Human Respiratory System: Anatomy and Gas Exchange

The Human Respiratory System

The respiratory system is responsible for gas exchange, capturing oxygen from the air and delivering it to the blood, while the blood collects carbon dioxide to remove it from the body.

Key Respiratory Functions

• Airway: Collecting ducts where air is oxygenated.
• Lungs: The site of gas exchange between blood and air.
• Cellular Respiration: A process where combustion occurs in food to obtain energy.

Air Conditioning and Vocalization

The air entering the lungs must be clean, moist, and warm. Mucus is responsible for moistening the air and trapping dust and microbes. Additionally, the vocal cords vibrate to produce sounds as air passes through, which are then modified by the language, lips, and teeth.

Anatomy of the Respiratory Tract

• Nostrils: The entry point for air; the inner walls contain abundant capillaries.
• Pharynx: A passageway for both the respiratory and digestive tracts. It directs food into the esophagus and air into the larynx. The tonsils located here produce white blood cells to defend against infection.
• Larynx: Entry is regulated by the epiglottis, which closes when food is present in the pharynx.
• Trachea: A 12cm tube with open cartilage rings. The interior contains mucus to trap foreign particles and cells with filaments called cilia.
• Bronchi and Bronchioles: The trachea divides into two bronchi, each penetrating a lung. These branch into the bronchial tree, ending in approximately 400 million alveoli.

Lung Structure and Mechanics

Lungs are highly elastic, sponge-like organs:

• Right Lung: Consists of three lobes.
• Left Lung: Consists of two lobes.
• Pleura: The lungs are surrounded by two membrane sheets known as the pleura.

Pulmonary Ventilation

The movement of gas from one location to another occurs via diffusion. Pulmonary ventilation is the process where air in the alveoli is constantly renewed.

• Inspiration: Air enters the lungs, caused by the contraction of the ribcage muscles and the diaphragm.
• Expiration: Air leaves the lungs. The ribs move in the opposite direction of inspiration, and the diaphragm relaxes, curving and rising.

The Ribcage

The ribcage is a thoracic chamber that houses the lungs, heart, and esophagus.