A human being is composed of closely interlinked body systems that perform various functions of the human body. These functions of the human body include support, movement, gas exchange, regulation, protection, elimination, transport, energy acquisition, and continuity. Although the human body systems have separate roles, two of them have general control over other functions of the human body. These two systems, the nervous system and endocrine system, are responsible for homeostasis, or the maintenance of a steady state within the body.
In human anatomy the muscular and skeletal systems, called the musculoskeletal system, work together in providing support and in allowing the body to move. Through alternate contraction and relaxation of muscles, movement of body parts becomes possible. Even automatic movements of the body, such as heartbeat, occur due to the actions of muscles. Meanwhile, the adult human skeleton is a collection of 206 bones that are specialized to perform various functions. Bones maintain the body’s posture and protect the vital organs.
Oxygen, which is a gas necessary for human life, is naturally present in air that is taken in by the respiratory system. Inside the body, oxygen combines with the substances that provide energy, which come from food, in order to provide fuel for cells. Carbon dioxide is a waste material produced by the respiration process. The main organs of respiration are the lungs because they are responsible for the oxygen-carbon dioxide exchange, the most essential function of the respiratory system.
The nervous and endocrine systems generally integrate the functions of the human body. With the brain and spinal cord as its components, the nervous system receives and transmits signals through its network of nerve fibers. This allows the body to respond to its external environment. Meanwhile, the endocrine system controls body processes through its glands that produce hormones. Acting as messengers, hormones are released into and transported by blood to influence the activities of body organs.
An elaborate defense system, which includes the skin, mucous membranes, and lymph, protects the body against disease-causing agents. The skin and mucous membranes, or the first line of defense, prevent germs from getting inside the body. When they fail, the second line of defense, or the lymph, does its work by filtering and trapping germs. Meanwhile, most liquid wastes are removed by the urinary system. The kidneys filter wastes from the blood then these wastes mix with excess water so that urine is formed.
The heart propels blood that transports nutrients and oxygen, gets rid of wastes, and protects the body against infections. It is joined by the blood vessels and blood as components of the circulatory system. Meanwhile, a long tube called the digestive tract is responsible for the entire digestion process, allowing the body to acquire nutrients and energy from food, as well as to remove solid waste materials. Human beings have a comparatively brief life span; therefore, reproduction is necessary. With the action of the reproductive system, however, the continuity of the humankind is ensured.