39 - Control of arterial blood pressure. Mechanisms of rapid short-term, rapid continuous and long-term regulation.

sections

types of regulation

mechanism of rapid short-term regulation

baroreceptor reflexes

rapid continuous regulation (other reflexes and responses)

rapid long term regulation of arterial bp

types of regulation

There are two main mechanisms for regulation of blood pressure:

1. Short-term- autonomic nervous system-sympathetic and parasympathetic. alterations of cardiac output and total peripheral resistance ,as well as influences on the heart, veins and arterioles

   • Blood pressure = cardiac output x peripheral resistance

2. Long-term (requiring minutes to days) -controlling total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst.

   • The total blood volume, in turn, has a profound effect on CO and mean arterial blood pressure.

mechanism of rapid short-term regulation

• Mean arterial pressure is constantly monitored by baroreceptors (pressure sensors) within the circulatory system.

• Baroreceptor reflexes are found in:

  • Carotid Sinuses

  • Aortic Arch

• When there is a decrease in aterial blood pressure the baroreceptors are inhibted

• Fewer action potentials are generated so fewer impulses travel up the afferent nerves to the Medullary

• Cardiovascular centre resulting in:

  1. ↑heart rate because of ↑sympathetic activity and ↓parasympathetic activity to the heart

  2. ↑ventricular contractility because of ↑sympathetic activity to the ventricular myocardium

  3. ↑arteriolar contraction because of ↑sympathetic activity to the arterioles

  4. ↑plasma concentrations of angiotensin II and vasopressin The net result is an increased CO (↑HR and SV), increased total peripheral resistance TPR (arteriolar constriction) and return of the blood pressure towards normal.

  5. ↑venous constriction because of ↑sympathetic activity to the veins

     *Conversely, ↑arterial blood pressure for any reason, causes ↑firing of the arterial baroreceptors which reflexively induces compensatory ↓in CO and TPR.

baroreceptor reflexes

• Baroreceptor reflexes are found in:

  • Carotid Sinuses

  • Aortic Arch

• Long term response in falling aterial blood pressure

• When there is a decrease in aterial blood pressure the baroreceptors are inhibted

• Fewer action potentials are generated so fewer impulses travel up the afferent nerves to the Medullary

• Cardiovascular centre resulting in:

  1. ↑heart rate because of ↑sympathetic activity and ↓parasympathetic activity to the heart

  2. ↑ventricular contractility because of ↑sympathetic activity to the ventricular myocardium

  3. ↑arteriolar contraction because of ↑sympathetic activity to the arterioles

  4. ↑plasma concentrations of angiotensin II and vasopressin The net result is an increased CO (↑HR and SV), increased total peripheral resistance TPR (arteriolar constriction) and return of the blood pressure towards normal.

  5. ↑venous constriction because of ↑sympathetic activity to the veins

     *Conversely, ↑arterial blood pressure for any reason, causes ↑firing of the arterial baroreceptors which reflexively induces compensatory ↓in CO and TPR.

rapid continuous regulation (other reflexes and responses)

• The below stimuli cause increase in blood pressure

  • Arterial blood gas concentrations:↓arterial O2 concentration, ↑arterial CO2 concentration

  • Pain, anxiety, stress, and sexual activity

  • Cushing’s phenomenon occurs when there is an increase in intracranial pressure (ICP), often due to a rapidly growing brain tumor, swelling (edema), or internal bleeding. The rise in ICP reduces blood flow to the brain, which can be life-threatening. To compensate, the body responds by sharply increasing arterial blood pressure in an effort to restore adequate blood flow to the brain. This reaction is triggered by signals from higher brain centers to the medullary cardiovascular center, or sometimes through alternative neural pathways from these centers.

rapid long term regulation of arterial bp

• blood volume is a long-term regulator of arterial BP

• it affects the venous pressure, venous return, end-diastolic volume, Stroke Volume and CO.

• the ↑ blood volume causes ↑BP.

• The body tries to lower BP by lowering blood volume by ↑ excretion of salt and water by the kidney

• Renin-angiotensin-aldosterone mechanism

  • renin released by kidney in response to low bp

  • Promotes production of angiotensin II, which causes vasoconstriction and increase in aldosterone secretion

  • aldosterone helps maintain blood volume by decreasing urine production

• Vasopressin (ADH) mechanism

  • causes ADH release from posterior pituitary in response to substantial decrease in bp

  • ADH causes vasoconstriction and helps maintain blood volume by decreasing urine production