What is an organ system? Learn about the organ system definition and see organ system examples. Learn about the 11 body systems and organ system functions.
Updated: 11/21/2023
Organ System | Definition, Function & Examples
Table of Contents
- Organ System Definition
- Human Organ Systems
- Body Systems and Functions
- Types of Tissue in Organ Systems
- Lesson Summary
What is an organ system? Organ systems are collections of anatomical structures in the body that work together to achieve a function. Organ systems include multiple organs, but organs may be involved in more than one organ system. Each organ system depends on the others, but scientists find it helpful to divide the body into organ systems for study.
Organ systems and their functions are important for multicellular organisms to maintain homeostasis or a balance in the body. These specialized systems allow for complex functions to be carried out to maintain life, such as gas exchange, nutrient absorption and distribution, and more. There are 11 organ systems in the human body. Some organ system examples include the respiratory system, the digestive system, and the cardiovascular system.
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How many organ systems are there? Human organ systems include the following:
- Integumentary system
- Muscular system
- Skeletal system
- Circulatory system
- Respiratory system
- Nervous system
- Urinary/Excretory system
- Digestive system
- Reproductive system
- Lymphatic system
- Endocrine
The different types of organ systems are explained in detail below.
Integumentary System
The integumentary system is the organ system made up of our skin, nails, and hair. The main function of the integumentary system is to protect the body. Our skin is the largest organ in the body and the dead, keratinized layer on the outside helps to shield the body from environmental changes and pathogens. The inner layers of the skin help regulate temperature homeostasis. Specialized sensory neurons help the body detect changes in the environment, such as temperature, pressure, and pain.
Muscular System
The muscular system is the organ system that includes our muscles and its main function is to facilitate movement. There are three main types of muscle: cardiac, skeletal, and smooth. Cardiac muscle makes up the heart. Skeletal muscle is attached to the skeleton and is responsible for voluntary movement. Lastly, smooth muscle makes up hollow organs, such as the stomach, intestines, and uterus, and is involuntary. Some classifications of organ systems include the cardiac and smooth muscle within other organ systems as these types of muscles play an integral role in those organ systems.
Skeletal System
The skeletal system is the organ system that includes the bones, joints, and cartilage. This body system's main function is for structure, support, and movement. For example, the skull encases the brain and provides protection from the environment. Other skeletal components act like anchors for the muscular system and allow for movement. Cartilage is more flexible than bone and both acts as a flexible barrier and provide cushioning between bones, such as between the vertebrae of the spine.
Circulatory System
The circulatory system, also known as the cardiovascular system, includes the heart, blood vessels, and blood. The main function of the circulatory system is to bring oxygen and nutrients to all of the cells in the body and remove metabolic waste. The heart is the main organ of the circulatory system and uses its muscular action to pump blood through the blood vessels to the body. Blood is pumped to the body through the arteries and returns to the heart through the veins.
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Respiratory System
The respiratory system includes the lungs and accessory organs. The main function of the respiratory system is to carry out gas exchange. Air enters the lungs through the nose and mouth and travels through the trachea to the bronchi. Each bronchi branches into smaller bronchioles and eventually dead-ends in the alveoli, where gas exchange occurs. Here, carbon dioxide diffuses into the lungs for exhalation and oxygen diffuses from the lungs into the blood.
Nervous System
The nervous system is the body system that includes the brain, spinal cord, and nerves. The main function of the nervous system is communication. The brain acts as the processing center for all information and communicates with the body by sending messages through the spinal cord. Nerves in the body control our motor function and sense changes in both the external and internal environment and communicate this information to the brain. Neurons are the main cell of the nervous system and are specialized for sending and receiving information.
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Urinary/Excretory System
The urinary/excretory system is the body system that removes metabolic waste from the body and regulates water homeostasis. It includes the kidneys, which filter metabolic waste from the blood to produce urine. Urine is stored in the bladder and carried out of the body through the urethra. The urinary system plays an important role in maintaining blood pressure. When our blood pressure is too high, extra water can be released as urine to regulate our water and salt balance. If water levels in the body are low, less urine is produced.
