Regional Circulations

Question 1

Why do organs have different amounts of blood flowing through them and why do they differ in their ability to increase the amount of blood flow

Answer 1

Different organs have differing amounts of blood through them as they provide differing amount of resistance to blood flow through them. Organs that provide high resistance like skeletal muscles have less blood flow

The 2 reasons as to why the organs would differ in their capacity to increase blood flow is:

1. Number of beta 2 receptors in the organs
2. Extent of sympathetic nervous sytem innervation in those organs

Question 2

Local influences

Answer 2

Organs can regulate their own blood flow by themselves. Blood flow through an organ is determined by the metabolic rate or rate of oxygen consumption. High metabolic rate allows the organs to dilate by releasing vasodilator metabolites

Question 3

What are the 3 organs that are most significant for local control

What does this mean for these organs

Answer 3

Brain, heart and kidneys

There is very little sympathetic nerve innervation in these organs so vasodilator metabolites play a key role in these organs

Question 4

What is the formula for O2 uptake

Answer 4

O2 uptake = Blood flow x difference in O2 content between arterioles and veins

Question 5

If kindeys can increase blood flow by only 16% does that mean they can increase O2 consumption by only 16%

Answer 5

No, they increase their capacity to uptake O2, which was given by the last equation, the veins as a result would have a less O2 content

Precapillary sphincters open and more blood flow through the capillaries take place

Question 6

What does the ability to extract oxygen depend upon and what is it independent upon

Answer 6

Precapillary sphincters that regulate the number of perfused capillaries

This is independent upon blood flow

Question 7

What is a fundamental difference in the heart and kidneys when they endeavor to increase O2 consumption

Answer 7

Heart does not have precapillary sphincters so it cannot increase O2 uptake. The only way heart increases O2 consumption is by increasing blood flow.

On the other hand kidneys cannot increase blood flow and hence they increase O2 uptake by opening more precapillary sphincters.

In other organs it is a combination of both, heart and kidneys are the extreme

Question 8

Autoregulation

Answer 8

Organs that regulate their own blood flow like brain, heart and kidneys can regulate their blood flow through them regardless of MAP. There is a range of autoregulation.

Autoregulation happens primarily independent of MAP in these organs

Question 9

What is the mechanism of autoregulation

Answer 9

1. Vasodilators
2. Myogenic response

Question 10

What is myogenic response

Answer 10

This experiment shows that once pressure is increased in an artery in the brain, the diameter of the artery initially goes up but then it goes down becuase the stretching causing increasing AP which causes the Ca gates to open up which causes influx of Ca and constraction of the vascular smooth muscles

Ca is pumped out during dilation

Question 11

What determines levels of vasodilators and how does this explain irreversible shock

Answer 11

Level of vasodilators depends upon their rate of production and the rate at which it is taken away by blood.

In shock blood pressure stays low for a certain time and it then just tanks resulting in irreversible shock. This happens becuase blood supply has been low enough to stop the rate of transport of vasodilators which causes a massive decrease in TPR causing irreversible shock

Question 12

What are some of the examples of vasodilators

Answer 12

1. Increased levels of lactic acid, protons and CO2
2. Adenosine levels rise when ATP formation is impaired (when you take off the last phosphate from AMP it forms adenosine). Adenosine is a potent vasodilator
3. K ions play an important role regulation of blood flow. There are 2 mechanism (i) when AP are fired some K leaks out of the cell causing local hyperkalemia which causes reduced Ca influx into the smooth muscles (know why) and this causes them to relax (ii) low ATP levels causes special K-ATP channels to open up causing local hyperkalemia

Question 13

What does all vasodilators do

Answer 13

Decrease Ca levels in vascular smooth muscles causing them to relax

Question 14

Active Hyperemia

Answer 14

Question 15

What happens to pulse pressure during exercise

Answer 15

It increases since there is an increase in inotropic state and there is a decrease in afterload so SV increases dramatically causing the pulse pressure to increase

Question 16

Is there increased sympathetic firing to the skeletal muscles arterioles during exercise

Answer 16

Yes there is, more NE is released but it is not effective as vasodilators are more potent.

Same thing happens in distributive shock, there is an increased sympathetic firing to the skeletal muscles but it is not effective as histamine and other vasoconstrictors are more effective

Question 17

What causes reactive hyperemia

Answer 17

Increase in the concentration of vasodilators

Question 18

Ischemia vs reactive hyperemia

Answer 18

Question 19

Focal active hyperemia in the brain

Answer 19

When we are performing a certain function, the part of the brain that is involved increases AP firing, causing local hyperkalemia which increases blood flow in that part of the brain

Question 20

Explain the dilemma of cereberal blood flow

Answer 20

Cereberal blood flow only starts to increase when the partial pressure of O2 drops below 50%. This is not a fault as owing to the non linear curve of O2 content and pO2 as O2 content gets only from 20 to 15mm with a 50% reduction in partial pressure

Question 21

What are cereberal arterioles supersensitive to

Answer 21

To an increase in pCO2

Question 22

Why is the brain so sensitive to CO2

Answer 22

Neurons are supersensitive to pH

Question 23

When does maximum flow in the left and right coronary artery occur

Answer 23

Maximum in the left coronary artery occurs during diastole as contraction of the left ventricle causes the artery to be compressed.

In the right ventricle maximum occurs during systole

Question 24

What is the absolute critical determinant of O2 consumption in the heart

Answer 24

Inotropic state

Question 25

What are some of the other effect

Answer 25

1. A rise in pressure of MAP
2. An increase in heart rate

These 2 have about the same O2 consumption effects

3. Increasing preload increases O2 consumption only slightly.

So increasing CO efficiently would be to increase preload, the most expensive would be to increase inotropic state

Question 26

Answer 26

Reperfusion injury

Question 27

Explain the blood constriction mechanism in lungs

Answer 27

In those alveoli that are hypoxic, there is constriction of blood flow so that blood goes to those alveli that are well ventilated

In edema or when living at high altitude, there is constriction of all arterioles to the lungs that causes high pulmonic pressure leading to right ventricular hypertrophy

Question 28

Portal circulation

Answer 28

Liver gets blood from hepatic artery and portal vein, however most of it is from portal vein, about 80%. Most of this blood is deoxygenated.

Liver cirrhosis increases the resistance of blood flow through the liver which causes portal hypertension. There is splanchnic edema and ascites development. Edema develops in the peroitoneal cavity. This causes decreased blood volume and systemic vasopressors are released to regulate MAP which further increases edema and causes a further increase in portal hypertension.

Blood pressure in the portal vein can get so high that it can cause the esophageal veins to rupture. This further leads to edema and possible a life threatening hemorrhage