Respiratory system and gas exchange

1. The respiratory system plays a critical role in enabling the exchange of gases (primarily oxygen and carbon dioxide) between the external environment and the body.
2. This exchange facilitates cellular respiration, a process that provides the energy required for cellular functions.

Structure of the Respiratory system

The respiratory system is made up of the following structures:

1. Nose and Mouth: Air enters the body through the nose or mouth, where it is warmed, moistened, and filtered.
2. Pharynx: A shared pathway for air and food.
3. Larynx: Contains the vocal cords and connects the pharynx to the trachea.
4. Trachea: A tube that carries air to the lungs, supported by cartilage rings.
5. Bronchi: The trachea divides into two bronchi, one for each lung.
6. Bronchioles: Smaller branches of the bronchi that lead to the alveoli.
7. Alveoli: Tiny air sacs where gas exchange occurs.
8. Diaphragm: A muscle that helps control breathing by changing the volume of the thoracic cavity.

Gas Exchange: O₂ and CO₂ Transport

Gas exchange refers to the movement of oxygen and carbon dioxide across the alveolar membrane into and out of the blood.

Process of Gas Exchange

1. Inhalation: Air rich in oxygen enters the body through the nose/mouth and travels through the pharynx, larynx, trachea, bronchi, and bronchioles.
2. Alveoli: The bronchioles lead to tiny air sacs called alveoli. Here, oxygen from the inhaled air diffuses across the thin walls of the alveoli into the capillaries that surround them.
3. Diffusion: Oxygen moves from the high-concentration area (air in the alveoli) to the low-concentration area (blood in the capillaries). Conversely, carbon dioxide, which is in higher concentration in the blood, diffuses from the blood into the alveoli to be exhaled.
4. Exhalation: The body expels carbon dioxide from the lungs back into the atmosphere through the same pathway.

Functions of the Respiratory System

The respiratory system has several important functions:

1. Gas Exchange: Oxygen is taken in from the air and carbon dioxide is expelled.
2. Regulation of Blood pH: By controlling the levels of carbon dioxide, the respiratory system helps maintain the acid-base balance in the blood.
3. Protection: The respiratory system filters out dust, pathogens, and other particles from the air.
4. Sound Production: The larynx contains the vocal cords, which produce sound when air passes through them.

Mechanics of Breathing

Inhalation

1. At rest: The diaphragm contracts and moves downward, expanding the chest cavity. Pressure inside the lungs drops below atmospheric pressure and air flows in.
2. During exercise: The diaphragm is helped by the external intercostal, abdominal, and accessory neck muscles. The chest cavity expands faster and further, drawing in more air per breath.

Exhalation

1. At rest (passive): The diaphragm and external intercostals relax. Their elastic recoil shrinks the chest cavity, pressure inside the lungs rises above atmospheric, and air flows out. No muscle actively pushes air out at rest.
2. During exercise (active): The internal intercostal and abdominal muscles contract to compress the lungs faster and harder than elastic recoil alone could manage. Active exhalation costs energy.

Key Parameters in Respiratory Function

The body adapts to different levels of activity and physical demands by adjusting several key parameters of the respiratory system, including: