Baroflex

Pagina 1

BAROREFLEX Physiological reaction (or reflex) to arterial pressure changes It is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The control output is generated by balancing the sympathetic action that tends to increase pressure and the parasympathetic one that lows it. At normal conditions it provides 2 closed-loop mechanisms to regulate blood pressure (the 2 branches in the schema): x The HEART RATE ADAPTATION It provides a rapid negative feedback loop: in normal condition the action is performed in less than the duration of a cardiac cycle Æ this allows to deal with postural hypotension, then to restore a normal blood pressure level after a decrease on standing due to gravity The mechanism reacts when blood pressure increases by decreasing the heart rate and vice versa. x The VASOCONSTRICTION MECHANISM A slower-acting system that regulates the vessels’ tone to increase the blood pressure by increasing the peripheral resistance . BARORECEPTORS They are specialized neurons located in vessels’ walls, mainly in the aortic arch and carotid sinuses. They have the capability of monitoring changes in blood pressure: Î If the blood pressure increases the tension on vessels’ wall increases Î Pressure induced stretching of baroreceptors Î Receptors catch the input and relay to the medulla oblongata CONTROLLER CNS PLANT CONTROL VARIABLES CONTROLLED VARIABLE SAP FEEDBACK SENSOR Baroreceptive fibers FEEDBACK SIGNAL Afferent neural signal PR EMBEDDED REFERENCE Intrinsic set point RR Arteries Heart + - + - + - RR = Cardiac Period, i.e. the interval between two R peaks PR = Peripheral Resistance CNS = Central Nervous System SAP = Systolic Arterial Pressure Blood pressure changes with respect to normal values (= intrinsic WP)…