Breathe in and out. Notice your chest and belly moving and feel the soft air passing from the nose. Listen to the quiet sounds of breathing in and out. Imagine the air moving from the nose into the throat, through the air tubes, and into the airsacs.

The parts of the respiratory system that are in charge of supplying oxygen are the nose, nasal passageways, windpipe, lungs, and diaphragm. In the nose and nasal passages, the entering air is made warm, damp, and clean of unknown particles. Next, the air moves down through the trachea, bronchi, bronchioles, and alveoli. Trachea is the empty tube that serves as passageway of air into the lungs. Bronchi are the two branching tubes that connect the trachea to the lungs. Bronchioles are the hairlike tubes that connect to the alveoli. Alveoli are the airsacs that allow gas exchange in the lungs.

KEY CONCEPTS

The air we breathe goes through the nose, nasal passages, and then through the trachea or windpipe, which separates into two branches, called bronchial tubes or bronchi, one entering each lung. The bronchi subdivide many times inside the lungs, analogous to the branching pattern of grapes, finally becoming hairlike tubes called bronchioles. In the last part of the terminal bronchioles are tiny bubble-like bunch of structures called alveoli or airsacs.

KEY CONCEPTS

When you breathe in or inhale, the diaphragm muscle contracts. Inhaling moves the diaphragm down and expands the chest cavity. Simultaneously, the ribs move up and increase the size of the chest cavity. There is now more space and less air pressure inside the lungs. Air pushes in from the outside where there is higher air pressure. It pushes into the lungs where there is lower air pressure. When you breathe out or exhale, the diaphragm muscle relaxes. The diaphragm and ribs return to their original place. The chest cavity returns to its original size. There is now less space and greater air pressure inside the lungs. It pushes the air outside where there is lower air pressure.

KEY CONCEPTS

Air first enters your lungs and then into the left part of your heart. It is then driven by your heart into the bloodstream, all the way through your body. The heart pumps blood, which transports essential nutrients, oxygen, and other chemicals to every cell in your body. Once it reaches the cells, oxygen processes the nutrients to release energy. Carbon dioxide is given off during this process. The blood delivers carbon dioxide into the right portion of your heart, from which it is pumped to the lungs. Carbon dioxide leaves your body through the lungs when you exhale.

The circulatory system is the life support structure that nourishes your cells with nutrients from the food you eat and oxygen from the air you breathe. It can be compared to a complex arrangement of highways, avenues and lanes connecting all the cells together into a neighborhood. Sequentially, the community of cells sustains the body to stay alive. Another name for the circulatory system is the cardiovascular system.

The circulatory system functions with other body systems to deliver different materials in the body. It circulates vital elements such as oxygen and nutrients. At the same time, it also transports wastes away from the body.