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.

Side view of female doctor examining senior patient in medical clinic
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Circulatory System

When we think of—and talk about—the circulatory system, we're usually talking about the cardiovascular system, which includes the:

  • Heart
  • Blood vessels (arteries and veins)
  • 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.

Lymphatic System

The heart and blood vessels are not the only organs circulating fluid around the body, and blood is not the only circulated fluid.

The lymphatic system transports lymph (a fluid) using:

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 create and circulate vital cells that fight disease (part of the immune system, which is covered below) including lymphocytes, monocytes, and antibodies.

Respiratory System

The respiratory system contains the:

  • Lungs
  • Trachea (windpipe)
  • Airways of the respiratory tree

It's 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.

Integumentary System

The integumentary system is skin, which includes all the:

  • Sweat glands
  • Hair follicles
  • Lots 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.

Endocrine System

The endocrine system includes all the glands that secrete hormones into the bloodstream. The endocrine system and the nervous system are generally considered two of the most complicated systems in the body.

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

Gastrointestinal (Digestive) System

The gastrointestinal (GI) system is colloquially known as the gut. It includes all the organs that carry food from where it enters to where it exits, including the:

  • Esophagus
  • Stomach
  • Intestines

The GI tract and the endocrine system have a lot of interaction.

The GI 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 metabolism, lowering heart rate and blood pressure, and stimulating the mechanics of digestion.

Urinary (Excretory) System

The urinary system is made up of the:

  • Kidneys
  • Ureters
  • Bladder
  • 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.

Musculoskeletal System

This is the:

  • Skeleton
  • All the muscles, tendons, and ligaments attached to it

The musculoskeletal system provides the framework and the engine for our movement, posture, and productivity.

The three types of muscles in the body are:

  • Striated (skeletal or voluntary)
  • Smooth (visceral or involuntary)
  • Cardiac (heart muscle)

Only striated muscle is in the musculoskeletal system.

Nervous System

The nervous system includes the:

  • Brain
  • Spinal cord
  • All the nerves 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.

Reproductive System

The reproductive system the only system that is split into two parts. Half of us have:

  • Penis
  • Testicles

The other half has:

  • Vagina
  • Uterus
  • Ovaries

This is the only organ system that is not complete in any one body and requires another person (or medical intervention) to complete its mission.

Immune System

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
  • Skin

Because of the interplay between organs from various other systems, the immune system is one of the most complicated systems of all.

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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. How does the blood circulatory system work? InformedHealth.org [Internet].  January 2019.

  2. Overview of the Lymphatic System. Merck Manuals. July 2019.

  3. Overview of the Respiratory System. Merck Manuals. June 2019.

  4. Endocrine Glands. Merck Manuals. April 2019.

  5. Overview of the Digestive System. Merck Manual. September 2019.

  6. Overview of the Urinary Tract. Merck Manual. June 2019.

  7. Overview of the Musculoskeletal System. Merck Manuals.

  8. Overview of the Nervous System. Merck Manual. March 2018.

  9. Overview of the Immune System. Merck Manual. December 2019.