Short-term Control of Blood Pressure

 

Short-term control of blood pressure:

Blood pressure is normally maintained by the complex interaction of several physiological system. Rapid control of blood pressure is accomplished primarily by the baroreceptors reflex which monitors and correct changes in blood pressure with in a matter of seconds by altering cardiac output and peripheral vascular resistance.

1.Baroreceptor reflex:

Baroreceptor are the receptors which give response to change in blood pressure. receptors are also called pressor receptors.

Situation of baroreceptor: baroreceptors are situated in carotid sinus and wall of the aorta.

Function of baroreceptor:

Role of baroreceptors when blood pressure increases:

When arterial blood pressure rises rapidly baroreceptors are activated and send stimulatory impulses to nucleus of tractus solitarius through glossopharyngeal and vague nerves. Now the nucleus of tractus solitarius acts on both  vasoconstrictor area and vasodilator area of vasomotor center. It inhibits the vasoconstrictor area and excites the vasodilator area.

Inhibition of vasoconstrictor area reduces vasomotor tone. Reduction in vasomotor motor to causes vasodilation resulting in decreased peripheral resistance. Simultaneous excitation of vasodilator center increases vagal tone. This decreases the rate and force of contraction of heart leading to reduction in cardiac output. These two factors for example decreased peripheral resistance and reduced cardiac output bring the arterial blood pressure back to normal level.

Role of baroreceptors when blood pressure decreases:

The fall in arterial blood pressure or the occlusion of common carotid arteries decrease the pressure in carotid sinus. This causes inactivation of baroreceptors. Now there is no inhibition of vasoconstrictor center for excitation of vasodilators center.

 Therefore the blood pressure rises.

Information regarding blood pressure with in the range of 50 to 200 mmHg reaches the vasomotor center through the carotid baroreceptors. Information about the blood pressure range of 100 to 200 mmHg a goes through aortic baroreceptors.

Both carotid and aortic baroreceptors are stimulated by the rising pressure then the steady pressure and their response depends upon the rate of increase in the blood pressure. Since the barro receptor mechanism acts against the rise in arterial blood pressure it is called pressure buffer mechanism or system and the nerves from the baroreceptor are called the buffer nerves.

2.Chemoreceptors:

Chemoreceptors are the receptors giving response to change in chemical constituents of blood. Peripheral chemoreceptors influence the vasomotor center.

Situation of chemoreceptors: peripheral chemoreceptors are situated in the carotid body and aortic body.

Function of chemoreceptors:

 Peripheral chemoreceptors are sensitive to lack of oxygen, excess of carbon dioxide and hydrogen ion concentration in blood. Whenever blood pressure decreases, blood flow to chemoreceptor decreases, resulting in decreased oxygen content and excess of carbon dioxide and hydrogen ion.  

These factors excite the chemoreceptors, which send impulses to stimulate vasoconstrictors center. Blood pressure rises and blood flow increases. Chemoreceptors play a major role in maintaining respiration rather than blood pressure.

Sinaortic mechanism:

 Mechanism of action of baroreceptors and chemoreceptors in carotid and aortic regions institute sin aortic mechanism. Nerves supplying the baroreceptors and chemoreceptors are called buffer nerves because these nerves regulate the heart rate, blood pressure and respiration.

Higher centers: vasomotor center is also controlled by the impulse  from the two higher center's in the brain.

1) Cerebral cortex:

 Area 13 in cerebral cortex is concerned with emotional reactions. During emotional conditions this area sends impulses to vasomotor center. Vasomotor center is activated, the vasomotor  tone is increased and the pressure increases.

2) Hypothalamus:

 Stimulation of posterior and lateral nuclei of hypothalamus causes vasoconstriction and increase in blood pressure. Stimulation of preoptic area cause vasodilation and decrease in blood pressure. Impulses from hypothalamus are mediated via vasomotor center.

Respiratory centers:

 During the beginning of expiration, blood pressure increases slightly for example by 4 to 6 mmHg. It decreases during later part of expiration and during inspiration. It is because of two factors:

• Radiation of impulses from respiratory center towards vasomotor center at different phases of respiratory cycle.

