Cardio X Flashcards
Adrenal glands are controlled by the […]
sympathetic nervous system
Describe the path of sympathetic control of adrenal glands, including the major chemicals and receptors involved.
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.
How does sympathetic control of the adrenal glands affect the heart? State the relevant factors and formulas.
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.
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
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.
Where are baroreceptors found?
On the aortic arch and on the carotid artery (carotid sinus baroreceptors).
How do baroreceptors work?
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.
How does the rate of baroreceptor firing vary with mean arterial pressure? Explain why.
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.
In the baroreflex, what are the changes can be observed after a low BP is signalled?
- Increased heart rate
- Increase in contractility
- Increased constriction of resistance vessels
- Increased constriction of capacitance vessels
Explain how, in the baroreflex, an increase in heart rate responds to a fall in blood pressure.
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.
Explain how, in the baroreflex, an increase in contracility is used to counteract a fall in blood pressure.
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.
Explain how, in the baroreflex, increased constriction of resistance vessels counteracts a fall in blood pressure.
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.
Explain how, in the baroreflex, increased constriction of capacitance vessels counteracts a fall in blood pressure.
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.
In the baroreflex, compare the effects that can be attributed to the sympathetic system vs the parasympathetic system.
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.
xfHow does the arterial blood pressure change without the baroreceptor reflex?
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.
The baroreceptor reflex is also called the […] reflex
buffer
What is the cause of labile hypertension?
Missing the baroreceptor reflex
The lack of a baroreceptor reflex causes a condition called […]
labile hypertension
Explain the renal control of blood volume mechanism in response to high blood pressure.
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.
What are diuretics used to treat? What mechanism do they affect and how?
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.
Draw a diagram showing the major organs involved in the RAA system and the major chemicals released.
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.
In the RAA system, what is the first response to a decrease in blood pressure? What effect does this have?
The kidney secretes renin, which will convert angiotensinogen, which was produced by the liver and was already in the blood, to angiotensin 1.