Digestive System
The digestive system is the body system responsible for breaking down food and absorbing nutrients. The digestive system is also known as the gastrointestinal system and includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, anus, and accessory organs, like the pancreas, gall bladder, and liver. Together, these organs work to break down food and absorb macromolecules into the blood.
Reproductive System
The reproductive system is the body system responsible for creating offspring, or reproduction. The male reproductive system includes the testes and penis and the main function is to produce sperm for reproduction. The female reproductive system includes the ovaries, uterus, vagina, and vulva and its main purpose is to incubate a fetus during gestation and birth of the child.
Lymphatic System
The lymphatic system, also known as the immune system, protects the body from pathogens and maintains the homeostasis of fluids inside the body. The lymphatic system includes the lymph fluid, lymphatic vessels, lymph nodes, and leukocytes, or white blood cells. Fluid expelled from the circulatory system accumulates in the tissues and is returned to the heart via the lymphatic vessels. The lymph system also produces mature white blood cells, which are needed to identify and fight off pathogens.
Endocrine System
The endocrine system is the organ system that produces hormones, which are chemical messengers that regulate body functions and maintain homeostasis between organ systems. The endocrine system consists of endocrine glands and the hormones they produce. Examples of endocrine organs include the pituitary gland, adrenal glands, testes, and ovaries. These organs produce hormones. Examples of hormones include:
- Estrogen
- Testosterone
- Insulin
- Antidiuretic hormone
- Oxytocin
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Body systems and functions are interdependent, meaning that all organ systems depend on each other. Organ systems and functions require coordinated communication. Without such, homeostasis in the body can be disrupted.
For example, body system functions include the ability to remove waste from the body. Several organ system functions participate in this. The circulatory system moves blood from the body to the lungs. Here, the lungs are able to remove carbon dioxide from the lungs. Thus, the circulatory system and the respiratory system must work together for this function.
Another example is digestion. Although the digestive system breaks down food and absorbs the nutrients, the nutrients must be transported throughout the body by the circulatory system. The endocrine system is required to coordinate the response by cells to increased blood glucose as well as to maintain homeostasis after a meal. Thus, all three systems, digestive, circulatory, and endocrine play a role in obtaining and distributing nutrients.
Control and Coordination
Control and coordination of organ systems are necessary to ensure that the body systems are working together. Without proper controls and coordination, diseases can occur. For example, during diabetes, the pancreas does not produce insulin, a problem with the endocrine system. However, this affects all other body systems. As a result of a lack of insulin, blood glucose levels remain too high. All body systems can't get enough glucose to make energy and the high blood glucose levels damage the circulatory system and the nervous system.
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Organ systems are composed of multiple organs, and organs are made of different tissues or collections of cells of the same origin. There are four main tissues in the human body and most organs are made of a combination of all four.
Muscle Tissue
Muscle tissue is an excitable tissue that can contract. There are three main types of muscle tissue:
- Cardiac muscle - found in the heart
- Skeletal muscle - found attached to the skeleton
- Smooth muscle - found in hollow organs
Although the muscular system is the obvious source of muscle tissue in the body, muscle tissue makes up many organ systems. For example, cardiac muscle makes up the heart, which is part of the circulatory system. Smooth muscle makes up the hollow organs of the digestive system and the organs of the female reproductive system, like the uterus and vagina.
Epithelial Tissue
Epithelial tissue produces coverings on the body and organs. This tissue type is specialized for protection as well as absorption and secretion. Epithelial tissue makes up our skin, as well as the coverings and internal barriers of hollow organs. Epithelial tissue can be found in all body systems. For example, the lining of the stomach and intestines in the digestive system is made of epithelial tissue. The lining of blood vessels in the circulatory system is also made of epithelial tissue.
Connective Tissue
Connective tissue is a tissue type that holds together parts of the body and provides structure and support. Connective tissue is an important component of the extracellular matrix, which holds cells, tissues, and organs in place. Connective tissue also includes bone tissue, blood, and cartilage.
