2.7.5 Human Gas Exchange System

Question 1

In humans what is the gas exchange surface

Answer 1

The lungs

Question 2

All gas exchange surfaces have features in common which allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time, they include:

Answer 2

1. Large surface area to allow faster diffusion of gases across the surface

Question 3

(Breathing Structures Table) Ribs Description

Answer 3

Bone structure that protects internal organs such as the lungs.

Question 4

(Breathing Structures Table) Intercostal Muscle Description

Answer 4

Muscles between the ribs which control their movement causing inhalation and exhalation

Question 5

(Breathing Structures Table) Diaphragm Description

Answer 5

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

Question 6

(Breathing Structures Table) Trachea Description

Answer 6

Windpipe that connects the mouth and nose to the lungs

Question 7

(Breathing Structures Table) Larynx Description

Answer 7

Also known as the voice box, when air passes across here we are able to make sounds

Question 8

(Breathing Structures Table) Bronchi (pl) Description

Answer 8

Large tubes branching off the trachea with one bronchus (sin) for each lung

Question 9

(Breathing Structures Table) Bronchioles Description

Answer 9

Bronchi split to form smaller tubes called bronchioles in the lungs connected to alveoli

Question 10

(Breathing Structures Table) Alveoli Description

Answer 10

Tiny air sacs where gas exchange takes place

Question 11

(Breathing Structures Table) Pleural Cavity Description

Answer 11

The fluid-filled space between the pleural membranes which reduces friction and allows the lungs to move freely

Question 12

The passages down to the lungs are lined with, what?

Answer 12

ciliated epithelial cells

Question 13

Describe the function of Cilia Cells

Answer 13

Cilia 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

Question 14

What is mucus made by

Answer 14

The mucus is made by special mucus-producing cells called goblet cells because they are shaped like a goblet, or cup

Question 15

What does the mucus do?

Answer 15

The mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them from getting into the lungs and damaging the cells there

• Mucus traps particles, dust, and pathogens and cilia beat and push it up and away from the lungs

Question 16

Exam Tip

Answer 16

You may notice that several of the features of alveoli that make them suited to their function are the same as those that make villi suited to their function or root hair cells suited to their function – the reason for this is because all of these structures are involved in transporting substances across their surfaces – by diffusion, active transport, osmosis or a combination.

So if you learn the features for one, you also know many of the features of the others!

Question 17

How are alveoli highly specialized for gas exchange

Answer 17

1. There are many rounded alveolar sacs that give a very large surface area to volume ratio

Question 18

Alveoli are specifically adapted to, do what?

Answer 18

maximize gas exchange

Question 19

Muscles are only able to pull on bones, what can they not do?

Answer 19

not push on them

Question 20

Because muscles cannot push on bones, there must be two sets of intercostal muscles to work antagonistically to facilitate breathing, what are they?

Answer 20

External intercostal muscles, pull the rib cage up

Internal intercostal muscles pull the ribcage down

Question 21

Describe the process of Inhalation

Answer 21

The diaphragm contracts and flattens

The external set of intercostal muscles contract to pull the ribs up and out

This increases the volume of the chest cavity (thorax)

Leading to a decrease in air pressure inside the lungs relative to outside the body

Air is drawn in

Question 22

Describe the process of exhalation

Answer 22

The diaphragm relaxes it moves upwards back into its domed shape

The external set of intercostal muscles relax so the ribs drop down and in

This decreases the volume of the chest cavity (thorax)

Leading to an increase in air pressure inside the lungs relative to outside the body

Air is forced out

Question 23

Describe the process of breathing in

Answer 23

• External Intercostal Muscles contract
• Ribcage moves up and out
• Diaphragm contracts and flattens
• Volume of thorax increases
• Pressure inside Thorax decreases
• Air is drawn in

Question 24

Describe the process of breathing out

Answer 24

• External Intercostal muscles relax
• Ribcage moves down and in
• Diaphragm relaxes and becomes dome-shaped
• Volume of thorax decreases
• Pressure inside thorax increases
• Air is forced out

Question 25

Exam Tip

Answer 25

You may see the terms inhalation OR inspiration (breathing in), and exhalation OR expiration (breathing out). Both sets of terms mean exactly the same thing, so don’t let them confuse you!

This sequence of events is a common exam question and you should be able to explain in detail what is happening to the external and internal intercostal muscles, the rib cage, the diaphragm, the volume and the pressure-volume of the lungs when breathing in and out.

Remember, if you learn one, the other is almost exactly the opposite

Question 26

The external and internal intercostal muscles work as, what?

Answer 26

antagonistic pairs (meaning they work in different directions to each other)

Question 27

When we need to increase the rate of gas exchange (for example during strenuous activity) the internal intercostal muscles will also, do what?

Answer 27

work to pull the ribs down and in to decrease the volume of the thorax more, forcing air out more forcefully and quickly – this is called forced exhalation

Question 28

What are the differences between inspired air and expired air during ventilation (Oxygen, Carbon Dio, Nitrogen)

Answer 28

Inspired Air (Oxygen): 21%
Inspired Air (Carbon): 0.04%
Inspired Air (Nitrogen): 78%
Expired Air (Oxygen): 16%
Expired Air (Carbon) 4%
Expired Air (Nitrogen) 78%