The Respiratory System

Respiratory System Overview

• The body needs oxygen to produce energy through respiration, and expels carbon dioxide as a byproduct.
• The respiratory system is responsible for breathing in oxygen and breathing out carbon dioxide.

Nasal Cavity

• Most air is inhaled through the nose, with some entering through the mouth.
• The nasal cavity warms, moistens, and cleans the air.
• Large dust particles are trapped by nostril hairs, while finer particles and bacteria are caught by sticky mucus and cilia, which can be swallowed.

Trachea

• The trachea is a thick tube that air passes through.
• It is reinforced by rings of cartilage that prevent it from collapsing.

Bronchi and Bronchioles

• The trachea divides into two bronchi, which then divide into smaller tubes called bronchioles.
• Bronchioles are located inside the lungs.

Alveoli

• Bronchioles end in clusters of air sacs called alveoli.
• There are approximately 600 million microscopic alveoli in the lungs.
• Alveoli provide a large surface area for gas exchange between the lungs and bloodstream.

Breathing In (Inhale)

• Intercostal muscles contract, lifting the ribs upwards and outwards.
• The diaphragm contracts, moving downwards.
• The lungs expand and fill with air, allowing oxygen to enter the bloodstream through diffusion.

Breathing Out (Exhale)

• Intercostal muscles relax, moving the ribs down and inwards.
• The diaphragm relaxes, moving upwards.
• The lungs contract, forcing the air out, and carbon dioxide enters the lungs through diffusion.

Gas Exchange

• The walls of alveoli are one cell thick and surrounded by tiny blood vessels called capillaries.
• Oxygen moves from the alveoli into the capillaries through diffusion.
• Oxygen is carried throughout the body by red blood cells in the bloodstream.