The Systems of the Human Body

A Summary of the Systems of the Body

The systems of the human body can be a complex subject to understand. Here we briefly outline the main systems and the part they play in the human body.


The nervous system is comprised of the Central Nervous System and the Peripheral Nervous System.

The brain and spinal cord make up the central nervous system which connects to the autonomic and somatic peripheral nervous systems through a network of nerves.

Information in the form of nerve impulses travels along the spinal cord to the brain via sensory nerves and from the brain via motor nerves. This information is used to control all bodily functions, allow all parts of the body to communicate with each other and allow us to be aware of and interact with the environment around us.


The digestive system is comprised of the alimentary canal and a series of accessory organs which assist with the digestion, absorption and storage of food substances.

The organs that make up the alimentary canal are the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.

The alimentary canal is approximately nine metres long and starts at the mouth and ends at the anus.

When we eat, food enters the alimentary canal through the mouth, where it is chewed and swallowed, starting the digestion process. The food moves through the digestive tract, mixing with digestive juices, which breaks down large molecules of food into smaller molecules. The digestive process starts in the mouth and is completed in the small intestine.

Once fully digested, nutrients are absorbed through the intestinal walls and transported throughout the body.


The respiratory system is comprised of air passages and lungs.

When we breathe in through our nose, air is filtered through nasal hairs and humidified before entering the lungs through the windpipe.

The breathing process starts with inspiration of air into the lungs, where the intercostals muscles between the ribs contract and lift the ribs upwards and outwards, causing a vacuum which is quickly filled with air.

The intercostals muscles then relax which exerts pressure on the lungs to expel the air.

During the breathing process, the respiratory system takes up oxygen from the air breathed in and expels unwanted carbon dioxide. This exchange of gases takes place through capillaries, which are situated in air sacs know as ‘alveoli’. Blood, containing carbon dioxide enters the capillaries and the gas moves from the blood and into the alveoli. The carbon dioxide is the exhaled. On inhalation, the process is reversed where oxygen, drawn into the alveoli passes through the capillaries and into the blood.

It is especially important to build up a strong immune defence in order to protect the respiratory system.


The lymphatic system is comprised of a network of tube like structures situated throughout the body.

The main function of the lymphatic system is to manage the fluid levels of the body and filter tissue fluids of bacteria, tumour cells and damaged cells to prevent them from entering the blood stream.

The system performs this function through the lymph nodes which are situated at various points throughout the body. When tissue fluids enter the lymphatic vessels, the fluid Lymph is formed. The lymph passes through the spleen, thymus and lymph nodes where bacteria is trapped and attacked and destroyed by white blood cells. The filtered lymph is then secreted back into the blood stream.

Lymph nodes are situated close to arteries throughout the body, including the throat, armpits, chest, abdomen and groin area. The nodes drain the tissues from around the specific area that they are situated within the body.


The urinary system is comprised of the kidneys, ureters, bladder and the urethra.

The main function of the urinary system is to regulate the amount of fluid in the body and remove waste products.

The human body has two kidneys which filter blood through a mass of tiny internal filters called nephrons in order to remove waste and produce urine. Urine is drained from the kidneys via the ureters and stored in the bladder where it remains until eliminated from the body via urination. The ureters, urinary bladder and urethra together form the urinary tract.

The kidneys maintain the fluid balance of the body by maintaining blood pressure, maintaining the alkalinity and electrolyte balance of the blood and excreting waste products and urea.