Organ System Overview

Organ System Overview

An organ system is a group of organs that work together to perform a complex function. There are 11 organ systems in the human body. All of these are required for survival, either of the person or of the species.

This article discusses the 11 organ systems, including how they work, what organs they contain, and why they're important.

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 and nutrients to all corners of the body. It also carries away carbon dioxide and other waste products.

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 damages the body slowly and quietly, while low blood pressure brings on symptoms 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:

  • Lymph vessels
  • Lymph nodes
  • Lymph ducts
  • Various glands

The lymphatic system plays an important role in your immunity, blood pressure regulation, digestion, and other functions.

The lymphatic system is the drainage system of the body. It carries excess fluid, proteins, fats, bacteria, and other substances away from the cells and spaces between cells.

The lymphatic vessels filter the lymph fluid. They then move the fluid into collecting ducts, which return the fluid to your bloodstream.

The lymphatic system also helps create and circulate vital cells that fight disease (part of the immune system, which is covered below). This includes lymphocytes and monocytes (white blood cells) and antibodies (proteins that recognize bacteria and viruses).

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). It also moves 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, or the body's balance of acids and bases.

Carbon dioxide is made into carbonic acid, which affects the pH balance. The respiratory system regulates this pH level when it releases carbon dioxide from the body. Breathing issues may indicate a condition that affects the body's acidity.

Integumentary or Epidermal System

The integumentary system is skin and all the structures in it, including the:

  • Sweat glands
  • Hair follicles
  • Nails
  • 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 uses the products of digestion.

Gastrointestinal (Digestive) System

The gastrointestinal (GI) system is sometimes referred to 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, which regulates bodily functions. The vagus nerve 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 includes 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 physical abilities.

The three types of muscles in the body are:

  • Skeletal (voluntary)
  • Smooth (visceral or involuntary), which are inside walls of organs like the intestines
  • Cardiac (heart muscle)

Only skeletal muscle is considered part of 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 is the only system that is split into two parts (Male and Female). 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's important for survival, all of its organs 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 other jobs.

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.


Your body has 11 different organ systems. Each group of organs has a different complex function, such as movement, breathing, or digestion.

In some cases, one organ system works closely with another on a particular task. For example, the endocrine system interacts with the gastrointestinal system to control digestion and metabolism.

When your organ systems are working properly, they help your body stay in balance and maintain your health.

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