7.2 Mammalian Gas Exchange System

Question 1

Why do mammals need a gas exchange system?

Answer 1

They have a low SA:V ratio
They are active and have a high metabolic rate
Lots of O2 required for respiration and lots of CO2 needs to be removed

Question 2

How is the nasal cavity adapted to do its job?

Answer 2

Larger surface area and rich blood supply - warms air entering the nose
Hairy lining - secretes mucus to trap dust and bacteria
Moist surfaces - increase humidity of air to prevent water loss in the alveoli

Question 3

How is the trachea adapted to do its job?

Answer 3

Layer of cartilage supports it - holds open and prevents collapse
Incomplete rings, so that it can bend when food is swallowed down the oesophagus
Lined with ciliated epithelial cells and goblet cells, which prevent bacteria entering

Question 4

Describe how goblet cells work

Answer 4

Goblet cells secrete mucus into lining of the trachea
Traps dirt and microorganisms which are wafted up by the cilia so it can be swallowed
The hydrochloric acid in the stomach kills microorganisms

Question 5

Structure of bronchus

Answer 5

Extensions of trachea that split into 2 for the lungs

Similar structure to trachea, contain cartilage, but smaller

Question 6

Bronchioles

Answer 6

Bronchus divides to form bronchioles
No cartilage - have smooth muscle, that can contract to cause constriction
Lined with thin layer of ciliated epithelium facilitating gas exchange

Question 7

Passage of air after inhalation

Answer 7

Nasal passage - trachea - bronchi - bronchiole - alveoli

Question 8

Where does most gas exchange take place?

Answer 8

In the alveoli

Question 9

What are the alveoli made of?

Answer 9

Flattened epithelial cells as well as collagen and elastin fibres

Question 10

Why are the alveoli made of elastin fibres?

Answer 10

To allow elastic recoil of the lungs and squeeze air out

Question 11

Adaptations of alveoli

Answer 11

Thin layers - one cell thick - short diffusion distances
Good blood supply - maintains steep concentration gradient
Good ventilation - breathing moves air in and out of the alveoli to maintain steep diffusion gradients

Question 12

What are the inner surfaces of alveoli covered in?

Answer 12

Water, salts and lung surfactant

Question 13

What allows the alveoli to remain inflated?

Answer 13

Lung surfactant

Question 14

Function of ribs

Answer 14

Provide protection to lungs and heart

Question 15

Function of diaphragm

Answer 15

Broad dome muscle, which forms the floor of the thorax - separates thorax and abdominal cavity

Question 16

What is the thorax lined with?

Answer 16

Pleural membranes

Question 17

Is inspiration active or passive?

Answer 17

Active - requires energy

Question 18

Inspiration

Answer 18

Diaphragm contracts and flattens 
External intercostal muscles contract, moving ribs up and out 
Volume of thorax increases
Pressure decreases 
Air rushes in from outside

Question 19

Is expiration active or passive?

Answer 19

Mostly passive - doesn’t require much energy

Question 20

Expiration

Answer 20

Diaphragm relaxes
External intercostal muscles relax, so ribs move down and in
Elastic fibres in alveoli return to their usual length
Volume of thorax decreases
Pressure increases
Air is forced out of the lungs