The Human Body is very complex. It involves numerous organs working closely together to carry out a specific task. This functional association of organs are called organ systems or, in some references, body systems or biological systems. The main function of the organ systems is to maintain the homeostatic environment or internal condition of the human body. Thus, making humans work with great efficiency and flexibility. Disruption of this internal balance may lead to certain diseases, complications, and worst, even death.

In this article, I will discuss the different organ systems and their role in maintaining the internal balance of the human body.
1.      THE NERVOUS SYSTEM – The Nervous System is considered as the “mother of all systems.” Why? Because this system regulates the different physiological processes of the body and organizes communication lines between organs and organ systems. It serves as the CPU or Central Processing Unit of the human body. Just like how useless a computer is without the CPU, so does the human body without the Nervous System.

The Nervous System is divided into two major parts: the CNS (Central Nervous System) which includes the Brain and Spinal Cord; and the PNS (Peripheral Nervous System) which is “made up of the nerve fibers that branch off from the spinal cord and extend to all parts of the body.” (US NIH, 2012)

2.      THE ENDOCRINE SYSTEM – The Endocrine System is composed of the Hypothalamus, Pituitary Gland, Pineal Gland, Thyroid Gland, Parathyroid Glands, Adrenal Gland, Pancreas, and Gonads (Testes for Males and Ovaries for Females). These organs and/or glands secrete hormones into the bloodstream going to the target cells, tissues or organs; and act as biochemical regulator into various processes in the human body.
One good example of the hormone’s regulatory function can be observed in Parathyroid Glands. “Parathyroid Glands control the calcium in the body--how much calcium is in the bones, and how much calcium is in the blood.” (Norman Parathyroid Center, 2013)

3.      THE MUSCULAR SYSTEM – The Muscular System is divided into three muscle types namely, skeletal, smooth and cardiac.

  • Skeletal Muscles are generally responsible in sustaining body movements and posture.  This type of muscle is usually attached to a bone.  
  • Smooth Muscles are generally responsible in providing contractile movements to the hollow or void organs of the body such as blood vessels, alimentary canal, urinary bladder and the uterus. Without the smooth muscles, it would be impossible to swallow foods, excrete waste products such as feces and urine, etc.
  • Cardiac Muscles, from the name itself, can only be found in the heart. It is responsible for the rhythmic contraction of the heart. Without it, it would be impossible for the heart to pump.


4.      THE SKELETAL SYSTEM - The Skeletal System is composed of bones, cartilages, tendons, ligaments and joints. Generally, the skeletal system assists in different movements, provides framework and gives protection to the human body and its organs. But aside from these, the skeletal system, particularly the long bones where bone marrow is present, is also an important site for haematopoiesis or the process of blood creation.

5.      THE DIGESTIVE SYSTEM – The Digestive System or Alimentary System is composed of the mouth, pharynx, esophagus, stomach, liver, gall bladder, small intestine, large intestine and the rectum.
The main responsibility of this system is to break down, physically and chemically, all the foods we ingest, so that the useful contents can be utilized by the body in different internal and external processes. While, the non-useful contents will be eliminated, through the rectum, in the form of excrement or feces.


6.      THE URINARY SYSTEM – “The urinary system removes most waste products from the body. The kidneys also maintain the right balance of water and salt in the blood. The urinary system is made up of kidneys, bladder, ureters and the urethra.” (Better Health Channel, 2012)

7.      THE INTEGUMENTARY SYSTEM – The Integumentary System is composed of the largest organ of the body, the Skin, and its accessories (Nails, Hair and Exocrine Glands). 
The primary function of this system is to protect the human body from internal damages and imbalances (water loss, regulation of body temperature, etc.).

8.      THE CIRCULATORY SYSTEM – The Circulatory System is composed of the Heart, the Blood Vessels (Arteries, Veins and Capillaries) and the Blood.
It serves as transport system that “delivers nutrients” to the different cells of the body and “collect the cells’ waste products” for excretion. (Sekar, etal 2006).

