Session 3

Question 1

What is the ideal gas equation?

Answer 1

PV=nRT

Question 2

What is Boyle’s law?

Answer 2

Pressure in a ga is inversely proportional to its volume

Question 3

What is the total partial pressure exerted in a mixture of gases equal to?

Answer 3

The sum of the partial pressure of the individual gases

Question 4

What is composition of atmospheric air?

Answer 4

20.9% = Oxygen
78% = Nitrogen
0.03% = CO2

Question 5

How do gases diffuse in the body?

Answer 5

Down the partial pressure gradient

Question 6

What happens when gas molecules come into contact with body fluids?

Answer 6

• Gas molecule will enter the fluid to dissolve

- The water molecules evaporate to enter air

Question 7

What is the saturated vapour pressure at body temperature?

Answer 7

6.28 kPa

Question 8

What happens to inhaled air in the upper respiratory tract?

Answer 8

Saturated with water

Question 9

How does water vapour affect the partial pressure of other gases at 101 kPa?

Answer 9

101-6.28

The use the normal ratios

Question 10

When is the equilibrium of gases established in a fluid?

Answer 10

Rate of gas molecules entering water = rate of gas molecules leaving the water

Question 11

What is occurring at equilibrium of gas in fluid?

Answer 11

Partial pressure of the gas in the liquid = partial pressure gas in the air above it

Question 12

Partial pressure is the same as the amount of dissolved gas. True/False. Why?

Answer 12

False

Amount of gas dissolved = Partial pressure X solubility coefficient of gas

Question 13

When is partial pressure established if there is a component of liquid that the gas reacts with?

Answer 13

Partial pressure is established after the gas reacts with component

Question 14

What happens when oxygen encounters plasma?

Answer 14

• Enters plasma and dissolves in it
• Dissolved oxygen enter red blood cells to bind to Hb
• Process continues till Hb fully saturated
• After Hb is fully saturated, oxygen continues to dissolve until the equilibrium is established
• At equilibrium pO2 of plasma=pO2 of alveolar air

Question 15

What happens to the dissolved oxygen in plasma when it encounters tissues?

Answer 15

It is available to diffuse into tissues and is replaced by the oxygen bound to haemoglobin

Question 16

Why does alveolar air equilibrate with the blood air?

Answer 16

The is constantly gas moving out and into the alveolus. Oxygen move into the blood stream constantly .

Question 17

What happens to the atmospheric pressure and gases at high altitudes?

Answer 17

• The atmospheric pressure is lower

- There are fewer molecules of gas.

Question 18

What happens to pressure as you dive further into the sea?

Answer 18

The pressure increase dramatically

Pressure below sea level = Atmospheric pressure+weight of water

Question 19

What is decompression sickness in divers?

Answer 19

• Nitrogen moves from high pressure in the lungs into the blood during a dive
• A slow return to the surface lets the nitrogen return to the lungs where it is breathed out
• A quick return doesn’t give the nitrogen enough time to leave the blood so instead it can form painful bubbles

Question 20

What are the features of oxygen binding?

Answer 20

• Reaction has to be reversible
• Oxygen must dissociate at the tissue to supply them
• Oxygen combines reversibly

Question 21

What are 2 examples of oxygen binding pigments?

Answer 21

• Haemoglobin: Tetramer to bind 4 oxygen molecules

- Myoglobin: binds 1 oxygen molecule

Question 22

What is myoglobin?

Answer 22

• Pigment found in muscles

- Contains 1 subunit of haem

Question 23

Why is myoglobin not a good carrier of oxygen?

Answer 23

It will not give up oxygen at the tissues due having a high affinity for oxygen even at low partial pressure. It acts as a storage molecule that will give up oxygen if the oxygen in the tissue gets very low. Also acts as a pigment for the muscle giving it the red appearance

Question 24

What is the structure of haemoglobin?

Answer 24

• Tetramer consisting of 2 alpha and 2 beta subunits
• Each subunit has a haem group and a globin group
• 4 oxygen molecules bind to each molecule of haemoglobin

Question 25

What are the forms of haemoglobin?

