We have learned that the cells of the body need oxygen, and that the oxygen is obtained from the air. ln order to obtain oxygen we must first get air into our bodies, which we do by inhaling, or breathing in.
Across the body cavity, and below the lungs,is a flat, powerful muscle called the diaphragm. When this muscle is moved downward, it causes the ribs to move upward and outward. The result is a partial vacuum that is produced in the lungs. The pressure of the air outsidethe bodyis now greater than the pressure in the lungs, and air is pushed into the nose, down the throat though a tube called the trachea, and finally into the lungs.
The trachea divides into two parts, each entering a lung.Each part is called a bronchial tube. Each bronchial tube branches many times until the smallest branches are almost as small as capillaries. These smallest branches are called alveoli. The tissues that make up the alveoli contain capillary arteries and veins.
Oxygen passes from the air through the walls ofthe arteries,ancl combineswith the red blood cells. Carbon dioxide passes through the walls of the veins, and into the air in the lungs.
When the diaphragm relaxes, the ribs move down-ward,compressthe|ungs,and force the carbon-dioxide rich air out of the lungs by the same path through which it entered.
Across the body cavity, and below the lungs,is a flat, powerful muscle called the diaphragm. When this muscle is moved downward, it causes the ribs to move upward and outward. The result is a partial vacuum that is produced in the lungs. The pressure of the air outsidethe bodyis now greater than the pressure in the lungs, and air is pushed into the nose, down the throat though a tube called the trachea, and finally into the lungs.
The trachea divides into two parts, each entering a lung.Each part is called a bronchial tube. Each bronchial tube branches many times until the smallest branches are almost as small as capillaries. These smallest branches are called alveoli. The tissues that make up the alveoli contain capillary arteries and veins.
Oxygen passes from the air through the walls ofthe arteries,ancl combineswith the red blood cells. Carbon dioxide passes through the walls of the veins, and into the air in the lungs.
When the diaphragm relaxes, the ribs move down-ward,compressthe|ungs,and force the carbon-dioxide rich air out of the lungs by the same path through which it entered.
