The respiratory system consists of organs involved in breathing. They include nose, throat (pharynx), windpipe, bronchi, bronchioles and lungs. The nasal cavity and pharynx are together referred as the upper respiratory system. The lower respiratory system comprises of windpipe (trachea) and lungs. The respiratory system performs the function of inhaling oxygen and exhaling carbon dioxide. Apart from this key function it also allows us to talk and smell.

During inhalation air travels through nose and reaches the lungs via pharynx, larynx and trachea. Once air is in the lungs it enters tiny balloon-like air sacs called alveoli. The alveoli are surrounded by tiny blood vessels called capillaries. Here carbon dioxide is removed from the blood and oxygen passes into your blood. Blood then goes to your heart which pumps it throughout the body.

Cardiovascular system consists of heart, blood and blood vessels. The heart located in the middle of the chest keeps pumping the blood day and night through the blood vessels. The heart has two sides and each of it has two chambers. The cardiovascular system moves inhaled oxygen from lungs to body tissues and removes carbon dioxide while exhaling. Oxygen deprived blood comes to the right side of the heart and is sent to the lungs. In the lungs, blood absorbs oxygen and gets rid of carbon dioxide. Oxygenated blood then returns to the left side of the heart. This is called pulmonary circulation. The left side of the heart pumps the oxygen-laden blood to the tissues in the body. The oxygen-deprived blood then again returns to the right side of the heart to complete the circuit. This is referred as systemic circuit.

As the left side of the heart has to pump blood to the entire body, muscles in this part is thicker than left side.

The digestive system consists of gastrointestinal tract, a long continuous tube that extends from the mouth to the anus, pancreas and gallbladder, and liver. It includes the mouth, throat, esophagus, stomach, small intestine, and large intestine. The digestive system is one of the most complex and diverse systems in the body. Each of the food coming through this system is broken down to the level of molecules so that they can be utilised and absorbed by the cells.

The process of digestion starts in mouth where it is chewed and mixed with saliva. The chewed food then passes through esophagus and reaches the stomach where acids and enzymes help further break down the food. It then moves into small intestine where it continues to be broken by digestive enzymes for absorption by bloodstream. The large intestine absorbs water and electrolytes from the remaining indigestible food matter, and then compacted into feces which are passed out from the body through the rectum and anus. The liver and pancreas also produce enzymes and bile which aid in the digestion process.

The main function of urinary or renal system is to filter blood and eliminate waste and excess water from the body. It consists of kidneys, ureters, bladder and urethra. The kidneys are located in the upper abdomen and filter blood removing the waste products in the form of urine.

The ureters are two thin tubes that move urine from the kidneys to the bladder. The bladder stores urine until it is eliminated from the body through the urethra. The urethra is a tube that runs from the bladder to the outside of the body. The kidneys filter the blood and maintains the electrolyte balance and also regulates the pH of the blood.

The urinary system plays very important role in maintaining the overall health and balance of the body by eliminating waste products and excess fluids.