3A - Gas exchange in humans

Question 1

Describe the pathway of air in humans

Answer 1

Pharynx
Larynx
Trachea
Bronchus
Bronchioles
Alveoli

Question 2

What are the 2 types of intercostals we need to know about?

Answer 2

Internal and external

Question 3

What is ventilation?

Answer 3

Breathing in and out.

Question 4

What is the word for breathing in and out?

Answer 4

Ventilation

Question 5

What is the word for breathing in?

Answer 5

Inspiration

Question 6

What is the word for breathing out?

Answer 6

Expiration

Question 7

Describe inspiration

Answer 7

External intercostals and diaphragm contract.

This causes the ribcage to move up and out and the diaphragm to flatten, increasing the volume of the thoracic cavity.

As the volume of the thoracic cavity increases, the lung pressure decreases (to below atmospheric pressure).

Air always flows from high pressure to low pressure, down a pressure gradient, so air flows down the trachea into the lungs.

Question 8

Is inspiration active or passive?

Answer 8

Active

Question 9

Describe expiration

Answer 9

External intercostals and diaphragm relax.

Ribcage moves down and in and diaphragm becomes curved again.

The internal intercostals contract, pulling the ribcage further down and in.

The volume of the thoracic cavity decreases, causing air pressure to increase (to above atmospheric pressure).

Air is forced out of the lungs, down the pressure gradient.

Question 10

Is expiration passive or active?

Answer 10

Passive

Question 11

What do the external and internal muscles make up?

Answer 11

An antagonistic pair.

Question 12

Where does gas exchange in humans occur?

Answer 12

In the alveoli

Question 13

What is each alveolus made from?

Answer 13

A single layer of thin, flat cells called alveolar epithelium.

Question 14

How are alveoli adapted for gas exchange?

Answer 14

Huge number of them so large SA for exchange of carbon dioxide and oxygen.

Surrounded by a network of capillaries which maintain a concentration gradient.

Thin exchange surface so short diffusion pathway.

The alveoli are connected by a collagen cable which can contract to push air out of the alveoli.

Question 15

Apart from the adaptations of the alveoli, what other adaptations are there for human gas exchange?

Answer 15

RBC slowed as they pass through narrow capillaries, increasing the time for diffusion to occur.

RBC flattened against capillary walls, decreasing the diffusion pathway.

Breathing movements keeps lungs ventilated, replacing the external medium.

Flow of blood maintains concentration gradients for exchange.

Question 16

How does oxygen get into the blood?

Answer 16

Moves down the trachea, bronchi and bronchioles into the alveoli, down a pressure gradient. Once in the alveoli, the oxygen diffuses across the alveolar epithelium, down a diffusion gradient, then the capillary endothelium, ending up in the capillary itself.

Question 17

What is the structure of the trachea&bronchi?

Answer 17

Has cartilage rings for support.

Walls are lined with goblet cells and epithelial cells.

Question 18

What is the structure of the bronchioles?

Answer 18

Heavily branched.

Muscular walls to regulate air flow in and out of the alveoli by contraction of the pipes.

Question 19

What is the structure of the alveoli?

Answer 19

100-300μm across.

At end of bronchioles.

Stretch to pull air in.

Collagen and elastic fibres help the alveoli.

Question 20

What do the goblet and epithelial cells do in the trachea&bronchi?

Answer 20

Goblet cells produce mucus to stop pathogens entering the lungs.

Epithelial cells waft the mucus out of the lungs.