Mechanism of respiration in higher animals - SS2 Biology Lesson Note

The mechanism of respiration in higher animals, such as mammals, involves a series of steps and structures that facilitate the exchange of gases, particularly oxygen and carbon dioxide. Here is an overview of the respiratory mechanism in higher animals:

1.       Breathing:

·         Breathing refers to the process of inhaling and exhaling air, which involves the movement of air in and out of the respiratory system.

·         It is controlled by the respiratory center in the brain, specifically the medulla oblongata, which regulates the rate and depth of breathing based on the body's oxygen and carbon dioxide levels.

·         During inhalation, the diaphragm, and intercostal muscles contract, 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, reducing the volume of the chest cavity. This increases the pressure in the lungs, forcing air out.

2.       Conducting Airways:

·         The respiratory system includes a network of airways that lead from the nostrils or mouth to the lungs.

·         The air enters the nasal cavity or oral cavity and passes through the pharynx, larynx, trachea, bronchi, and bronchioles, eventually reaching the alveoli in the lungs.

·         The airways are lined with ciliated cells and mucus-producing cells that help trap foreign particles and filter the air.

3.       Gas Exchange:

·         The actual exchange of gases occurs in the alveoli, which are small, thin-walled sacs found at the ends of the bronchioles.

·         The walls of the alveoli are surrounded by a dense network of capillaries, allowing for the exchange of gases between the air in the alveoli and the bloodstream.

·         Oxygen from the inhaled air diffuses across the thin alveolar walls into the capillaries, where it binds to hemoglobin in red blood cells for transport to the body tissues.

·         Carbon dioxide, a waste product of cellular respiration, diffuses from the capillaries into the alveoli and is exhaled during expiration.

4.       Oxygen Transport:

·         Oxygen is transported in the bloodstream attached to hemoglobin; a protein found in red blood cells. Each hemoglobin molecule can bind to four oxygen molecules.

·         Oxygen-rich blood is carried from the lungs to the heart by the pulmonary veins and is then pumped to the rest of the body through the systemic circulation.

5.       Carbon Dioxide Transport:

·         Carbon dioxide produced by cells diffuses into the bloodstream and is transported in three ways: dissolved in plasma, bound to hemoglobin, or as bicarbonate ions.

Most carbon dioxide is converted into bicarbonate ions in red blood cells and transported in the plasma. In the lungs, carbon dioxide is released from the bicarbonate ions and exhaled.