Gas Exchange Topic 6.4

Assessment Statements 6.4.1 Distinguish between ventilation, gas exchange and cell respiration. 6.4.2 Explain the need for a ventilation system. 6.4.3 Describe the features of alveoli that adapt them to gas exchange. 6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli. 6.4.5 Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.

Overview Lungs act with heart and blood vessels to supply body cells with oxygen and remove carbon dioxide Cell respiration – process which requires oxygen to break down bonds within glucose molecules to release energy and store it as ATP and carbon dioxide to be released Ventilation – repeat filling and emptying our lungs with air Gas exchange – diffusion of gases (oxygen, carbon dioxide)

Locations of gas exchange In lungs where oxygen moves from the air of the lungs into the bloodstream (and carbon dioxide moves in the opposite direction) In a capillary bed elsewhere in the body where the opposite gas exchange occurs – oxygen diffuses out of the bloodstream and into a body cell (and carbon dioxide diffuses out of the body cell into the capillary bed)

Why we need a ventilation system Our bodies are thick Diffusion of oxygen from outside environment directly to all cells is impossible To ensure that the concentration of the respiratory gases within the lungs encourages the diffusion of each gas in a direction that is beneficial to the body

Adaptations of alveoli that allow efficient gas exchange Advantage Spherical shape of alveoli Provides a large surface area for respiratory gases to diffuse through Flattened, single cell thickness of each alveolus Prevents respiratory gases from having to diffuse through more cell layers Moist inner lining of alveolus Allows for efficient diffusion Associated capillary bed nearby Respiratory gases do not have to diffuse far to reach single cell thick capillaries

Anatomy of the human respiratory system

Mechanism of ventilation Based on the inverse relationship between pressure and volume An increase in volume will lead to a decrease in pressure; a decrease in volume will lead to an increase in pressure

Mechanism of inspiration Diaphragm contracts and at the same time the abdominal muscles and intercostal muscles help to raise the rib cage. Collectively, all of these actions act to increase the volume of the thoracic cavity. Pressure inside thoracic cavity decreases. This leads to less pressure ‘pushing on’ the passive lung tissue.

The lung tissue increases its volume because there is less pressure exerted on it This leads to a decrease in pressure inside the lungs, also known as a partial vacuum Air comes in through your open mouth or nasal passages to counter the partial vacuum within the lungs and fills alveoli with air Note: These steps are reversed for an expiration.