Chapter 21: Blood Vessels Flashcards
Artery Linings
Tunica interna (= intima)
Lined with endothelium
Tunica media
Contains the largest amount of smooth muscle, elastic fibers
Controls blood flow and blood pressure
Tunica externa (boring)
Arterioles
Deliver blood to capillary beds
Anastomosis
union of artery branches that provides an alternate pathway (collateral circulation) to a region
An end artery has no anastomosis
Capillaries
site of exchange of gases, nutrients, wastes with tissues
Microcirculation
blood flow through all capillaries
Sinusoids
wide “leaky” capillaries (liver, red marrow, spleen)
Venules
Union of several capillaries
Venous return:
Blood flow back to heart
Blood Flow
Blood flows from areas of higher pressure to areas of lower pressure
Blood pressure highest in aorta and almost zero as blood enters right atrium
Diffusion
most important for solute exchange
Bulk flow
Large numbers of ions, molecules, and particles in a fluid move in the same direction at a greater rate than diffusion alone; pressure driven
Important for regulation of relative volumes of blood and interstitial fluid
Filtration vs Reabsorption
Filtration – fluid moves from blood vessel to interstitial space
Reabsorption – fluid moves from interstitial space into blood vessel
Starling’s Law of Capillaries:
Volume of reabsorbed fluid (almost) equals volume of fluid filtered. Excess interstitial fluid returns (lymph vessel)
Resistance
friction between walls of blood vessels and the blood
