Ventilation: Lungs and Gas Exchange

• Ventilation is the act of moving air into and out of the lungs to allow gas exchange to occur.

Key Structures and General Information

• Lungs are the main organs where gas exchange occurs.
• Ribs and intercostal muscles work together to expand and contract the rib cage during breathing and provide physical protection to the lungs and heart.
• The larynx contains the vocal cords
• The trachea connects the throat to the bronchi
• C-shaped cartilage rings provide structural support to keep the trachea open
• The bronchi are hollow tubes with cartilage rings that carry air from the trachea to the lungs and split into two tubes to enter each lung, further branching.
• Bronchioles are smaller tubes branching off the Bronchi.
• Alveoli are tiny air sacs with a capillary network where gas exchange occurs; oxygen diffuses into the capillaries while carbon dioxide diffuses out.

Breathing In

• During breathing in, the internal intercostal muscles relax, while the external intercostal muscles contract, pulling the ribs up and out.
• The diaphragm flattens, pushing the abdominal muscles downwards.
• The volume in the thorax increases, causing air to diffuse into the lungs due to a lower concentration of air inside compared to outside.

Breathing Out

• The volume of the thorax decreases, which increases pressure, forcing air out.
• Breathing out is typically a passive process, but the internal intercostal muscles contract during forced exhalation.

Air Composition

• The majority of air is composed of nitrogen, oxygen, and carbon dioxide with more oxygen in inhaled air than exhaled air.
• Oxygen is absorbed into the blood and used for respiration, producing carbon dioxide as a waste product.
• There is more carbon dioxide and water vapour in exhaled air compared to inhaled air.

Adaptations of Exchange Surfaces

• Large surface area: The alveoli provide an extensive surface area (80-100 square metres) to allow more efficient diffusion.
• Thin surface: A short diffusion distance facilitates rapid exchange.
• Good blood supply: Maintains a concentration gradient by carrying away substances that have already diffused.
• Good ventilation with air: Ensures waste gases diffuse out of the blood into the air, while oxygen diffuses into the blood.
• Moist: Gases dissolve more readily before diffusing across the membrane.

Protection from Foreign Pathogens

– Goblet cells in the trachea and bronchi secrete mucus into the respiratory tract.

• Mucus traps foreign pathogens and particles, which are then moved upwards towards the throat by cilia.
• Swallowed mucus is destroyed in the acidic conditions of the stomach.

Physical Activity Impact

• During physical activity, the rate and depth of breathing increases.
• Muscles increase the rate of respiration to produce more energy, requiring more oxygen and producing more carbon dioxide.
• An increase in blood carbon dioxide levels is detected by the brain, leading to an increase in the breathing rate for faster gas exchange.
• Heart rate also increases to facilitate faster substance transport around the body.

Learn about ventilation, the process of moving air in and out of the lungs for gas exchange. Key structures like the lungs, ribs, intercostal muscles, larynx, and trachea are explained. Understand the roles of bronchi, bronchioles, and alveoli in respiration.