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Controlling MAP • Why do we need to control it? • Short term • Long term Brain Centers for Short Term MAP Control • Vasomotor • Cardioinhibitory • Cardioacceleratory Increased vasomotor center activity __creased sympathetic output to arterioles Vaso__________ __creased peripheral resistance __creased blood pressure What about a decrease in vasomotor activity? Increased cardioacceleratory center activity __creased sympathetic output to heart __creased heart rate and stroke volume __creased cardiac output __creased blood pressure What about a decrease in cardioacceleratory activity? Increased cardioinhibitory center activity __creased parasympathetic output to heart __creased heart rate __creased cardiac output __creased blood pressure What about a decrease in cardioacceleratory activity? Baroreceptor Reflex Baroreceptor Reflex • Baroreceptors signals the cardiac and vasomotor centers via CN IX and X. • Frequency of these impulses is proportional to MAP. • Cardiac and vasomotor centers adjust their output accordingly. MAP rises MAP falls Demonstrating the Baroreceptor Reflex • Take the subject’s radial pulse. • Find the carotid pulse point and GENTLY press on it. • What will happen to the radial pulse? • Why? Adrenal Medullary Mechanism • Release epinephrine (and a small amt of NE) in response to: – Large drops in MAP. – Increases in physical activity. – Stressful situations. Adrenal Medullary Mechanism • How would activation of the adrenal medulla affect: – – – – – HR SV CO PR BP Renin-Angiotensin-Aldosterone System Renin Angiotensin II Indirect Mechanism System Renin-Angiotensin-Aldosterone Angiotensin II Vasoconstriction Aldosterone & Antidiuretic hormone Thirst Increased TPR Increased BV Increased BP Indirect Mechanism System Renin-Angiotensin-Aldosterone • In response to a fall in MAP, renin release by the kidney would: • In response to a rise in MAP, renin release by the kidney would: A 25yo woman complains to her doctor of headaches and blurred vision. Her blood pressure is 200/130 mmHg. After the BP has been reduced, investigations are made to find the cause of the problem. It’s discovered that her left renal artery is narrowed. Why would this cause the rise in BP? Long Term BP Control • Achieved by the... • Primarily done by altering... Long Term BP Control Large increase in BP ____________ urine formation ____________ urine output ____________ blood volume _________BP • As we go from the aorta to the billions of capillaries, what happens to the total crosssectional area? • What happens to the velocity of blood flow? • As we go from the billions of capillaries to the venae cavae, what happens to the total crosssectional area? • What happens to the velocity of blood flow? The Paradoxical Problem of the Vasomotor Center Local Regulation of Blood Flow • Autoregulation - adjustment of blood flow to each tissue according to its immediate needs. • Surplus or deficiency of local chemicals influences local vessel diameter and blood flow. Local Regulation of Blood Flow Tissue temp. ____ Working Muscle Tissue Tissue CO2 levels ___ Tissue O2 levels ___ Arterioles serving tissue vaso________ Lactic acid levels ___ ______blood flow to tissue CO2 _______ Lactic acid _______ Heat _______ O2 ________ Capillary Exchange • Btwn blood plasma and tissue fluid. • Nutrients, wastes, signaling molecules • FLUID Capillary Fluid Exchange • 4 forces – Capillary osmotic pressure. – Capillary hydrostatic pressure. – Interstitial osmotic pressure. – Interstitial hydrostatic pressure. Capillary Hydrostatic Pressure • A.k.a… • What does it do? ISF CAPILLARY HP Capillary Osmotic Pressure • Mostly due to… • What does it do? ISF CAPILLARY OP Interstitial Hydrostatic Pressure • Usually inconsequential b/c… • What would it do? ISF HP CAPILLARY Interstitial Osmotic Pressure • Usually inconsequential b/c… • What would it do? ISF OP CAPILLARY Capillary Fluid Exchange • Thebalance of what 2 forces typically determines if fluid enters or exits the capillary? • Net filtration pressure Capillary Filtration • If capillary HP >> capillary OP, – What kind of fluid movement will occur? ISF CAPILLARY Capillary Reabsorption • If capillary HP << capillary OP, – What kind of fluid movement will occur? ISF CAPILLARY Capillary Fluid Exchange Pressure • Is capillary HP constant?? • Is capillary OP constant?? Arterial end Venous end Distance along the capillary Capillary Fluid Exchange Pressure • At which end of the capillary is filtration likely to occur? • At which end is reabsorption likely to occur? Arterial end Venous end Distance along the capillary Capillary Fluid Exchange • Capillary HP usually slightly exceeds capillary OP. • Why does this matter?
