APK 2105C Study Guide - Quiz Guide: Venae Cavae, Pressure Gradient, Blood Pressure
16 Jun 2018
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Chapter 14 All Lectures
Lecture 1
Chapter 14, Lecture 1
Vessels & Blood Pressure
• Stroke volume = blood flow from heart per cardiac cycle (heartbeat)
• Cardiac output = blood flow leaving per minute
o How quickly heart is beating, how strong heart is beating
o CO = HR x SV
o Regulation is both intrinsic and extrinsic
▪ Intrinsic = from within the organ
▪ Extrinsic = from the nerve system
• Physical laws of blood flow and BP
o Same laws that describe liquid flowing through pipes
o Flow = deltaP / R = (P1-P2)/R
▪ Delta P = pressure gradient = change in pressure
▪ R = resistance
• Any factors that hinder blood flow
▪ Flow is inversely proportional to resistance
▪ Flow is directly proportional to pressure gradient
▪ P1 = starting pressure, P2 = ending pressure
o How do you increase or decrease flow?
▪ Increase P1 to increase flow
▪ Decrease P2 to increase flow
▪ Decrease R to increase flow
▪ Inverse of above is true to decrease flow
• Pressure gradients in the CV system
o Bulk flow = regardless of the medium (gas, liquid, air), the driving force for bulk
flow is a pressure gradient—direction of flow is always down gradient
▪ High BP → low BP
o Rate of flow depends on pressure DIFFERENCE, not absolute pressure
▪ Without pressure gradient—no driving force
o DeltaP for systemic blood flow = MAP – CVP
▪ Difference between blood flow from aorta (right after it leaves the heart)
and other end of system before it comes back into the heart
▪ Aortic pressure = 85 mmHg (MAP) = P1
• Driving force for blood flow through system
• Very tightly regulated
▪ Pressure gets lower as it gets close to capillaries
▪ Vena cava pressure = 0 mmHg (dumping into RA—central venous
pressure = CVP) = P2
• CVP is actually 2-5 mmHg but is so low—negligible
o Pulmonary vs. systemic circuit flow
▪ Same in pulmonary AND systemic
• Pressure is maintained through
large arteries
o Falls off with smaller
arteries, arterioles
find more resources at oneclass.com
find more resources at oneclass.com
• Veins, vena cava have very low pressure
▪ Pressure generated in pulmonary is much lower than in systemic
• Have same P2 though—still 0 mmHg
▪ RV is pumping pulmonary, LV is pumping systemic
• LV walls are much thicker—able to generate more force/pressure
• Flow out of R side of heart is the same as L side of heart
o CO is same on both sides
o CO = blood flow out of the heart every minute
o Same pressure…how? Resistance is very different
Lecture 2
Chapter 14, Part 2
Vessels & Blood Pressure
• Resistance in the CV system
o Resistance of individual vessels depends on
▪ Physical dimensions of tube
• Lots of branches in the “tubes” through the body
▪ Properties of the fluid
• Viscosity
o Factors impacting resistance
▪ Vessel radius = NUMBER ONE factor in impacting resistance
• Vasoconstriction
• Vasodilation
▪ Vessel length
• Longer vessels = far more resistance
• Not a factor in the body—vessels don’t just get longer instead in
periods of growth
▪ Blood viscosity
• Thicker blood = more resistance
• Determined by cell/protein conc
• Not normally factor in the body
o Poiseuille’s Law
▪ Fluid flowing through a tube encounters resistance from the walls of the
tube and the fluid itself
▪ Resistance = (8Ln)/(pi r^4)
• L = length of tube
• n = viscosity of fluid
• r = internal radius
o r is to ^4
▪ As r decreases, it impacts resistance to the ^4—
very big impact
▪ If radius is decreased by 1/2, resistance increases
16 fold
▪ Biggest impact on resistance
• L and n are directly proportional to resistance
o Total peripheral resistance (TPR) = combines resistances of all the vessels in the
network
▪ Vasoconstriction and dilation ANYWHERE changes the TOTAL
resistance of the network of vessels
find more resources at oneclass.com
find more resources at oneclass.com
▪ Flow = pressure gradient / resistance
▪ CO = MAP (mean arterial pressure) / TPR
• May need to be rearranged
• Refers to CO to a specific location/organ
Lecture 3
Chapter 14, Lecture 3
Vessels & Blood Pressure
• Review of the vessels
o Lumen
o Endothelium
▪ Only layer in capillaries
▪ Allow for diffusion
o Smooth muscle
▪ Veins have less smooth muscle than arteries
o Connective tissue
o Arterioles have highest ability to generate resistance against blood flo
o Arteries are both stiff and flexible
o Artery → arteriole → capillary → venule → vein
▪ Arteries are both stiff (collagen) and flexible (elastic)
• Have lots of smooth muscle in them
• Very elastic—good for blood flow
• Lots of collagen in walls of arteries—more than in veins
o Collagen is very strong—add stiffness to artery walls
▪ Vein has larger lumen
• Blood vessels and pressure
o Blood vessels expand when pressure inside it increase—contracts when
pressure falls
▪ Degree of distention depends on transmural pressure
• Dependent on pressure inside and outside the vessel
o Ex: if pressure outside is high, won’t be able to expand as
much when pressure increases inside
o Elasticity acts to push back on pressure trying to expand
the vessel
▪ More important in arteries—more elastic
o Compliance = change in volume per unit change in transmural pressure
▪ The ease with which a vessel expands
• If walls are very stiff, generates lots of pressure inside (arteries)
• Arteries have low compliance—veins have higher
▪ Compliance = change in volume / change in (pressure inside – pressure
outside)
o Arteries = pressure reservoir
▪ Low compliance from collagen, elasticity
▪ Wall stores pressure and help maintain BP
▪ Takes a lot of transmural pressure to get them to distend
o Arterial BP
▪ Systolic BP (SBP) = max pressure in aorta occurs
▪ Diastolic BP (DBP) = min pressure in the aorta occurs
find more resources at oneclass.com
find more resources at oneclass.com
