Cardio X

Question 1

Adrenal glands are controlled by the […]

Answer 1

sympathetic nervous system

Question 2

Describe the path of sympathetic control of adrenal glands, including the major chemicals and receptors involved.

Answer 2

The preganglionic axon releases ACh onto the adrenal medulla. This triggers the release of catecholamines, epinephrine and norepinephrine. These go all over the body and bind to alpha and beta-adrenergic receptors to have effects.

Question 3

How does sympathetic control of the adrenal glands affect the heart? State the relevant factors and formulas.

Answer 3

Norepinephrine and epinephrine bind to alpha and beta receptors (they are agonists). They increase heart rate, stroke volume, and TPR, which all serve to increase blood pressure.

HR, SV, and TPR will all increase, so MAP will increase.

Question 4

How do different blood pressure control systems vary in terms of time-scales of operation? How long does it take the following systems to activate:
a) Baroreceptors
b) Renin-angiotensin
c) Renal-body fluid pressure control

Answer 4

The range in time of these reflexes span from seconds the days. Baroreceptors activate within seconds, renin-angiotensin activates within minutes, and renal-body fluid pressure control activates within a few hours.

Question 5

Where are baroreceptors found?

Answer 5

On the aortic arch and on the carotid artery (carotid sinus baroreceptors).

Question 6

How do baroreceptors work?

Answer 6

These receptors are in the nerve terminals. When arteries have a change in stretch, the receptors will fire action potentials that will travel to the brain to signal this change.

Question 7

How does the rate of baroreceptor firing vary with mean arterial pressure? Explain why.

Answer 7

As arterial blood pressure increases, there’s an increase in the rate of firing. If you have elevated MAP, during the rising portion, the wall of the artery is being stretched more than normal. The transmural pressure is increased, which will cause the wall to stretch. The rate of firing will go up.

It is the other way around with reduced MAP. Fewer action potentials.

Question 8

In the baroreflex, what are the changes can be observed after a low BP is signalled?

Answer 8

1. Increased heart rate
2. Increase in contractility
3. Increased constriction of resistance vessels
4. Increased constriction of capacitance vessels

Question 9

Explain how, in the baroreflex, an increase in heart rate responds to a fall in blood pressure.

Answer 9

To increase the heart rate, the sympathetic nervous system activity goes up and parasympathetic tone (activity) will go down. This increased heart rate will increase cardiac output and thus increase MAP, balancing out the decrease in MAP. This is a negative feedback system.

Question 10

Explain how, in the baroreflex, an increase in contracility is used to counteract a fall in blood pressure.

Answer 10

An increase in contractility will increase the stroke volume, which in turn increases cardiac output and MAP, counteracting the drop in MAP that triggered the reflex. This is a negative feedback loop.

SV will increase, which will increase MAP.

Question 11

Explain how, in the baroreflex, increased constriction of resistance vessels counteracts a fall in blood pressure.

Answer 11

The constriction of the arteries and arterioles will increase the total peripheral resistance (TPR), which increases MAP and counteracts the decrease in MAP that triggered the reflex. This is a negative feedback loop.

Question 12

Explain how, in the baroreflex, increased constriction of capacitance vessels counteracts a fall in blood pressure.

Answer 12

The constriction of the veins and venules causes the pressure driving the blood back into the right atrium to increase. So, the perfusion pressure for that part of the circuit will increase, as will venous return. Since this blood will eventually get pumped out by the heart and there will be a higher volume of blood entering the left ventricle, the pressure of ejection will be higher and the stroke volume will increase. This will increase the MAP. This is a negative feedback system.

SV will increase, so MAP will increase.

Question 13

In the baroreflex, compare the effects that can be attributed to the sympathetic system vs the parasympathetic system.

Answer 13

Most of the changes observed in the baroreflex are the result of the sympathetic system. The only exception is the decrease in parasympathetic outflow to the heart, which will increase the HR.

Question 14

xfHow does the arterial blood pressure change without the baroreceptor reflex?

Answer 14

With the baroreflex, the range of arterial blood pressure remains within a fairly narrow range. Without it, the blood pressure is all over the place. The baroreflex converts the naturally fluctuating blood pressure into a more standardized range. It’s buffering them. This is why this is often called the “buffer” reflex as well. However, note that MAP does not change either way.

