Pulmonary blood flow, gas exchange and transport Flashcards
In 1 litre of systemic arterial blood there is how many ml of O2
200 ml
how many ml of O2 is dissolved in free water of plasma?
3 ml
what happens if gases in the gaseous state are present in plasma
a fatal air embolism
bubbles in the blood
gas that travels in the blood travels in what state
solution
which two ways are blood supplied to the lungs
bronchial arteries- Supply oxygenated blood to the smooth muscle, nerves and lung tissue. Arises from systemic circulation- separate to pulmonary.
pulmonary circulation- gas exchange. Returns oxygenated blood to L atrium
difference between bronchial and pulmonary circulation
bronchial circulation is small, only carries about 1% of cardiac output. It is part of the general systemic circulatory system.
pulmonary circulation carries entire cardiac output from the right ventricle to the lungs
how does air diffuse across membranes?
down partial pressure gradient
what does A stand for in partial pressure
alveolar
what does a stand for
arterial blood
what does ṽ stand for
mixed venous blood
What are the normal values for partial pressure of O2 in both arterial and alveolar blood?
100 mmHg
13.3 kPa
this reflects/ is the same as the lung values
normal values for partial pressure of CO2 in both
arterial blood and alveolar blood
40 mmHg
5.3 kPa
this reflects/ is the same as the lung values
normal values for partial pressure of O2 in mixed venous blood- this reflects tissue values
40 mmHg
5.3 kPa
reflects/ is the same as the tissues value
normal values for partial pressure of CO2 in mixed venous blood
46 mmHg
6.2 kPa
reflects/ is the same as the tissues value
which 2 key features of alveoli help with gas exchange
thin membrane, short diffusion distance
larfe surface area
which has a higher partial pressure gradient? PO2 or PCO2?
PO2
250ml/min
what is emphysema
destruction of alveoli which reduces SA for gas exchange
what is pulmonary oedema
fluid in the interstitial space increases diffusion distance
describe what fibrotic lung disease is
thickened alveolar membrane slows gas exchange. Loss of lung compliance may decrease alveolar ventilation
what does fibrosis look like on chest x-ray?
shadows that indicate scar tissue- (not fully black which means it isn’t air)
describe the ventilation- perfusion relationship
ideally they compliment/ match each other concentration
ventilation= air getting to alveoli
perfusion= local blood flow
blood flow is higher than ventilation where in the lung?
At the base because arterial pressure exceeds alveolar pressure.
Gravity pulls blood to the base of the lung and so blood vessels push on alveoli. This compresses the alveoli
why is blood flow low at the apex of the lungs
because arterial pressure is less than alveolar pressure. This compresses the arterioles.
what does ‘shunt’ mean
moving blood from the right to the left side of the heart without it being properly oxygenated- movement of blood through areas of lung that are poorly ventilated
what happens when ventilation is less than blood flow
when ventilation decreases in a group of alveoli ultimately PO2 decreases and PCO2 increases
-blood is poorly oxygenated and this means it’s harder to remove CO2
shunt would occur
how does the body try to keep ventilation and perfusion matched?
pulmonary vessels constrict (bronchial constriction) in response to hypoxia and this diverts blood to better-ventilated alveoli. When pulmonary vessels constrict systemic ones dilate
what is alveolar dead space and when does it occur
alveoli that are ventilated but not perfused ie ventilation is higher than blood flow. Low blood flow around alveoli means gas exchange cannot occur and air can’t pass through
what is physiological dead space
alveolar DS + anatomical DS
what does haemoglobin in RBCs help increase
the O2 carrying capacity to 200ml/L
how is CO2 transported through blood
in solution in plasma
true or false: O2 solubility in water is low
true
what is the O2 demand of resting tissues?
250 ml/min
with red blood cells (increased haemoglobin) what happens to the amount of O2 getting to tissues
it increases- demand is met
what is reserved O2 used for
we can tap into it when we need to during periods of hypoxia but when O2 demand increases in tissues we tend to increase respiratory and cardiovascular rates to meet this instead
in systemic arterial blood, is there more O2 in haemoglobin or plasma
haemoglobin- it is more than 98% saturated normally
is pulmonary arterial pressure low
yes
how much oxygen does each litre of systemic arterial blood contain?
