Lecture 6 - Carriage of O2 and CO2 in the blood Flashcards Preview

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Flashcards in Lecture 6 - Carriage of O2 and CO2 in the blood Deck (37)
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1

In what 2 forms is oxygen carried in the blood

dissolved in the blood
combined with haemoglobin

2

What is the relationship between temperature and proportion of gas dissolved?

amount of gas dissolved in solution is proportional to the temperature.
more dissolves at a lower temperature and depends on partial pressure also.

3

Volume of O2 in blood is

solubility (0.0232) x PO2 (Partial pressure)

4

Oxygen saturation equation

oxy haemoglobin/ (deoxy +oxy haemoglobin)

5

Volume of oxygen carrying haemoglobin

Saturation x concentration of haemoglobin (14) X hufners constant (1.39)

6

What are the different structures of haemoglobin

Primary, secondary, tertiary and quartenary

7

Primary structure of

141-146 AA's per chain

8

Secondary

globular structure

9

tertiary structure

crevice for haem and O2 binding

10

Quartenary structure

hb A 4 chains - 2 alpha and 2 beta chains

11

what does one haemoglobin molecule comprise of

4 globin chains
4 haem groups
4 iron atoms
4 oxygen molecules

12

What is the molecular basis of o2 binding?

o2 binding occurs in a crevice of haem
when in relaxed form (oxygenated) - o2 can access the binding site
when in a tense form (deoxygenated) - O2 is pushed out

13

Hb- O2 dissociation curve concept

the tense nature of deoxyhaemoglobin makes it difficult for oxygen to bind and so starts off having a low saturation. as oxygen molecules one by one the saturation shoots up, the oxy hb is relaxed and O2 binding sites become available to acces. this eventually happens until there is maximum saturation and curve levels off.

14

whys is systemic blood only 97% saturated?

because of a mix in the blood that crosses the pulmonary capillaries

15

What causes a right shift in haemoglobin dissociation curve?

Carbon dioxide
Acid (decrease in pH)
Diphospho-glycerate increase
Exercise
Temperature increase

16

What shifts the dissociation curve to the left?

an increase in pH
A decrease in temperature
a decrease in DPG

17

What happens in thalassaemia

absent globin chain

18

Defective blobin chain

sickle cell disease (HbS)
single amino-acid defect

19

Defective Fe atom (Fe3+)

Methaemoglobin
Drug induced: metHb does not carry oxygen

20

Wrong ligand

CO Hb
smoking/house fires
CO blocks O2 binding site

21

What is a buffer?

a solution that can minimise changes in the Free H+ concentration and therefore in pH

22

Example of a buffer

usually a weak acid and its base in equilibrium

23

Blood buffer systems in the body

includes proteins - carboxyl and amino groups at each end of the chain and basic?acidic

bicarbonate, plasma proteins, haemoglobin and phosphate

24

Normal Blood pH

7.35-7.45, H+ concentration 35-45 nmol-1

25

in what 3 forms is CO2 carried in the blood?

1. dissolved in the blood
temperature dependent
at 37 degrees = 3ml CO2 per dl of blood
2. Carbamino compounds
- bound to R-NH2 groups on proteins. includes terminal amino group and side chains of lysine and arginine - 4ml
3. as carbonic acid/bicarb
= 45 ml CO2

26

how is carbonic acid formed in the blood and broken down?

formed from co2 and water and is broken down by carbonic anhydrase into H+ ions and HCO3-

27

How are H+ ions and HCO3- handled from breakdown of carbonic acid buffered?

H + buffered by Hb ions.
HCO3- pumped out of RBC's in exchange for a chloride ion (Hamburger shift)

28

What happens in the CO2 dissociation curve and the haldane effect

since deoxygenated blood binds more H+ than oxyhaemoglobin, and forms carbamino groups readily, binding of O2 to haemoglobin reduces its affinity for CO2 which is the haldane effect. consequently, venous blood carries more CO2 than arterial blood.

29

What is Henderson-Hesselbalch equation

Measure of pH in a biological system, assuming all CO2 is converted into H2CO3 and using law of mass action, equation can be rearranged to:

pH= pK (6.1) + log10 [HCO3-]/[CO2]

30

Compensatory systems of acid base balance?

Respiratory: blood pH regulates ventilation and so controls PCO2 - rapid response

Renal: excretion of H+ in urine controlled by pH - slow response