Gas Transport in the Blood Flashcards
What are the two forms that oxygen travels in?
• In solution in plasma and bound to haemoglobin protein in red blood cells.
How much ml of oxygen dissolves in one litre of plasma.
• 3ml
What is meant by whole blood?
• when we take a count of the red blood cells and the plasma.
How much ml, out of 200ml, is bound to haemoglobin in red blood cells.
• 197ml
What percentage of carbon dioxide is transported in solution in plasma?
• 77%
What percentage of carbon dioxide is stored with haemoglobin?
• 23%
What is the relationship between alveolar partial pressure of oxygen and arterial partial pressure of oxygen when oxygen is transported without haemoglobin?
• Alveolar PO2 = Arterial PO2
What is the cardiac output at rest?
• 5L/min
What is the oxygen demand of resting tissues?
• 250 ml/min
What percentage of arterial oxygen is used when the peripheral tissues are at rest?
• 25%
What makes up a typical hamoglobin moelcules?
• It has 4 polypeptide chains, its got two alpha chains and two beta chains
What makes up a typical hamoglobin moelcules?
• It has 4 polypeptide chains, its got two alpha chains and two beta chains
What does each chain in haemoglobin contain?
• They contain a heme group.
What does each heme group contain?
• An iron molecule.
What does each heme group bind to?
• One oxygen molecule
What is the reaction between the haemoglobin and the iron molecule in haemoglobin known as?
• oxygenation
What is the amount of oxygen carried by haemoglobin determined by?
• it is determined by how much oxygen is present in the plasma.
What does partial pressure not describe?
• It doesnt describe the amount of oxygen wrapped up in haemoglobin, it describes the amount of oxygen not in solution in the plasma.
What determines the partial pressure of oxygen in the plasma?
• The partial pressure of oxygen in the alveoli (lungs)
What determines the partial pressure of oxygen in the alveoli?
• The alveolar ventilation
What is the movement of oxygen from the alveoli to the haemoglobin?
• The oxygen is pulled into the plasma and once the oxygen is in the plasma it is pulled into the haemoglobin.
What is fundamental in determining how much oxygen will bind to haemoglobin?
• the partial pressure of oxygen.
How long does it take for haemoglobin to be full saturated?
• 0.25s
What percentage of haemoglobin is saturated at the normal systemic arterial PO2 of 100 mmHg?
• almost 100%
At a partial pressure of 60mmHg what percentage of haemoglobin is saturated with oxygen, and what does this permit?
• Haemoglobin is 90% saturated with oxygen. This permits a relatively normal uptake of oxygen by the blood even when alveolar PO2 is moderately reduced.
What happens to haemoglobin when the partial pressure of oxygen falls below 60mmHg?
• The haemoglobin molecule loses its affinity for oxygen molecules.
- What percentage of saturation is haemoglobin at at the normal venous partial pressure?
• 75%
What is anaemia?
• any condition where the oxygen carrying capacity of the blood is compromised.
What are three examples of anaemia?
• iron deficiency, haemorrhage, vitamin B12 deficiency because it is need to make red blood cells.
What would happen to PO2 in anaemia?
• nothing, PO2 is normal despite total blood O2 content being low
Is it possiblt to have a normal plasma PO2, while total blood O2 content is low?
• Yes
Is it possible to have a low plasma PO2 and a normal total blood O2 content?
• no
Is it possible for red blood cells to be fully saturated with O2 in anaemia?
• Yes, red blood cells would still be fully saturated with oxygen as PO2 is normal. (except iron deficiency where there are less oxygen binding sites and so only the ones present are saturated.
What can change the affinity of haemoglobin to oxygen?
• A range of chemical factors - pH, PCO2, Temperature and DPG.
What causes the oxygen-haemoglobin saturation graph to move to the right?
• decrease in pH, increase in partial pressure of carbon dioxide and an increase in body temperature.
What is a shift in the oxygen-haemoglobin saturation graph to the right known as?
• The Bohr effect which aids oxygen unloading at the peripheral tissue
What is a complication of hypothermia?
• The affinity of haemoglobin at 20 degrees Celsius is 100% and so the haemoglobin doesn’t release any oxygen for the peripheral tissues even though the blood is jam packed with oxygen.
What is DPG?
• It is a byproduct of red blood cell metabolism.
What does an increase in DPG do?
• it decreases the affinity of haemoglobin for oxygen and so the haemoglobin releases some oxygen.
When do cells begin to produce more DPG?
• In situations of hypoxia
- What cells make the DPG?
• Erythrocytes
What forms carbon monoxide?
• incomplete combustion of carbon fuel.
Why is carbon monoxide toxic?