Nervous Tissue
Nervous tissue is a highly specialized tissue that makes up the nervous system. Nervous tissue is able to send electrochemical signals that enable it to facilitate communication in the body. Nervous tissue makes up the nerves, brain, and spinal cord. Nerves are found throughout organs in the body and allow our body to detect pain and changes in internal and external stimuli.
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The organ system definition is a collection of anatomical structures that facilitate a common function in the body. Organ systems work together and organs may be a part of multiple organ systems. The 11 organ systems in the body include:
- Integumentary system - Protects the body and includes skin, hair, and nails
- Muscular system - Facilitates movement and includes cardiac, skeletal, and smooth muscle
- Skeletal system - Protects and facilitates movement and includes bone, cartilage, and joints
- Circulatory system - Transports oxygen, nutrients, and waste and includes the heart, blood vessels, and blood
- Respiratory system - Facilitates gas exchange and includes the lungs and accessories
- Nervous system - Facilitates communication and includes the brain, spinal cord, and nerves
- Urinary/Excretory system - Removes metabolic waste and maintains water homeostasis and includes the kidneys, bladder, ureter, and urethra
- Digestive system - Breaks down food and absorbs nutrients and includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, anus, liver, gall bladder, and pancreas
- Reproductive system - Allows for reproduction and includes the penis, testes, ovaries, uterus, vagina, and vulva
- Lymphatic system - Protects the body from pathogens and includes lymph fluid, lymphatic vessels, lymph nodes, and leukocytes
- Endocrine - Produces hormones for communication and includes endocrine glands and their hormones
Organ systems are made of organs, which are made up of four main tissues:
- Muscle
- Epithelial
- Connective
- Nervous
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Video Transcript
Organ System Defined
An organ system is a group of anatomical structures that work together to perform a specific function or task. Although we learn about each organ system as a distinct entity, the functions of the body's organ systems overlap considerably, and your body could not function without the cooperation of all of its organ systems. In fact, the failure of even one organ system could lead to severe disability or even death.
The human body is composed of 11 different organ systems. These include the following:
- Integumentary
- Muscular
- Skeletal
- Nervous
- Circulatory
- Lymphatic
- Respiratory
- Endocrine
- Urinary/excretory
- Reproductive
- Digestive
Some scientists add the immune system to this list to make a total of 12 organ systems, but most people consider the immune system to be a part of the lymphatic system. You may also find texts where the lymphatic and immune systems are both included within the circulatory system, which would give us a total of ten organ systems. Still other sources separate the immune system, the vestibular system (the organs of balance) and the neurotransmitter system (chemicals that control our moods, memory, appetite, sleep, etc.) from the other organ systems, which would spawn 13 organ systems.
Regardless of how you separate the different organ systems within the human body, as you study these systems, keep in mind that an organ or structure that is included in one system may also be included in another. For example, the testes and ovaries produce hormones and are therefore part of the endocrine system; however, these same structures are also involved in reproduction and thus are included in the reproductive system.
Integumentary, Muscular and Skeletal Systems
The integumentary system includes your skin, hair, subcutaneous fat and nails. The integumentary system offers protection from the environment, provides form and individual recognition characteristics and aids in temperature and water regulation. Your skin is the site where vitamin D is generated. The integument, or skin, also serves as an anchor for sensory receptors (which are part of the nervous system) that detect pain, cold, warmth and pressure.
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The muscular system includes the skeletal muscles but excludes smooth and cardiac muscles, which are included in other organ systems. The muscular system provides locomotion and support, allows us to manipulate our surroundings and - due to its high metabolic activity - produces heat.
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The skeletal system is composed of bones, joints, cartilage, ligaments and tendons. Your skeleton provides structural support and protection for your internal organs. In cooperation with your muscular system, your skeletal system participates in movement and locomotion. Your skeleton also serves as a reservoir for calcium, phosphorus, magnesium and other minerals that are important in a wide array of physiological processes.
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Nervous, Circulatory and Lymphatic Systems
The nervous system includes the brain, spinal cord, autonomic and somatic nerves (i.e., involuntary and voluntary nerves) and all sensory organs, including those that serve vision, smell, sensation, balance, hearing and taste. Your nervous system coordinates your movements and controls your responses to both external and internal stimuli. It serves as the storehouse and processing center for memories, it regulates mood and it provides the mechanisms for social interaction and development.