Question 15

The baroreceptor reflex is also called the […] reflex

Answer 15

buffer

Question 16

What is the cause of labile hypertension?

Answer 16

Missing the baroreceptor reflex

Question 17

The lack of a baroreceptor reflex causes a condition called […]

Answer 17

labile hypertension

Question 18

Explain the renal control of blood volume mechanism in response to high blood pressure.

Answer 18

If you increase arterial blood pressure (and thus the pressure in the renal artery), the kidneys extract more water from the blood, which becomes urine that you excrete (pressure diuresis). Your urine volume will go up and plasma volume will go down.

Since the plasma is 60% of the blood volume, the blood volume will go down. This will decrease the venous pressure and, consequently, the venous return. If the blood coming into the heart is less, the end-diastolic volume right before contraction will be less too. This will decrease the stroke volume by the Frank-Starling mechanism. If you increase stroke volume, CO will decrease, which will in turn decrease MAP. This is a negative feedback loop.

Question 19

What are diuretics used to treat? What mechanism do they affect and how?

Answer 19

They are used to treat high blood pressure (hypertension). It affects the renal control of blood volume, making the patient urinate more so that more water is extracted from the blood stream, thus lowering the blood volume, and ultimately the MAP.

Question 20

Draw a diagram showing the major organs involved in the RAA system and the major chemicals released.

Answer 20

Kidney releases renin.
Liver releases angiotensinogen.
Renin converts angiotensinogen to angiotensin 1.
Angiotensin 1 gets converted to angiotensin 2 by ACE enzyme in the lung.
Angiotensin 2 goes to constrict arterioles, to the brain, and to the adrenal glands.
In the brain, it will cause the release of vasopressin (ADH). This will decrease H2O excretion.
In the Adrenal glands, it will cause the release of aldosterone. This will decrease Na+ excretion.

Question 21

In the RAA system, what is the first response to a decrease in blood pressure? What effect does this have?

Answer 21

The kidney secretes renin, which will convert angiotensinogen, which was produced by the liver and was already in the blood, to angiotensin 1.

Question 22

What is the role of the lungs in the RAA system? What are the major enzymes and chemicals involved and their destination?

Answer 22

It will convert the angiotensin 1 (produced from renin converting angiotensinogen) to angiotensin 2 using the ACE enzyme. Angiotension 2 will go to the arteries, to the brain, and adrenal gland.

Question 23

What is the effect of aldosterone-receptor antagonists? What system do they impact?

Answer 23

They impact the RAA system. They bind to aldosterone receptors and block aldosterone, so that it can’t increase the blood pressure. They therefore cause the blood pressure to fall.

Question 24

What is the effect of AT-II receptor blockers? What system do they impact?

Answer 24

They affect the RAA system. They bind to angiotensin 2 receptors all around so it can’t bind to anything. So the AT2 will just float around and will not be able to exert its effect. The blood pressure will therefore fall.

Question 25

What is the effect of ACE inhibitors? What system do they impact?

Answer 25

They impact the RAA system. They inhibit the action of ACE, so angiotensin 1 can’t be converted into angiotension 2, which is the active compound that causes blood pressure to rise. The blood pressure will therefore fall.

Question 26

What is the effect of renin inhibitors? What system do they impact?

Answer 26

They impact the RAA system. If you inibit the action of renin, you will make less angiotensin 1 and thus less angiotensin 2, so the blood pressure will drop.

Question 27

What is orthostatic hypotension?

Answer 27

It is when your blood pressure drops when you stand up after sitting/lying down.

Question 28

How does the arterial blood pressure change when you stand up?

Answer 28

As the person stands, there’s immediately a fall in the blood pressure. If you did not have a baroreflex, the blood pressure would keep falling, but instead it comes back up.

The systolic pressure has gone down a little and the diastolic pressure

Question 29

Why does blood pressure fall when you stand up?

