4. Haemoglobin and gas transport Flashcards
How much oxygen dissolves in plasma per litre?
3ml
What is oxygen carrying capacity in the blood with the help of haemoglobin?
200ml per litre
Is arterial partial pressure of O2 the same as arterial 02 content?
No Arterial partial pressure refers to the O2 in solution and is determined by the O2 solubility and the partial pressure of the O2 in the gaseous phase that is driving O2 into solution.
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 O2 solubility in water?
LOW 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
What is average cardiac output?
5 litres per minute
What is 02 demand of resting tissues?
250ml/minute
How much oxygen can a gram of haemoglobin carry?
1.34 ml
What is the concentration of haemoglobin in the blood?
150 grams per litre
How much arterial O2 is extracted by peripheral tissues at rest?
25% 1000 ml/min O2 transport far greater than the 250 ml/min demand
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 relationship between haemoglobin and plasma O2?
Hb effectively sequesters O2 from the plasma Partial pressure gradient is maintained - continues to suck O2 out of the alveoli until haemoglobin becomes saturated with O2
How long does it take for haemoglobin to become saturated?
0.25 seconds
What is total contact time with alveoli?
0.75 seconds
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. Include graph
When will haemoglobin be almost 100% saturated?
When the arterial partial pressure of oxygen is 100mm Hg
What is anaemia?
Any condition where the oxygen carrying capacity of the blood is compromised. (e.g. iron deficiency, haemorrhage, vit B12 deficiency)
What factors affect the affinity of haemoglobin to oxygen?
Chemical factors pH - Increase pH = Increase saturation (alkalosis) PCO2 - Increase = decrease in saturation Temperature - increase = decrease in saturation DPG I
What is the purpose of the factors that alter the saturation of haemoglobin?
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 synthesises DPG?
Erythrocytes
When does production of 2,3 - DPG increase?
When there is inadequate oxygen supply (heart or lung disease) and helps maintain oxygen release in the tissues. (Increasing affinity therefore decreases affinity for oxygen, making release more likely)
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 ventilaiton?
Airway resistance Lung compliance Rate and depth of breathing
What influences oxygen diffusion between alveoli and blood?
Surface area Diffusion distance
How is carboxyhaemoglobin made?
CO binds to haemoglobin
Which has higher affinity O2 or CO?
CO - 250 times greater
What are the symptoms of carboxyhaemoglobin?
Hypoxia and anaemia, nausea and headaches Cherry red skin and mucous membranes. POTENTIAL BRAIN DAMAGE AND DEATH
Why does breathing rate stay normal even when there is carboxyhaemoglobin?
Normal arterial PCO2
What is hypoxic hypoxia?
Reduction in O2 diffusion at lungs either due to decreased PO2atmos or tissue pathology
What is anaemic hypoxia?
Reduction in O2 carrying capacity of blood due to anaemia (red blood cell loss/iron deficiency).
What is Ischaemic (stagnant) hypoxia?
Heart disease results in inefficient pumping of blood to lungs/around the body
What is histotoxic hypoxia?
Poisoning prevents cells utilising oxygen delivered to them e.g. carbon monoxide/cyanide
What is metabolic hypoxia?
Oxygen delivery to the tissues does not meet increased oxygen demand by cells
What is the fate of the carbon dioxide that diffuses from tissue to blood?
7% remains dissolved in the plasma and erythrocytes, 23% combines with deoxyhaemoglobin to form carbamino compounds 70% combines in erythrocytes with water to form carbonic acid
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.
Why is pH normally stable?
All CO2 produced is eliminated in the air.
How can breathing influence PCO2?
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?
Partial pressure of the Oxygen in the gas mixture
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
What is the Bohr effect?
Shift of haemoglobin binding curve to the right
Higher PO2 needed for the same saturation
When will haemoglobin pair with CO2?
When oxygen level decreases
What pathologies can cause hypoventilation?
Emphysema Fibrotic lung disease
