Pressure Reservoirs: ensures smooth flow of blood even when in diastole (when the heart stops).
Elastic fibers: act as springs that store elastic force and passively recoil.
Compliance: a measure of how the pressure of a vessel will change with a change in volume. Low compliance (arteries); High compliance (veins).

Arterial Blood Pressure = pressure in the aorta
Systolic blood pressure – Max pressure
Diastolic blood pressure – Min pressure
Mean arterial pressure – Average pressure

Arterioles: resistance levels
Part of microcirculation

• Connect arteries to capillaries or metarterioles
• Connect rings of smooth muscle to regulate radius, and therefore, resistance
• Best site where resistance to flow can be regulated

Arterioles and resistance to blood flow
TBR = combined resistance of all blood vessels with the circuit
Largest pressure drop in vascular occurs along arterioles

Changes in arteriole radius

• Arteriole tone
• Vasoconstriction
• Vasodilation

Intrinsic Control of Arteriole Smooth Muscle happens via:

• Changes in metabolic activity (active hyperemia)
• Changes in blood flow (reactive hyperemia)
• Stretch of smooth muscles in arterioles (increases myogenic response)
• Local chemical messengers
• Capillaries and Venules

Microcirculation: Arterioles, Metarterioles, Precapillary sphincters
Transport mechanisms: Simple diffusion, Mediated transport, Transcytosis
Bulk flow across capillary walls: Move from blood to interstitial fluid and interstitial fluid to blood (Net filtration pressure= filtration pressure – absorption pressure).
Veins = volume reservoir and have high compliance

Factors influence pressure and return
Skeletal muscle pump = one way, absent from central veins, contraction/relaxation
Respiratory pump = Inspiration and Exhalation
Blood Volume = increased blood volume–increased pressure vice-versa
Venomotor tone = 2 effects: constriction raises pressure–blood moves to heart, increase tension reduces compliance–raises pressure–increases stroke volume