Key Terms
Blood moves
Heart -> Arteries -> Arterioles -> Capillaries -> Venules -> Veins -> Heart.
Wall
Endothelium + basement membrane only (no tunica media or externa).
Metarteriole
Vessel with characteristics of both arteriole and capillary; feeds a capillary bed of 10-100 capillaries.
Precapillary sphincters
Rings of smooth muscle at the entrance to each capillary.
Vascular shunt
When all precapillary sphincters are closed, blood flows from metarteriole through a thoroughfare channel directly to th
Venules
8-100 micrometers; postcapillary venules drain capillary beds.
Veins
Thin walls, large irregular lumens, low pressure.
Venoconstriction
Smooth muscle contraction in vein walls; rounds the lumen, reduces surface area, decreases resistance, and increases flo
Blood flow
Volume of blood moving through a vessel per unit of time.
Blood pressure
Force blood exerts against vessel walls; measured in mm Hg. Resistance: anything that slows or opposes blood flow.
Systolic pressure
Higher number; pressure during ventricular contraction (systole). Normal ~120 mm Hg.
Mean Arterial Pressure (MAP)
Average driving force of blood to tissues.
Formula
MAP = diastolic + (systolic - diastolic) / 3 Normal MAP: 70-110 mm Hg. MAP below 60 mm Hg for extended period = ischemia
Pulse
Expansion and recoil of an artery from each heartbeat; palpable at radial artery (wrist), carotid (neck), and other supe
Korotkoff sounds
Turbulent blood flow sounds heard through a stethoscope during blood pressure measurement. First sound heard = systolic