• Carbon monoxide binds to haemoglobin to form carboxyhemoglobin with an affinity 250 times greater than O2, binds readily and dissociates very slowly so very problematic once dissolved in circulation.
What are the symptoms of carbon monoxide inhalation?
• It is characterised by hypoxia, anaemia, nausea, headache, cherry red skin and mucous membranes. potential
Does carbon monoxide poisoning affect respiratory rate?
• No, because there is normal arterial CO2
What is the treatment for carbon monoxide poisoning?
• 100% oxygen.
Where does carbon dioxide diffuse from and where does it go?
• it diffuses from the tissues into the blood.
What percentage of carbon dioxide remains dissolved in the blood?
• 7%
What percentage of carbon dioxide combine with erthyrocytes, what do hey combine with and what do they form?
- 23%, combine with deoxyhaemoglobin and they form carbamino compounds
- 70% combine react with an enzyme called carbonic anhydrase which dissociates to yield bicarbonate and H+ ions.
What happens to the bicarbonate ions that are formed from carbon dioxide?
• They move out of the erythrocytes into the plasma in exchange for chloride ions (chloride shift)
What happens when the carbon dioxide is passed into the lungs via the pulmonary circulation?
• The haemoglobin releases the hydrogen ions, That causes the bicarbonate to shift back into the blood cells to neutralise those hydrogens, carbonic anhydrase works in reverse to give carbon dioxide and water from the carbonic acid that has formed.
What is the partial pressure of a gas in solution equal to?
The partial pressure in the gaseous phase that is driving the gas into solution.
What is the solubility of oxygen in water?
0.03ml/L/mmHg
PO2 in solution is said to be ….?
Equal to the PO2 in the gaseous phase that results in that oxygen concentration in the liquid phase
How does fatal air embolism occur?
Bubbles In the blood, gases travelling in the gaseous phase in the plasma
How much oxygen can a gram of haemoglobin carry?
1.34ml
What is the concentration of haemoglobin in the blood?
150g per litre.
What form does 92% of haemoglobin take?
HbA
Describe the types of haemoglobin that comprise 8% of total haemoglobin.
HbA2 (δ chains replace β), HbF (γ chains replace β), and glycosylated Hb (HbA1a, HbA1b, HbA1c)
What is the total contact time with alveoli?
0.75s
Is there a small or large drop in haemoglobin saturation when alveolar PO2 is reduced?
Small This permits a relatively normal uptake of oxygen by the blood even when alveolar PO2 is moderately reduced.
How does the affinity of HbF and myoglobin compare to HbA?
Higher affinity - necessary for extracting O2 from maternal/arterial blood.
What factors affect the affinity of haemoglobin to oxygen?.
Reflect conditions found in actively metabolising tissues and act to facilitate the dissociation of oxygen from haemoglobin. OR Can act to aid the collection of oxygen in the pulmonary circulation
What is oxygen dissolved in plasma influenced by?
(PO2) Composition of inspired air Ventilaiton Perfusion Oxygen diffusion between alveoli and the blood
What influences alveolar ventilation?
Airway resistance Lung compliance Rate and depth of breathing
What influences oxygen diffusion between alveoli and blood?
Surface area and diffusion distance
What is the fate of carbonic acid formed by carbon dioxide and water?
Dissociates to yield bicarbonate and H+ ions Most of the bicarbonate then moves out of the erythrocytes into the plasma in exchange for Cl- ions (chloride shift) & the excess H+ ions bind to deoxyhemoglobin. The reverse occurs in the pulmonary capillaries and CO2 moves down its concentration gradient from blood to alveoli.
How can breathing affect pH?
Hypoventilation and hyperventilation Plasma H+ will vary accordingly
What causes respiratory acidosis?
Hypoventilation, causing CO2 retention, leads to increased [H+] bringing about respiratory acidosis
What causes respiratory alkalosis?
Hyperventilation, blowing off more CO2, lead to decreased [H+] bringing about respiratory alkalosis.
What is the driving force of Oxygen in gas to the blood?
Driving force of Oxygen in gas to the blood?
What determines how much O2 binds to haemoglobin?
Partial pressure of the Oxygen in the gas mixture
What stores oxygen in muscle cells?
Myoglobin - high content in oxidative muscle fibres
What is the function of foetal haemoglobin?
Pulls oxygen from adult haemoglobin and delivers it to the foetus
Does anaemia affect PaO2 (arterial)?
No - there is no change in the ability of the oxygen to reach the blood
Is saturation of haemoglobin affected by partial pressure?
No
When temperature falls is it easier or harder for tissues to extract oxygen?
Harder
When will haemoglobin pair with CO2?
When oxygen level decreases
