Body Systems

For those people who want to take an active role in the state of their body's health, knowledge of how the various systems in the body function is a good starting point.

Starting with the very basics, there is the cell.  Cells form together to create tissues, and tissues group together to make the body's organs.  Organs work in conjunction with each other to make the systems of the body, and these systems make up a human being.

Each body system is tasked with a particular function or a group of functions which are related to each other. 

The skeletal system is made up of the bones, cartilage and ligaments.  This system supports and protects the soft tissues of the body and provides the form for muscle attachment.  The muscular system allows movement in the body and is composed of muscles, tendons and sheaths around muscles, as well as the lubricating sacs called bursae.

The nervous system consists of the central nervous system, which is the brain and spinal cord; and the autonomic nervous system, which controls all of the automatic functions in the body which occur internally.  This system partially overlaps with the central and peripheral nervous systems.

The endocrine system uses circulating hormones or chemical "messengers" to exert its effects on the body.  The circulatory system is composed of the heart, the blood vessels (veins, arteries and capillaries) and is in charge of moving nutrients, waste, special proteins and cells around to the various parts of the body.

The lymphatic system plays an important role by moving excess tissue fluids back to the veins and transporting fat from the gut to the blood.  This system is also responsible for the exchanges of gas which occur and the intake of oxygen, which is necessary for virtually all of the body's cells and tissues. 

The body's digestive system performs acts related to the ingestion, processing and absorption of nutrients.  It also eliminates some types of waste.  The urinary system controls salt and fluids balance in the body and excretes nitrogen waste. 

The reproductive system is responsible for the future generations of children and is also linked during fetal development to the newly-developing urinary system.

Along with responding to the constant changes in its external environment and producing the actions which others observe as an individual's behavior, the body must also provide a fairly constant internal environment, which is known as homeostasis. 

This process has many different internal facets, including:

  • Maintaining a constant body temperature

  • Ensuring blood sugar levels are relatively even and constant

  • Controlling blood pressure

  • Maintaining calcium levels in the blood

The state of homeostasis can only be achieved through all the body's parts and systems acting in unison.  Part of this balance is maintained by the actions of one system and its effect on the others.  For instance, the hormones which are produced by the endocrine system's glands stimulate the production of other hormones in other organs.  These secretions, which are called secondary hormones, in turn cause reactions on the gland that produced the first hormone, and thus reduces its production.  This circular means of feedback is essential in bringing about the constant balancing act of proper internal functioning in the body.

The Body's Organ Systems

There are 11 major organ systems in the body.  Each has its own specific functions, but all of them work together to maintain life.  The following gives some brief details on these systems.

  • Integumentary System - This system is composed of the skin and the various accessory organs which are associated with the skin.  These include the nails, hair, sweat glands and sebaceous (oil) glands.  These components protect the underlying tissues from water loss and injury and contain sense receptors which aid in temperature regulation and the synthesizing of chemicals which will be used in other parts of the body.

  • Skeletal System - Aside from serving as the framework of the body and duly protecting its organs, the tissues within the bones produce blood cells and store inorganic salts containing calcium and phosphorous.

  • Muscular System - When muscles contract they produce movement and maintain the body's posture.  Muscles also store energy and are the primary source of heat within the body.

  • Nervous System - Neurons, or nerve cells, transmit impulses from one point in the body to another.  In this manner, the different parts of the body communicate with one another and with the outside world.  Nerve cells also help recognize changes in the environment.

  • Endocrine System - This system works in conjunction with the nervous system in order to maintain a healthy balance in the body.  While the nervous system responds quickly to changes, the endocrine system is slower but has a more sustained effect. 

  • Cardiovascular System - This system transports blood with nutrients, oxygen and hormones to the cells and tissues and removes carbon dioxide.  Some cells within the bloodstream also help to defend the body against diseases.

  • Lymphatic System - The vessels in this system transport lymph fluid from the tissues back to the blood.  The system is composed of the lymph nodes, the tonsils, the spleen and thymus, all of which filter the lymph to remove foreign particles.

  • Digestive System - This system is composed of the mouth, pharynx, esophagus, stomach, small intestine and large intestine, or colon.  This system functions to ingest food and process it into molecules which can be used by the body.  The digestive system then eliminates the residue as waste.

  • Respiratory System - Bringing oxygen into the lungs, the respiratory system removes carbon dioxide and aids in the exchange of these gases as they pass between the lungs and the blood.

  • Urinary System - This system removes various waste materials from the body, and helps to regulate the chemical content and fluid levels.  The urinary bladder is the storage area for urine.

  • Reproductive System - The primary organs of this system are the gonads, which produce reproductive cells.  These are the testes in males and the ovaries in females. 

The body is a highly complicated masterpiece of parts.  Learning more about its anatomy and physiology is not only interesting, but helpful in maintaining optimum health.


  1. Marieb, E.N. & Hoehn, K. Human Anatomy & Physiology (8 edition), Pearson Education, Inc (2004)
  2. McCracken, T. & Walker, R. New atlas of human anatomy, London : Constable (2001)
  3. Parker, S. The Concise Human Body Book, Dorling Kindersley Limited (2009)
  4. Winston, R. et al. Human: The Definitive Visual Guide, DK Publishing, Inc (2004)
  5. Ullmann, H.F. Atlas of Anatomy, Elsevier GmbH, Munich (2009)

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