96. Regulation of Blood Pressure – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• Blood pressure (BP) is the lateral force exerted by blood on arterial walls. Its regulation is essential to maintain tissue perfusion. Acute hypotension reduces blood supply to vital organs, whereas chronic hypertension predisposes to cardiovascular, cerebrovascular, and renal diseases.
• Vascular tone is the resting partial contraction of vascular smooth muscle. It is maintained mainly by sympathetic vasoconstrictor tone and determines peripheral resistance, a major factor controlling arterial pressure. Vascular contraction depends on intracellular calcium and myosin light-chain kinase, while nitric oxide and prostacyclin promote relaxation.
• Normal adult systolic BP is <120 mm Hg and diastolic BP is <80 mm Hg. Pulse pressure equals systolic minus diastolic pressure (30–50 mm Hg). Mean arterial pressure (MAP) is the effective perfusion pressure and is calculated as DBP + ⅓ pulse pressure. A MAP of at least 60 mm Hg is generally required for adequate organ perfusion.
• Blood pressure is determined by cardiac output × peripheral resistance. Cardiac output depends on heart rate and stroke volume, which are influenced by preload, afterload, and myocardial contractility. Peripheral resistance depends mainly on arteriolar diameter and blood viscosity.
• Physiological variations occur with age, sex, posture, exercise, sleep, emotion, temperature, meals, and pregnancy. Systolic pressure rises with age because of reduced arterial compliance. During dynamic exercise, systolic pressure increases while diastolic pressure changes little. Standing transiently lowers BP, which is rapidly corrected by the baroreceptor reflex.
• Regulation of BP occurs by short-term and long-term mechanisms. Short-term regulation acts within seconds through neural reflexes, vascular adjustments, and hormones, whereas long-term regulation depends mainly on the kidneys, extracellular fluid volume, and hormonal mechanisms.
• Sympathetic nervous system is the most important short-term regulator. It causes vasoconstriction, venoconstriction, increased heart rate, increased myocardial contractility, and catecholamine release, thereby increasing BP. Parasympathetic activity mainly reduces heart rate through the vagus nerve. The vasomotor center in the medulla maintains resting vascular tone, while the cardioinhibitory center decreases sympathetic activity and increases vagal discharge. The hypothalamus and cerebral cortex modify cardiovascular responses during stress, emotion, and exercise.
• The baroreceptor reflex is the most important mechanism for moment-to-moment regulation of BP. Baroreceptors are located in the carotid sinus and aortic arch. Increased BP increases baroreceptor firing, causing vasodilation, bradycardia, and reduced cardiac output. Decreased BP produces the opposite response. Baroreceptors function between 50–200 mm Hg, with maximum sensitivity between 70–140 mm Hg, and reset during chronic hypertension.
• The chemoreceptor reflex is activated by hypoxemia, hypercapnia, and increased hydrogen ion concentration. It causes peripheral vasoconstriction and helps maintain BP during severe hypotension. The CNS ischemic (Cushing) reflex is activated when cerebral perfusion falls markedly, producing intense vasoconstriction and hypertension, followed by reflex bradycardia. Other important reflexes include the somatosympathetic reflex, atrial stretch (Bainbridge) reflex, cardiopulmonary stretch reflexes, and Bezold–Jarisch reflex.