Oxygen In Blood

Question 1

What two states can haemoglobin have?
How does the affinity differ?

Answer 1

• T state: tense |no O2 bound | low affinity for O2
• R state: relaxed | O2 bound | higher affinity for O2

Question 2

Define cyanosis

Answer 2

Bluish colouration due to unsaturated haemoglobin
(Deoxygenated Hb is less red than oxygenated Hb)

Question 3

What is the pO2 in alevolar air?

Answer 3

13.3 kPa

Question 4

What is the pCO2 in alevolar air?

Answer 4

5.3 kPa

Question 5

What is the pO2 in venous blood?

Answer 5

6kPa

Question 6

What is pO2 in alevolar blood?

Answer 6

13.3kPa

Question 7

What is pCO2 in alevolar blood?

Answer 7

5.3kPa

Question 8

What is pCO2 in venous blood?

Answer 8

6kPa

Question 9

Why is haemoglobin needed to transport oxygen?

Answer 9

• Oxygen’s solubility in water is very low
• there is not enough dissolved O2 in blood to meet the body’s demand
• Hb is needed to meet the demand + transport oxygen

Question 10

Why is arterial blood brighter red than venous blood?

Answer 10

• Hb molecules with more O2 bound are brighter red
• oxygenated arterial blood is brighter than deoxygenated venous blood

Question 11

What is formed when O2 binds to Hb?

Answer 11

Oxyhaemoglobin

Question 12

Structure of haemoglobin

Answer 12

• 2 alpha + 2 beta subunits
• Each subunit has 1 haem group containing an iron ion to which O2 binds to

Question 13

Describe the shape of the haemoglobin-oxygen dissociation curve

Answer 13

Sigmoidal shape
First O2 is hard to bind
Easier to bind subsequent O2
Plateaus after 4 bind

Question 14

What is the cooperatively concept of haemoglobin?

Answer 14

• once the first O2 has bound, a small change in the structure of Hb is made
• this change makes it easier for O2 to bind
• it is hard to bind the first O2 molecule but subsequent binding is progressively easier
• as O2 dissociates, changes in the shape prompts remaining O2 to be released quickly

Question 15

How do you calculate the total O2 content of the blood?

Answer 15

Amount chemically bound + amount dissolved

Question 16

How much O2 is bound to Hb in arterial blood leaving the lungs?

Answer 16

8.8mmol/L

Question 17

Normal conc of Hb

Answer 17

2.2mmol/L

Question 18

Define hypoxaemia

Answer 18

Low pO2 in arterial blood

Question 19

Define hypoxia

Answer 19

Low O2 levels in body/tissues

Question 20

How does severe anaemia change oxygen in the blood?

Answer 20

O2 sats normal
pO2 normal
Reduced O2 content (less Hb)

Question 21

How low can tissue pO2 get?

Answer 21

Cannot fall below 3kPa

Question 22

What does a shift in the haemoglobin oxygen dissociation curve mean?

Answer 22

• R ightward shift: R educed affinity > O2 unloads
• leftward shift: increased affinity > O2 held on tighter

Question 23

What causes a rightward shift of the Hb-O2 curve?
How does this affect affinity?

Answer 23

Increased H+
Increased 2,3-DPG
Increased temp
reduces affinity

Question 24

What causes a leftward shift in the Hb-O2 curve?
How does this affect affinity?

Answer 24

Decreased H+
Decreased 2,3-DPG
Decreased temp
CO
increases affinity

Question 25

Why are metabolically active tissues at a lower pH?

Answer 25

- decreased pH shifts curve to right - reduced pH promotes the T state of Hb - lower affinity for O2 - O2 unloads

Question 26

What affect does 2,3 DPG have on affinity of Hb for O2?

Answer 26

Decrease affinity Rightwards shift

Question 27

What is the Bohr effect?

Answer 27

The rightwards shift of the Hb-O2 dissociation curve when H+ or CO2 bind to Hb causing the release of O2

Question 28

What is the haldane effect?

Answer 28

CO2 binding to Hb is higher with deoxygenated than oxygenated Hb

Question 29

What is the mechanism of the haldane effect?

Answer 29

**Deoxygenated Hb has higher affinity for CO2** Due to allosteric modulation of CO2 binding sites

Question 30

What affect does carbon monoxide have on arterial pO2?

Answer 30

No affect Dissolved levels of O2 remains the same

Question 31

Clinical presentation of carbon monoxide poisoning

Answer 31

- Headache - Nausea + vomiting - Slurred speech - Confusion

Question 32

Who are at an increased risk of CO poisoning?

Answer 32

Children

Question 33

How does carbon monoxide poisoning occur?

Answer 33

- CO binds to Hb - Hb has 200x affinity for CO than O2 - reduced O2 transport - increases affinity of unaffected subunits for O2 - leftward shift in Hb-O2 dissociation curve - reduced O2 release to peripheral tissues

Question 34

What is peripheral cyanosis due to?

Answer 34

Poor local circulation

Question 35

What is central cyanosis due to?

Answer 35

Poorly saturated blood in systemic circulation

Question 36

Ways to measure O2 saturation

Answer 36

Pulse oximetry Arterial blood gas

Question 37

Outline pulse oximetry

Answer 37

Non invasive way to measure percentage of Hb saturated with O2

Question 38

How does a pulse oximetry work?

Answer 38

Detects difference in absorption of light between oxygenated + deoxygenated Hb

Question 39

Downfalls of pulse oximetry

Answer 39

- Less accurate in darker coloured skin - Less accurate if patient has poor circulation to peripheries - affect by severe anaemia - may not be able to differentiate between Hb-CO or mathaemoglobins

Question 40

Outline an arterial blood gas

Answer 40

- Invasive - Sample of blood taken form artery (often radial) - analysed by machine to assess pO2, pCO2, bicarbonate + pH

Question 41

What cases have high levels of 2,3-DPG?

Answer 41

Anaemia High altitude

Question 42

Difference between partial pressure of O2, Hb saturation of O2 + content of O2

Answer 42

- **partial pressure**: pressure exerted by O2(**in kPa**) - **Hb saturation**: how saturated a Hb molecule is with O2 (**as a %**) - **content of O2**: conc of O2 (**in mmol/L**)

Question 43

Where do you take blood from in an arterial blood gas?

Answer 43

Radial artery

Question 44

If you cant take blood from the radial artery for a ABG, where else could you take blood from? Why is this not as good of an option?

Answer 44

- Brachial or femoral artery - They are less superficial and have delicate structures in close proximity which you do not want to damage such as nerves.