Small artery and arteriole muscular A Struetural characters 1. Diameter<lmm 2. Present internal elastic lamina 3. A few layers of smooth muscle F 4. No external elastic lamina 5. Arteriole: diameter <0.3mm 1-2lavers of smooth muscle F Functions regulate blood pressureSmall artery and arteriole muscular A. Structural characters 1.Diameter<1mm 2. Present internal elastic lamina 3. A few layers of smooth muscle F. 4. No external elastic lamina 5.Arteriole: diameter < 0.3mm 1~2layers of smooth muscle F. Functions 1. regulate blood flow to organs and tissues 2. regulate blood pressure