The Respiratory System

• The respiratory system facilitates the exchange of oxygen and carbon dioxide between blood, air, and tissues.

Components of the Respiratory System

• Nose
• Pharynx (throat)
• Larynx (voice box)
• Trachea (windpipe)
• Bronchi
• Lungs

Function of the Nose

• Warms, moistens, and filters air before it enters the lungs
• Hairs in the nasal cavity trap large dust particles, while mucus moistens air and traps dust and smoke.

Other Components

• Pharynx (throat) serves as a passageway for both air and food.
• Larynx (voice box) is located on top of the trachea.
• Trachea (windpipe) is covered by the epiglottis, a tissue flap that closes when swallowing.
• The trachea branches into bronchi at the lungs.

Bronchi and Lungs

• The bronchi are two large passageways in the chest cavity, each leading to a lung.
• Within each lung, the bronchus subdivides into smaller bronchioles, leading to millions of tiny air sacs called alveoli.
• Alveoli are clustered like grapes and surrounded by capillaries.
• Cilia sweep trapped particles and mucus away from the lungs.

Gas Exchange

• A healthy lung has over 150 million alveoli.
• Oxygen dissolves in the moisture on the surface of the alveoli and diffuses into the capillaries.
• Simultaneously, carbon dioxide diffuses in the opposite direction.
• Inhaled air contains roughly 21% oxygen and 0.04% carbon dioxide
• Exhaled air contains less than 15% oxygen and 4% carbon dioxide.
• Hemoglobin's efficiency means that without it, blood volume would need to be 300 liters for the same results.

Breathing Mechanics

• The lungs lack connected muscles, so the force driving air into the lungs derives from air pressure.
• Lungs are sealed in pleural membranes inside the chest cavity.
• The diaphragm, a large flat muscle, is located at the bottom of the chest cavity.
• The diaphragm contracts and the rib cage rises, creating a vacuum that causes air to rush into the lungs.
• Breathing is regulated by the nervous system.

Control of Breathing

• Breathing is controlled by the medulla oblongata.
• Cells in the breathing center monitor the amount of carbon dioxide in the blood.
• When carbon dioxide levels rise, nerve impulses from the breathing center cause the diaphragm to contract.