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Human Respiratory System
Human Respiratory System
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The human respiratory system brings oxygen into the body and removes carbon dioxide, a waste gas made by cellular respiration. It includes the airways, lungs, and breathing muscles that work together to move air in and out. This system is essential because every cell needs a steady oxygen supply to release energy from food. Efficient gas exchange also helps keep blood chemistry stable.
Air enters through the nose or mouth, passes through the pharynx, larynx, trachea, bronchi, and smaller bronchioles, and finally reaches the alveoli. In the alveoli, oxygen diffuses into nearby capillaries while carbon dioxide diffuses from the blood into the air spaces. Breathing depends on pressure changes created mainly by the diaphragm and intercostal muscles. The respiratory system also helps with speech, smell, and regulation of blood pH.
Key Facts
- Air pathway: nose or mouth -> pharynx -> larynx -> trachea -> bronchi -> bronchioles -> alveoli
- Gas exchange occurs by diffusion: oxygen moves from alveoli to blood, carbon dioxide moves from blood to alveoli
- During inhalation, diaphragm contracts and moves downward, increasing thoracic volume
- During exhalation, diaphragm relaxes and moves upward, decreasing thoracic volume
- Breathing rate can be estimated by minute ventilation: VE = tidal volume x respiratory rate
- Large alveolar surface area and thin alveolar walls increase the rate of gas exchange
Vocabulary
- Alveoli
- Tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged with the blood.
- Trachea
- The windpipe, a tube that carries air from the larynx to the bronchi.
- Bronchi
- The two main branches from the trachea that carry air into each lung.
- Diaphragm
- A dome-shaped muscle below the lungs that helps draw air in and push air out.
- Diffusion
- The movement of particles from an area of higher concentration to an area of lower concentration.
Common Mistakes to Avoid
- Thinking the lungs are muscles that pull in air, which is wrong because breathing is driven mainly by the diaphragm and intercostal muscles changing chest volume and pressure.
- Mixing up the bronchi and bronchioles, which is wrong because bronchi are the larger main branches and bronchioles are the much smaller airways deeper in the lungs.
- Assuming oxygen is actively pumped into the blood, which is wrong because oxygen enters the blood by diffusion across alveolar walls.
- Believing exhalation always requires strong muscle contraction, which is wrong because quiet exhalation usually happens when the diaphragm relaxes and the lungs recoil.
Practice Questions
- 1 A student has a tidal volume of 500 mL per breath and a respiratory rate of 12 breaths per minute. What is the minute ventilation in mL per minute and in L per minute?
- 2 During exercise, a person breathes 18 times per minute with a tidal volume of 750 mL. Calculate the minute ventilation.
- 3 Explain why damage to alveoli reduces oxygen delivery to the body even if air can still move through the trachea and bronchi.