Understanding the 11 Body Organ Systems

An organ system is a group of organs that work together to perform a complex function. There are eleven organ systems in the human body. All of these are required for survival, either of the person or of the species.

When we think of—and speak about—the circulatory system, we are usually talking about the cardiovascular system, which includes the heart and blood vessels (arteries and veins), as well as the blood itself. The circulatory system transports oxygen nutrients to all corners of the body and carries away byproducts of metabolism.

In order for blood to make it everywhere it needs to go, the circulatory system maintains the blood flow within a certain pressure range. Blood pressure that's too high puts undue stress on other organs and tissues. Low blood pressure means the blood—and its nutrients—won't make it to where it needs to go. High blood pressure kills you slowly while low blood pressure can kill you immediately.

The heart and the blood vessels are not the only organs circulating fluid around the body, and blood is not the only fluid circulated. The lymphatic system transports lymph (a fluid) using lymph vessels, lymph nodes, lymph ducts, and various glands. The lymphatic system is key for immunity, blood pressure regulation, digestion, and other functions.

The lymphatic system is the drainage system of the body, carrying excess fluid, proteins, fats, bacteria, and other substances away from the cells and spaces between cells to be filtered, excreted, and recycled. The lymphatic system also helps to create and circulate vital cells used to fight disease (part of the immune system, which is covered below) including lymphocytes, monocytes, and antibodies.

The respiratory system contains the lungs, trachea (windpipe) and all of the airways of the respiratory tree. It is responsible for breathing, which is the controlled movement of air in and out of the body (ventilation) and the movement of oxygen and carbon dioxide into and out of the bloodstream (respiration).

One of the least understood responsibilities of the respiratory system is to help regulate the body's pH balance. Carbon dioxide is made into carbonic acid, which the respiratory system can regulate through carbon dioxide levels. When a patient has a condition that affects the body's acidity, respiratory rate and depth can be a sign of the problem.

The integumentary system is skin, which includes all the sweat glands, hair follicles and plenty of nerves. The integumentary system is unique because it is the only single-organ system. Skin is both an organ and the entire organ system.

The endocrine system includes all the glands that secrete hormones into the bloodstream. Most people find the endocrine system and the nervous system as the two most complicated systems in the body.

The endocrine system mostly regulates metabolism and utilizes the products of digestion.

The gastrointestinal system is affectionately known as the gut, which includes all the organs that carry food from where it enters to where it exits. The esophagus, stomach, and intestines are all part of the gastrointestinal system. There is a lot of interaction between the gastrointestinal system (often called the GI tract) and the endocrine system.

The gastrointestinal system also plays host to a very important nerve called the vagus nerve. This is the main contributor to the parasympathetic nervous system and has a lot to do with slowing down metabolism, lowering heart rate and blood pressure, and stimulating the mechanics of digestion.

The urinary system is made up of the kidneys, ureters, bladder, and urethra. These organs work together to filter blood and remove toxins and waste from body tissues. The removal of excess fluid through the urinary system also helps to regulate blood pressure.

This is the skeleton and all the muscles, tendons and ligaments that are attached to it. The musculoskeletal system provides the framework and the engine for our movement, posture, and productivity.

There are three types of muscles in the body: striated (skeletal or voluntary), smooth (visceral or involuntary) and cardiac (heart muscle). Only striated muscle is in the musculoskeletal system.

The nervous system includes the brain and spinal cord, plus all the nerves that are connected to both of these organs. The nervous system is incredibly detailed and includes the only tissue that isn't fed directly through contact with blood.

The reproductive system the only system that is split into two parts. Half of us have a penis and testicles while the other half has a vagina, uterus, and ovaries. This is the only organ system that is not complete in any one body and the only organ system that requires another person to complete its mission.

The immune system is listed last because while it has a vital function in the survival of both the person and the species, all of the organs that make up the immune system are borrowed from other organ systems. The immune system organs work like sailors on a navy ship: every sailor has a primary duty and is cross-trained for the safety of the vessel.

The primary organs of the immune system are lymph nodes, bone marrow, thymus, spleen, adenoids, tonsils, and skin. Because of the interplay between organs from various other systems, the immune system is one of the most complicated systems of all.