Question

MCAT Biology Tutorial: Blood Pressure & Flow

Answer 1

\({\bf{Measuring~Blood~Pressure:}}\) systole: the contraction of the blood vessels, highest pressure
diastolic: relaxation of ventricles, lowest pressure

flow = (delta P)/R where P = pressure and R is resistance

can also use Poiseuille's Law (see hydrostatics tutorial)

highest in the aorta and lowest in veins

blood does not perfectly follow bernoulli's b/c it's not ideal fluid

\({\bf{Regulating~Blood~Pressure:}}\)
- blood pressure must be maintained to exchange nutrients/waste in the capillaries
- total peripheral resistance: resistance of the entire circulatory system
- changed by changing the output level of the heart & the muscle lining of arterioles

- two methods:
> baroreceptor reflex (quick).
- changes cardiac output and resistance
- activates SNS or PNS (depending on whether the pressure needs to be raised or lowered)
- uses baroreceptors in arteries

> renin-angiotensin-aldosterone: (will refer to this as angiotensin system from now on)
- changes volume of plasma
- uses mechanoreceptors to signal to kidneys to secrete hormones
- renin --> increase blood volume through water intake --> increase in blood pressure

Answer 2

\({\bf{Fluid~Exchange~in~the~Capillaries:}}\)
- low overall pressure
- two ends of a capillary (arteriole end and venule end)
- at arteriole end, hydrostatic pressure is high compared to osmotic, so blood diffuses out
- at venule end, the hydrostatic pressure is lower b/c of the fluid that has exited, and now the fluid will flow back into the capillary
- throughout this process the osmotic pressure is relatively constant so the exchange is governed by the hydrostatic pressure differential

blood is not ideal but can be approximated w/ continuity Q = Av where velocity is inversely proportional to cross-sectional area assuming constant flow

Answer 3

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 9th Edition ExamKracker's Biology 2 Prep book for the new MCAT