Lecture 11 - Controlling regional blood flows

Question 1

Blood flow throughout the cardiovascular system is ___________

Answer 1

unidirectional

Question 2

Arteries in the systemic circuit carry ….

Arteries in the pulmonary circuit carry ….

Answer 2

Oxygen rich blood

Oxygen poor blood

Question 3

The heart has _____ chambers

Answer 3

4 chambers

Question 4

Blood flow in pulmonary vs systemic circuit

Answer 4

Flow through the two circuits is equal

Question 5

Blood flows away from the heart in ______ and towards the heart in _______

Answer 5

Arteries

Veins

Question 6

The distribution of cardiac output

Answer 6

How flow of blood is distributed through the body to meet different needs

Question 7

Mean arterial pressure

Answer 7

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

Question 8

Blood flow in and blood flow out

Answer 8

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

Question 9

Arterial blood volume and pressure is determined by…

Answer 9

balance between blood flowing in and blood flowing out

Question 10

Why does arterial blood pressure need to stay high?

Answer 10

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

Question 11

Pressure and control of flow equation

Answer 11

Q=ΔP/R where Q is flow, R is resistance and P is pressure

Question 12

Low pressure and high pressure

Answer 12

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

Question 13

Parallel design of systemic circulation

Answer 13

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

Question 14

Distribution of cardiac output at rest

Answer 14

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

Question 15

Distribution of cardiac output during exercise

Answer 15

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 )

Question 16

During exercise increase blood flow …

Answer 16

Muscle
Heart
Skin

Question 17

During exercise decreases blood flow …

Answer 17

GI tract
Kidneys
(most internal organs)

Question 18

Constant blood flow to …

Answer 18

Brain

Question 19

How is MAP controlled during exercise?

Answer 19

Systemic circulation - increased cardiac output (CO), constant mean arterial pressure (MAP), decrease in total peripheral resistance

Question 20

Controlling MAP by decreasing TPR….

Answer 20

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.

Question 21

MAP equation

Answer 21

MAP = CO x TPR

Question 22

Resistance involved in controlling regional blood flows

Answer 22

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

Question 23

Arterioles

Answer 23

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

Question 24

Capillary bed location

Answer 24

Capillary beds are very closely in contact with the different cells for optimal transfer of oxygen

Question 25

Resistance to blood flow and vessel radius

Answer 25

R=1/(r^4)

Smaller radius, more resistance to fit movement of blood

Question 26

Blood flow to an organ or region is controlled by ….

Answer 26

Adjusting arteriolar (‘vascular’) tone and radius

Question 27

Vasoconstriction

Answer 27

Less flow as a result, smooth muscle around the vessel contracts which closes up the space and makes it more narrow

Question 28

Vasodilation

Answer 28

Expansion of the blood vessels by the relaxation of the smooth muscle around the vessels

Question 29

Vasoconstriction and vasodilation during exercise

Answer 29

The body takes advantage of vasodilation during exercise and vasoconstriction (determines where blood goes, controls it)

Question 30

How does the internal radius of a vessel affect the resistance of that vessel? What is the equation that defines this relationship?

Answer 30

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.

Question 31

How do arterioles constrict and dilate?

Answer 31

With the smooth muscle that surrounds these vessels

Question 32

What is the rule of 16?

Answer 32

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)

Question 33

What controls vascular resistance?

Answer 33

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