Mechanism of respiration in man - SS2 Biology Lesson Note

The mechanism of respiration in humans involves the following steps and structures:

·         Breathing:

·         Breathing in humans is a rhythmic process that involves inhalation and exhalation.

·         During inhalation, the diaphragm, and intercostal muscles contract. The diaphragm moves downward, and the intercostal muscles lift the ribcage, expanding the chest cavity. This expansion lowers the pressure in the lungs, causing air to rush in through the nose or mouth.

·         During exhalation, the diaphragm and intercostal muscles relax. The diaphragm moves upward, and the ribcage returns to its resting position. This reduces the volume of the chest cavity, increasing the pressure in the lungs and forcing air out.

·         Nasal Cavity and Oral Cavity:

·         The air enters the respiratory system through the nostrils and passes through the nasal cavity. The nasal cavity is lined with mucous membranes and has tiny hair-like structures called cilia, which help filter, warm, and moisten the incoming air.

·         If necessary, air can also enter through the mouth, bypassing the nasal cavity.

·         Pharynx and Larynx:

·         From the nasal cavity or oral cavity, the air passes through the pharynx, a shared passage for both air and food.

·         The air then moves into the larynx, commonly known as the voice box, which contains the vocal cords. The larynx helps produce sound and prevents food or liquid from entering the airway.

·         Trachea and Bronchial Tree:

·         The air enters the trachea, a tube-like structure also known as the windpipe, which extends downward into the chest.

·         The trachea branches into two bronchi, one leading to each lung. Inside the lungs, the bronchi divide further into smaller bronchioles, forming a complex network called the bronchial tree.

·         Alveoli and Gas Exchange:

·         At the ends of the bronchioles, there are tiny air sacs called alveoli. The alveoli are surrounded by a dense network of capillaries.

·         Gas exchange occurs across the thin walls of the alveoli. Oxygen from the inhaled air diffuses into the bloodstream through the capillaries, while carbon dioxide, a waste product, diffuses out of the bloodstream into the alveoli to be exhaled.

6.       Oxygen and Carbon Dioxide Transport:

·         Oxygen binds to hemoglobin in red blood cells and is transported throughout the body via the bloodstream.

·         Carbon dioxide, produced by cellular respiration, is transported in the blood mainly as bicarbonate ions. It is also dissolved in plasma and bound to hemoglobin to a lesser extent.

·         Carbon dioxide is eventually exhaled from the lungs during expiration.

(onlinebiologynotes.com)