Hypertension Flashcards
(29 cards)
Hypertension is actually a disease of the
Kidney
Short term control of blood pressure
Can be modelled in a closed system
Balance between CO and TPR
How is short term blood pressure control regulated?
Baroreceptors
Where are low pressure baroreceptors located?
Large systemic veins, in the pulmonary arteries, in the walls of the atria, and ventricles of the heart.
Where are high pressure baroreceptors located?
Arch of aorta and carotid sinus
What are type I high pressure baroreceptors?
Large type A myelinated afferent fibers.
Lower activation thresholds and fire more rapidly upon stimulation.
What are type II high pressure baroreceptors?
Unmyelinated or small poorly myelinated type C afferent fibers.
Higher activation thresholds and discharge at lower frequencies.
Which high pressure baroreceptors are responsive to both increases and decreases in arterial pressure?
Carotid sinus
Which high pressure baroreceptors are responsive to only an increase in pressure?
Aortic arch
How do baroreceptors signal in response to a rise in blood pressure?
Stretches the wall of the blood vessel, triggering the baroreceptors.
Firing of afferents (glossopharyngeal nerve via carotid sinus nerve from the carotid body and vagus nerve from aortic bodies).
These afferents project to the cardiovascular nuclei in the medulla (NTS), this acts to effectively inhibit the sympathetic input
Efferent projections are then sent via the ANS (parasympathetic fibres - vagus nerve) which act to reduce the heart rate and cardiac contractility - reducing blood pressure.
How do baroreceptors respond to a fall in blood pressure?
Decreased arterial pressure: is detected by baroreceptors
Decreased firing rates then trigger a sympathetic response, sympathetic is no longer inhibited.
This stimulates an increase in heart rate and cardiac contractility leading to an increased blood pressure.
What cant baroreceptors act long term?
Mechanism of triggering baroreceptors resets itself once a more adequate blood pressure is restored.
When changes in pressure are sustained for several minutes, baroreceptors are reset
rapidly and the baroreceptor pressure-activity curve
shifts in the direction of pressure change to function at a new set point.
What happens to the baroreceptor reflex in hypertensives?
Baroreceptors are impaired in chronic hypertension and are said to become chronically reset. This is characterized by elevations in pressure threshold and decreases in baroreceptor activity
Why is it good baroreceptors can reset?
This allows baroreceptors to buffer fluctuations of arterial pressure effectively because the new pressure set point remains on the steep portion of the reset pressure-activity curve
How did Guyton challenge the cardiocentric view of BP?
Guyton successfully coupled the venous return and circulation to the cardiac output.
How did Guyton challenge the vasculocentric view?
Added circulatory volumes and compliances to initial considerations of CO and TPR and linked them to sources of fluid entry (absorption of salt and water by the digestive tract) and loss (chiefly salt and water excretion by the kidney).
What is the pressure-natriuresis relationship?
Renal perfusion pressure can directly regulate sodium reabsorption in the proximal tubule.
If BP rises, so too does renal arterial pressure (RAP) and the kidney responds by increasing sodium excretion and reducing ECFV; the converse applies if blood pressure falls.
What is the set point blood pressure in terms of PN?
Set-point BP is the point at which ECFV (extracellular fluid volume) and PN (pressure-natriuresis) are in equilibrium.
Theoretically why should we not get hypertension?
PN (pressure natriuresis) should offset completely any change in BP
What modulates PN?
RAAS (acts as a confounder to pure PN)
Are RAAS and PN both needed for long term pressure regulation?
Yes
What is theorised to underpin hypertension?
Whatever the cause of hypertension, it must in the end somehow modify the kidney’s ability to excrete salt and water for a given BP; otherwise, the hypertension would lead to an increased excretion of salt and water through the PNR, ultimately returning BP to regular levels.
Therefore PN curve changes - pushed to the right (higher pressure for same Na+ excretion) and the gradient of the slope can also be blunted
Halls dog experiments show that
The kidney sets an arterial pressure that depends markedly upon sodium excretion, probably revealing innate renal function (PN) devoid of its normal fine endogenous neuroendocrine regulation (RAAS).
Hypertensives have higher perfusion threshold to produce the same urine.
Why is hypertension an disease of the kidney?
A change in BP can only be sustained if the acute PN response is impaired, making hypertension a disease of the kidney.
