BLOOD PRESSURE

 various methods of regulation of Blood pressure 9

Blood pressure:

 • Blood pressure is the pressure of circulating blood against the walls of blood vessels.

 • Blood pressure is measured using an automated blood pressure monitor, or manually using a stethoscope and sphygmomanometer.

 • It is given as two values (eg 120/80 mmHg), measured in “millimetres of mercury (mmHg)

 • Systolic pressure – the first number (120 mmHg in the example) is the pressure of the blood during the heart contraction.

 • Diastolic pressure – the second number (80 mmHg in the example) is the pressure of the blood after one contraction but before the next contraction.

Regulation of Blood Pressure:

Short-Term:

Short-term regulation of blood pressure is controlled by the autonomic nervous system.

Changes in blood pressure are detected by baroreceptors- located in the arch of the aorta and the carotid sinus.

 I. Increased arterial pressure stretches the wall of the blood vessel, triggering the baroreceptors

 • These baroreceptors then send feedback to the autonomic nervous system.

 • The ANS then send signal via efferent parasympathetic fibres to reduce the heart rate and cardiac contractility, thus reduceing Blood pressure.

 II. Decreased arterial pressure is detected by baroreceptors,

 • It send signal to ANS , and in trun ANS , trigger sympathetic response.

 • This stimulate increase in heart rate and cardiac contractility. Thus Blood pressure increases.

Long-Term:

There are several physiological mechanisms that regulate blood pressure in the long-term:

 1. Renin-Angiotensin-Aldosterone System (RAAS)

 👉Renin is peptide hormone released by juxtaglomerular apparatus in the kidney.

 👉 it is released in response to :

 • Reduced sodium chloride delivery to the distal convoluted tubule

 • Decrease blood flow to kidney

 👉 Renin converts angiotensinogen to angiotensin I . Angiotensin is converted to angiotensin II by using angiotensin-converting enzyme (ACE)

 👉Angiotensin II is a potent vasoconstrictor. It increase sodium reabsorption.

 👉This results in decreased water excretion and therefore increased blood volume and thus blood pressure

 2. Anti-Diuretic Hormone (ADH)

 The second mechanism by which blood pressure is regulated is release of Anti Diuretic Hormone (ADH)

 👉ADH acts to increase the permeability of the collecting duct to water

 👉It also stimulates sodium reabsorption

 👉This increases water reabsorption thus increasing plasma volume and decreasing osmolarity.

 3. natriuretic peptides

 These are

 i. Atrial natriuretic peptide (ANP):

 • It is synthesised and stored in cardiac myocytes..

 • It is released when the atria are stretched, indicating of high blood pressure.

 • ANP acts to promote sodium excretion. It dilates the afferent arteriole of the glomerulus, increasing blood flow

 ii. Prostaglandins

 • act as local vasodilators to increase GFR and reduce sodium reabsorption

 • They also act to prevent excessive vasoconstriction triggered by the sympathetic nervous and renin-angiotensin-aldosterone systems.