The Digestive System
Food provides us with fuel to live, energy to work and play, and the raw materials to build new cells. All the different varieties of food we eat are broken down by our digestive system and transported to every part of our body by our circulatory system.
Our digestive system is a 9 meter long tube. The digestive process begins in the mouth, where the teeth and tongue break up the food after it has been softened with saliva. The food is then swallowed and travels down the esophagus to the stomach.
While the food is in the stomach, it is mixed with a mild acid which breaks the food down into a paste similar to porridge. The food then passes, a little at a time, into the small intestine, which is roughly 6 meters long. Here the food is broken down even further until it is small enough to pass through the walls of the small intestine into the bloodstream. Food that cannot be digested passes into the large intestine, where the water and minerals are absorbed into the blood stream. The solid waste, the feces, is then expelled from the body through the rectum and anus.
The Circulatory System
The blood is the transport system by which oxygen and nutrients reach the body's cells, and waste materials are carried away. The heart, a muscular organ, positioned behind the ribcage and between the lungs, is the pump that keeps this transport system moving.
Blood that is poor in oxygen appears blue.
Blood leaves the left side of the heart and travels through arteries, which gradually divide into capillaries. In the capillaries, food and oxygen are released to the body cells, and carbon dioxide and other waste products are returned to the bloodstream. The blood then travels in veins back to the right side of the heart, where it is pumped directly to the lungs. In the lungs, carbon dioxide is exchanged for oxygen, and this renewed blood flows back to the left side of the heart, and the whole process begins again.
The Respiratory System
The respiratory system is the system of the body that deals with breathing. When we breathe, the body takes in the oxygen that it needs and removes the carbon dioxide that it doesn't need.
First the body breathes in the air which is sucked through the nose or mouth and down through the trachea (windpipe). The trachea is a pipe shaped by rings of cartilage. It divides into two tubes called bronchi. These carry air into each lung. Inside the lung, the tubes divide into smaller and smaller tubes called bronchiolies. At the end of each of these tubes are small air balloons called alveoli.
Capillaries, which are small blood vessels with thin walls, are wrapped around these alveolies. The walls are so thin and close to each other that the air easily seeps through. In this way, oxygen seeps through into the bloodstream and carbon dioxide, in the bloodstream, seeps through into the alveoli, and is then removed from the body when we breathe out.
(A close up view of an alveoli)
The diaphragm is the muscle that controls the breathing process. As the diaphragm flattens, it causes the chest to expand and air is sucked into the lungs. When the diaphragm relaxes, the chest collapses and the air in the lungs is forced out.