The mechanism of breathing 02/11/11 The mechanism of breathing WAL: how the parts of the respiratory system work together to enable breathing. All Most Some What is meant by pulmonary ventilation and how is it calculated? How is air moved in and out of the lungs? What features of the gas-exchange system are responsible for the pressure changes in the lungs?

Key words & Definitions Ventilation - Scientific term for “breathing” – where air is constantly moving in and out of the lungs. Inspiration - Also known as “inhalation”, occurs when air pressure in the atmosphere is greater than that of the lungs; forcing air into the alveoli. Expiration - Also known as “exhalation”, occurs when air pressure in the lungs is greater than that in the atmosphere; forcing air out of the alveoli. 10min into lesson – students copy definitions down

How does ventilation happen? Ventilation requires pressure changes to occur in the lungs, so that air can be forced in an out of the alveoli. The pressure changes are brought about by the movement of two sets of muscles....

How does ventilation happen? The diaphragm, which is a sheet of muscle that separates the thorax (chest) from the abdomen. The intercostal muscles which lie between the ribs. There are two sets of intercostal muscles....

The intercostal muscles – an antagonistic pair The internal intercostal muscles, whose contraction leads to expiration. The external intercostal muscles, whose contraction leads to inspiration.

Ventilation 15min into lesson

Ventilation 15min into lesson

Ventilation 15min into lesson

Ventilation 15min into lesson

Task – 15 minutes Draw a table like the one below.... Fill in what happens to the things on the left (i.e diaphragm, air pressure in lungs...) during inspiration and expiration. Use your textbook to help you. Inspiration Expiration External intercostal muscles Internal intercostal muscles Diaphragm Air pressure in lungs Air movement along pressure gradient Lung volume

Answers, please! Inspiration Expiration External intercostal muscles Internal intercostal muscles Diaphragm Air pressure in lungs Air movement along pressure gradient Lung volume

Answers, please! Inspiration Expiration External intercostal muscles Contract – pulling ribs upwards and outwards. Relax – permitting rib cage to move downwards and outwards. Internal intercostal muscles Are relaxed. Contract – moving the ribs downwards and decreasing the volume of the thorax. Diaphragm Contracts – moves downwards from domed position. Relaxes – elasticity returns to domed position, Air pressure in lungs Decreases Increases Air movement along pressure gradient Into lungs Out of lungs Lung volume 30min into lesson

Back to the lungs! Demo the lungs with the bicycle pump. Ask students the key question “The lungs have taken in quite a significant amount of air. But how could we work out exactly how much air is taken into the lungs?” – to introduce the idea of pulmonary ventilation.

Pulmonary Ventilation Pulmonary ventilation is the total volume of air that is moved into the lungs during one minute (dm3min-1). To calculate it we multiply together two factors....

Pulmonary Ventilation Tidal volume – the volume of air normal taken at each breath when the body is at rest. This is usually around 0.5dm3 (half a litre). Ventilation (breathing) rate – i.e the number of breaths taken in one minute. This is normally 12-20 in a healthy adult.

Pulmonary Ventilation – to summarise = tidal volume x ventilation rate ventilation (dm3min-1) (dm3) (min-1)

But how to we measure tidal volume? We can use a spirometer 40min into lesson

Demonstrate your understanding Complete summary questions 1 to 3 on page 145 in your textbook. You have 10 minutes.

Answers, please 50min into lesson

Homework – due 2nd March Complete the exam questions