B. Respiration System - Part 2
B. Respiration System - Part 2
B. Respiration System - Part 2
IN HUMAN
GASEOUS EXCHANGE RESPIRATORY SYSTEM
The most important are the two lungs. Each lung is filled with many tiny air spaces called air sacs or alveoli. It is here that the oxygen diffuses into the blood. Because they are so full of spaces, lungs feel very light and spongy to touch. The lungs are supplied with air through the windpipe or trachea.
2. The TRACHEA
The air then passes into the windpipe or trachea. At the top of the trachea, is a piece of cartilage called epiglottis. This closes the trachea and stops food going down the trachea when you swallow. This is a reflex action, which happens automatically when a bolus of food touches the soft palate. The air then passes into the windpipe or trachea. At the top of the trachea, is a piece of cartilage called epiglottis. This closes the trachea and stops food going down the trachea when you swallow. This is a reflex action, which happens automatically when a bolus of food touches the soft palate.
Just below the epiglottis is the voice box or larynx. This contains the vocal cords. The vocal cords can be tightened by muscles so that they make sounds when air passes over them. The trachea has rings of cartilage around it, which keep it open.
3. The BRONCHI
The trachea goes down through the neck and into the thorax. The thorax is the upper part of your body from the neck down to the bottom of the ribs and diaphragm. In the thorax, the trachea divides into two. The two branches are called the right and the left bronchi. One bronchus goes to each lung and then branches out into many smaller tubes called bronchioles.
4. The ALVEOLI
At the end of each bronchiole are tiny air sacs or alveoli. This is where gaseous exchange takes place.
As the volume of the thorax decreases, the pressure inside it increases. Air is squeezed out through the trachea into the nose and mouth, and on out of the body.
Sometimes, cells may need a lot of oxygen very quickly. Imagine, you are running in a race. The muscles in your legs are using up a lot of energy. To produce this energy, the mitochondria in the muscles will be combining oxygen with glucose as fast as they can, to provide the energy for the muscles.
A lot of oxygen is needed to work as hard as this. You breathe deeper and faster to get more oxygen into your blood. Your heart beats faster to get the oxygen to the leg muscles as quickly as possible.
Eventually a limit is reached. The heart and lungs cannot supply oxygen to the muscles any faster. But more energy is still needed for the race. How can that extra energy be found? Extra energy can be produced by anaerobic respiration. Some glucose is broken down without combining it with oxygen :
Glucose
It doesnt release very much energy, but a little extra might make all the difference.
When you stop running, you will have quite a lot of lactic acid in your muscles and your blood. This lactic acid must be broken down by combining it with oxygen. So, even though you do not need the energy anymore, you go on breathing hard. You are taking in extra oxygen to break down the lactic acid. While your are running, you built up an oxygen debt. You borrowed some extra energy without paying for it with oxygen.
Now, as the lactic acid is combined with oxygen, you are paying off the debt. Not until all the lactic acid has been used up, does your breathing rate and rate of heart beat return to normal?