Respiratory General

Question 1

What is Boyle’s law?

Answer 1

Boyle’s Law – The pressure of a gas is inversely proportional to its volume. (when temperature and number of gas molecules remains constant in a closed system).

Question 2

What controls respiratory muscle?

Answer 2

Ventilatory muscle controlled by the respiratory centre in the medulla. Action potentials sent to the muscles at regular intervals allowing for contraction and then long period of relaxation.

Question 3

How do we breath in and out?

Answer 3

When we breathe in we increase the volume of our lungs causing a decrease in pressure below that of atmospheric pressure so air moves in to satisfy the gradient. When we breathe out we compress the air in our lungs by decreasing the volume and so increasing the pressure above that of the atmosphere and so air moves out.

Question 4

What is partial pressure?

Answer 4

Partial pressure is a measure of the concentrtion of a gas. Denoted by the letter P i.e. PO2.

Question 5

What is Dalton’s law?

Answer 5

Dalton’s law – partial pressure of a gas is the individual pressure exerted by that gas in a mixture of other gases. So partial pressure of a molecule in a as mixture is proportional to its % in the mixture.

Question 6

How does gas interact with water and how does water interact with gas?

Answer 6

Gas molecules will dissolve into water when they come into contact, whilst water will evaporate until the gas mixture of saturated with water vapour. This water vapour exerts a pressure which is known as the saturated vapour pressure and is about 6.28kPa at body temperture. Before you can work out the partial pressure of a gas in a mixture you must take this pressure into account.

Question 7

Do all gases have the same solubility?

Answer 7

At equilibrium different gases will dissolve different amounts into water – they have different solubilities.

Question 8

Does it take the same amount of gas molecules to reach the same partial pressure in air as it does in a liquid?

Answer 8

The partial pressure of a gas in a liquid can be reached with less molecules than you would need if it wasn’t dissolved because in a liquid there are more molecuels around for collisions.

Question 9

What is the amount of gas that will dissolve in a liquid proportional to?

Answer 9

The amount of gas dissolved is proportional to the pressure of the gas in contact with the liquid.

Question 10

Why does very little oxygen actually dissolve in blood plasma?

Answer 10

Very little oxygen actually dissolves in plasma because it is then taken up by Hb this allows more oxygen to dissovle. Hb is saturated at normal PO2 and so if you double the air pressure only the dissolved oxygen in the plasma will double.

Question 11

What are the partial pressures of oxygen and carbon dioxide in the capillaries and the interstitial fluid?

Answer 11

The partial pressure of oxygen and carbon dioxide in the blood plasma will be the same as the partial pressures of these gases in the air in the alveoli because they reach equilibrium.

PO2 in blood - 13.3kPa
PO2 in interstitum - 6kPa

PCO2 in blood - 5.3kPa
PCO2 in interstitium - 6kPa

Question 12

Why is the PO2 and PCO2 different to what you’d expect in alveoli?

Answer 12

Also because there is always a little bit of air left in the alveoli this PO2 is lower than you would expect and the PCO2 is higher.

Question 13

What is tension?

Answer 13

Note partial pressure sometimes reffered to as tension.

Question 14

What does the partial pressure of oxygen in blood inlcude?

Answer 14

The PO2 in blood includes that of the oxygen bound to Hb.

Question 15

What detects changes causing an increase or decrease in the RR?

Answer 15

The respiratory generator in the Medulla can be stimulated to send action potentials to the ventilator muscle more or less freqeuntly. This occurs from chemoreceptors in the blood and fromreceptor reflexes in the chest wall and airway.

Question 16

What does the solubility co-efficient allow you to do?

Answer 16

Solubility coefficient allows you to work out the partial pressure of a gas dissolved in a liquid if you know the partial pressure of the gas it is being exposed to.

Question 17

Describe the 2 layers of pleura surrounding the lung?

Answer 17

Each lung is surrounded by 2 layers of pleura: The parietal pleura which is continuous at the root of the lung with the visceral pleura which is adherent to the surface of the lung and also extends between the lobes of the lung. The space between the 2 layers of pleura is the pleural cavity.

Question 18

What are lines of pleural reflection?

Answer 18

The abrupt lines along which the parietal pleura changes direction from its costal surface to the diaphragmatic and mediastinal surfaces are known as the lines of pleural reflection.

Question 19

Describe the surface markings of the pleural cavity

Answer 19

The apex of the lung and pleural cavity extends about 3 cm above the medial 1/3rd of the clavicle, into the root of the neck.

From the apex, the line of pleural reflection of each side slopes down behind the sterno-clavicular joints to meet each other near the midline, behind the sternal angle. The sternal angle which can be easily palpated is used to identify the 2nd rib.

From the sternal angle both pleural reflections pass vertically down behind the sternum, to the fourth costal cartilage, where the left pleura deviates laterally, (due to the presence of the heart) to the edge of the sternum and descends lateral to the sternum down to the 6th cc.

On the right side the pleura continues vertically behind the sternum to the 6th cc. At the sixth costal cartilage, the pleura on both sides turn laterally to pass around the chest wall crossing the 8th rib at the mid clavicular line, the 10th rib at the mid axillary line and the 12th rib at the scapular line (line of medial border of the scapula).

The posterior medial border of the pleural cavity ascends vertically.

Question 20

Describe the surface markings of the lungs and the different lobes and fissures of the lungs

Answer 20

The landmarks to note are the even ribs 2, 4, 6, 8, 10. The surface marking of the lungs are the same as that of pleural cavity, except inferiorly and at the cardiac notch.

Inferiorly the lower border of the lung lies about two ribs higher than the pleura. Thus it crosses the 6th rib at the mid clavicular line, 8th rib in the mid axillary line and the 10th rib in the scapular line. The inferior part of the pleural cavity is not occupied by lung is known as the costodiaphragmatic recess.

The cardiac notch of the lung curves further laterally than the pleural reflection; it curves from the 4th costal cartilage to the 5th intercostal space just medial to the mid clavicular line.

The left lung has 2 lobes: – the upper and lower lobes, separated by the oblique fissure.

The right lung has 3 lobes: - the upper, middle and lower lobes. The horizontal fissure separates the right upper and middle lobes, while the oblique fissure separates the right lower lobe from the upper and middle lobes.