Component 3.1 - Human Breathing System

Question 1

How are cartilage rings around the trachea adapted to allow the function of the oesophagus?

Answer 1

They are not complete and do not meet at the back. This allows the oesophagus, behind it, to expand as food is swallowed

Question 2

How do mammals ventilate their lungs?

Answer 2

By negative pressure breathing. This means that for air to enter the lungs, the pressure inside the lungs must be below atmospheric pressure.

Question 3

Explain the process of inspiration

Answer 3

1) The external intercostal muscles contract
2) The ribs are pulled upwards and outwards
3) At the same time, the diaphragm muscles contract, so it flattens
4) Both actions increase the thorax volume
5) This reduces the pressure in the lungs
6) Atmosphere air pressure is now greater than the pressure in the lungs, so air is forced into the lungs

Question 4

Describe the function and structure of the pleural membranes

Answer 4

There are two pleural membranes which have a cavity containing pleural fluid. This fluid acts as a lubricant, allowing friction- free movement against the inner wall of the thorax during ventilation.

Question 5

Describe function of the surfactant on the inside of alveoli

Answer 5

It has a low surface tension preventing the alveoli collapsing during exhalation

Question 6

What are the 4 adaptations of alveoli for gas exchange?

Answer 6

1) They provide a large surface area
2) Gases dissolve in the surfactant moisture lining in the alveoli
3) The alveoli have walls made of squamous epithelium, only one cell thick, so the diffusion pathway for gases is short
4) An extensive capillary network maintains the diffusion gradients, as carbon dioxide is rapidly brought to the alveoli and oxygen is rapidly carried away

Question 7

Why is there 20% oxygen in inspired air but 16% in expired air?

Answer 7

Oxygen is absorbed into the blood at the alveoli and used in aerobic respiration

Question 8

Why is there 0.4% carbon dioxide in inspired air but 4% in expired 4% in expired air?

Answer 8

Carbon dioxide produced by respiration diffuses from plasma into the alveoli

Question 9

Why is the water content of air variable when inspired but saturated with water when than expired?

Answer 9

The water content of the atmosphere is variable but alveoli are permenantly lined with moisture, water evaporates from the, and is exhaled