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

3.1.4 Exchange of gases in the lungs Text p.78 The exchange of gases in the lungs. The essential features of the alveolar epithelium as a surface over which gas exchange takes place.

Gas exchange 1.Copy the table 2.What happens to oxygen 3.What happens to carbon dioxide 4.Why does water vapour increase? 5.If no N 2 is used or given off how come the % by volume decreases? The Relative Composition (% by Volume) of Inspired, Expired air Gas Inspired air % Expired air % Oxygen Carbon dioxide Water vapour Nitrogen

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 alveoli During 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 clear The 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.