Control of circulation Flashcards
Why do we need control of circulation?
To maintain blood flow, arterial pressure, distribute blood flow, auto-regulate/ homeostasis and to function normally.
Percentages of blood flow to organs?
Liver= 27%. Kidneys= 22%. Muscle= 15%. Brain=14%.
What are arterioles known as? What is TPR? Determined by what? Major roles in what?
The principal site of resistance to vascular flow.
Total arteriolar resistance- total resistance to flow from aorta to vena cava- arterioles= most resistance.
Local, neural and hormonal factors.
Determining arterial pressure and in distributing flow to tissue/ organs.
What happens when vascular smooth muscle contracts? VSm is never completely relaxed- known as what?
Radius decreases, resistance increases and flow decreases.
Myogenic tone.
Flow of ECF from between capillaries determined by what?
TPR and number of pre-capillary sphincters.
Valves within veins aid what? What also aids return?
Venous return against gravity and prevent back flow.
Skeletal muscle and respiratory pump.
Excess fluid in lymphatics re-enters CVS via where? Uni-directional flow aided by what?
Thoracic duct; left subclavian vein.
Smooth muscle, skeletal muscle and respiratory pumps.
What is the equation for blood pressure?
Cardiac output x total peripheral resistance= CO x TPR.
What is the equation for pulse pressure?
PP= systolic- diastolic pressure
What is the equation for mean arterial pressure?
MAP= Diastolic pressure+ 1/3PP
What are the two laws for what governs flow?
Ohm’s law- F= pressure gradient/ resistance
Poiseuille’s equation- F= radius to the power of 4
What is Starling’s law? Due to what relationship of muscle?
The force of contraction is proportional to the end diastolic length of cardiac muscle fibre- more ventricle fills, harder it contracts.
Length-tension relationship of muscle.
Due to increased end diastolic volume, what also increases?
Stroke volume and cardiac output (even if heart rate is constant.)
What is preload? What decreases preload?
The volume of blood in the left ventricle which stretches the cardiac myocytes before contraction.
Vasodilation- venous return decreases.
What is after load? What decreases after load?
The pressure the left ventricle must overcome to eject blood during contraction.
Vasodilation.
What is contractility?
The force of heart contraction that is independent of sarcomere length.
What is diastolic dispensability?
The pressure required to fill the ventricle to the same diastolic volume.
What is compliance?
How easily the heart chamber expand when filled with blood volume.
What is intrinsic auto regulation?
Arterioles vasoconstrict/ vasodilator in response to changes in resistance with aim of maintaining constant blood flow.
What is myogenic auto regulation?
Blood flow is increased and stretches vascular smooth muscle- automatically constricts until diameter is normalised.
What is hyperaemia? What is active hyperemia? What is reactive hyperaemia?
Increase in blood flow.
Increase in blood flow when metabolic activity is increased.
Organ/ tissue has had its blood supply completely occluded, profound increase in its blood flow if blood flow is reestablished.
What are examples of vasoconstrictors?
Examples of vasodilators?
Compared to pulmonary circulation?
Endothelin-1 and internal blood pressure (myogenic contraction.)
Hypoxia, adenosine, bradykinin, NO, K+, CO2, H+ and tissue breakdown products.
Opposite in pulmonary circulation.
What are circulating hormonal vasoconstrictors? Vasodilators?
Adrenaline, angiotensin II and vasopressin.
Adrenaline and atrial natriuretic peptide.
Where are primary arterial baroreceptors found? Secondary ones found? What do primary ones do? What about cardiopulmonary baroreceptors?
In carotid sinus and aortic arch.
Veins, myocardium and pulmonary vessels.
Involved in short term blood pressure control.
Control long term BP.
What two regions does the medulla have? Which one raises blood pressure? Does this by doing what?
Which region decreases blood pressure?
Pressor and depressor regions. Pressor region= sympathetic. By increasing vasoconstriction.
Depressor region= parasympathetic.
What do central chemoreceptors in medulla respond to?
Decrease in pH due to CO2 diffusing across BBB reducing pH of CSF.
When baroreceptors are stimulated what do they inhibit?
The pressor region in the medulla and the renin-angiotensin and aldosterone systems. ADH also inhibited as it stimulates more water reabsorption which increases blood volume and pressure.
What two things also triggers vasodilation? What thing can be classed as a vasoconstrictor/ vasodilator depending on which receptors are present?
Prostacyclin/ prostaglandin I2(PGI2)- released by endothelial cells.
Adrenaline (epinephrine.)
Where are peripheral chemoreceptors found? What are they stimulated by?
In the aortic arch and carotid sinus( base of internal carotid artery at division between internal and external carotid.)
A fall in PaO2 and a rise in PaCO2 and a fall in pH causing BP to increase.
What is fainting known as? Physiology involved? Treatment?
Neuro-cardiogenic syncope. Fall in HR and venous pooling– CO and BP falls so perfusion to brain is reduced.
Lay supine and elevate limbs to increase VR.
What condition has similar symptoms and treatment to fainting? Common cause?
Orthostatic hypotension.
BP drugs, B blockers and vasodilators.
