How the Lungs, Thoracic Cage, and Alveoli Work

1. The Human Respiratory Pathway

Explain the pathway of air in our body and why it is beneficial to breathe through the nose:

It is highly recommended to breathe through the nasal cavities (nasal pits) rather than the mouth. This is because the nasal hairs (iletxoek) filter and clean the incoming air, while the rich blood supply warms (epelago) and moistens it. These cavities connect directly to the interior of the pharynx.

The Larynx and Voice Production

The pharynx connects to the larynx, which is a structure made of monitoring cartilage (kartilago). Inside the larynx lie the vocal folds (vocal cords), which vibrate to produce sound. Thus, the larynx is the primary organ of the voice.

The Trachea and Bronchial Tubes

Following the larynx is the trachea, a tube measuring between 12 cm and 15 cm in length. It is kept open by C-shaped cartilaginous rings (kartilaginosoei). The trachea eventually divides into two pipes called bronchial tubes (bronchi), which enter the lungs.

The cartilaginous rings of the trachea are incomplete (open at the back) so that the neighboring esophagus (hestegorria) can easily expand when food passes through. In contrast, the bronchial tubes feature completely closed rings.

2. Structure of the Thoracic Cage

How is the thoracic cage (torazikoa) made up?

The thoracic cage protects the lungs and is composed of the following structures:

• Sides: The ribs (saihetsezurrak).
• Front: The sternum bone (esterno).
• Back: The spine (vertebral column).
• Base: The diaphragm muscle.

Additionally, the respiratory muscles (arnasketakoak) are inserted into the ribs and the spine to facilitate breathing.

Mechanics of Breathing Movements

During inhalation (air entry), the volume of the thoracic cage increases. During exhalation (air expulsion), the volume of the thoracic cage decreases.

This increase in thoracic volume during inhalation happens due to two main physical mechanisms:

1. When the diaphragm contracts and becomes flatter (lauagoa), the base of the thoracic cage moves downward.
2. The contraction (uzkurdura) of the respiratory muscles raises the ribs (saihetsezurrak) and moves the sternum (esternoia) forward.

3. Pulmonary Gas Exchange Process

Explain how and where gas exchange occurs:

Gas exchange (ematen) takes place in the alveoli (albeolora) of the lungs, where deoxygenated blood from the arteries reaches the respiratory surface.

• In the Alveoli: Because there is a high concentration of oxygen in the inhaled air, oxygen binds to hemoglobin to form oxyhemoglobin. At the same time, carbon dioxide (CO₂) is released from the blood into the alveoli to be exhaled. The oxygen-rich blood then travels from the lungs back to the heart through the veins (benak).
• In the Body Cells: Carbon dioxide is more abundant in the cells than oxygen. Therefore, oxyhemoglobin releases its oxygen to the cells, leaving plain hemoglobin behind. The CO₂ produced by the cells dissolves into the blood plasma to be carried away.