Answer 29

When you stand, gravity is pulling down on the blood in your body. The hydrostatic pressure is about 80 mm Hg at your feet. The veins have high compliance, so a small change in pressure causes a big change in volume. So these veins stretch out more the lower in the body you go, collecting a lot of blood in the lower extremities. This causes a decrease in the central blood volume.

Question 30

How does standing up affect the central blood volume?

Answer 30

The central blood volume drops significantly, as the hydrostatic pressure caused by gravity after you stand causes blood to flow into the veins in the lower body and out of the thorax, lungs, heart, and great vessels.

Question 31

How does the right atrial pressure change after standing up? Explain why.

Answer 31

The right atrial mean pressure drops significantly, as the migration of blood towards the lower body means that there is temporarily less blood coming back into the heart than usual. This change in volume will cause a large change in pressure.

Question 32

How do cardiac output and stroke volume change after standing up? Explain why.

Answer 32

Cardiac output decreases to 0.75 of what it was, while stroke volume decreases to 0.5 of what it was. This is because with the decrease in central blood volume, less blood is coming back into the heart. Therefore, the end diastolic volume will be lower and the stroke volume will be lower. The lower stroke volume also causes cardiac output to be lower. There is also an increase in venous constriction (baroreflex) that boosts the stroke volume.

Question 33

After standing up, why does cardiac output decline to 3/4 of what it started as despite the halving of the stroke volume? What mechanism is responsible for this?

Answer 33

There’s an increase in heart rate that compensates and reduces the change in cardiac output. This increase in the heart rate is due to the action of the baroreflex (which also boosts the stroke volume)
CO = HR x SV

Question 34

How does the heart rate change after standing up? Explain why.

Answer 34

The heart rate increases up to 1.5X what it started as. This is due to the action of the baroreflex, which increases the sympathetic tone and decreases the parasympathetic tone to increase the heart rate.

Question 35

How does MAP change after standing up? Explain why.

Answer 35

It stays the same (despite the drop in cardiac output). This is because the TPR increases due to the action of the baroreflex, which increases via arteriolar constriction to compensate for the decline in blood flow.

Question 36

How do the splanchnic and renal blood flow change after standing up? Explain why.

Answer 36

They both decline, because the blood flow decreases.

Question 37

What must be done in order to avoid orthostatic hypotension?

Answer 37

You must flex your calf muscles to utilize the muscle pump. The muscle pump brings all the variables that changed after standing up back to normal.

Question 38

Explain how muscle pumps work to avoid orthostatic hypotension

Answer 38

In the legs, there are venous valves. Venous valves allow the blood to flow one way towards the heart.

If you contract the muscles in your calf, the muscles will squeeze down on the vein and the pressure will go up, opening the top valve and closing the bottom valve. This will pump more blood into the heart and everything will increase. The MAP will not fall so low that you faint.

Question 39

Aside from the decrease in central blood volume, what is the other way in which standing up affects the blood pressure?

Answer 39

When you’re standing, there’s a high pressure both on the arteriolar and venous side. This pressure gets transferred to the capillaries.

If you increase the pressure in the capillaries, due to Starling forces, you will leak water out of the capillaries. After several minutes of standing, you’ve lost quite a bit of water. The blood pressure thus decreases.

Question 40

How can the muscle pump be used to reduce capillary leakage?

Answer 40

You squeeze your calf muscles (muscle pump) and pump blood out of the vein, so the pressure in the vein drops. This reduces pressure in capillaries, which stops the flow of water out of the vessels, since the capillaries normally cause flow of water out due to the hydrostatic pressure.

Question 41

Where does the fluid lost through the capillaries from standing up go?

Answer 41

It goes into the lymphatic system and eventually gets dumped back into the veins.

Question 42

Fluid returns into the veins from the lymphatic system via the […]

Answer 42

thoracic duct and right lympatic duct

Question 43

What is the formula for maximum heart rate?

Answer 43

Max HR = 220 - age (years)

Question 44

How does heart rate change during exercise? Why?

Answer 44

As you work at a higher intensity, the power (work/unit time) increase and the heart rate goes up more or less linearly. Heart rate goes up because you have a decrease in the vagal tone and an increase in sympathetic tone, which both work to increase heart rate. At maximum power, HR is 3X higher than at rest.

