Response to Exercise and Haemorrage Flashcards
What is dyspnoea?
Breathlessness
Is hyperventilation during exercise caused by using PO2 and producing more PCO2?
No because these values are virtually unchanged during exercise
Why might PCO2 fall a little during exercise?
Because Co2 is being blown off
Is hyperventilation during exercise causes by a change in H+ ion concentration?
No as it remains unchanged in the arterial blood
What is it about breathing that means there are oscillation in PO2 and PCO2?
Since there are more beats that there are breathes not every lot of blood going to the left atrium will have the same PCO2 and PO2 concentration which means there are oscillations in the PCO2 and PO2 on a beat by beat basis
How are these oscillations involved in influencing the effect on peripheral chemoreceptors and therefore breathing during exercise?
Excerise increases these ossilations which can change the activity of the peripheral chemoreceptors
Apart from the changes in the ossiclations in PO2 and PCO2 what 4 other factors influence breathlessness during exercise?
- Increased body temperature
- Neural input from limbs
- Secretion of noradrenaline and adrenaline
- Input from higher centres
Why does exercise lead to a fall in total peripheral resistance?
As muscle activity increases metabolite production increases which cause local dilation of arterioles
How does a fall in total peripheral resistance affect cardiac output?
Because since blood pressure = TPR x CO, CO must increase to maintain blood pressure
Is there a fall in blood pressure during exercise?
No
Why is there no fall in blood pressure during exercise?
Because systolic volume rises and diastolic volume falls so there is overall no change (BP = DBP + (MBP/3)
What would happen to lead to an increase in cardiac output when TPR decreases?
Starlings law of the heart says the more you stretch the ventriles the greater the force of contraction so if metabolite generation as a result of exercise leads to vasodilation and a decrease in TPR there is an increase venous return and therefore the ventriles are stretched more leading to an increased force of contraction (stroke volume) and since CO = SV x HR that leads to an increase in CO
Apart from increase in SV to increase cardiac output what is another response to the decrease in TPR
The increase in venous return and therefore increase in the force of blood being pumped out by the ventricles causes arterial stretch reflex which then increases HR and therefore CO
What is the problem with the starling mechanism of how exercise increases cardiac output?
The heart diameter of patients exercising does not increase
What is the evidence that the nervous system is involved in increasing CO?
Heart rate increases in anticipation of exericise (feed forward mechanism activating the sympathic nervous system)
Apart from increasing heart rate and stroke volume what 4 other things does activation of the sympathic nervous system cause during exercise cause?
- Vasocontriction of blood vessels in GI tract and kidneys to divert blood to the exercising muscles
- Increasing venous return
- Promotes sweating
- Promotes glucose release
What two ways does activation of the sympathetic nervous system increase venous return?
- Contraction of the skeletal muscle causes squeezing of the veins and venoconstriction
- Deeper breathing lowers the pressure in the thorax and draws blood back into the heart - the respiratory pump
What is a haemorrage?
A sudden loss of blood
What is the response to a sudden loss of blood and therefore blood pressure?
Baroreceptor activation
What does activation of the baroreceptors cause?
Increased activation of the sympathetic nervous system
Why does a loss of blood and therefore blood pressure trigger the baroreceptor to activate the sympathetic nervous system?
the SNS Increases heart rate and force of contraction (SV) leads to an increased CO an therefore increases blood pressure back to normal
Apart from increasing CO what else does the sympathetic nervous system do to increase blood pressure in respond to a haemorrage?
Causes vasoconstriction of the atrioles leading to an increase is TPR and therefore an increase in blood pressure
Are the baroreceptors only activated when blood pressure rises?
No they are activated when it falls in order to lower it back to normal
What formulae could be used to explain the reason why a decrease in blood volume leads to a decrease in blood pressure?
Because if blood volume decreases the gap between EDV and ESV decreases and since SV = EDV - ESV that means SV decreases and since CO = SV x HR, CO then decreases and since blood pressure = CO x TPR, blood pressure then decreases
Apart from sympathetic nervous system activation what are 3 other effects of the baroreceptor reflex in response to decreased blood volume and blood pressure?
- Venoconstriction to increase venous return
- Stimulation of adrenal medulla to release catechloamines
- Activation of the renin-angiotensin system to retain salt and water and increase blood volume
What two things does the sympathetic nervous system innervate in order produce its effect?
- Innervates the thoraco-lumbar outflow through noradrenaline which innvervates organs and the skin
- Innverates the adrenal medulla to release catechloamines
What is a problem involving the baroreceptor reflex of people subject to weightlessness/bed ridden?
The lack of challenge to the baroreceptor reflex (as its active when you stand up sit down) means it resets so when you stand up you feel dizzy