9.      THE RESPIRATORY SYSTEM – The Respiratory System is composed of the Nasal and Oral Cavity, Epiglottis, Lungs, Trachea, Larynx, Bronchial Tubes and Diaphragm.
The Respiratory System involves two mechanical processes: Inhalation or Inspiration and Exhalation or Expiration. Inhalation is the process of getting air, particularly oxygen, into the human body. Whereas, exhalation is the process where the waste products of the body, such as carbon dioxide, is being expelled out of the body. Oxygen is a very important element because it aids the body in performing various biochemical processes such as Glycolysis, or the process of releasing energy by breaking down the glucose molecule. This energy is needed by the body in performing different physical and chemical activities.
10.  THE LYMPHATIC SYSTEM - “The lymphatic system is a network of organs, lymph nodes, lymph ducts, and lymph vessels that make and move lymph from tissues to the bloodstream. The lymphatic system is a major part of the body's immune system.” (Dugdale, 2012)

In other words, the lymphatic system generally acts as the “Armed Forces” of the human body, because it fights off foreign intruders that are harmful to the body’s normal physiological processes.


11.  THE REPRODUCTIVE SYSTEM – The primary function of the reproductive system is the perpetuation of the human species.

In males, the reproductive system consists of the Penis, Testicles, Prostate Gland, Seminal Vesicle, Vas Deferens, Epididymis and the Urethra.


While, in females, it consists of the Ovaries, Fallopian Tubes, Uterus, Cervix and Vagina. 

You may also watch the video presentation below for a much clearer and broader understanding of the Human Organ Systems:

Guide Questions:

  1. How many organ systems are there in the Human Body? Identify each of them.
  2. Which, do you think, is the most important among the organ systems? Why?

Please provide your answers in the comment section below.


About the Author:

Randolf Flores, the contributor, is a graduate of Bachelor of Science Major in Biology at the Far Eastern University, Manila. He is currently taking up Master of Arts in Science Education at the Rizal Technological University, Mandaluyong City.


Please spare some time in answering this e-learning short quiz that I prepared below, so you can assess for yourself how much you've learn about the human organ systems.




Better Health Channel. (2012, March). Urinary system. Retrieved February 08, 2014, from http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Urinary_s...

Dugdale, D. (2012, November 02). Lymph system. Retrieved February 08, 2014, from the US National Library of Medicine Website: http://www.nlm.nih.gov/medlineplus/ency/article/002247.htm

Guyton, A. & Hall, J. (2006). Textbook of Medical Physiology 11th Edition. Philadelphia:Elsevier Inc.

Norman Parathyroid Center. (2013, December 2013). Introduction to Parathyroid Glands. Retrieved February 08, 2014, from http://www.parathyroid.com/parathyroid.htm

Sekar T., et al. (2006). Biology (Zoology). Chennai:Tamil Nadu Textbook Corporation.

United States National Institutes of Health. (2007, August). Your Urinary System and How it Works. Retrieved February 07, 2014, from http://kidney.niddk.nih.gov/kudiseases/pubs/pdf/YourUrinary.pdf

United Stated National Institute of Child Health and Human Development. (2012, November 30). What are the parts of the nervous system?. Retrieved February 07, 2014, fromhttp://www.nichd.nih.gov/health/topics/neuro/conditioninfo/pages/parts.aspx



I find this article very informative. The author was able to make a summary of the human systems using simple words, that even children can be able to understood.

I can say that you can learn from this article in just 15 minutes of reading and taking the quiz, although the visual aid should be a little larger. Good Job to the contributor!

The first time I accessed this article (yesterday), it has no figures/pictures/videos (or it did not load yesterday???). Now I can see that it has pictures/video which are very good and made this article more informative. It is very easy to understand also. When I was a student, I can learn easier with this kind of lectures (summarized, with pictures/visuals). Good job to the author of this article ;)

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