L18 Cardiovascular control system

Question 1

What are the 6 elements of the CVS control system

RAAS also induced by reduced renal perfusion pressure and reduced NaCl delivery to Macula Densa cells

Answer 1

1. Arterial baroreceptors (blood pressure)
2. Cardiopulmonary receptors (blood volume)
   - —>
3. Brain+ Spinal cord (process info)
4. Vagal efferents: heart
5. Sympathetic efferents: heart, vasculature & kidneys (adjusts vascular flow to organs and acts directly)
   - -> 6. RAAS system (which increases gains by symp activity and is activated by symp activity)

Question 2

Where are the systemic arterial baroreceptors located, what is their firing related to and what is the path until output

Answer 2

Carotid sinus and Aortic arch (via aortic nerve).

1. Increase firing due to increased stretch on transmural stretch sensitive receptors (higher BP)
2. Signal activates inhibitory fibre on the sympathetic efferent, but directly activates vagal efferent

Therefore increase in BP=
decrease HR, contractility, peripheral vasoconstriction = BP back to normal.

Question 3

What are 3 characteristics of carotid sinus baroreceptors

Answer 3

1. Threshold: below 30-50 mmHg, a decrease in pressure doesn’t alter firing rate
2. Saturation: an increase pressure above 150-180 mmHg has no further effect on firing frequency
3. Rate sensitivity: For a given mean pressure, the rate of firing is greater for pulsatile pressure than steady pressure

Question 4

In hypertensive patients: at a given BP, how an increase in BP affect # of carotid sinus baroreceptor impulses fired

Answer 4

The baroreceptors have reset to maintain BP at a higher level along the curve, so for a given change in BP, the gain in impulse rate is a lot more shallow bc they are at a shallower part of the overall curve.

As a result they can have spikes in pressure without restraint bc the gain is diminished

Question 5

What is a therapy that could potentially help with resistant Hypertension

Answer 5

Electrodes to stimulation Sinus baroreceptors : did get reduction in some but SE facial nerve paralysis

Question 6

What are the 5 outputs when arterial bp sensed by baroreceptors falls

Answer 6

1. Increased HR and cardiac inotropic state
2. Graded constriction of precapillary resistance vessels in skeletal, splanchnic, cutaneous and renal circulations (not cerebral/coronary)
3. Venoconstriction (venous return)
4. Increased catelcholamine secretion by adrenal medulla
5. Increased circulating levels of ADH, Ang 2 and other hormones

Question 7

What do cardiac receptors measure, where are they, and what is the effect of activation

Answer 7

Send info about the filling of different chambers of the heart = blood volume (can be independent of pressure)

• A receptors (atrial filling/volume)
• B receptor (ventricle filling/volume)

Step activation of myelinated A receptor–> increase selective symp efferent

• increased HR,
• reduced renal sympathetic stimulation (less water retention)

Question 8

What do osmoreceptors sense (sensitive to small changes), where are they and what is the output

Answer 8

Osmoreceptors: in hypothalamus.

• sense changes in effective plasma osmolality by altering their volume.
• this modulates synthesis and release of ADH by posterior pituitary.

More ADH= more water retention

Question 9

What do peripheral chemoreceptors sense (sensitive to small changes), where are they and what is the output

Answer 9

In the Aortic and Carotid body increase PaO2 (pH, PaCO2)

When PaO2 is lo: stimulates increased sympathetic drive to heart + vessels–> increase blood pressure.

Question 10

What is the part of the brainstem which controls symp drive to vasculature (BP control) . Is this the only brain region that controls symp?

Answer 10

Rostral ventro-lateral medulla

There is 8-9 different brain regions that send different symp info to different regions allowing preferential control.