carry blood away from heart

rapid transit pathways from heart to tissues

little resistance to flow

Contain smooth muscle, can change radius of arteriole

this ability is the major way to regulate blood flow to specific organs, & a major way that arterial blood pressure is controlled

What controls Arteriolar Radius:

Intrinsic Local Factors

Local metabolic changes: increased metabolic demands usually result in vasodilation & increased blood flow to that area

decreased demand --> vasoconstriction

Histamine Release: histamine stored & synthesized in special connective tissue

During allergic reaction or damage tissue, histamine released causing vasodilation & increased blood flow (swelling)

Temperature local heat application causes vasodilation, cold-->vasoconstriction

What Controls Arteriolar Radius:

Extrinsic (Neural Hormonal) Factors

Sympathetic Norepi & Epi control

alpha receptors bind norepi, cause vasocontstriction  in arterioles found in most organs

beta 2 receptors bind epi and cause vasodilation in cardiac and skeletal muscle

capillary walls very thin minimize diffusion distance

flattened layer of endothelial cells

large overall surface area

velocity of blood very slow to maximize time for exchange

Passive diffusion: capillaries and interstitial fluid

lipid soluble pass thru endothelial cells

water soluble pass thru pores

Bulk Flow: distributing ECF between plasma and interstitial fluid

more fluid filtered out of capillaries during bulk flow, lymph system gets it back

returns cardiovascular excess fluid 

returns cardiovascular proteins lost from capillaries

disease defense: lymph nodes contain specialized cells to destroy pathogens

low resistance passageways return to heart

storage vesses, 60% blood in veins during resting

thin stretchable walls, distends to accomodate blood

delicate balance between capacity of veins, extent of venous return & cardiac output

as venous capacity increases, venous return decreses

as venous capacity decreases, venous return increase

Driving pressure from cardiac contraction

Sympathetic (fight or flight) activity

Skeletal Muscle activity increases venous return

Venous Valves - 1 way valves prevent backflow away from heart

Respiratory ACtivity

Cardiac Suction