Cardio 9 Flashcards
In addition to the baroreceptors, what is another rapid response system to pressure changes?
The peripheral chemoreceptors
Where are the peripheral chemoreceptors and what do they do?
They are in the carotid and aortic bodies
They sense PO2, PCO2 and pH to act on breathing as well as increasing HR
What are the two systems that are important in long-term control of mean BP?
Pressure diuresis
Renin Angiotensin Aldosterone (RAA) system
When is pressure diuresis effective? why?
It is effective at high arterial pressure since the system relies on pressure “pushing out” more fluid. At low pressure, no extra volume will be pushed out
Explain how a Pressure diuresis reaction would work
High arterial pressure causes more urinary loss of sodium and water, and everything else in order drops:
plasma volume –> BV –> VP –> VR –> End-diastolic volume
Because of the FS mechanism, SV drops and CO drops
Overall, having a negative feedback loop where MAP is dropped to a level where diuresis is no longer happening
What are the three systems important in the RAA system? what re their primary function?
- Pressure sensing in the kidneys via filtration rate signalling release of RENIN
- Pressure sensing in the brain via
- osmoreceptors
- Baroreceptors resulting in ADH release (especially in large fluid loss) - ALDOSTERONE release from the adrenal gland, stimulated by renin release
What class of drugs exploits the pressure diuresis system to lower BP?
DIuretics
What will be the effects (↓ or ↑) of releasing Renin:
Low MAP: ↑ Renin: ↑ MAP
High MAP: ↓ Renin: ↓MAP
What will cause Renin release?
a decrease in MAP, sensed by a low Na+ in filtrate
What happens once Renin is released into circulation?
(KIDNEY) Renin converts angiotensinogen (LIVER) into angiotensin I
in the LUNGS, ACE (enzyme) converts angiotensin I into angiotensin II, which is the active form, it’s a vasoconstrictor (↑ TPR = ↑ MAP)
What will cause ADH release? Where is it released from?
- Low output from the baroreceptors (DROPS in blood volume)
- Circulating angiotensin II
Released from the pituitary gland?
What happens once ADH is released into circulation?
ADH is a vasoconstrictor that will decrease renal Na+ and H2O excretion, resulting in increased
PV –> BV –> VR –> end-diastolic volume and the FS mechanisms will increase SV and so CO
What will cause aldosterone release? Where is it released from?
A low MAP results in increased renin and angiotensin II, which is the stimulus here. Aldosterone will be released from the adrenal gland
What will be the result of releasing ADH:
Low MAP: ↑ ADH: ↑ MAP
High MAP: ↑ ADH: ↓MAP
How does aldosterone wcause water retention?
It binds to receptors in the kidneys to cause Na+ and H2O retention to increase Co and so MAP
What will be the result of releasing aldosterone:
Low MAP: ↑ aldosterone: ↑ MAP
High MAP: ↑ aldosterone: ↓MAP
What are the four main classes of hypertension drugs?
- Aldosterone receptors antagonist
- Angiotensin II receptor antagonist (ARBS)
- ACE inhibitors
- Renin inhibitors
At the level of arterial blood pressure, how can we tell that the baroreflex is in action when standing up?
The systolic pressure drops a little, and the diastole pressure increases a little; if it wasn’t for the baroreflex, there would be a more significant drop –> MAP stays unchanged
What is orthostasis hypertension?
A sudden blood pressure drop when standing up
Why is there a pressure drop when standing up?
Veins have a high compliance. Because of that, a small change in pressure causes a large change in volume. All of this results in blood pooling in the legs.
This decreases VR, CO and so SV and MAP
What are the two things that the baroreflex needs to do to compensate for the drop in SV when standing up?
Increase HR
Increase contractility to increase TPR
What explains that SV(standing)=0.5 SV(laying) BUT CO(standing)=0.75 SV(laying)?
by compensating and increasing HR and TRP to maintain a stable MAP
What are the two things that can happen when standing for too long, causing someone to collapse?
- Blood pools in the leg veins, lowering VR
- Loss of plasma volume (after 15 mins of standing, high pressure in the legs can cause plasma loss into the interstitial fluid of about 720 ml) This drops VR
How can the effects of standing for too long be countered? (blood pooling and loss of plasma volume)
Contracting the leg muscles results in higher VR and, so a higher SV. The contractions help blood flow out of the legs and reduce the pressure in the veins, which also helps reduce loss in plasma volume
