Lecture 11 - Controlling regional blood flows Flashcards
Blood flow throughout the cardiovascular system is ___________
unidirectional
Arteries in the systemic circuit carry ….
Arteries in the pulmonary circuit carry ….
Oxygen rich blood
Oxygen poor blood
The heart has _____ chambers
4 chambers
Blood flow in pulmonary vs systemic circuit
Flow through the two circuits is equal
Blood flows away from the heart in ______ and towards the heart in _______
Arteries
Veins
The distribution of cardiac output
How flow of blood is distributed through the body to meet different needs
Mean arterial pressure
MAP drives unidirectional flow and therefore must be maintained, you need a big difference between the arteries and the veins to drive the flow. Therefore if MAP falls then the difference between arteries and veins is smaller and this would reduce the amount of flow through the system which is bad
MAP is a factor that we are trying to regulate at all times, comes down to the flow of blood into the arteries and the flow of blood out of the arteries
Maintenance is importance control mechanism as it allows each organ to control its own perfusion that is sufficient to meet its own metabolic needs
Blood flow in and blood flow out
Blood flow in - filled the arteries, increases arterial blood volume, raises arterial pressure
Blood flow out - drains arteries, decreases arterial blood volume, lowers arterial pressure
Arterial blood volume and pressure are determined by balance between blood flowing in and blood flowing out
Arterial blood volume and pressure is determined by…
balance between blood flowing in and blood flowing out
Why does arterial blood pressure need to stay high?
If it fell then there would be less flow in the system which would not be good for the organs/regions the blood is supplying
Pressure and control of flow equation
Q=ΔP/R where Q is flow, R is resistance and P is pressure
Low pressure and high pressure
At high pressure, we can have fine control over the flow in different directions - can reduce or increase the amount of resistance to flow. If it is low pressure then we get low flow everywhere
If resistance is small then you get a larger flow according to the equation. If resistance is large then you get a smaller flow
Fine vascular control by an organ depends on a sufficiently high arterial blood pressure
Parallel design of systemic circulation
Cardiac output is distributed to all organs - splitting of the aorta to multiple branches which each go to different organs and then reconnect on the other end to go back to the heart and we call this system parallel in design.
Continual branching of arterial network. Divides blood flow among the regional (organ) circulations. - branch out to individual organs and then come back together to meet at the heart
Distribution of cardiac output at rest
Systemic is very high pressure in the arteries and very low in the veins. In the systemic circuit there are little branches which are the mini circuits that are in parallel with one another. Whatever goes into one of these branches goes out the other side and all the branches meet back up and go into the right side of the heart and the process starts again
Distribution of cardiac output during exercise
When you start exercising, you are going to get a little bit of a sympathetic response, which is going to make my heart rate go up which is going to make stroke volume go up which is going to mean that cardiac output increases. Extra flow of blood is going to go to the skeletal muscle (to meet up with metabolic demands), more blood is going to be cycling around and going back to the heart, blood also carries heat and therefore need to move blood to the skin to maintain body temperature.
Overall trend is that move blood towards muscle and heart and move resources away from everything to do with rest and digest.
Heavy exercise just results in a massively increased blood flow but same trend as light exercise
Brain has very high energy demands so it has very high volume of blood coming at all times to meet these demands. Brain always protects its own blood supply over everything else.
Dont forget that a little bit of blood from the heart loops back because the heart needs its own circulation (coronary circulation )
During exercise increase blood flow …
Muscle
Heart
Skin
During exercise decreases blood flow …
GI tract
Kidneys
(most internal organs)
Constant blood flow to …
Brain
How is MAP controlled during exercise?
Systemic circulation - increased cardiac output (CO), constant mean arterial pressure (MAP), decrease in total peripheral resistance
Controlling MAP by decreasing TPR….
Does this to compensate..TPR is the resistance of all our vessels through our body to the movement of blood.
Makes sense because we want more blood pumping in from the heart and we want more of the blood moving around the system and going out towards the organ supply during exercise. Resistance is not falling for all the different arteries.
MAP equation
MAP = CO x TPR
Resistance involved in controlling regional blood flows
Even though TPR overall has decreased…Individual circulations can differ …
Muscle = increased flow= decreased resistance
Kidneys = decreased flow = increased resistance (because we don’t want blood going here while we are exercising because it has better places it can go)
Resistance increases for kidneys, intestines, spleen etc, and resistance decrease for muscle, heart and skin which allows for more flow to these organs
Arterioles
Resistance vessels - vessels that put the resistance on the movement of blood from the arteries out to the capillary beds that surround the different organs. They act as gate keepers and determine how open or closed the area is for the movement of blood
Arterioles have smooth muscle wrapped around the vessel
Capillary bed location
Capillary beds are very closely in contact with the different cells for optimal transfer of oxygen
Resistance to blood flow and vessel radius
R=1/(r^4)
Smaller radius, more resistance to fit movement of blood
Blood flow to an organ or region is controlled by ….
Adjusting arteriolar (‘vascular’) tone and radius
Vasoconstriction
Less flow as a result, smooth muscle around the vessel contracts which closes up the space and makes it more narrow
Vasodilation
Expansion of the blood vessels by the relaxation of the smooth muscle around the vessels
Vasoconstriction and vasodilation during exercise
The body takes advantage of vasodilation during exercise and vasoconstriction (determines where blood goes, controls it)
How does the internal radius of a vessel affect the resistance of that vessel? What is the equation that defines this relationship?
Increase in radius will reduce resistance. The change in radius alters resistance to the fourth power of the change in radius. For example, a 2-fold increase in radius decreases resistance by 16-fold. Therefore, vessel resistance is exquisitely sensitive to changes in radius.
How do arterioles constrict and dilate?
With the smooth muscle that surrounds these vessels
What is the rule of 16?
If we change the size of a vessel from a 1 to a 2 (halving or doubling), we change the resistance by a factor of 16 (a huge difference)
What controls vascular resistance?
Mechanical, response to force
From within the vessel (blood pressure) or from outside the vessel (e.g. swelling) - this is local
Neural - (central)
Vascular sympathetic nerves - communicate to the brain to various arterioles about whether they are vasodilation or vasoconstricting. Don’t just communicate to heart but to the arterioles themselves so can be used in fight or flight response
Humoral (blood) - (central)
Hormones released from remote organs such as adrenaline
