Structure of the respiratory system

The respiratory system consists of all the body parts involved in breathing. It is mainly located in the chest cavity, where it enables the intake of oxygen and removal of carbon dioxide.

Key components of the respiratory system

• Trachea - A large tube that carries air from the nose or mouth into the chest.
• Bronchi - The two main tubes that branch from the trachea, with one bronchus going to each lung.
• Bronchioles - Smaller tubes that branch off from the bronchi, getting progressively narrower as they spread through the lungs.
• Alveoli - Tiny air sacs at the end of the bronchioles where gas exchange takes place. Each sac is called an alveolus.

Pathway of air through the respiratory system

1. Air enters through the nose or mouth and travels down the trachea.
2. The trachea divides into two bronchi, one for each lung.
3. Each bronchus branches into smaller bronchioles.
4. The bronchioles end in clusters of alveoli, where gases are exchanged with the blood.

Mechanism of breathing

Breathing is the process of moving air into and out of the lungs. It involves coordinated muscle actions that change the size of the chest cavity, creating pressure differences to draw in or push out air.

Inhalation process

• The diaphragm (a dome-shaped muscle at the base of the chest) contracts and flattens, moving downwards.
• The external intercostal muscles (between the ribs) contract, lifting the ribcage upwards and outwards.
• As a result, the chest cavity enlarges, drawing air into the lungs through the air passages.

Exhalation process

• The diaphragm relaxes and returns to its dome shape, moving upwards.
• The external intercostal muscles relax, allowing the ribcage to move downwards and inwards.
• As a result, the chest cavity shrinks, pushing air out through the air passages.

Gas exchange in the lungs

Gas exchange is the process where oxygen enters the blood and carbon dioxide is removed. This happens in the alveoli and relies on close cooperation between the respiratory and cardiovascular systems.

How the respiratory and cardiovascular systems work together

• The cardiovascular system (which includes the heart, blood vessels, and blood) transports gases around the body.
• It partners with the respiratory system to swap oxygen and carbon dioxide at the lungs.
• Oxygenated blood (blood rich in oxygen) leaves the heart and circulates to body tissues, delivering oxygen and picking up carbon dioxide.
• Deoxygenated blood (blood low in oxygen and high in carbon dioxide) returns to the heart and is pumped to the lungs.
• In the lungs, gas exchange occurs between the alveoli and tiny blood vessels called capillaries.
• Freshly oxygenated blood then returns to the heart to be pumped out again.

Process of diffusion in gas exchange

Diffusion is the movement of gases from an area of high concentration to low concentration. In the lungs, this happens across the thin walls of the alveoli and capillaries, which are adapted for efficiency.

How diffusion works in the alveoli:

• Alveoli have a large surface area and very thin walls to speed up diffusion.
• In the alveoli, there is a high concentration of oxygen (from inhaled air) and low carbon dioxide.
• In the capillaries, there is a low concentration of oxygen and high carbon dioxide (from deoxygenated blood).
• As a result, oxygen diffuses from the alveoli into the capillaries, where it binds to red blood cells (cells in the blood that carry oxygen).
• At the same time, carbon dioxide diffuses from the capillaries into the alveoli to be exhaled.

Composition of inhaled and exhaled air

The air we breathe in and out has different compositions due to the body's use of oxygen and production of carbon dioxide.

Key gases in air

Inhaled air comes from the atmosphere, while exhaled air has been altered by gas exchange in the lungs. Both contain nitrogen and small amounts of water vapour, with exhaled air having slightly more water vapour due to moisture from the lungs.

Comparison of air composition:

Lung volumes and effects of exercise

Lung volumes measure how much air the respiratory system can handle. These change during exercise to meet the body's increased needs for oxygen and waste removal.

Tidal volume

Tidal volume is the amount of air inhaled or exhaled in a single normal breath.

Effects of exercise on tidal volume:

• During exercise, tidal volume increases to allow more air per breath.
• This helps bring in extra oxygen for muscle energy production in aerobic activities.
• It also aids in expelling more carbon dioxide produced during aerobic respiration.
• Additionally, increased tidal volume supports the removal of lactic acid (a substance produced in muscles during intense, anaerobic activity without enough oxygen).

Vital capacity

Vital capacity is the maximum volume of air that can be forcibly exhaled after inhaling as much as possible.

Effects of exercise on vital capacity:

• A larger vital capacity means more oxygen can be delivered to muscles in each breath, improving performance in endurance activities.
• Vital capacity can be increased through regular exercise, as it strengthens respiratory muscles and improves lung efficiency.