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This model illustrates the various stages in human respiration process.

The first stage in respiration - ventilation - occurs by alternating inhalations and exhalations. During inhalation, the ribs spread out due to contractions of intra-rib muscles. The diaphragm lowers, and the volume of the chest increases. The pressure in the lungs becomes lower than the atmospheric pressure, and the air moves into the lungs. Exhalation occurs passively during normal breathing. It is made possible by the elastic nature of the alveoli and the surface strain that is caused by their decrease in volume, which causes air to leave the lungs.

The next stage in breathing is known as diffusion. During diffusion, oxygen enters blood in the capillaries that densely cover the walls of the alveoli. Diffusion is made possible by the fact that partial pressure of gases in the blood and in the alveoli is different. Oxygen bonds with hemoglobin in the erythrocytes and is carried throughout the organism with the blood flow. Carbon dioxide passes from blood to alveoli, and it leaves the lungs during exhalation.

Press "Run" button to initiate the animation. Press "Stop" to bring it to a halt, and press "Reset" to return the model to its initial state.

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