There are 11 major organ systems in the human body. For this article, there is an overview for five of these organ systems. Each contains at least one vital organ and other structures that are important for healthy body function. The nervous system is the main command system that directs function for all other systems. However, without proper functioning of the cardiovascular system and respiratory system, the nervous system shuts down within a short period of time.
The nervous system sends signals throughout the body to control function and movement. It is composed of the brain, spinal cord and peripheral nervous system. It directs quick responses to stimuli, such as automatic reflexes. The nervous system works in conjunction with the endocrine system to control metabolism and other body functions.
While the nervous system relies mostly on electrical signals for messaging, the endocrine system uses chemical messengers. It secretes hormones into blood and other body fluids. Water balance, body growth and responses to stress are some of the activities regulated by the endocrine system. Glands that secrete hormones include the pituitary, thyroid, adrenal, pancreas and hypothalamus.
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The cardiovascular system is occasionally referred to as the circulatory system. It contains the heart, blood vessels and blood. The blood transports nutrients, hormones, gases and waste products by using the blood vessels. The heart pumps the blood throughout the body and maintains blood pressure. Arteries pump blood away from the heart, and veins return blood toward the heart.
The respiratory system contains the nasal cavities, throat areas and lungs. The pharynx is shared with the digestive tract. Air moves from the pharynx to the larynx, which protects the opening to the trachea. The trachea is the main passageway to the lungs. It acts as an air filter. Inside the lungs, oxygen is extracted from the air, and carbon dioxide is exhaled as a waste product.
In the digestive system, food is absorbed and processed by the body. After being swallowed through the mouth, food moves through the esophagus and into the stomach. The stomach breaks down the food mechanically and chemically so it can be digested by the small intestine and used for nutrition. Any undigested material is then moved through the large intestine and excreted through the anus. The liver is also considered part of the digestive system. It releases bile to aid in digestion.