Control of circulation

Question 1

Why do we need control of circulation?

Answer 1

To maintain blood flow, arterial pressure, distribute blood flow, auto-regulate/ homeostasis and to function normally.

Question 2

Percentages of blood flow to organs?

Answer 2

Liver= 27%. Kidneys= 22%. Muscle= 15%. Brain=14%.

Question 3

What are arterioles known as? What is TPR? Determined by what? Major roles in what?

Answer 3

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.

Question 4

What happens when vascular smooth muscle contracts? VSm is never completely relaxed- known as what?

Answer 4

Radius decreases, resistance increases and flow decreases.

Myogenic tone.

Question 5

Flow of ECF from between capillaries determined by what?

Answer 5

TPR and number of pre-capillary sphincters.

Question 6

Valves within veins aid what? What also aids return?

Answer 6

Venous return against gravity and prevent back flow.

Skeletal muscle and respiratory pump.

Question 7

Excess fluid in lymphatics re-enters CVS via where? Uni-directional flow aided by what?

Answer 7

Thoracic duct; left subclavian vein.

Smooth muscle, skeletal muscle and respiratory pumps.

Question 8

What is the equation for blood pressure?

Answer 8

Cardiac output x total peripheral resistance= CO x TPR.

Question 9

What is the equation for pulse pressure?

Answer 9

PP= systolic- diastolic pressure

Question 10

What is the equation for mean arterial pressure?

Answer 10

MAP= Diastolic pressure+ 1/3PP

Question 11

What are the two laws for what governs flow?

Answer 11

Ohm’s law- F= pressure gradient/ resistance

Poiseuille’s equation- F= radius to the power of 4

Question 12

What is Starling’s law? Due to what relationship of muscle?

Answer 12

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.

Question 13

Due to increased end diastolic volume, what also increases?

Answer 13

Stroke volume and cardiac output (even if heart rate is constant.)

Question 14

What is preload? What decreases preload?

Answer 14

The volume of blood in the left ventricle which stretches the cardiac myocytes before contraction.
Vasodilation- venous return decreases.

Question 15

What is after load? What decreases after load?

Answer 15

The pressure the left ventricle must overcome to eject blood during contraction.
Vasodilation.

Question 16

What is contractility?

Answer 16

The force of heart contraction that is independent of sarcomere length.

Question 17

What is diastolic dispensability?

Answer 17

The pressure required to fill the ventricle to the same diastolic volume.

Question 18

What is compliance?

Answer 18

How easily the heart chamber expand when filled with blood volume.

Question 19

What is intrinsic auto regulation?

Answer 19

Arterioles vasoconstrict/ vasodilator in response to changes in resistance with aim of maintaining constant blood flow.

Question 20

What is myogenic auto regulation?

Answer 20

Blood flow is increased and stretches vascular smooth muscle- automatically constricts until diameter is normalised.

Question 21

What is hyperaemia? What is active hyperemia? What is reactive hyperaemia?

Answer 21

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.

Question 22

What are examples of vasoconstrictors?
Examples of vasodilators?
Compared to pulmonary circulation?

Answer 22

Endothelin-1 and internal blood pressure (myogenic contraction.)
Hypoxia, adenosine, bradykinin, NO, K+, CO2, H+ and tissue breakdown products.
Opposite in pulmonary circulation.

Question 23

What are circulating hormonal vasoconstrictors? Vasodilators?

Answer 23

Adrenaline, angiotensin II and vasopressin.

Adrenaline and atrial natriuretic peptide.

Question 24

Where are primary arterial baroreceptors found? Secondary ones found? What do primary ones do? What about cardiopulmonary baroreceptors?

Answer 24

In carotid sinus and aortic arch.
Veins, myocardium and pulmonary vessels.
Involved in short term blood pressure control.
Control long term BP.

Question 25

What two regions does the medulla have? Which one raises blood pressure? Does this by doing what?
Which region decreases blood pressure?

Answer 25

Pressor and depressor regions. Pressor region= sympathetic. By increasing vasoconstriction.
Depressor region= parasympathetic.

Question 26

What do central chemoreceptors in medulla respond to?

Answer 26

Decrease in pH due to CO2 diffusing across BBB reducing pH of CSF.

Question 27

When baroreceptors are stimulated what do they inhibit?

Answer 27

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.

Question 28

What two things also triggers vasodilation? What thing can be classed as a vasoconstrictor/ vasodilator depending on which receptors are present?

Answer 28

Prostacyclin/ prostaglandin I2(PGI2)- released by endothelial cells.
Adrenaline (epinephrine.)

Question 29

Where are peripheral chemoreceptors found? What are they stimulated by?

Answer 29

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.

Question 30

What is fainting known as? Physiology involved? Treatment?

Answer 30

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.

Question 31

What condition has similar symptoms and treatment to fainting? Common cause?

Answer 31

Orthostatic hypotension.

BP drugs, B blockers and vasodilators.