7 Cardiovascular System – Blood Flow / Pressure
Objectives
- Arteries and Arterial Blood Pressure
- Overview of Arterioles and Resistance to Flow
- Factors Affecting Arterial Blood Pressure
- Veins
Interactive Activities
Critical Thinking Questions
Learning Summary
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