CH01 The Human Body

The human body works a like a machine operating diverse systems at once.

Know what your body is made up of.


More than 93% of human body consists of 3 major chemical elements

  1. Oxygen
  2. Carbon
  3. Hydrogen

In addition, Nitrogen, Calcium and phosphorus are also present in significant amounts


The human body contains a tiny amount of gold, it weighs less than that of a sand grain and is mostly present in the blood


The human body comprises of 12 systems that work efficiently non-stop to keep us going all day.

Let’s take a look at few of them in detail.

1. Integumentary system

It consists of skin, hair & nails and extends over the entire surface of our body. They work together to cover and protect the other body systems against the outside world. Skin performs some of the important functions, including regulating body temperature, activate Vitamin D from sun’s rays, filter harmful rays, provide protection from invading infections and help us feel and touch things around.


Skin is the largest organ of the body. The thinnest skin being eyelids while the thickest are the soles of the feet!

2. Skeletal system

The skeleton shapes and supports the body, allows it to move, and protects internal organs. These bones together create a framework that is strong but light. There are 5 different types of bone in our body, that have varied shape and sizes depending on their functions

  1. Short bones that are present in our wrist and ankle. They provide stability to joints.
  2. Long bones in our arms, hands and legs. The support body’s weight and allow it to move.
  3. Flat bones protect organs such as heart and brain.
  4. Irregular bones have complex structures to perform specific roles. For e.g. The Vertebrae that protects the spinal cord.
  5. Sesamoid bones which are roundish bones. E.g. The patella bone that protects the knee joint.


Babies are born with about 300 bones which while growing as an adult fuse together to 206 bones.

3. Digestive system

Breaks down food particles into simple substances that the body can absorb into the bloodstream and utilize, while any indigestible waste is removed. Digestive system starts with the mouth and travels down to esophagus, to the stomach, runs through the small and large intestines to the anus.


An adult digestive tract would be around 23 ft long

4. Urinary System

The Urinary system not just works on excreting waste but also performs other functions such as

  • Maintaining a healthy balance of minerals and salts
  • Keeping the volume and pressure of the blood stable

5. Immune system

The body's collective defense measures are known as the immune system. It identifies pathogens and targets them to destroy. Over time, the body remembers some pathogens and gives immunity so the same diseases do not return.

Every day our body comes under the attack or contact of microscopic invaders that cause disease. Our body is equipped with all kinds of defensive measures that are in place to stop these invaders.

A Barricade!

Skin is the first line of defense, being the body's outer covering it provides a barrier against infections. Other ways the pathogens make an entry into the body is through the food we eat and through air, to fight this, internal passages are lined with protective fluids such as saliva, tears and mucus.

Fighting back!

When the pathogens manage to get past the body's defense barriers, they face the immune systems other warriors- White blood cells. White blood cells circulate in bloodstream and other fluids and hunt for the pathogens to destroy.

6. Nervous system

This system is the body’s communication and control network. It is made up of billions of interconnecting nerve cells wired up around every part of our body through which brain sends and receives signals along with spinal cord. The body’s nervous system can transmit signals at speed of 350 km/h (220 mph). The messages can go all the way from brain to feet in 0.01 seconds


“Left handers are more creative”

The scientific evidence that confirms that left handedness means more creativity is very poorly emerging to make any conclusion.

While it is true that the right hemisphere controls the left side of the body and vice versa, and each hemisphere has specialties, it is not however true that creative side lies on the right side of the brain and is dominantly used by the left handers.


Your body needs nutrition as its basic necessity to sustain growth, development and health.



  • Waugh, A., & Grant, A. (2014). Ross & Wilson Anatomy and physiology in health and illness E-book. Elsevier Health Sciences
  • Knowledge Encyclopedia Human Body!