Question 45

How does stroke volume change during exercise? Explain why.

Answer 45

Stroke volume does go up with power because that increase in sympathetic activity from the exercise is increasing the contractility of the muscle, so the stroke volume will increase.

Unless you’re a well-trained athlete, there’s always an eventual fall in stroke volume at very high heart rates despite the increase in contractility. This is because you decrease the duration of the systolic period and an even further decrease in the duration of the diastolic period. Remember that the ventricles are filled during the diastolic period, so if this is shortened, the end-diastolic volume will fall and through the Frank Starling mechanism the heart will contract less strongly and the stroke volume will fall.

Question 46

How does cardiac output change during exercise? Explain why.

Answer 46

The cardiac output continually rises linearly, largely due to the increase in the heart rate. They are directly proportional (3X increase in heart rate = 3X increase in cardiac output).

Question 47

How does mean arterial blood pressure change during exercise? Explain why.

Answer 47

MAP is only 1.2X more than it was before. The systolic pressure rises quite a lot, while the diastolic pressure does not. The small increase is due to the balance between the increase in the cardiac output (x3) and the decrease in the TPR (0.4) due to skeletal muscle vasodilation.

Question 48

How does TPR change during exercise? Explain why.

Answer 48

The TPR massively falls to 40% of its original value. Why? When you start to exercise, your muscles are producing waste products and the pO2 in the tissues is going down. So you get local metabolic control where there is a massive increase in the flow of blood to the exercising blood due to dilation (which decreases resistance).

Question 49

How does oxygen consumption change during exercise? Explain why.

Answer 49

Oxygen consumption increases linearly as work increases.
If CO goes up by a factor of 3, you’re bringing 3X as much oxygen, so you would expect OC to increase by 3. Why does it increase by a factor of 9? For every mL of blood going by, you’re taking out 3X as much oxygen from that blood.

At rest, in every 100 mL of arterial blood there is 20 mL of oxygen. On the venous side, 15 mL is left, so the arterio-venous difference between them is only 5 mL/100 mL of blood at rest. The extra oxygen therefore comes from a higher arteriovenous oxygen difference.

Question 50

How does the arteriovenous oxygen difference change during exercise?

Answer 50

The arteriovenous oxygen difference rises from 5 to 15 ml O2/100 mL of blood.

Question 51

How does the breakdown of regional blood flow change during exercise? Where are the most major increases and decreases?

Answer 51

If you do strenuous exercise, most of the blood goes to the muscles. The increase of blood flow to the muscles is by a factor of 12.

You also get a big increase in the flow to the skin by a factor of 5. Why? Muscle is not an efficient engine. Most of the energy gets converted into heat, so if you were to exercise at a strenuous level. There is a dilation in the vessels of the skin and more blood flow.

There is also increase in flow to heart muscle, which is contracting at a faster rate and at a higher force. The heart needs the extra blood, as it has no stores of fuel.

There’s a fall in the flow of blood to the kidneys and organs, because there’s constriction there to keep the TPR up to keep the blood pressure from falling. If there were no constriction in the organs and non-exercising muscle, the TPR would not be as high and the MAP would fall in heavy exercise

Question 52

How does endurance training affect cardiac output and workload?

Answer 52

Training = can do greater amount of work because maximum CO is increased. The maximum workload is larger in trained individuals and they can reach a higher CO.

Question 53

How does endurance training affect heart rate during exercise? Explain why.

Answer 53

Note that training has no effect on your maximum heart rate.

At the same workload, an untrained person will have a higher heart rate than a trained person. Why? Because at this workload, whether you’ve trained or not, you need the same amount of oxygen consumption and CO. Since cardiac output remains the same, stroke volume had to have gone up.

Question 54

How does endurance training affect stroke volume at a given workload (what is this phenomenon called)? Explain why.

Answer 54

Looking at stroke volume at a given workload, a trained person will have a higher stroke volume. This higher stroke volume is because the contractility of the heart has increased NOT because there are more heart cells, but because each of the heart cells becomes larger (hypertrophy), leading to more ventricular muscle (bigger ventricle). This is also why there’s a fall in the resting heart rate.