Blood pressure regulation systems

2021-05-27 08:56 AM

The first system that responds to acute changes in arterial blood pressure is the nervous system. Renal mechanisms for long-term control of blood pressure. However, there are different pieces of the problem.

By now, arterial blood pressure is regulated not by a single control system but instead by many interrelated systems, each of which performs a specific function. For example, when a person has severe bleeding, blood pressure drops suddenly, two problems confront in the blood pressure control system. The first is survival; Arterial blood pressure must rise rapidly enough for the person to survive the acute phase. The second is to restore blood volume and arterial blood pressure eventually to their normal levels so that the circulatory system can re-establish normality, not merely return to the levels necessary for the maintenance of normal blood pressure. living.

The first system that responds to acute changes in arterial blood pressure is the nervous system. Renal mechanisms for long-term control of blood pressure. However, there are different pieces of the problem.

The figure shows approximate immediate (seconds and minutes) and long-term (hours and days) conditioning responses, expressed as increased feedback, eight mechanisms controlling arterial blood pressure. These mechanisms can be divided into three groups: (1) those who respond quickly, in seconds or minutes; (2) the response in an intermediate period, that is, minutes or hours; and (3) permanent harmonic group for the day, month and year.

Figure. Approximate efficacy of different arterial pressure control mechanisms at different time intervals after the onset of arterial pressure disturbances. Of particular note is the infinite increase in the body fluid pressure control mechanism that occurs over a period of several weeks. CNS, central nervous system.

Mechanism of rapid regulation of blood pressure seconds or minutes

Mechanisms of rapid blood pressure control are almost entirely acute neurogenic reflexes or other neurological responses. Note three mechanisms that show a response within seconds. They are (1) baroreceptor feedback mechanisms, (2) central nervous system ischemia mechanisms, and (3) chemoreceptors. Not only are the mechanisms responsive within seconds, but they are also very powerful. After a sudden drop in blood pressure, as can be caused by severe bleeding, neural mechanisms come together to cause (1) constriction of the veins and blood flow to the heart, (2) increased heart rate heart and heart contractions to increase cardiac output, and (3) constrict most of the peripheral arterioles that pump to impede the flow of blood out of the arteries. All effects occur almost immediately to return arterial blood pressure to the vital threshold.

When blood pressure suddenly rises too high, as can happen in response to rapid transfusion and excess blood, the same control mechanisms work in reverse, once again bringing blood pressure toward normal.

The blood pressure regulation mechanism works after many minutes

Several mechanisms of blood pressure control respond significantly only a few minutes after an acute change in arterial blood pressure. Three of the mechanisms are (1) the renin-angiotensin vasoconstriction mechanism, (2) stress relaxation - of the blood vessels, and (3) the variation of fluid through the capillary wall inward or outward to regulate Adjust blood volume as needed.

Role of the renin-angiotensin vasoconstrictor system to provide a subacute means to raise arterial blood pressure when needed. The mechanism of stress relaxation is demonstrated by the following example: When the pressure in the blood vessels becomes too high, they become tense and continue to stretch for several minutes or hours; As a result, the pressure in the circuit decreases to normal. The constant tension in the pulse, called relaxation stress, can act as medium-term blood pressure "buffer".

The mechanism of capillary displacement simply means that when the capillary pressure drops too low, fluid will be absorbed from the tissue through the capillary membrane and into the bloodstream, thereby re-establishing blood volume and increasing circulating blood pressure. Conversely, when capillary pressure is too high, fluid exits the circulation into the tissues, reducing blood volume, as well as pressure in the circulatory system.

Three intermediate mechanisms are activated within 30 minutes to several hours. During this time, neural mechanisms often become less effective, which explains the importance of intermediate-stage blood pressure control measures.

Long-term mechanisms for blood pressure regulation

Mechanisms of renal-humoral blood pressure regulation demonstrate that it takes a few hours to initiate a significant response. However, in the end, its control is endless.

Many factors can affect the degree of blood pressure regulation by the renal-humoral mechanism. One of them is aldosterone. A decrease in arterial blood pressure within a few minutes leads to an increase in aldosterone secretion, and in the following hours or days this effect plays an important role in modulating the blood pressure control features of the mechanism. kidney - humour.

Of particular importance is the interaction of the renin-angiotensin system with aldosterone and the renal translocation mechanism. For example, a person's salt intake varies greatly from day today. We have seen that salt intake can be reduced to one-tenth of normal or can be increased to 10-15 times normal but blood pressure changes only by a few mm Hg if the renin-angiotensin-aldosterone system is complete. However, without the renin-angiotensin-aldosterone system, blood pressure becomes very sensitive to salt intake.

In summary, life-protecting blood pressure regulation begins with a neural mechanism, then continues with an intermediate regulatory mechanism, and finally, blood pressure is stabilized in the long term by a renal mechanism - translatable. The long-term mechanism, which is a combination of multiple systems, the renin-angiotensin-aldosterone system, the nervous system, and other factors provides specific blood pressure regulation for specific purposes.