Blood Pressure Regulation: Short and Long Term
Key facts on baroreflex, hormonal and renal control of mean arterial pressure.
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Questions Covered in This Set
11 cards to master
What is the core equation for mean arterial pressure?
MAP ≈ CO × TPR, where CO = HR × SV; estimated as DBP + ⅓(SBP − DBP).
Where are the arterial baroreceptors and which nerves carry their afferents?
Carotid sinus via glossopharyngeal nerve (CN IX) and aortic arch via vagus nerve (CN X); both converge on the nucleus tractus solitarius.
Describe the baroreflex response to a fall in arterial pressure.
Decreased baroreceptor firing releases inhibition of the rostral ventrolateral medulla → increased sympathetic outflow and reduced vagal tone → ↑HR, ↑contractility, venoconstriction (↑preload) and ↑TPR, restoring MAP within a few heartbeats.
Why can't the baroreflex cause or cure chronic hypertension?
It adapts (resets) within 1–2 days to defend the new prevailing pressure, so it only buffers acute changes.
Define orthostatic hypotension and name causes of a blunted baroreflex.
A fall of ≥20 mmHg systolic or ≥10 mmHg diastolic on standing; caused by diabetic autonomic neuropathy, β-blockers or hypovolaemia.
What stimuli trigger peripheral chemoreceptors, and what is their cardiovascular effect?
PaO₂ < 60 mmHg, rising PaCO₂ or falling pH; they drive sympathetic vasoconstriction, important in severe hypotension.
What is the Cushing reflex and its triad?
A CNS ischaemic response to brainstem ischaemia (e.g. raised ICP): massive sympathetic outflow causing hypertension, reflex bradycardia and irregular respiration.
What are the three stimuli for renin release from juxtaglomerular cells?
Decreased renal perfusion pressure (intrarenal baroreceptor), decreased NaCl delivery to the macula densa, and β1-sympathetic stimulation.
List the main actions of angiotensin II.
Arteriolar vasoconstriction, efferent arteriolar constriction preserving GFR, aldosterone release (Na⁺ reabsorption), ADH release and thirst, and increased proximal tubule Na⁺/H⁺ exchange.
How does ADH/vasopressin support blood pressure?
Released for rising osmolality or volume loss >10%; V1 receptors cause vasoconstriction and V2 receptors cause renal water retention.
How do capillary Starling forces help restore blood pressure?
Falling arterial pressure lowers capillary hydrostatic pressure, favouring reabsorption of interstitial fluid into plasma, expanding blood volume over minutes to hours.
