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