Download English on Duty page 72-73

English on Duty page 72-73
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THE RESPIRATORY SYSTEM
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The Respiratory System consists of two main phases: external and internal respiration. External
respiration is the exchange of gases within the lungs. Internal respiration is the exchange of oxygen and
carbon dioxide taking place within the body cells. Oxygen passes from the alveolus into the capillary and
carbon dioxide passes from these capillaries back into the alveoli where it is then breathed out which
is known as external respiration. The Respiratory System consists of the lungs, the nose, the larynx, the
windpipe and the bronchi.
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The Lungs
The lungs are situated in the chest cavity, which is formed by the ribs radiating from the : spine at the
back to the sternum at the front. The lungs are separated by the heart, blood : vessels and esophagus.
The left lung has two lobes and is slightly smaller than the right : lung which has three lobes. The
pleura surrounds and protects the lungs. It is a double : layer of membrane lining the ribs and totally
enveloping the lung. The lubricating fluid | contained in the pleura allows the lungs and ribcage to
move against each other without : causing friction. Air enters the body through the nose and mouth to
reach the back of the pharynx before passing along to the larynx to reach the windpipe. The two main
bronchi subdivide as small bronchi for the lobes of each lung, which further subdivide into smaller and
narrower tubes called bronchioles. Bronchioles branch into the alveolar ducts of the alveolar sacs
which end in clusters of tiny air sacs or alveoli. The lungs take up most of the space in the chest cavity.
They are elastic structures and their elasticity aids breathing movements.
The diaphragm and the intercostal muscles are the main muscles for breathing. When normal
breathing occurs, the diaphragm contracts and becomes flat thus allowing the ribcage to expand.
This mechanism which increases the chest volume and whereby air is drawn down the windpipe
into the lungs is called inspiration. Air is expelled from the lungs during expiration and this takes
place passively by the natural elasticity of the lung tissue. When the diaphragm and the external
intercostal muscles relax, the chest cavity resumes its normal size. The exchange of gas takes place in
less than a second in the alveoli.
Carbon dioxide must be dissolved and eliminated from of the plasma, through the capillary wall into the
tiny space between the capillary and the alveolar walls. From there, it passes through the alveolar walls
into each alveolus.
Carbon dioxide and oxygen dissolve on their way out of and into the blood. The gases move by diffusion
from a high pressure area to a low one. Oxygen and carbon dioxide travel in different directions.
Oxygen combines with the hemoglobin in the red blood cells and forms oxyhemoglobin. As the
capillaries are so thin and tiny, only one red blood cell at a time can pass. The pulmonary venous
system receives the oxygenated blood through the left atrium. Venous blood enters the right ventricle,
and from there it is pumped out into the pulmonary artery and to the lungs. There are four pulmonary
veins.