Homework 1.Q 2,3,4 pp38-9 2.Complete todays lesson work (role of the alveolus in gas exchange) 3.Red p75 mah 4.Red p77 mah 5.Red q p79 mah.

Homework

1. Q 2,3,4 pp38-92. Complete todays lesson work (role

of the alveolus in gas exchange)3. Red p75 mah4. Red p77 mah5. Red q p79 mah

3.1.4 Exchange of gases in the lungsText p.78

The exchange of gases in the lungs.

The essential features of the alveolar epithelium as a surface

over which gasexchange takes place.

Gas exchange

1. Copy the table2. What happens

to oxygen3. What happens

to carbon dioxide

4. Why does water vapour increase?

5. If no N2 is used or given off how come the % by volume decreases?

The Relative Composition (% by Volume) ofInspired, Expired air

Gas Inspired air%

Expired air%

Oxygen 20.71 14.6

Carbon dioxide 0.04 3.8

Water vapour 1.25 6.2

Nitrogen 78.0 75.4

Essential features of exchange surfaces text p.78

• Make a list• Label around a diagram of Fick’s law

to show how the features of exchange surfaces in relation to the law

Gases are exchanged across the alveoli by diffusion

According to Fick’s Law...

Rate of diffusion is proportional to

Surface area x Difference in concentration

Thickness of exchange surface

Fick’s Law

Copy this

Gas exchange in the alveoli

Cell types so far• Epithelium – cells on outside of

something• Endothelium – cells on inside of

something• Ciliated columnar epithelium e.g.

lines trachea/bronchi adaptations = column shaped with lots of mitochondria (respiration) and cilia to sweep away mucus dirt and germs

• Squamous cells e.g. alveolar epithelium, capillary endothelium adaptations = flattened cells so a short diffusion distance for gas exchange

• The Gas Exchange Surface

• How many phospholipid bilayers does a molecule of oxygen go through between the alveolar space and the plasma of the blood?

Role of the alveoli in gas exchange

• Make a cartoon to show the alveolus as a character.

• Give it speech bubbles etc. to list the features and adaptations described on page 79

There are 300 million of us! We’d cover a whole tennis court if we were

spread out(that’s a large surface

area for diffusion!)

My squamous epithelial cell lining and my capillary endothelial cells are flattened - a

very short diffusion distance for exchanging

gases!!

my capillaries are narrow so red blood cells get slowed as they pass through –

this allows more time for diffusion

My concentration gradients are

maintained by constant ventilation and

movement of blood in the capillaries

Role of the alveolus in gas exchange

Red cells are squeezed so are pushed up against the capillary endothelial cell wall reducing the distance for diffusion of oxygen

Maintaining the structure of the alveoliDuring inhalation, the chest cavity increases in volume, lowering the pressure in the lungs to draw in fresh air.

Lung surfactant is a phospholipid that coats the surfaces of the lungs. Without it, the watery lining of the alveoli would create a surface tension, which would cause them to collapse. surfactant

alveoli

This decrease in pressure leads to a tendency for the lungs to collapse. Cartilage keeps the trachea and bronchi open, but the alveoli lack this structural support.

Keeping the airways clearThe walls of the trachea and bronchus contain goblet cells, which secrete mucus made of mucin. This traps micro-organisms and debris, helping to keep the airways clear.

The walls also contain ciliated epithelial cells, which are covered on one surface with cilia. These beat regularly to move micro-organisms and dust particles along with the mucus. They contain many mitochondria to provide energy for the beating cilia.