Section 2g Gas Exchange

Question 1

Describe structure of thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes.

Answer 1

The lungs are encaged in ribs, which have intercostal muscles holding the ribs together (internal and external intercostal muscles).

A diaphragm is at the bottom of the thorax and is shaped like a dome or flat depending on ventilation.

A trachea leads into the thorax and divides into bronchi. The bronchi divide into bronchioles and then into alveoli.

Pleural membranes separate the lungs form the thorax and contain pleural cavity. This cavity contains pleural fluid which acts as lubrication so the lungs dont stick to the surfaces of the inside of the chest when we breath.

Question 2

Describe what happens when we breath in.

Answer 2

1. External intercostal muscles contract, pulling ribs up and out. Internal intercostal muscles relax.
2. Diaphragm relaxes.
3. Lower pressure in thoraic cavity.
4. Higher volume in thoraic cavity.

This process requires respiration because there is muscle contraction.

Question 3

Describe what happens when we breath out.

Answer 3

1. Internal intercostal muscles contract, and the ribcage moves down and inwards. External intercostal muscles relax.
2. Diaphragm contracts.
3. Higher pressure in thoraic cavity.
4. Lower volume in thoraic cavity.

This process doesn’t require energy because there is no muscle contraction.

Question 4

Describe the adaptations of alveoli in gas exchange.

Answer 4

Alveoli are adapted for gas exchange in these ways:

1. Many alveoli - large surface area.
2. Thin walls - capillary and alveoli are one cell thick.
3. Constant concentration gradient within the alveoli as we constantly breath in and out.
4. Constant concentration gradient within the capillary as the blood flows back to heart.

Question 5

Explain the biological consequences of smoking in relation to the lungs and the circulatory system, including coronary heart disease.

Answer 5

Nicotine, a chemical present in cigarette smoke, speeds up the heart rate and causes furring in the artery walls.

Carcinogens - chemicals that can disrupt the DNA of the alveoli. This causes them to duplicate abnormally fast, eventually creating a tumor and leading to cancer.