Hypertension Flashcards
How is blood pressure regulated? Give relevant equations
Pressure = flow x resistance mABP = CO x TPR CO = SV x HR
How is blood pressure managed in the short term?
Baroreceptor reflex-stretch receptors in aortic arch and carotid sinus. Issue is, it resets to a new set point after 15 minutes (as threshold for firing changes)
When is renin released?
Renin is released from granular cells of afferent arterioles (granular cells of juxtaglomerular apparatus) in response to reduced perfusion pressure.
Factors that stimulate renin release are:
a) reduced NaCl delivery to distal tubule (macula densa)
b) reduced perfusion pressure in kidney (baroreceptor reflex)
c) sympathetic stimulation to JGA increases release of renin
How is angiotensin converted into its active form?
Angiotensinogen is converted into angiotensin 1 with renin.
Angiotensin 1 is converted into Angiotensin 2 via ACE.
What are the main actions of Angiotensin 2.
Mainly acting via AT1 receptors:
Arterioles= Vasoconstriction Kidney= Na+ reabsorption SNS= Increased NA release (positive feedback) Adrenal cortex= aldosterone release Hypothalamus= ADH release
What are the actions of aldosterone?
acts on principle cells of collecting ducts.
- Stimulates Na+ (and therefore water reabsorption)- via ENaC and
- increases basolateral Na+ extrusion via Na+K+ATPase
How does ACE interact with bradykinin?
Bradykinin has vasodilatory actions. ACE causes it to break down into peptide fragment. So ACE inhibitors cause dry cough as bradykinin accumulates.
What is the significance of the SNS in blood pressure regulation?
Increased sympathetic stimulation means decreased renal blood flow (vasoconstriction of arterioles, decreased GFR, decreased Na+ excretion and activation of Ang2 system)
What does Anti Diuretic Hormone do?
It increases water reabsorption in distal nephron (via AQP2) and release is stimulated by increased plasma osmolarity and severe hypovolemia. It increases sodium reabsorption in thick ascending limb via apical Na+/K+/Cl-.
What are natriuretic peptides?
peptides synthesised and stored in atrial myocytes that ar released in response to stretch. Increased filling means increased stretch and more ANP released.
What does ANP do physiologically?
Supports blood pressure:
- vasodilation of afferent arterioles
- increased GFR
- Inhibition of Na+ reabsorption
What effect do prostaglandins have?
They act as vasodilators. They are locally acting and have a short half life.
- PGE2 mainly enhances glomurelar filtration and reduces Na+ reabsorption.
- hypothesised that they may have important protective function (i.e. a buffer to excessive vasoconstriction from SNS and RAAS) so important when Ang2 levels high
How does dopamine affect blood pressure?
- locally formed in kidney from L-DOPA.
- dopamine receptors on renal blood vessels and PCT and TAL cells cause vasodilation and increased NaCl reabsorption.
- therefore Parkinson’s treatment side effects can include low blood pressure and fainting etc
How are the different stages in hypertension defined?
Stage 1= above 140/90 (in clinic) and above 135/85 (ABPM/HBPM)
Stage 2= above 160/100 (in clinic) and above 150/95 (ABPM/HBPM)
Severe= above 180 systolic or 110 diastolic
How can renovascular disease cause hypertension?
- renal artery stenosis causes fall in perfusion pressure in that kidney
- decreased perfusion pressure- increased renin production, increased RAAS activation, vasoconstriction and sodium retention at other kidney
