- Pigment found in muscles - Contains 1 subunit of haem

Resp: Oxygen Exchange Flashcards by Kofi Antwi

What are the features of oxygen binding?

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

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What are 2 examples of oxygen binding pigments?

Haemoglobin: Tetramer to bind 4 oxygen molecules

- Myoglobin: binds 1 oxygen molecule

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What is myoglobin?

Pigment found in muscles

- Contains 1 subunit of haem

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Why is myoglobin not a good carrier of oxygen?

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

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What is the structure of haemoglobin?

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

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What are the forms of haemoglobin?

Low affinity T state

- High affinity R state

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What happens to haemoglobin when the pO2 is low?

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

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What happens as each O2 molecules bind to the haemoglobin?

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

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What is the shape of the haemoglobin dissociation curve?

Sigmoidal curve

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What are the features of the haemoglobin dissociation curve?

Saturation changes greatly over a narrow range

- Reaction is highly reversible and depends on pO2 levels

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

pO2 is normal

- Oxygen content is much lower

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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?

-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

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

Increased dissociation

- Lower saturation of venous blood

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What is the saturation of haemoglobin in venous blood?

-Over half the oxygen is still bound

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

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

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What is the Bohr effect?

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

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

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

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What is maximum unloading of oxygen?

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

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

Tissues have improved extraction of oxygen.

This is due to a number of factors

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What is the function of 2,3 BPG?

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

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What is the result of carbon monoxide poisoning?

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%

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What is hypoxaemia?

Low pO2 in arterial blood

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What is hypoxia?

Low oxygen levels in the body and tissues

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What is cyanosis?

Bluish coloration due to unsaturated haemoglobin

- Can be peripheral due to poor local circulation or systemic due poorly saturated blood in systemic circulation

Why is cyanosis difficult to detect sometimes?

- Poor lighting | - Skin colouration

What is pulse oximetry?

- 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

What is the limitation of pulse oximetry?

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

Why does cyanosis appear blue?

-Deoxygentated haemoglobin is less red that oxygenated haemoglobin

What are the features of carbon dioxide when compared with oxygen

It is more soluble It reacts chemically with water React with haemoglobin as well at a different site 2.5 times as much in arterial blood

CO2 control is more important for pH than for transporting it from the tissues to the lungs. True/False

True

What is the pH range that arterial blood must be kept in?

7.35-7.45

How does CO2 interact with arterial blood?

- Reacts with water in plasma to form carbonic action - Reacts with water in red blood cells. - It is not there as a waste product

What happens to carbonic acid in the blood?

Dissociates quickly to hydrogen ions and hydrogen carbonate ions.

The reaction that form carbonic acid from CO2 and water is irreversible. True/False

False. It reversible and rate of reaction depends on amount of reactants and products

What does the pH of plasma depend on?

-Depends on how much CO2 reacts to form H+ (dissolved CO2 pushes the reaction to the right and HCO3- pushes the reaction to the left) This depends on dissolved CO2 and concentration of hydrogen carbonate

What determines how much CO2 dissolved in the plasma?

-Partial pressure of CO2

What happens to plasma pH when pCO2 rises?

Becomes more acidic

What happens to the plasma pH when the pCO2 falls?

It will become more alkaline

What is the determining factors for dissolved CO2?

pCO2 of alveoli which is controlled by rate of breathing

What does high HCO3- prevent from happening in the blood?

Prevent nearly all dissolved CO2 from reacting by shifting the equilibrium

What determines the pH of arterial blood?

Ratio of HCO3- and pCO2.

What is the Henderson-Hasselbalch equation?

pH=pK+log([HCO3-])/(pCO2 X 0.23))

What enzyme speeds up the reaction that speeds up hydrogen carbonate production in red blood cells?

Carbonic anhydrase

How do the red blood cells produce hydrogen carbonate?

- H+ ions bind to the negatively charged Hb inside the red blood cells - Chloride-bicarbonate exchanger transports HCO3- out of red blood cells which is left front he reaction between CO2 and H2O.

Eythrocytes control concentration of HCO3- in plasma. True/False

False. They merely produce HCO3-.

What determine the amount of HCO3- that is produced by the erythrocytes?

Binding of H+ to haemoglobin

What is the main determant of plasma hydrogen carbonate? pCO2 or erythrocytes ?

Most of the HCO3- comes from the red blood cells

What is the role of the kidney in controlling HCO3-?

The kidney controls the amount of HCO3- by varying the excretion of bicarbonate. Concentration present in blood is controlled by the kidneys

How does hydrogen carbonate buffer extra acid?

Acids react with HCO3- to produce CO2. Therefore the bicarbonate decreases. CO2 produced is removed by breathing and pH changes are minimised

What determine arterial pCO2?

Alveolar pCO2 which determine how much CO2 is dissolved. This therefore affects pH.

pCO2 is higher in venous blood than arterial blood. True/false

True. It is returning from metabolically active tissue so more CO2 is dissolved

What does the buffering of H+ by the haemoglobin depend on?

Level of oxygenation

What happens to the amount of H+ ions that can bind to Hb as more O2 binds to Hb?

The haemoglobin switches into the R state | -Less H+ ions bind as a result

What happens to the amount of H+ ions that can bind to Hb as less O2 binds to Hb?

The haemoglobin switches to the T state | -More H+ ions bind

How does the amount of CO2 increase in plasma in the venous system? How does this affect the pH?

- Less O2 bound to Hb so haemoglobin switches to the T state - More H+ ions bind to Hb - More HCO3- can be produced and is exported to the plasma - Therefore more CO2 is present in plasma in venous system. -More HCO3- is also present so therefore ratio is similar. Small change in plasma pH as both CO2 and HCO3- have increased

What happens when venous blood arrives at the lungs?

- Hb picks up O2 and goes into R-state - Causes Hb to give up the extra H+ it took on at the tissues - H+ reacts with HCO3- to form CO2 - CO2 is breathed out

How are carbamino compounds formed?

- CO2 binds directly to amine groups on the globulin on Hb. - This contribute to the CO2 transport but it is not part of the acid base balance - This is CO2 given up at the lungs

Why are more carbamino compounds formed at the tissues?

-The pCO2 is higher and unloading of oxygen facilitates binding of CO2 to haemoglobin

What are the forms that CO2 is transported in?

- Dissolved CO2 - Hydrogen carbonate - Carbamino compounds