3D-HuBEd No.6 -LUNG-

Refer to chapter 0 for more information on how to use this textbook.

　　6.1 The structure of the Lung
　　6.2 The Mechanism of Respiration
　　6.2 The Exchanging System of Gas

The Structure of the Lung

Lungs are in the chest and they share a part of the chest except a heart . On the average, lungs of the male weigh about 1060 grams and female about 930 grams. The right lung is lighter than the left, because there is a heart in a left side. They have a pulmonary artery and bronchus. With the pulmonary artery, the blood is carried from a right ventricle to exchange two gases. The form of the bronchus that air is carried with is like branches and spread over the lungs.

Trachea and Bronchus

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A trachea is about 10 centimeters long from a larynx to a turning point of a bronchus and it is about 1.5 centimeters wide. There are cilia on mucous membrane inside, and it expels dust to the mouth. The trachea branches at its end. That is called a bronchus. It repeats branching and becomes a terminal bronchiole at last. There is an alveoli at the end of the terminal bronchiole.
Alveoli
An alveoli is a place where two gases are exchanged and important to breathe. There are many spherical alveolus at the end of the terminal bronchiole called HAIHOUDO. Generally, an adult has about 600 million alveolus. It is about 0.14 millimeters across. The area of the surface of all alveolus is about 60 square meters. There are meshy capillaries on the surface and two gases are exchanged by the medium of the capillaries.

6.2 The mechanism of respiration

Respiration is done as follows: The chest volume is changed by the diaphragm and intercostal muscles. The diaphragm and intercostal muscles that move ribs make lungs expand and contract and this causes respiration. The following is an explanation of the mechanism of respiration.

Respiration with the Diaphragm

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The area of the diaphragm is about 300 square centimeters. When it goes down for 1 centimeter, the volume of the chest increases for 250 -- 300 cubic centimeters. Then, air is drawn into lungs for the volume.
Respiration with the intercostal muscles

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When intercostal muscles and cartilages contract, a chest is stretched and then air comes in. Then ribs in the upper part mostly contract to the front, and ribs in the lower part to sideways in the main.

The exchanging system of gas

The Exchange of gases means the operations that are oxygen inhalation from the air to blood and putting carbon dioxide out of blood. These operations are carried out through a thin membrane that is about 0.001 millimeters thick and the membrane is made of both walls of alveolus' and capillary vessels'. Oxygen and carbon dioxide move rapidly from higher pressure to lower one through that membrane. This is how the exchange is carried on.

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As we can see, it is indispensable for gas exchange not only breathing ventilation but also erythrocyte transportation by blood circulation. In other word, respiration can be realized by both functions of heart and lung. Blood is pumped into the whole body when a heart beats. Venous blood that has returned from the whole body goes to lungs by way of right ventricle and a pulmonary artery. Blood plasma carries carbon dioxide up here and hands it over into alveoli. After that erythrocytes receive oxygen and go back to left atrium, and pumped out of a left ventricle into the whole body again.

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