds the body needs to live.


One change in an organism’s environment that can limit survival is disease. Diseases in humans are often blood borne, which means that they can transmitted through bodily fluids, or airborne, which means they are transmitted through the air. Diseases have been prevented in recent years by increased sanitation and vaccination. Sanitation means preventing the spread of pathogens (or germs). Vaccines prevent disease by stimulating a body’s immunity to a disease.








Brain:  Gall & Spurheim/Wellcome Images; Skeleton Photo:  User Sklmsta/Wikimedia