The respiratory system

Write the path followed by an oxygen molecule from the moment it enters the nasal cavity until it reaches an alveolus in the lungs, naming in order all the structures it passes through.

Order the following structures according to the path of air from outside the body to the alveoli: bronchi, trachea, nasal cavities, larynx, bronchioles, pharynx.

Explain why the pharynx is said to be a "crossroads" between the digestive and respiratory systems, and what two types of substances pass through it.

The airways are lined with mucus and cilia. Explain what each of these elements is and how they work together to clean the air we breathe.

Explain in your own words what alveoli are and why they are the suitable site for gas exchange between air and blood to take place.

Explain the difference between inhalation and exhalation, and state which gas the lungs mainly take in from inhaled air and which gas is expelled with exhaled air.

The walls of the alveoli and of the capillaries that surround them are extremely thin. Explain why this thinness is essential for gas exchange and reason what would happen if these walls were thick.

Inhaled air contains about $21\ \%$ oxygen and $0.04\ \%$ carbon dioxide; exhaled air, about $16\ \%$ oxygen and $4\ \%$ carbon dioxide. Compare both compositions, explain what the lungs have done to the air, and reason, in light of the data, why exhaled air can still be used in mouth-to-mouth resuscitation.

Explain what two movements the rib cage makes to renew the air in the lungs and which muscle located beneath the lungs is mainly responsible for these movements.

Describe what happens to the diaphragm and ribs during inhalation (inspiration) and exhalation (expiration), and explain how these movements cause air to enter and leave the lungs.

A balloon inside a bottle with an elastic bottom is a homemade model of the respiratory system: pulling the rubber sheet at the bottom causes the balloon to inflate. Explain what the balloon, the bottle, and the rubber sheet at the bottom represent, and point out a major limitation of this model compared to the real human body.

When running, we breathe faster and more deeply. Explain which muscles carry out the ventilation movements and why muscle cells need more oxygen during exercise.

When we regularly breathe through the mouth, air reaches the lungs colder, drier, and with more particles than when we breathe through the nose. In view of the numbered structures in the image, explain what happens to the air as it passes through the nasal cavity and why breathing through the nose is recommended.

When our nose is congested because of a cold, we breathe through the mouth and notice a dry, irritated throat. Relate this discomfort to what happens to the air as it passes through the nasal cavities, and explain why congestion usually gets worse when we lie down.

If you blow on a cold pane of glass, it fogs up with the exhaled air. Explain what this phenomenon shows about the content of the air we breathe out, and relate it to one of the functions the nasal cavities perform on inhaled air.

At rest, a person inhales about $0.5\ \text{L}$ of air with each breath and takes about $14$ breaths per minute. Calculate the volume of air moved in one hour. If during exercise the volume per breath rises to $2\ \text{L}$ and the rate to $30$ breaths per minute, calculate how many times greater the volume of air moved per hour is, and explain why the body needs this increase.

Over time, smokers destroy part of the walls of their alveoli (pulmonary emphysema), causing the alveoli to merge into larger cavities with less total surface area. Reasoning from how gas exchange occurs, explain why these individuals become short of breath when exercising even though their lungs still fill with air.

Two patients with oxygenation problems are admitted to an emergency department:

• Patient 1: Suffers from a severe asthma attack; they struggle to ventilate and air barely enters their lungs.

• Patient 2: Has inhaled carbon monoxide from a faulty brazier. Their respiratory rate and volume are normal, and air enters their alveoli without difficulty.

A trainee student claims that Patient 2 is in no life-threatening danger because "their lungs are taking in air and ventilating completely normally."

1. a) Refute the student's conclusion: identify at which stage of respiratory function (pulmonary ventilation, diffusion in the alveoli, transport in the blood, or cellular respiration) the failure occurs in each patient.
2. b) Explain why, even though Patient 2 fills their lungs well with air, their cells are at imminent risk of dying from lack of oxygen.

In a pulmonology clinic, a spirometry test is performed on two teenagers who practice sports:

• Patient 1 (healthy): Exhales $3.6\ \text{L}$ of air in the first second of a forced exhalation.

• Patient 2 (during a respiratory distress crisis): Only manages to exhale $1.5\ \text{L}$ in the first second, but after inhaling a bronchodilator drug their value increases to $3.3\ \text{L}$.

1. a) Interpret patient 2's data: deduce what physical change occurred in the diameter of their bronchi and bronchioles during the crisis and what effect the drug has had on the muscles of these airways.
2. b) A relative of patient 2 states: "If the alveoli are not damaged, oxygen exchange with the blood should be completely normal during the crisis." Refute this statement, justifying why a failure in bronchial ventilation can reduce oxygen exchange even if the alveoli are healthy.