Respiratory System - Lec 6 Flashcards
Explain the transport of oxygen to the peripheral tissues via tissue systemic capillaries
The oxygenated blood from the pulmonary capillaries will travel through the systemic circuit and to the tissue capillaries to deliver oxygen
The tissue capillaries allow the O2 to diffuse across the membrane into the IF following a pressure gradient (partial pressure of O2 on IF is variable amongst regions of tissue - AV. 40 mmHg).
The O2 will then diffuse from IF and into cells. We will find that the intracellular P O2 is always lower than IF because oxygen is always used by cells
What’s the partial pressure of oxygen in cells
Can be very variable (but lower than IF)
Ranging from 5 - 60 mmHg (av. 25 mmHg)
But literally a P O2 1-3 mmHg is suffiecnt to support the cellular processes, like metabolism
How is oxygen situated in blood for travel?
Oxygen can be found in 2 forms in blood
- physically dissolved
- bound to Hb molecules within erythrocytes
How much oxygen is actually in blood and how much is transported during a normal cardiac output?
There’s only 3mL of oxygen physically dissolved for every litre of blood, but there’s a P O2 of 100 mmHg in the arterial blood!
Normal Q = 5 L of blood/min, therefore 15 ml of oxygen is dissolved and is delivered to tissues
BUT normal oxygen consumption at rest should be around 250 ml/min
And this can be adhered to by oxygen being bound to Hb molecules (98.5% of oxygen is in this form, where 1 g of Hb is combined with 1.36mL of oxygen)
- 100 mL of blood has 15 g Hb (decreases if anemic )
- therefore, 100 mL of blood has 20.4 ml of oxygen bound to Hb
- therefore, 1 L of blood has 204 ml of oxygen
-therefore, normal Q = 5 L of blood/min which will now have has 1020 ml of oxygen delivered to tissues every min (60-70 times greater than dissolved form alone)
What’s the reaction that occurs where Oxygen is bounded to Hb
Reduced Hb + O2 <>HbO2 (Oxyhaemoglobin)
Each Hb bind with 4 molecules of oxygen
It’s a reversible reaction because we need to allow oxygen gas to diffuse across the systemic (tissue) capillary and into the IF, so oxyhaemoglobin would need to unbind from the oxygen in order to allow diffusion
DIFFUSION OF OXYGEN CAN ONLY OCCUR WHEN OXYGEN IS IN ITS DISSOLVED FORM IN THE BLOOD (hence for reversible nature)
Explain the axis on the oxygen-Hb dissociation curve
Y axis:
- % Hb saturation = proportion of Hb bound to oxygen. Have all the Hb become saturated with oxygen binding?
- Volume % of O2 in blood (oxygen saturation test)= how many ml of oxygen in 100 ml of blood is carried. Normally 20.4 ml of oxygen, and 15 g Hb in 100 ml blood, unless the person is anaemic (don’t have enough Hb). YOU CANT WORK OUT THE AMOUNT OF OXYGEN IN BLOOD UNTIL WE FIND OUT THE AMOJNT OF Hb IN BLOOD.
IE. a oxygen saturation test with 100% suggests that all oxygen molecules and bound to Hb, but we don’t know how much oxygen that is tho, unless we find out the amount of Hb (BECAUSE THE PERSON CAN BE ANAEMIC AND STILL HAVE 100% oxygen saturation)
x axis:
Partial pressure of oxygen in blood (systemic capillary region and pulmonary capillary region)
Explains on the concepts of features of the oxygen-Hb dissociation curve
You can see that the curve is much more flatter with very little deviation in Hb saturation between the P O2 of 70-100 mmHg, therefore, travelling to altitudes up to 3000m or experiencing a respiratory disease that reduces arterial P O2 to 70 mmHg will have no drastic effect on arterial blood content
The curve is steep in 10-50 mmHg range of P O2 because this is the the blood that has delivered oxygen to tissues that metabolise (and has become “deoxygenated”). SO IF THERES LESS OXYGEN, means Hb saturation (binding) will also decrease (that’s why it’s steep)
What’s the utilisation coefficient, how is it relevant to the curve?
