The 11 Organ Systems of the Body and How They Work

An organ system is a group of organs that work together in the body to perform a complex function, such as pumping blood or processing and utilizing nutrients.

There are 11 major organ systems in the human body:

• The circulatory (cardiovascular) system
• The lymphatic system
• The respiratory system
• The integumentary system
• The endocrine system
• The gastrointestinal (digestive) system
• The urinary (excretory) system
• The musculoskeletal system
• The nervous system
• The reproductive system
• The immune system

Organ systems work together to keep the body in good health. For example, the circulatory and digestive systems work jointly to deliver nutrients throughout the body.

Except for the reproductive system, each system is necessary for survival.

The Circulatory System

The circulatory system transports oxygen and nutrients to all corners of the body. It also carries away carbon dioxide and other waste products.

When people talk about this organ system, they’re usually talking about the cardiovascular system at large, which includes:

• The heart
• Blood
• Blood vessels (arteries and veins)

The circulatory system maintains blood flow within a certain pressure range so that the blood can make it to everywhere it needs to go.

Blood pressure that’s too high puts extra 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.

The Lymphatic System

The lymphatic system is the drainage system of the body. It plays an important role in your immunity, blood pressure regulation, digestion, and other functions.

This organ system carries excess fluid, proteins, fats, bacteria, and other substances away from the cells and spaces between cells. It does this using:

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

The lymphatic vessels 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, which is why it is also a part of the immune system. This includes lymphocytes and monocytes (white blood cells) and antibodies (proteins that recognize bacteria and viruses).

The Respiratory System

The respiratory system is 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).

This organ system contains the following:

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

One of the least understood responsibilities of the respiratory system is to help regulate the body’s pH balance (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.

The Integumentary System

The integumentary system is unique because it is the largest and only single-organ system in the body. It protects the body from the external environment and helps regulate body temperature.

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

• Sweat glands
• Hair follicles
• Nails
• Nerves
  

The Endocrine System

The endocrine system mostly regulates metabolism and uses the products of digestion. Along with the nervous system and immune system, it’s generally considered one of the most complicated systems in the body.

This organ system includes all the glands that secrete hormones into the bloodstream, including:

• Adrenal
• Gonads (ovaries and testicles)
• Hypothalamus
• Pancreas
• Parathyroid
• Pineal
• Pituitary
  
• Thymus
• Thyroid
  

The Digestive System

The gastrointestinal (GI) system is sometimes referred to as the gut or the digestive system. It is responsible for breaking down foods into nutrients, which the body needs for energy, growth, and cell repair.

This system includes all the organs that carry food from where it enters the body to where it exits, including the following:

• Mouth
• Esophagus
• Stomach
• Small intestine
• Large intestine
• Rectum
• Anus

The pancreas, gallbladder, and liver are also part of this organ system.

The GI tract and the endocrine system have a lot of interaction. The endocrine system produces the hormones that regulate digestion and the absorption of nutrients.

The GI system also owes a lot to the vagus nerve, the main contributor to the parasympathetic nervous system, which regulates bodily functions. The vagus nerve is involved in slowing metabolism, lowering heart rate and blood pressure, and stimulating the mechanics of digestion.

The Urinary (Excretory) System

The urinary system includes:

• 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 this organ system also helps regulate blood pressure.

The Musculoskeletal System

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

This organ system includes:

• The skeleton
• All the muscles, tendons, and ligaments attached to the skeleton
  

Muscles in the Body

There are three types of muscles in the body:

• 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.

Skeletal System

Your body's skeletal system contains 206 bones:

• The 80 bones of the axial skeleton (your spine and the core of your body)
• The 126 bones in the appendicular skeleton (your arms, legs, and bones away from the core)

In addition to providing your body's structure and facilitating its mobility, the skeletal system contains bone marrow to produce blood and lymph cells. It stores fat in the body, as well as key minerals like calcium.

The Nervous System

The nervous system is a network that makes it possible for different parts of the body to communicate with one another. Think of it as your body’s command station. All body processes, reactions, thoughts, and movements stem from this organ system.

The nervous system is incredibly detailed and includes:

The Central Nervous System

• The brain
  
• The spinal cord

The Peripheral Nervous System

• All the nerves connected to both of these organs

The nervous system contains the only tissue that isn’t fed directly through contact with blood.

The Immune System

The immune system helps the body fight against infection and other diseases. All of its organs are borrowed from other organ systems.

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

The primary organs of the immune system include:

• Lymph nodes
• Bone marrow
• Thymus
• Spleen
• Adenoids
• Tonsils
• Skin

Immune system organs work like sailors on a ship: Each one has a primary duty and is cross-trained for other jobs.

The Reproductive System

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, producing offspring.

The male reproductive system consists of the:

• Epididymis
• Testes
• Prostate
• As well as the external structures of the scrotum and penis.

The female reproductive system consists of the:

• Vagina
• Uterus
• Ovaries

Aside from their direct roles in reproduction, the ovaries and testicles also play important roles in the endocrine system, producing estrogen, testosterone, and progesterone.

Summary

The 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 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.