What is the Respiratory System?
The respiratory system is the group of organs that bring oxygen into the body and remove carbon dioxide, powering every cell's energy production. Air travels from the nose and mouth through the airways to millions of tiny air sacs in the lungs, where gases are exchanged with the blood. Breathing rate and depth adjust automatically to match the body's oxygen demand.
The respiratory system moves air in and out of the lungs and exchanges oxygen for carbon dioxide across the thin walls of the alveoli, the lungs' tiny air sacs.
- 1↓InhalationThe diaphragm and rib muscles contract, expanding the chest and drawing air in through the nose or mouth.
- 2↓AirwaysAir passes through the pharynx, larynx, trachea, and branching bronchi into the lungs.
- 3↓BronchiolesAir flows through progressively smaller bronchioles toward the alveoli.
- 4↓Gas exchangeIn the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses out, across capillary walls.
- 5ExhalationThe diaphragm relaxes, the chest recoils, and carbon dioxide-rich air is pushed back out.
Try it: interactive calculator
Step-by-step worked examples
A resting adult breathes 16 times per minute, each breath moving about 500 mL of air. What is their minute ventilation?
Minute ventilation = breathing rate × tidal volume = 16 × 500 mL = 8,000 mL/min = 8 L/min
During exercise, breathing rate rises to 25 breaths/min and tidal volume to 700 mL. Find the new minute ventilation and the increase from rest (8 L/min).
New ventilation = 25 × 700 mL = 17,500 mL/min = 17.5 L/min Increase = 17.5 − 8 = 9.5 L/min more air per minute
Blood entering the lungs has low O2 (40 mmHg) and high CO2 (46 mmHg). After passing the alveoli, what happens to these values?
In the alveoli, O2 (~104 mmHg) diffuses into blood and CO2 diffuses out Blood leaving the lungs: O2 rises to ~100 mmHg, CO2 falls to ~40 mmHg This oxygen-rich, low-CO2 blood returns to the heart to be pumped to the body
Flashcards
Quick quiz
Q1.Where does gas exchange between air and blood occur?
Q2.What happens to the diaphragm during inhalation?
Q3.A person breathes 20 times/min with a tidal volume of 400 mL. What's their minute ventilation?
Q4.Which gas is removed from the blood during gas exchange?
The full card deck, worked steps and AI-tutor support for “What is the Respiratory System?” are in Notek — study by hand before your exam.
Common mistakes
The lungs actively 'suck in' air like a vacuum. — Correct: Muscle contraction (diaphragm, ribs) expands the chest, and air flows in due to a pressure difference — the lungs don't pull air themselves.
Gas exchange happens in the trachea and bronchi. — Correct: Those are just airways; exchange only occurs in the alveoli, where walls are thin enough for diffusion.
Breathing rate is always constant. — Correct: It rises automatically during exercise, fever, or stress to meet higher oxygen demand.
Oxygen and carbon dioxide are pumped by the heart across the lungs. — Correct: They move by passive diffusion down concentration gradients — no active pumping is needed for gas exchange itself.
FAQ
What is the respiratory system?
It's the set of organs — nose, airways, and lungs — that bring oxygen into the body and expel carbon dioxide through breathing.
What is the formula for minute ventilation?
Minute ventilation = respiratory rate × tidal volume (V̇E = RR × TV), measured in liters per minute.
What are examples of respiratory system function?
Resting breathing (~8 L/min), exercise hyperventilation (~17+ L/min), and gas exchange in the alveoli are common examples.
How do you calculate minute ventilation?
Multiply breaths per minute by the volume of air per breath (tidal volume) — use the calculator above with your own numbers.