APK 2105C Lecture Notes - Lecture 32: Smooth Muscle Tissue, Mean Arterial Pressure, Aorta
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
▪ Mean arterial pressure (MAP) = average pressure in the aorta during a
cardiac cycle
• MAP = (SBP + DBP + DBP) / 3
• MAP = [SBP + (2 x DBP)] / 3
▪ At rest, we spend more time filling our hearts
o Measuring BP
▪ Best way is inter-arterioly—direct method
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