Download ARTERIAL BLOOD PRESSURE REGULATION

ARTERIAL BLOOD
PRESSURE REGULATION
Definitions
• Arterial blood pressure
• Mean arterial pressure
– = Diastolic + 1/3 pulse pressure
• Systolic blood pressure
• Diastolic blood pressure
Physiological variations in BP
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•
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Age
Sex
Body mass index.
Meals
Exercise
Posture.
Anxiety
Determinants of ABP
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Total peripheral resistance.
Cardiac output.
Blood viscosity.
Blood volume.
ABP = CO X TPR
Site of Resistance in the
circulation: arteries Or capillaries?
Total Peripheral Resistance
Factors affecting diameter of
arterioles
• Vasodilator agents:
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–
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Atrial natriuretic peptide (ANP)
Histamine
Adrenomedullin
Nitric oxide
Prostacyclin
• Vasoconstrictor agents:
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–
–
–
–
Noradrenaline
Sympathomimetic drugs.
Vasopressin
Angiotensin II
Endothelin-1
Blood viscosity: Hematocrit
Blood Viscosity
• Plasma Proteins:
Normal Plasma protein level:
Plasma protein
Hypoalbumenimia:
Burns.
Malnutrition
blood viscosity
• Effect of Blood Volume :
• Changes in blood volume affect arterial pressure by
changing cardiac output:
• An increase in blood volume increases central venous
pressure.
right atrial pressure, right ventricular
end-diastolic pressure and volume.
ventricular
preload
ventricular stroke volume by the FrankStarling mechanism.
• right ventricular stroke volume
pulmonary venous
blood flow to the left ventricle, thereby increasing left
ventricular preload and stroke volume.
• stroke volume
cardiac output and arterial blood
pressure.
Regulation of ABP
• Short-term regulation:
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Baroreceptor reflexes.
Chemoreceptor reflexes.
Atrial reflexes.
CNS-ischemic response.
• Long-term regulation:
– Role of the kidney.
• Intermediate regulation:
– Capillary fluid shift
Higher Control of ABP
Baroreceptors
Of these two sites for arterial baroreceptors, the carotid sinus is
quantitatively the most important for regulating arterial pressure. The
carotid sinus receptors respond to pressures ranging from 60-180
mmHg (Figure 2). Receptors within the aortic arch have a higher
threshold pressure and are less sensitive than the carotid sinus
receptors. Maximal carotid sinus sensitivity occurs near the normal
mean arterial pressure; therefore, very small changes in arterial
pressure around this "set point" dramatically alters receptor firing so
that autonomic control can be reset in such a way that the arterial
pressure remains very near to the set point. This set point changes
during exercise, hypertension, and heart failure. The changing set
point explains how arterial pressure can remain elevated during
.exercise or chronic hypertension
Long-Term:
Blood volume regulation by kidneys
• Blood volume is determined by the amount of water and sodium
ingested, excreted by the kidneys into the urine, and lost through the
gastrointestinal tract, lungs and skin. The amounts of water and
sodium ingested and lost are highly variable. To maintain blood
volume within a normal range, the kidneys regulate the amount of
water and sodium lost into the urine. For example, if excessive water
and sodium are ingested, the kidneys normally respond by excreting
more water and sodium into the urine. The details of how the
kidneys handle water and sodium are beyond the scope of this
cardiovascular web site; therefore, the reader is encouraged to
consult general medical physiology textbooks to learn more about
this topic. The following paragraphs briefly describe how renal
excretion of water and sodium are regulated and how blood volume
affects cardiovascular function.
Regulation of Blood Volume by Renal
Excretion of Water and Sodium
• The primary mechanism by which the kidneys
regulate blood volume is by adjusting the
excretion of water and sodium into the urine.
• Mechanisms:
• Pressure Natriuresis:
– ed blood volume
arterial pressure, renal
perfusion, and glomerular filtration rate. This leads to
an increase in renal excretion of water and sodium
(Pressure natriuresis).
– In certain types of renal disease, the pressure
natriuresis relationship is altered so that the kidneys
retain more sodium and water at a given pressure,
thereby increasing blood volume.
Renin Angiotensin System
• The renin-angiotensinaldosterone system
(RAAS) plays an
important role in
regulating blood volume
and systemic vascular
resistance ,which
together influence cardiac
output and arterial
pressure .
Functions of Ang II
1. Constricts resistance vessels (via AII [AT ]1receptors )thereby
increasing systemic vascular resistance and arterial pressure
2. Acts on the adrenal cortex to release aldosterone ,which in
turn acts on the kidneys to increase sodium and fluid retention
3. Stimulates the release of vasopressin )antidiuretic hormone,
ADH) from the posterior pituitary, which increases fluid retention
by the kidneys
4. Stimulates thirst centers within the brain
5. Facilitates norepinephrine release from sympathetic nerve
endings and inhibits norepinephrine re-uptake by nerve endings,
thereby enhancing sympathetic adrenergic function
Stimulates cardiac hypertrophy and vascular hypertrophy