How air travels to the lungs, how breathing works and how oxygen reaches the blood.
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Air enters through the nostrils, where hairs and mucus trap dust, and passes through the pharynx, larynx (voice box) and trachea (windpipe, kept open by rings of cartilage). The trachea divides into two bronchi, one to each lung; each bronchus branches into bronchioles that end in millions of tiny air sacs called alveoli. The lungs sit in the chest cavity protected by the rib cage, above the dome-shaped diaphragm, and are covered by a double membrane, the pleura.
Why does the trachea have rings of cartilage?
They keep the windpipe open so air can always pass.
Name the structures that air passes through from nose to alveoli.
Nostrils, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, alveoli.
How does the nose clean the air?
Hairs and sticky mucus trap dust and germs, and the nose also warms and moistens the air.
In inspiration the diaphragm contracts and flattens, and the intercostal muscles pull the ribs up and out. The chest volume increases, the pressure inside falls below atmospheric pressure and air rushes in. In expiration the diaphragm relaxes and domes up, the ribs move down and in, the volume decreases, the pressure rises and air is pushed out. An adult breathes about 15 to 18 times a minute at rest.
A person breathes 500 mL of air per breath, 16 breaths per minute. How much air is that per minute and per day?
500 × 16 = 8,000 mL = 8 L per minute; × 60 × 24 = 11,520 L per day.
What happens to the diaphragm and ribs during inspiration?
The diaphragm contracts and flattens; the ribs move up and out.
Why does air enter the lungs when the chest expands?
The larger volume lowers the pressure inside the lungs below that outside, so air flows in.
Each alveolus has a wall one cell thick, moist, and wrapped in blood capillaries, so gases diffuse quickly: oxygen goes from the alveolar air into the blood (where haemoglobin in red cells carries it) and carbon dioxide goes from the blood into the air to be breathed out. Inhaled air is about 21% oxygen and 0.04% carbon dioxide; exhaled air is about 16% oxygen and 4% carbon dioxide. Nitrogen stays about 78% in both. Smoking, pollution and infection (for example asthma, bronchitis, pneumonia and tuberculosis) damage this system.
Inhaled air has 21% oxygen, exhaled air 16%. By how many percentage points does oxygen fall?
21 − 16 = 5 percentage points.
Carbon dioxide rises from 0.04% to 4%. What is the rise?
4 − 0.04 = 3.96 percentage points, about 100 times the original amount.
Give two adaptations of alveoli for gas exchange.
Thin walls (one cell thick), a large total surface area, a rich supply of capillaries and a moist lining.
1. Name the organs of the respiratory system in order.
2. What is the function of the epiglottis?
3. What are alveoli?
4. Which muscle separates the chest from the abdomen?
5. What happens to the lungs' volume during expiration?
6. Which pigment carries oxygen in blood?
7. Differentiate breathing from respiration.
8. At 16 breaths a minute, how many breaths are taken in an hour?
9. Why is exhaled air richer in carbon dioxide than inhaled air?
10. Name two lung diseases and one cause of damage to the lungs.