So during rest, we have a P O2 of 40 mmHg (venous blood in systemic vessels), this indicates that we still have 75% of Hb still saturated (bound to oxygen),
Therefore, we’ve really only delivered 25% of our oxygen content to our tissue. 25% = 5 mL of blood from the 100 ml (you have 20 mL O2). And this is what we call the utilisation coefficient, since we delivered this to tissues
BUT the utilisation coefficient can increase greatly during exercise because more oxygen will be required by the muscles
What happens to the curve when you increase the P O2 to greater than 100 mmHg
Very little effect will be noticed as the individual has already reached 97.5% Hb saturation at 100 mmHg, thus, increasing oxygen supply won’t do anything since there aren’t any active sites on the Hb.
What factors can effect the affinity of oxygen for Hb?
Increase in P CO2 and decreased pH, increase in temp. at tissue level
- this will cause more oxygen to be unloaded (as there’s high metabolic activity occurring) than during controlled condition of the given P O2 on the curve, thus, the curve is moved more to the right and brought down
- occurs due to increase to metabolism (ie exercise)
- THUS O2-Hb affinity is decreased
- vice versa can occur
- so in the lungs, we see more of a controlled curve but in the tissues we see more of a rightward shifted curve as there’s high metabolic activity
2, 3-Bisphosphoglycerate (BPG)
- produced in red blood cells
- when oxygen levels decrease (chronic hypoxia), BPG levels increase and causes more oxygen to be unloaded into tissues
- moves curve to the right as well
- occurs in tissue with high metabolic activity
Why is carbon monoxide such a dangerous gas?
CO is produced through anaerobic reaction of combustion of organic matter (ie. wood, coal, natural gas, petrol)
It can bind to Hb active sites just like oxygen with a much greater affinity (200 timer greater affinity) to form carboxyhaemoglobin. Therefore, even small amounts of CO can deplete Hb of oxygen binding., OXYGEN CARRYING CAPACITY DECREASED
Literally a P CO of 0.8 mmHg, 0.1% of atmosphere conc (1/200th of P O2 in atmosphere) can bind to half of the Hb active sites.
Meaning if CO conc in atmosphere exceeds 0.15%, will be lethal.
Under these circumstances, P O2 still stays the same but it’s just it’s in very low content in blood due to affinity being less significant than CO
Therefore, CO causes hypoxia of tissues
Why does CO induced hypoxia not cause sensation of breathlessness?
process doesn’t occur as the molecule isn’t oxygen
Explain how CO2 is carried in the blood
CO2 is carried in 3 forms
- physically dissolved
- bound to Hb
- as bicarbonate ions
The amount of CO2 that’s physically dissolved is proportional to its P CO2. CO2 is more soluble that O2 but only 10% is able to dissolve
30% combines with Hb to form carbamino Hb (HbCO2)
- Reduced Hb has a greater affinity to CO2 than oxygen, thus, when HbO2 breaks apart in order for oxygen to diffuse out, this will allow CO2 from the tissue cells to diffuse across and readily bind to Hb more easily
60% of CO2 is carried in form of bicarbonate ions (most are) where the reactions go:
- CO2 + H2O <>H2CO3
- H2CO3 <> H+. + HCO3-
Carbonic anhydrase = enzyme that accelerates the rate of reaction In red blood cells
What muscles are involved in breathing?
Respiratory muscles (skeletal muscles) like the diaphragmatic and intercostal muscles contract during inspiration and so require somatic and motor neurone activation of muscular contraction
How is breathing done and how is it regulated?
Breathing is rhythmic, involuntary and occurs without conscious thought, therefore, because it’s involuntary it’s controlled by the brain stem rather than motor cortex
It’s regulated by
- increase with exercise, fear, arousal
- holding breath or hyperventilating
- cough (forced expiration)