• Pressure changes in thoracic cavity leading to alteration of venous return and cardiac output.

Renal mechanism for regulation of blood pressure: long term regulation:

Kidneys play an important role in the long term regulation of arterial blood pressure. when blood pressure alters slowly in several days, months, years The nervous mechanism adapts to the altered pressure and losses the sensitivity for the changes. It cannot regulate the pressure anymore. In such conditions the renal mechanism operates efficiently to regulate the blood pressure. Therefore it is called Long term regulation. Kidneys regulate blood pressure by two ways:

•  By regulations of extracellular fluid volume.
•  Through renin-angiotensin mechanism.

By regulation of extracellular fluid volume:

When the blood pressure increases kidneys excrete large amount of water and salt particularly sodium by means of pressure diuresis and pressure natriuresis. Pressure diuresis is the excretion of large quantity of water in urine because of increased blood pressure. Even a slight increase in blood pressure doubles the water excretion.

 Pressure natriuresis is the excretion or large quantity of sodium in urine.

Because of diuresis and natriuresis there is a decrease in extracellular fluid volume and blood volume which in turn brings the arterial blood pressure back to normal level. When blood pressure decreases the reabsorption of water from renal tubules is increased. This in turn increases extracellular fluid volume blood volume and cardiac output resulting in restoration of blood pressure.

Through renin-angiotensin mechanism:

Actions of angiotensin 2:

When blood pressure and extracellular fluid volume decreases renin secretion from kidney is increased. It converts angiotensin into angiotensin 1. This is converted into angiotensin 2 by ACE (angiotensin converting enzyme). Angiotensin 2 acts in two ways to restore your blood pressure:

• It causes construction of arteriole in the body so that the peripheral resistance is increased and blood pressure rises. In addition angiotensin 2 causes constriction of afferent arteriole in kidney so that glomerular filtration reduces. This result in retention of water and salts increases extracellular fluid volume to normal level. This in turn increases the blood pressure to normal level.

• Simultaneously and attention to stimulates the adrenal cortex to secrete at aldosterone. This hormone increases reabsorption of sodium from renal tubules. Sodium reabsorption is followed by water reabsorption resulting in increased extracellular fluid volume and blood volume. It increases the blood pressure to normal level.

Action of angiotensin 3 and angiotensin 4:

Like angiotensin 2 the angiotensin 3 and 4 also increase the blood pressure and stimulate adrenal cortex to see create aldosterone.

What are the symptoms of high blood pressure in athletes?

High blood pressure, or hypertension, often doesn't have noticeable symptoms, which is why it's frequently called the "silent killer". It can affect anyone, including athletes, and often goes undetected until it causes complications like heart disease or stroke.

That said, when symptoms of high blood pressure do manifest, they could include:

Headaches: Although not specific, some people may experience headaches due to high blood pressure.

Fatigue or confusion: Higher than normal blood pressure can cause feelings of fatigue or confusion, but these symptoms are generally non-specific and could be due to a variety of causes.

Vision problems: High blood pressure can cause blood vessels in the eyes to bleed or burst, leading to vision problems.

Chest pain: High blood pressure can cause chest pain, also known as angina, particularly during physical activity or emotional stress.

Difficulty breathing: If high blood pressure has led to heart problems or fluid in the lungs, it can cause shortness of breath.

Irregular heartbeat: An irregular heartbeat might be a sign of high blood pressure or its complications.

Blood in the urine: This can be a sign of kidney damage from high blood pressure.

Pounding in your chest, neck, or ears: Sometimes, a person with high blood pressure may hear or feel a pounding in their chest, neck, or ears. This can occur even at rest.

In athletes, the physical demands of intense training and competition can exacerbate these symptoms. However, it's important to note that these symptoms are not exclusive to hypertension and can be caused by a number of other conditions.

Therefore, athletes with high blood pressure might not know they have it until it's discovered during a routine medical examination. This highlights the importance of regular check-ups, especially for those involved in strenuous physical activities. If you're an athlete and have any concerns about high blood pressure, it's best to consult with a healthcare professional.

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What mechanism is involved in short-term control of blood pressure?

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