WINDSOR UNIVERSITY SCHOOL OF MEDICINE . Regulation of Blood Pressure Dr.Vishal Surender.MD. Learning objectives Define the bulk flow relationship in terms of arterial pressure, cardiac output and total peripheral resistance
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Regulation of Blood Pressure
Bulk Flow/Pouseuilles Law:
Flow = Pressure gradient/Resistance (P/R)
Equivalent to: CO = MAP/TPR
Therefore: MAP = CO x TPR
An in CO or TPR or both will MAP
A in either or both will MAP
There is a short term and long-term regulation of blood pressure
Fig. 1. Baroreceptor control of MAP. In this example is assumed that in MAP (violet box) is the primary insult
Fig. 2. Location of arterial baroreceptors
Fig. 3. Afferent pathways of the high-pressure baroreceptors. In (B), the chemoreceptors (i.e., aortic bodies) are located on the underside of the aortic arch, as well as at the bifurcation of the brachiocephalic artery.
2. Baroreceptors and the Afferent Pathways
3. The cardiovascular Coordinating Centers
Fig. 5. Medullary control centers for CVS. Ach, acetylcholine; CN, cranial nerves; NTS, nucleus tractus solitarius
4. Efferent Pathways and Efferent Organs
-Putting things together-postural hypotention.
Effects of α1 receptor antagonist drugs
Certain drugs used in the treatment of hypertension also cause marked postural hypotension as a side effect. These are the α1 receptor antagonists. They prevent the reflex NE-mediated vasoconstriction that normally restores the arterial pressure. As a consequence, individuals on α1 receptor antagonists must rise to their feet slowly in case they faint.
Control of Cardiovascular Centers by Higher Centers
Fig. 9. Summary of the components of the baroreceptor reflex. If the initial change were a decrease of BP, all the arrows in the boxes would be reversed
Chronic hypertension and re-setting of the set point
Chemoreceptor Reflex is other mechanism involved in short term control of blood pressure: Effects of PO2 on BP when it falls too low
Fig. 11. Chemoreceptor control of CVS. PO2 , PCO2 or pH is the primary insult (violet box). A, bradycardia occurs when ventilation is fixed or prevented (e.g. breath-holding). B, effects of breading overcome the intrinsic CV response, producing bradycardia
Other reflexes Involved in the Control of BP
Fig. 12. Low-pressure receptors. In B, A-type receptors (orange), located mainly in right atrium; B-type receptors are located mainly in superior and inferior vena cava; ECG, electrocardiogram
Direct effects on the vasomotor area: Cerebral Ischemic Response and Cushing Reaction (reflex)
2. BLOOD VOLUME and Long-term control of Blood Pressure
Fig. 13. Causal reciprocal relationship between BP and BV. in BP due to CO induces BV by promoting fluid excretion by the kidneys, which tends to restore BP to original value
Fig. 17. The renin-angiotensin-aldosterone axis
Fig. 18. Structure of the juxtaglomerular apparatus