Respiratory System: Structure and Gas Exchange

Posted on Feb 3, 2025 in Biology

Human Respiratory System

Anatomy

Nose: Organ containing the nostrils, which are two cavities separated by a septum. These form the nasal cavity. The interior is lined with a mucous membrane containing hairs, cilia, and glands that produce mucus. The mucus moistens the air and filters out dust particles. The blood in the capillaries warms the air.

Pharynx or throat: Muscular tube connected to the nasal cavity and the mouth. It forms part of both the digestive and respiratory systems. It contains almond-shaped structures, the tonsils, which participate in the body’s defenses.

Larynx: Short tube made up of various cartilages. One of them is the epiglottis, which is leaf-shaped. It is attached to the edge of the tube by its stem. When we swallow, the epiglottis folds, closing the larynx. This prevents solid and liquid food from passing into the respiratory tract. The larynx contains the vocal cords, which produce sounds when they vibrate.

Trachea: Flexible tube with C-shaped cartilage rings. It is located in front of the esophagus. The mucosal epithelium inside the trachea contains ciliated cells. These secrete mucus to trap harmful particles and microorganisms.

Bronchi: The two branches of the trachea that enter the lungs. These branch into increasingly narrow tubes, forming the bronchial tree. The ones with a smaller diameter are called bronchioles. Bronchi have complete cartilage rings, but bronchioles do not. Their interior is lined with a mucous membrane.

Lungs: Two spongy, elastic organs located in the thoracic cavity on each side of the heart. Covered by a double membrane called pleura. Contain the bronchial tree, whose bronchioles end in a set of small sac-shaped extensions. These are called pulmonary alveoli and make up the alveolar sacs.

Pulmonary Ventilation

This is the mechanism through which the air in the lungs and the respiratory tract is renewed. It allows air to flow in and out of the lungs. Ventilation is carried out through two respiratory movements: inhalation and exhalation. The diaphragm and the intercostal muscles mainly participate in these movements. By contracting and relaxing, these muscles produce changes in the volume of the lungs. This causes differences in pressure and allows air to flow.

Gas Exchange

In this exchange, oxygen from the air in the alveoli passes into the pulmonary blood capillaries. From there, the carbon dioxide from the blood in these capillaries passes into the alveoli. Gases pass through the walls of the alveoli and blood vessels in one direction or another by simple diffusion. This is due to the difference in the concentration of gases between one side and another. The circulatory system works with the respiratory system to carry oxygen and carbon dioxide in the blood between the lungs and the cells.

Process

1. The pulmonary arteries carry oxygen-poor blood to the lungs.
2. The concentration of oxygen is greater in the air of the alveoli than in the blood of the capillaries, so this gas diffuses into the blood. It then binds to the hemoglobin in the red blood cells, which carries it to the tissues.
3. The pulmonary veins carry oxygen-rich blood out of the lungs.
4. The concentration of carbon dioxide in the blood of the capillaries is greater than in the air of the alveoli. Therefore, this gas diffuses into the alveoli and is expelled from the body during exhalation.