Answer 25

- Low affinity T state | - High affinity R state

Question 26

What happens to haemoglobin when the pO2 is low?

Answer 26

The haemoglobin shift to the low affinity T state so it is harder for the first O2 molecule to bind

Question 27

What happens as each O2 molecules bind to the haemoglobin?

Answer 27

The molecule becomes more relaxed and the binding of the next O2 molecule is easier

Question 28

What is the shape of the haemoglobin dissociation curve?

Answer 28

Sigmoidal curve

Question 29

What are the features of the haemoglobin dissociation curve?

Answer 29

- Saturation changes greatly over a narrow range | - Reaction is highly reversible and depends on pO2 levels

Question 30

What happens to the oxygen content and pO2 if the patient is anaemic?

Answer 30

- pO2 is normal | - Oxygen content is much lower

Question 31

What is the oxygen content of blood when the haemoglobin is saturated (13.3 kPa)? How would you work out the amount of oxygen given up?

Answer 31

-2.2 mmol/l if the Hb concentration is normal Each haemoglobin bind 4 oxygen molecules 2.2X4 = 8.8 mmol/l Amount of oxygen given up = ((100 - Saturation at Partial pressure in the site)/100) X 8.8

Question 32

What happens to the dissociating at tissue with a lower pO2 and the result of this on venous blood?

Answer 32

- Increased dissociation | - Lower saturation of venous blood

Question 33

What is the saturation of haemoglobin in venous blood?

Answer 33

-Over half the oxygen is still bound

Question 34

Tissue pO2 drops to 0 kPa. True or False

Answer 34

It cannot fall beyond 3 kPa

Question 35

What is the adaptation of very metabolically active tissue to allow them to receive sfficnet oxygen?

Answer 35

Very high capillary density so that pO2 will fall lower due to decreased diffusion distance

Question 36

What is the Bohr effect?

Answer 36

- pH affects the affinity of haemoglobin - Acid condition shifts dissociation curve to the tight - Lower pH promotes shift to the T state and higher ph promotes a shift to the R state

Question 37

Why is the Bohr effect beneficial to the metabolically active tissues?

Answer 37

-pH is lower in most metabolically active tissue so extra O2 is given up

Question 38

What is maximum unloading of oxygen?

Answer 38

- Occurs in tissues where pO2 can fall to a low level - In conditions where increased metabolic activity results in more acidic environment and higher temperature - Under these conditions about 70% bound oxygen can be given up

Question 39

In extreme exercise , metabolism can increase 10x but the cardiac output only goes up by 5x. What supplies the tissues with oxygen?

Answer 39

Tissues have improved extraction of oxygen. | This is due to a umber of factors

Question 40

What is the function of 2,3 BPG?

Answer 40

Increased 2,3-BPG shift the Hb dissociation curve for O2 to the right This allows more O2 to be given up to tissues because of a shift in the curve

Question 41

What is the result of carbon monoxide poisoning?

Answer 41

- Reacts with Hb to form COHb - Increased affinity for unaffected subunits for O2 - Therefore O2 is not given up at tissues - This is fatal if the HbCO is greater than 50%

Question 42

What is hypoxaemia?

Answer 42

Low pO2 in arterial blood

Question 43

What is hypoxia?

Answer 43

Low oxygen levels in the body and tissues

Question 44

What is cyanosis?

Answer 44

- Bluish coloration due to unsaturated haemoglobin | - Can be peripheral due to poor local circulation or systemic due poorly saturated blood in systemic circulation

Question 45

Why is cyanosis difficult to detect sometimes?

Answer 45

- Poor lighting | - Skin colouration

Question 46

What is pulse oximetry?

Answer 46

- Detection of level of Hb saturation by detection of difference in absorption of light between oxygenated and deoxygenated Hb - It only detect the pulsatile arterial blood - Venous blood and blood in tissues is ignored

Question 47

What is the limitation of pulse oximetry?

Answer 47

- It doesn't say how much haemoglobin is present | - It will not detect anaemia but just how well saturated a person blood is

Question 48

Why does cyanosis appear blue?

Answer 48

-Deoxygentated haemoglobin is less red that oxygenated haemoglobin