Gas Exchange in Humans

Question 1

What is the role of the gas exchange system?

Answer 1

To supply your blood with oxygen, and remove carbon dioxide from your body.

Question 2

Why do humans need oxygen in the blood?

Answer 2

To take it to respiring cells.

Question 3

What is the structure of the human gas exchange system?

Answer 3

• As you breathe in, air enters through the trachea.
• The trachea splits into two bronchi, one bronchus leading to each lung.
• Each bronchus then branches off into smaller tubes called bronchioles.
• The bronchioles end in small ‘air sacs’ called alveoli.

Question 4

Where are gases exchanged in humans?

Answer 4

At the alveoli

Question 5

What work together to move air in and out of the gas exchange system?

Answer 5

• Ribcage
• Intercostal muscles
• Diaphragm

Question 6

Where are the intercostal muscles located?

Answer 6

Between the ribs.

Question 7

What are the two types of intercostal muscles?

Answer 7

• Internal intercostal muscles

* External intercostal muscles

Question 8

Where are the internal intercostal muscles found?

Answer 8

On the inside of the external intercostal muscles.

Question 9

What is ventilation?

Answer 9

It consists of inspiration (breathing in) and expiration (breathing out).

Question 10

What is ventilation controlled by?

Answer 10

The movements of the diaphragm, internal and external intercostal muscles and the ribcage.

Question 11

What does the structure of the human gas exchange system look like?

Answer 11

image

Question 12

What happens during inspiration?

Answer 12

• The external intercostal muscles and diaphragm contract.
• The ribcage moves upwards and outwards.
• The diaphragm flattens.
• Increasing the volume of thoracic cavity (the space where the lungs are).
• As the volume of thoracic cavity increases, the lung pressure decreases to below atmospheric pressure.
• Air flows down the trachea and into the lungs (as air always flows down the pressure gradient).

Question 13

What type of process is inspiration?

Answer 13

Active (it requires energy).

Question 14

What does inspiration look like?

Answer 14

image

Question 15

What happens during expiration?

Answer 15

• The external intercostal muscles and diaphragm relax.
• The ribcage moves downwards and inwards.
• The diaphragm curves upwards again (becoming dome shaped).
• This decreases the volume of the thoracic cavity (the space where the lungs are).
• This causes the lung pressure to increase above atmospheric pressure.
• Air is forced down the pressure gradient and out of the lungs.

Question 16

What does expiration look like?

Answer 16

image

Question 17

What type of process is expiration?

Answer 17

Passive (it does not require energy).

Question 18

What is forced expiration?

Answer 18

e.g. if you blow out the candles on your birthday cake.

Question 19

What happens during forced expiration?

Answer 19

• The external intercostal muscles relax.

* The internal intercostal muscles contract, pulling the ribcage further down and in.

Question 20

What is said about forced expiration?

Answer 20

That the movement of the two sets of intercostal muscles is said to be antagonistic (opposing).

Question 21

How many alveoli do lungs contain?

Answer 21

Millions of microscopic alveoli, where gas exchange takes place.

Question 22

What are the alveoli surrounded by?

Answer 22

A network of capillaries.

Question 23

What is the structure of the alveoli?

Answer 23

The wall of each alveolus is made from a single layer of thin, flat cells called alveolar epithelium.

Question 24

What do are the capillary walls that surround the alveoli made of?

Answer 24

Capillary endothelium.

Question 25

What do these alveoli walls contain?

Answer 25

A protein called elastin (which is elastic).

Question 26

What does elastin in the alveoli allow for?

Answer 26

It helps the alveoli return (recoil) to their normal shape after inhaling and exhaling air.

Question 27

What does the alveoli structure look like?

Answer 27

image

Question 28

How does oxygen move through the gas exchange system?

Answer 28

Air (containing oxygen) moves down the trachea, bronchi, bronchioles into the alveoli.

Question 29

What allows oxygen to move through the gas exchange system?

Answer 29

Because it moves down a pressure gradient.

Question 30

What happens to oxygen after it reaches the alveoli?

Answer 30

It moves into the blood, where it can be transported around the body.

Question 31

What allows oxygen to move around the body in blood?

Answer 31

Because it moves down a diffusion gradient.

Question 32

How does carbon dioxide move through the gas exchange system?

Answer 32

It moves down its own diffusion and pressure gradient, but in the opposite direction to oxygen, so that it can be breathed out.

Question 33

What gas exchange occurs in the alveoli?

Answer 33

* Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium, and into haemoglobin in the blood. * Carbon dioxide diffuses into the alveoli from the blood.

Question 34

What does alveolar gas exchange look like?

Answer 34

image

Question 35

Summarise how oxygen moves through the gas exchange system and into the blood

Answer 35

Trachea - Bronchi - Bronchioles - Alveoli DOWN A PRESSURE GRADIENT - Alveolar epithelium - Capillary endothelium - Blood DOWN A DIFFUSION GRADIENT

Question 36

What do alveoli contain, which increase the rate of diffusion?

Answer 36

* A thin exchange surface (one cell thick = short diffusion pathway). * A large surface area (millions of alveoli). * A steep concentration gradient of oxygen and carbon dioxide between the alveoli and the capillaries.

Question 37

How is the diffusion gradient of oxygen and carbon dioxide between the alveoli and the capillaries maintained?

Answer 37

By the flow of blood and ventilation.

Question 38

What does blood and ventilation maintaining the concentration gradient look like?

Answer 38

image