Structure and Function of Blood Vessels

Arteries

Convey blood from heart to capillaries

Capillaries

Microscopic porous blood vessels that exchange substances between blood and tissues

Veins

Transport blood from capillaries to heart

Tunica intima

Innermost layer of vessel wall composed of endothelium and subendothelial layer of areolar connective tissue

Tunica media

Middle layer of vessel with circularly arranged smooth muscle cells and elastic fibers; causes vasoconstriction and vasodilation

Tunica externa

Outermost layer of vessel with areolar connective tissue, elastic, and collagen fibers; helps anchor vessel to other structures

Vasa vasorum

Small arteries supplying very large vessels

Elastic arteries

Largest arteries conducting blood from heart to muscular arteries with a large proportion of elastic fibers allowing stretch and recoil

Muscular arteries

Medium arteries distributing blood to specific body regions with muscle allowing vasoconstriction and dilation

Arterioles

Smallest arteries with larger ones having three tunics and smaller ones having thin endothelium and single layer of smooth muscle; regulate systemic blood pressure and blood flow

Continuous Capillaries

Type of capillaries with endothelial cells forming a continuous lining and intercellular clefts allowing passage of smaller molecules but not large particles

Fenestrated Capillaries

Capillaries with endothelial cells having pores for small protein movement

Sinusoids

Capillaries with large gaps, incomplete basement membrane, found in bone marrow

Basement Membrane

Supportive structure under endothelial cells in capillaries

Pinocytotic Vesicles

Vesicles involved in fluid absorption in capillaries

Erythrocyte

Red blood cell

Intercellular Cleft

Space between endothelial cells in capillaries

Lumen

Central space within a blood vessel

Metarteriole

Vessel branch of an arteriole feeding capillary beds

Precapillary Sphincter

Smooth muscle ring controlling blood flow into true capillaries

Vasomotion

Cycle of precapillary sphincter contraction and relaxation

Perfusion

Blood flow entering capillaries per unit time per gram of tissue

Venules

Smallest veins, companion vessels with arterioles

Valves

Structures preventing blood pooling in veins, ensuring flow toward heart

Systemic Veins

Veins acting as blood reservoirs, holding 70% of blood in systemic circulation at rest

End Artery

Artery providing only one path for blood to reach an organ or region

Arterial Anastomosis

Convergence of two or more arteries to supply the same region

Venous Anastomosis

Convergence of two or more veins draining the same body region

Arteriovenous Anastomosis

Direct transport of blood from artery to vein, bypassing capillaries

Portal System

Path where blood flows through two capillary beds in sequence