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.

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.

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.

State whether these statements are true or false and justify your answer: a) the lungs are muscles that contract to draw air in; b) the alveoli are surrounded by blood capillaries; c) exhaled air contains more carbon dioxide than inhaled 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.

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.

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.

Look at the image of the respiratory system. State which number points to the trachea and which points to the diaphragm, and describe the function of each of these two structures.

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.

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.

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.

During dinner, a guest talks and laughs while chewing and swallowing. Suddenly, they suffer a violent coughing fit and clutch their neck. A witness states: "They choked because the epiglottis closed at the wrong time and diverted the food into the esophagus."

1. a) Refute the witness's explanation: explain the actual function of the epiglottis during swallowing, which duct it must protect, and where the food was actually diverted.
2. b) Justify why it is anatomically impossible to speak and swallow at the same time, and explain why the reflex of coughing forcefully is the respiratory system's most effective protective response in this situation.

In the emergency room, two cases of choking caused by foreign objects obstructing the airway are treated:

• Case A: A piece of food has become lodged in the larynx, blocking the glottis.

• Case B: A toy piece has descended beyond the trachea and has become firmly lodged in the right main bronchus.

The medical team considers performing an emergency tracheostomy (an artificial opening in the front part of the trachea).

1. a) Predict and justify in which of the two cases the tracheostomy will resolve the asphyxia by allowing air to reach both lungs, and why in the other case this procedure will not solve the problem.
2. b) In the case where the tracheostomy is not effective, explain what consequence the obstruction will have on gas exchange in each lung and reason whether the patient can survive temporarily with only one functional lung.