iphy 3430 10-13-11
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IPHY 3430 10-13-11. BLOOD PRESSURE Flow rate = P x radius of vessel 4 length x = viscosity (function of number of red blood cells and concentration of plasma proteins). - PowerPoint PPT PresentationTRANSCRIPT
IPHY 3430 10-13-11
BLOOD PRESSURE
Flow rate = P x radius of vessel4
length x
= viscosity (function of number of red blood cells and concentration of plasma proteins)
Blood pressure = cardiac output x peripheral resistance
Cardiac output = heart rate x stroke volume
Peripheral resistance = degree of vasoconstriction or vasodilation of arterioles
Cardiac output
Heart rate by SNS by PNS
Stroke volumevenous return by SNSstrength of contraction by SNS
Peripheral resistance
by SNS output
by SNS output
Regulation of blood pressure
Sensors: 1. baroreceptors in aorta and carotid2. chemoreceptors in aorta and carotid3. medulla itself
Integrator: medulla vasomotor center
Output: PNS and SNS
BP --> sensors --> medulla --> PNS--> heart rate SNS--> heart rate
venous return -->stroke volume
peripheral resistance
BP
BP --> sensors --> medulla --> PNS--> heart rate SNS--> heart rate
venous return --> stroke volume
peripheral resistance
BP
And…. BP --> kidney (sensor and integrator)--> renin--> renin converts angiotensinogen to angiotensin I--which is converted to--> angiotensin II by lung converting enzyme->angiotensin II causes:1.vasoconstriction -- peripheral resistance2. reduces GFR --> kidney reduces urine production->
blood volume --> venous return --> stroke volume
3. Stimulates thirst--> blood volume --> venous return ---> stroke volume
and …..
Angiotensin II also causes:
aldosterone release from adrenal gland ---> Na+ uptake from urine --> water uptake from urine --> blood volume --> venous return --> stroke volume --> cardiac output
net effect of angiotensin II --> BP
Circulatory Shock
1. Hypovolemic2. Cardiogenic3. Vasogenic4. Neurogenic
Shock Non-progressive--can recover with massive SNS output and renin-angiotensin
Progressive--positive feedback BP --> flow --> BP --> flow …
flow leads to BP because of lack of adequate oxygen to medulla, which loses control of SNS
Hypertension
peripheral resistance due to athlerosclerosis aldosterone secretion renin secretion neurogenic“essential hypertension”
Local control over blood flow
Exercise
Input from higher centers causes Medulla/SNS to change distribution of blood and change in BP regulation