Week 1: Cardiovascular control Flashcards
Describe the location of the CNS cardiovascular control center. Describe the afferent inputs from the cardiovascular stretch receptors.
CNS CV control center: medulla
-general inputs: pain, temp, touch
AFFERENT INPUTS FROM CV
1. high pressure stretch receptors: inputs from carotid sinus via IX and aortic arch via X
2. low pressure stretch receptors: minute nerve terminals in walls near venoatrial jxns, afferents via vagus nerve (X)
Special
-peripheral chemoreceptors: afferents same as high pressure stretch receptors in carotid sinus and aortic arch
Describe the major efferent (effector) pathways from the center to the heart and the circulation.
Involves sympathetics and parasympathetics to the heart, sympathetics to vasculature,
affecting factors below:
1. Heart Rate
2. force of contraction
3. TPR (organ specific)
For low pressure stretch receptors: effector responses also involve blood volume regulation via renal changes, and atria also have endocrine like function, can release atrial natriuretic peptide into blood that has vasodilator effects on arterioles, diuretic and natriuretic effects.
Describe the major modulating inputs to the center from the higher CNS centers.
Cortex and hypothalamus
The principle determinant of the distribution of cardiac output at any instant is the “tone” of blood vessels. Define tone. Describe factors that influence tone and how inhibition of the sympathetic nervous system can alter tone.
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Relate carotid sinus nerve firing to aortic pressure and describe the physical factors that determines the afferent signal from the carotid sinus baroreceptor. Trace the effect of both an increase and a decrease in firing through the CNS center to the response of the heart and blood vessels.
- as aortic pressure increases (and heart rate increases), carotid sinus firing increases
- increased firing leads to decreased CO (rate, force) and decreased TPR
- decreased firing leads to increased CO and TPR
In terms of the effect on arterial blood pressure, explain why this baroreceptor reflex is described as a negative feedback system.
- In a negative feedback system, then secondary change is opposite in direction to the initiating change. If output increases, afferent increases and efferent decreases, resulting in decreased output.
- If arterial bp increases above normal, baroreceptors firing more, leading efferents to decrease (decreasing sympathetic output to heart and vessels, increasing parasympathetic to heart), resulting in decreased CO and TPR, and decreased arterial bp
Describe the nature of an effective stimulus to the atrial receptors. Indicate neural and endocrine aspects of these receptors.
- effective stimulus is stretch of walls of the atria, pulmonary vein junction, vena cava junction due to transmural pressure (inside minus outside)
- these are highly compliant structures, and a small change of transmural pressure yields large changes in volume.
- called volume receptors even though they respond to stretch.
- have both nerve terminals in the walls that have afferents to medulla via vagus nerve and endocrine response that releases ANP (atrial natriuretic peptide) directly into blood. is a diuretic, natriuretic, and vasodilator.
Describe the cardiovascular effects resulting from the peripheral chemoreceptor sensing a low oxygen state.
- low oxygen sensed by a peripheral chmoreceptor leads to afferents from aortic arch (via vagus) or carotid sinus (via CN IX) to increase their firing rate.
- increased afferent firing leads to vasoconstriction of arterial and venous vessels, and some increase in CO via hr and contractility.
On a so-called “guyton graph”, indicate any changes of these curves and of the stable operating point resulting from:
1) only an increase of contractility
2) only a decrease of total blood volume
- increase of contractility
- can occur with sympathetic stimulation or via positive inotropes
- new ventricular function curve (cardiac output curve) is above and to left of normal curve
- The new equilibrium point has increased CO and decreased RAP - decrease in total blood volume
- changes the venous pressure curve by moving it down and to the left of normal
- decreased cardiac output and RAP
Describe the cardiovascular events that occur when a normal individual goes form a horizontal position to a vertical position. Include in the describe the control mechanisms, the source of the signal, the operation of the CNS center and the result of the effector outflow.
- Most of the blood when lying or sitting pools in the abdomen area in the venous system. When someone stands from sitting, there is a drop in pressure since blood is pulled down towards the legs. There is a decrease in blood volume->decrease in venous pressure->decrease venous return to heart->decrease atrial pressure-> decrease ventricular EDV -> decrease SV-> decrease CO -> decrease arterial bp which leads to less firing from baroreceptors
- ->sympathetic response to increase TPR and CO (hr increases)
Describe high pressure stretch receptors.
baroreceptors.
- the most important for moment to moment regulation of CV system
- located in carotid sinus (branch of internal and external carotid artery) and in aortic arch
- have minute nerve terminals in walls
- afferents: carotid sinus via CN IX, and aortic arch via CN X
- stimulus: stretch of walls due to transmural pressure
- response: high bp–>increased firing of receptors to medulla, decreases efferent firing, decreases CO and TPR (via changes in symp/para to heart, symp to arterioles), leads to lower bp
Rank the usual importance of the high pressure receptors, low pressure receptors and chemoreceptors.
- high pressure stretch receptors: most important for moment to moment regulation of CV system.
- Low pressure receptors: regulation of blood volume
- peripheral chemoreceptors: only really important under severe conditions such as extensive loss and shock.
Describe the guyton graph.
X axis: venous pressure (also right atrial pressure)
y axis: cardiac output.
Two curves:
1. venous pressure curve- basically a line with a negative slope
2. Cardiac output curve or ventricular function curve: line with positive slope until venous pressure of ~4, then curves and plateaus
The two lines cross at an equilibrium point at RAP 2mmHg and CO 5L/min
How does heart failure affect the guyton curve?
Heart failure results in decreased myocardial contractility.
- acute heart failure: decreased contractility with no change in blood volume. ventricular function curve shifts down and to right- increase RAP with decreased CO
- long term heart failure: there is increased blood volume due to fluid retention by kidneys, also has up and to the right shift of venous pressure curve (in addition to down and to the right shift of ventricular fxn curve). As a result, new equilibrium point has increased RAP with same CO (in moderate heart failure).
- in more severe long term heart failure, there is decreased CO and increased RAP.
