adaptations of gas exchange surfaces human

Question 1

1. Draw, label and describe the gas exchange surface of a human.

Answer 1

The mouth leads to the trachea that is held open by rings of cartilage so it can resist pressure changes. The trachea leads to the bronchi, then bronchioles, a series of branching tubes that deliver the gas to the alveoli. The bronchioles have muscle surrounding them, which can be used to constrict the airflow in and out of the alveoli. The alveoli are minute sacs that are made of epithelial cells, collagen and elastic fibres so the alveoli can stretch and recoil. Having many alveoli give a large surface area for exchange.

Question 2

2. Describe and explain the feature of an alveolus that allows efficient gas exchange.

Answer 2

The alveolar epithelium is one cell thick; Creating a short diffusion pathway;

Question 3

3. Describe the pathway an oxygen molecule takes from an alveolus to the blood.

Answer 3

Across alveolar epithelium; Then the endothelium of a capillary;

Question 4

4. Describe the gross structures of the human gas exchange system and how we breathe in and out.

Answer 4

1. The trachea, then bronchi, then bronchioles, then alveoli; 2. To breathe in – the diaphragm contracts and flattens/moves down and external intercostal muscles contract moving the ribcage upwards and outwards; 3. This causes an increase in volume of the thoracic cavity which decreases pressure 4. so air moves into the lungs down the pressure gradient; 5. To Breathe out – The diaphragm relaxes and external intercostal muscles relax and lung tissue is elastic so recoils; 6. This causes volume decrease and pressure increase in thoracic cavity so air moves out down the pressure gradient.

Question 5

5. Describe and explain the mechanism that causes forced expiration.

Answer 5

1. Contraction of internal intercostal muscles pulls the ribcage further inwards 2. Relaxation of diaphragm muscles and external intercostal muscles 3. Causes decrease in volume of thoracic cavity 4. Air pushed down pressure gradient.

Question 6

6. Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.

Answer 6

1. Oxygen moves down the trachea and bronchi and bronchioles 2. Down pressure gradient into the alveoli; 3. Then.. down diffusion gradient 4. Across alveolar epithelium.

Question 7

7. How can the pulmonary ventilation rate be calculated?

Answer 7

PVR = tidal volume (the volume breathed in) x breathing rate (the number of breaths per time)

Question 8

8. Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them.

Answer 8

1. Many alveoli provide a large surface area 2. Many capillaries provide a large surface area; 3. So fast diffusion; Alveoli and capillary walls are thin so short distance between alveoli and blood 4. There is flattened epithelium 5. So a short diffusion pathway; So fast diffusion 6. There is ventilation and circulation; to maintain a concentration gradient 7. So increased rate of diffusion