Blood Pressure Regulation PDF

Blood Pressure Dr. Suzan Hazzaa MD Professor Department of PHYSIOLOGY College of Medicine  What is Blood Pressure? Pressure = force/unit area Blood pressure = LATERAL Pressure exerted by blood on the walls of blood vessels. E.g: 120/80 mmHg Systolic Blood pressure:...

Blood Pressure Dr. Suzan Hazzaa MD Professor Department of PHYSIOLOGY College of Medicine  What is Blood Pressure? Pressure = force/unit area Blood pressure = LATERAL Pressure exerted by blood on the walls of blood vessels. E.g: 120/80 mmHg Systolic Blood pressure: the maximum pressure during systole (90:140 mmHg). Diastolic Blood pressure: the lowest pressure during systole (60: 90 mmHg). Systolic blood pressure(SBP): mainly depends on - Stroke volume and cardiac output (direct relationship). Increase the SV will increase the systolic BP. – Diastolic blood pressure (DBP): mainly depends on - Total peripheral resistance(TPR): when increases it will increase the DBP. TPR increases due to V.C. of the B.V. or due to increase in the viscosity of the blood. Pulse Pressure= Systolic blood pressure(SBP) – Diastolic blood pressure (DBP) Mean Arterial Pressure (MAP) average arterial blood pressure during a cardiac cycle MAP = DBP + 1/3 (SBP-DBP) PULSE PRESSURE MAP between 70 and 100 mmHg. If the MAP drops below 60 mmHg, the pressure is insufficient for organ perfusion. Factors influencing the Blood Pressure (BP) Systolic Blood Pressure ∞ Cardiac Output Diastolic Blood pressure ∞ Total Peripheral Resistance (TPR) Physiological factors affecting the Blood Pressure (BP) 1-Age: Infant 80/40 Children 100/60 Adult 120/80 old age: 140/90 2-Sex – Male have higher blood pressure than female (because female sex hormones decrease ABP). – ABP increases in female after menopause. 3-Race – Some races have higher blood pressure 4- Emotions: – Emotions increases the blood pressure. 5- Exercise It increases the systolic blood pressure and decreases the diastolic BP (due to V.D.) so increasing the pulse pressure. 6- Gravity – The pressure increases by about 0.77 mmHg for each cm below the level of the heart. – The pressure decreases by about 0.77 mmHg for each cm above the level of the heart. Short- term regulation of arterial Blood Pressure (BP) Nervous regulation Circulatory impulses Extra-Circulatory impulses 1- Baroreceptors: 1- higher centers. 2- peripheral chemoreceptors. 2- Somatic. 3- CNS ischemic response. Short term Regulation of Blood Pressure  (1) THE BARORECEPTOR REFLEX  C.V.S. centers 1- the pressor area It projects the sympathetic fibers from the pressor area in the medulla to the heart through the lateral horn of the spinal cord. It increases the ABP by effect on the: 1- heart: it increases the S.V. / heart rate / and COP. 2- B.V.: it causes Arteriolar V.C that increase total peripheral resistance. Venoconstriction: increasing the Venous return and COP.  2- the depressor area It projects the parasympathetic fibers from the depressor area in the medulla to the heart through the vagus nerve. It decreases the ABP by : it decreases the heart rate and COP. Activity of the CVS center can be altered by afferent fibers from different areas: that may either Stimulate vasomotor area (pressor area) and increase the ABP. Stimulate cardio-inhibitory area (depressor area) and decrease the ABP. 1- Arterial baroreceptors (High pressure receptors) RESPOND to: rapidly changing Blood Pressure in the range 60-180 mmHg Psns: parasympathetic nervous system. Sns: sympathetic nervous system.  How Baroreceptor Reflex works? Stimulates the Parasympathetic Centres (vagus nerve) in the medulla Inhibits the Vasomotor centre (VMC) in the medulla – Decreased excitatory discharge from the vasomotor centre (VMC) to the Sympathetic Nervous System in the spinal cord – This in turn causes decreased sympathetic discharge  (2) THE CHEMORECEPTOR REFLEX  Chemoreceptors Location: Peripheral chemoreceptors – Sense low O2 – Carotid and aortic bodies Mechanism of action: Respond to a ↓PaO2 , ↑ PaCO2, fall in pH Exert a positive drive on vasomotor Center (VMC)- Vasoconstriction RESPOND to: when Arterial Blood Pressure becomes less than 60 mmHg  (3) CNS ISCHEMIC RESPONSE  CNS ischemic response It operates as an emergency arterial pressure control system. Acts rapidly and powerfully to prevent further decrease in arterial blood pressure whenever blood flow to the brain decreases to lethal level. When BP < 40 mmHg → cerebral ischemia of vasomotor center → strong excitation of vasomotor center (VMC) → strong vasoconstriction of blood vessels. It is one of the most powerful activators of the sympathetic vasoconstrictor system. EXTRA CIRCULATORY IMPULSES  Higher brain Centres Descending fibres from the cerebral cortex (limbic system and prefrontal area) to hypothalamus to. Stimulate vasomotor area – Increase ABP at the beginning of exercise and during emotions.  Somatic afferent 1- From Pain receptors - Cutaneous pain : from the skin ……… Stimulates vasomotor area to increase ABP and H.R. - Visceral pain: has the reverse effect as it decreases the ABP. 2- From Thermal receptors - Exposure to cold: Stimulates vasomotor area and sympathetic ……… V.C. and increase ABP. - Exposure to worm: Inhibition of vasomotor area ……… decrease ABP. 3- From muscles receptors - Muscle exercise stimulates muscle receptor reflex ……. Stimulates vasomotor area and increase ABP. Long term Regulation of Blood Pressure Renal regulation of blood pressure and RENIN- ANGIOTENSIN-ALDOSTERONE SYSTEM (RAAS )  Renal Regulation of BP The baroreceptor reflex and other reflex mechanisms are important for the short term control of blood pressure. Long term control of blood pressure requires control of blood volume. Blood volume is controlled by the kidney. Kidneys can eliminate excess water by excreting a dilute urine Kidneys can conserve water by excreting a concentrated urine When blood volume and Blood Pressure is decreased: → Decreased glomerular capillary hydrostatic pressure → Decreased Glomerular Filtration Rate (GFR) → Oliguria (deceased urine formation) Thus KIDNEYS conserve Extra-Cellular Fluid (ECF) Volume RENIN- ANGIOTENSIN-ALDOSTERONE SYSTEM (RAAS) RENIN- ANGIOTENSIN-ALDOSTERONE SYSTEM (RAAS)  The effect of angiotensin II 1- Stimulates V.C. of the blood vessels → increase total peripheral resistance (TPR). 2- Stimulates of noradrenalin release from sympathetic nerve ending → increase TPR. 3- Stimulates hypothalamus: Release of ADH → increase TPR. Thirst mechanism → increase blood volume. 4- Stimulates release of aldosterone from adrenal cortex → increase blood volume by increasing sodium and water.  32 Thank you