200 ml
how much oxygen is bound to each gram of haemoglobin?
1.34 ml
what is the process called where O2 binds to haemoglobin
oxygenation
what is the main determinant of the degree of haemoglobin oxygen saturation
PaO2 (arterial blood)
what two molecules have a higher affinity for oxygen than haemoglobin? and why?
myoglobin
foetal haemoglobin
higher affinity needed to extract O2 from maternal/ arterial blood to get O2 into muscle cells or foetus
what use is myglobin and HbF?
necessary for extracting o2 from maternal/arterial blood
if there is a low partial pressure of O2 in arterial blood then haemoglobin…
releases O2
if there is a high partial pressure of O2 in arterial blood then haemoglobin..
accepts/ takes up O2 from plasma
where is myoglobin found
oxidative muscle fibres
what is aneamia
Anaemia is defined as any condition where the oxygen carrying capacity of the blood is compromised
examples of aneamia
. iron deficiency, haemorrhage, vit B12 deficiency (needed to resynthesise RBC’s
Affinity of haemoglobin for O2 changes in response to certain ______ factors?
chemical
what is normal extracellular fluid pH
7.4
which way does the ox-haem curve shift when there is a decrease in pH (acidosis) but increase in CO2 and body temp?
to the right…
meaning haemoglobin has a lower affinity for O2 and so more O2 can be stripped and given to metabolically active tissues
which way does the ox-haem curve shift when there is a increase in pH (alkalosis),
but decrease in CO2 and body temp?
to the left…
meaning haemoglobin has a higher affinity for O2 and so more O2 is pulled from the plasma by the haemoglobin
what is 2,3-DPG?
A metabolite produced by RBCs
when do levels of DPG rise?
when RBCs are stressed ie when there is inadequate O2 supply
when DPG binds what happens to the affinity of haemoglobin for O2?
It decreases. Curve shifts to the R
Why is CO so dangerous?
it has an affinity for haemoglobin 250 times greater than O2 so it can bind readily but it dissociates very slowly- hard to get rid of.
how do you treat CO poisoning
provide 100% O2 to increase PaO2
when you have carbon monoxide poisoning, why do you still have normal respiration rate?
because you have normal PCO2 level
normal pO2, because the carbon monoxide concentration required to cause poisoning is low enough that it does not alter the amount of oxygen physically dissolved in the plasma.
what is hypoxaemic hypoxia?
most common
reduction in O2 diffusion at the lungs either due to decreased PO2 or tissue pathology
what is anaemic hypoxia?
reduction in O2 carrying capacity of blood due to anaemia (RBC loss or iron deficiency
what is stagnant hypoxia?
heart disease results in inefficient pumping of blood to lungs/around the body- cardiovascular problem
histotoxic hypoxia?
poisoning prevents cells utilising oxygen delivered to them e.g carbon monoxide/ cyanide
metabolic hypoxia
oxygen delivery to the tissues does not meet increased oxygen demand by cells
how is CO2 transported?
in solution
it goes down partial pressure gradient into plasma from tissues (biproduct of metabolic processes)
a lot of CO2 enters RBCs
alveolar vs anatomical dead space - what is the difference?
Alveolar dead space is sum of the volumes of those alveoli which have little or no blood flowing through their adjacent pulmonary capillaries, i.e., alveoli that are ventilated but not perfused, and where, as a result, no gas exchange can occur.
Anatomical dead space is the total volume of the conducting airways from the nose or mouth down to the level of the terminal bronchioles, and is about 150 ml on average. The anatomic dead space fills with stale air at the end of each inspiration, but this air is exhaled unchanged.
what is arterial blood?
the oxygenated blood in the circulatory system found in the pulmonary vein, the left chambers of the heart, and in the arteries
what % of arterial O2 is extracted by tissues at rest?
only 25%
200ml/L of O2 in blood and 5L/min cardiac output so 1000ml/min
the O2 demand of resting tissues is 250ml/min so that’s 25% of 1000
