Respiratory System: Gas Exchange

Respiratory System: Gas Exchange

The respiratory system's primary function is the process of gas exchange, which involves inhalation and exhalation to supply oxygen to the body while removing carbon dioxide. This process takes place in three main regions of the body: the trachea, bronchioles, and alveoli.

Trachea, Bronchi, and Bronchioles

The trachea, also known as the windpipe, is a tube that starts from the larynx, extends downward into the thoracic region, and ends at the bifurcation point where it divides into two branches called the right and left main bronchus. Each branch further divides into smaller branches called bronchioles, which terminate in clusters of tiny air sacs called alveoli.

Alveoli and Capillaries

Alveoli, located within the lungs, are thin-walled structures filled with air. They are surrounded by capillaries, which form the pulmonary circulation part of the circulatory system. Oxygen diffuses across the alveolar membrane into the bloodstream through the capillaries. Conversely, carbon dioxide, a waste product created during cellular respiration, moves from the blood into the alveoli for expulsion upon inhalation.

Mucociliary Escalator and Cilia Beating

To protect the respiratory system from pollution and pathogens, it has several defense mechanisms, including the mucous blanket. A layer of mucus covers the entire length of the respiratory tract, from the nose to the terminal bronchioles. The beating of cilia on the surface of respiratory epithelial cells moves the mucous blanket towards the mouth. When these mechanisms fail or are compromised by factors such as air pollution or smoking, bacteria can run amok in the lower respiratory tract causing severe inflammations and diseases like asthma and chronic bronchitis.

Ventilation Mechanism

Ventilation refers to the movement of air into and out of the lungs for gas exchange. Inspiration occurs when the intrapleural pressure drops, allowing the lungs to expand. Exhalation then takes place due to elastic recoil of lung tissue and muscle contractions.

Lungs' Elasticity and External Intercostal Muscles

The lungs have an inherent property called elasticity, which allows them to expand and contract during breathing. In addition to muscles of respiration, external intercostal muscles between the ribs contribute to exhalation by pulling the rib cage together and compressing the lungs.

Muscles of Respiration: Diaphragm and Intercostals

The main muscles involved in breathing are the diaphragm, which separates the chest from the abdomen, and the intercostal muscles between the ribs. During inspiration, contraction of these muscles increases the volume of the thorax and reduces the pressure inside it, causing the lungs to expand.

Regulation of Breathing Rate and Depth

Central nervous system centers located in the medulla oblongata regulate respiration rate. A rise in carbon dioxide levels stimulates chemoreceptors located in the aortic arch and carotid bodies, increasing respiration rate and depth to remove excess carbon dioxide. Conversely, a decrease in oxygen levels causes peripheral receptors to send signals to increase ventilation. The respiratory center in the brain stem also receives signals from the higher brain centers and the body's acid-base balance to maintain proper respiratory rate and depth.

In summary, the respiratory system, particularly the alveoli and capillaries, plays a crucial role in gas exchange. It maintains a delicate balance between oxygen uptake and carbon dioxide removal to ensure the body's tissues receive adequate oxygen and are rid of waste products.