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The circulatory system includes your heart, blood vessels and blood. Your circulatory system is responsible for delivering oxygen and nutrients to every cell, tissue and organ in your body. It also conveys immune cells, electrolytes, hormones and other vital substances throughout your body. The circulatory system directly communicates with the lymphatic system, leading many to count these two systems as one.
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The lymphatic system is made up of the lymphatic vessels, which travel with your blood vessels, and the lymph nodes, where immune cells are produced. The lymphatic system returns a clear fluid called 'lymph' from your tissues and organs to your heart. Lymph is produced by the leakage of a small amount of fluid from your blood vessels into the surrounding tissues. The lymphatic system also transports fats absorbed from your intestine and carries immune cells from one place to another in your body.
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Respiratory, Endocrine and Urinary/Excretory Systems
The respiratory system encompasses the organs of breathing, which include your nose, pharynx (mouth), larynx (throat), trachea (windpipe), bronchi and bronchioles (airways), lungs and diaphragm. Your sinuses, which are lined by the same type of cells that line your upper airways, are included in the respiratory system. Your respiratory system is the principal site of gas exchange in your body. It is here that oxygen is absorbed into to your bloodstream and carbon dioxide is removed. Air moving through your respiratory system also provides you with the ability to vocalize (i.e., speak and sing).
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The endocrine system includes all hormone-producing organs, or 'glands,' such as the thyroid, pituitary, pancreas, adrenals, hypothalamus, gonads and pineal. The hormones produced by these organs are released directly into your bloodstream. These chemical messengers travel throughout your body and help regulate the activities of other organ systems. Many hormones, such as insulin from your pancreas and thyroxine from your thyroid gland, are essential for life.
The urinary/excretory system is your body's mechanism for eliminating metabolic wastes and excess water. It normally consists of two kidneys, two ureters, a urinary bladder and a urethra. Anatomical abnormalities sometimes lead to duplication or elimination of one or more of these organs. In addition to producing urine, your kidneys are intimately involved in maintaining the fluid and mineral balance in your bloodstream. They also participate in a number of important physiologic processes, such as producing vitamin D and controlling blood pressure.
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Reproductive System and Digestive System
The reproductive system, unlike other organ systems, is structurally quite different in human males and females. In males, the reproductive organs include the testes, epididymis, vas deferens, prostate, seminal vesicles and penis. In females, the reproductive system is composed of the ovaries, fallopian tubes, uterus (including the cervix), vagina and labia. The mammary glands of the female breast are usually included in the reproductive system as well. In males, the purpose of the reproductive system is to produce and deposit sperm. In females, the reproductive system is responsible for nourishing and protecting the developing infant as well as producing ova (eggs).
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The digestive system includes the lips, teeth, mouth, tongue, salivary glands, pharynx, esophagus, stomach, liver, gallbladder, pancreas, small and large intestines, rectum and anus and is responsible for receiving, digesting and absorbing nutrients. Following absorption of the useful substances from your food, the remaining waste material is excreted. Your digestive system also plays a role in maintaining proper fluid balance, and the trillions of microorganisms living within your intestine are essential for regulating your immune response.
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Lesson Summary
The 11 organ systems of the body are the integumentary, muscular, skeletal, nervous, circulatory, lymphatic, respiratory, endocrine, urinary/excretory, reproductive and digestive. Although each of your 11 organ systems has a unique function, each organ system also depends, directly or indirectly, on all the others. In addition to having overlapping functions, the various organ systems' structures also overlap. For example, the gonads of both males and females belong to the reproductive system as well as the endocrine system. Therefore, while dividing your body into different organ systems is useful from an educational standpoint, it minimizes the reality of these systems' interdependence.
Learning Outcomes
You should have the ability to do the following after this lesson:
- Identify the organ systems of the body
- Describe the structure and function of each organ system
- Explain how the organ systems are interrelated and dependent upon one another
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Organ System | Definition, Function & Examples
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