Chapter 11 - Gas exchange in humans

Question 1

How are alveoli adapted for gas exchange?

Answer 1

The features of gas exchange surfaces in humans are large surface area to allow faster diffusion of gases across the surface, thin walls to ensure diffusion distances remain short, good ventilation with air so that diffusion gradients can be maintained and a good blood supply to maintain a high concentration gradient, so diffusion occurs faster.

Question 2

What are the ribs?

Answer 2

The ribs are a bone structure that protects internal organs such as the lungs.

Question 3

What are the intercostal muscles?

Answer 3

Intercostal muscles are muscles between the ribs which control their movement causing inhalation and exhalation.

Question 4

What is the diaphragm?

Answer 4

Diaphragm is a sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation The diaphragm is a thin sheet of muscle that separates the chest cavity from the abdomen. It controls the ventilation in the lungs.

Question 5

What is the trachea?

Answer 5

Trachea is that windpipe that connects the mouth and nose to the lungs. Rings of cartilage surround the trachea and bronchi. The function of the cartilage is to support the airways and keep them open during breathing.

Question 6

What is the larynx?

Answer 6

Larynx is also known as the voice box, when air passes across here, we are able to make sounds.

Question 7

What is the bronchi?

Answer 7

Bronchi (plural) are the large tubes branching off the trachea with one bronchus for each lung.

Question 8

What are the bronchioles?

Answer 8

Bronchioles are smaller tubes that branch off the bronchi in the lungs connected to the alveoli.

Question 9

What are the alveoli?

Answer 9

Alveoli are the tiny air sacs where gas exchange takes place.

Question 10

Diagrams of the respiratory system and the lungs

Answer 10

Question 11

What gases are contained in inhaled air?

Answer 11

Inhaled air contains 78% nitrogen, 21% oxygen, 0.2-0.4% water vapour and 0.04% carbon dioxide.

Question 12

What gases are contained in exhaled air?

Answer 12

Exhaled air contains 78% nitrogen, 16% oxygen, 5-7% water vapour and 4% carbon dioxide.

Question 13

Why do oxygen levels decrease from inhaled to exhaled air?

Answer 13

Oxygen levels decrease because oxygen is removed from blood by respiring cells so blood returning to the lungs has a lower oxygen concentration than the air.

Question 14

Why do carbon dioxide levels increase from inhaled air to exhaled air?

Answer 14

Carbon dioxide is produced by respiration and diffuses into blood from respiring cells. The blood transports the carbon dioxide to the lungs where it diffuses into the alveoli and gets exhaled.

Question 15

Why does water levels increase from inhaled air to exhaled air?

Answer 15

Water evaporates from the moist lining of the alveoli into the expired air as a result of the warmth of the body.

Question 16

Why does nitrogen levels remain stable from inhaled air to exhaled air?

Answer 16

Nitrogen gas is very stable and so cannot be used by the body. For this reason, its concentration does not change in inspired or expired air.

Question 17

How does exercise effect breathing?

Answer 17

Exercise increases the frequency and depth of breathing. This is because the muscle are working harder and anaerobically respiring more and they need more oxygen to be delivered to them, and carbon dioxide to be removed, to keep up with the energy demand. If they do not meet the demand, they will respire anaerobically which produces lactic acid which lowers the pH of cells and can denature enzymes catalysing cell reactions. It can only be removed by combining with oxygen.

Question 18

How can the effect of exercise on breathing be investigated?

Answer 18

This can be investigated by counting the breaths taken during one minute at rest and measuring average chest expansion over 5 breaths using a tape measure held around the chest. Then performing exercise for at least 3 minutes and immediately after exercising, count the breaths take in one minute and measure the average chest expansion over 5 breaths.

Question 19

What happens when the diaphragm contracts?

Answer 19

When the diaphragm contracts, it flattens and this increases the volume of the thorax, which leads to a decrease in air pressure inside the lungs relative to the outside of the body, drawing the air in.

Question 20

What happens when the diaphragm relaxes?

Answer 20

When the diaphragm relaxes, it moves upwards back into its domed shape and this decreases the volume of the thorax which leads to an increase in air pressure inside the lungs relative to the outside body, forcing air out.

Question 21

How do the intercostal muscles work?

Answer 21

The external and internal intercostal muscles work as antagonistic pairs. During inhalation, the external intercostal muscles contact to pull the ribs up and out. During exhalation, the external intercostal muscles relax so the ribs drop down and in. When we need to increase the rate of gas exchange, the internal intercostal muscles will also work to pull the ribs down and in to decrease the volume of the thorax, forcing more air out. This is called forced exhalation.

Question 22

How is mucus trapped in the lungs?

Answer 22

The passages down to the lungs are lined with ciliated epithelial cells. These cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed. The mucus is made by special mucus-producing cells called goblet cells. The mucus trap particle, pathogens and dust and prevents them from getting into the lungs and damaging the cells there.