Vascular System Flashcards
Major functions of the vascular system
Regulating BP and distributing blood flow.
Arteries
- Large radii, high elasticity
- low-resistance tubes
- “Pressure reservoirs”
Systolic Pressure
max arterial pressure reached during the peak of ventricular contraction/ejection.
Compliance
change in volume / change in pressure
Higher compliance = more stretch
Diastolic Pressure
Min arterial pressure reached just prior to ventricular ejection.
Arterial Blood Pressure
Systolic Pressure / diastolic pressure
Pulse Pressure
systolic Pressure - diastolic pressure
Mean arterial pressure (MAP)
average pressure driving blood to the tissues over cardiac cycle
Factors affecting magnitude of the pulse pressure:
- SV
- Speed of ejection of the stroke volume
- Arterial compliance
Arterioles Function
- Determine relative blood flow to organs at any given MAP
- Determine MAP
Arteriole diameter is controlled by:
- Neural
- Hormonal
- Local chemicals
Flow-Pressure Relationship
Flow = change in pressure / resistance
Vasoconstriction of arterioles = increases resistance; if pressure remains constant what happens to blood flow to tissues/organs?
Decreased
Active hyperemia
increase in blood flow due to increased metabolic activity.
Ex: blood flow to skeletal muscles increases while exercising due to vasodilation.
Flow Autoregulation
the automatic adjustment of blood flow despite changes in pressures.
Ex: kidneys reacts to reduction in BF, due to diseased renal artery, by vasodilating its own arterioles.
Reactive Hyperemia
a temporary, significant increase in blood flow to an organ, following release of complete blood flow occlusion.
Ex: increase in BF to the arm, during a BP reading, after a brachial artery has been squeezed shut by the BP cuff.
Response to injury
chemicals released by injured cells or found in the blood cause vasodilation of blood vessels in injured area.
Ex: this occurs during the inflammatory repsonse to injury or infection.
Nitric Oxide is an example of a paracrine hormone secreted by endothelial cells. What is the function?
Induces relaxation or contraction.
Gas and nutrient exchange occurs at what level of vasculature?
Capillaries
Venules
- large capacity for blood (capacitance vessel)
- some permeability to macromolecules
- Site of migration of leukocytes into tissues during inflammation and infection.
Veins
Thin and compliant, blood reservoirs
Mechanisms that aid in venous return
- Respiratory pump
- Muscular pump
- Smooth muscle
Respiratory pump
increased venous pressure d/t diaphragm contraction = increased abdominal pressure which compressed abdominal veins to return blood to heart.
Muscular Pump
muscles contract and squeeze veins resulting in movement of blood towards heart.
Ex: calf pumps
Smooth Muscle
In veins is under Sympathetic NS control and contracts when stimulated = venous contraction which promotes venous return.
How is MAP calculated?
Cardiac Output x Total Peripheral Resistance
Where in the vascular system does the majority of resistance occur that effects MAP?
arterioles
Baroreceptor reflex
a group of homeostatic responses to changes in arterial blood pressure (MAP) that provide short term regulation of BP
How are baroreceptor reflexes initiated?
arterial stretch/pressure receptors
Baroreceptor reflexes are under control of
autonomic regulation
Arterial Baroreceptors are stretch/pressor receptors - where are they located?
carotid sinuses and aortic arch
Where is sensory input from the arterial baroreceptors input?
In the medullary cardiovascular control center
How does the action potential firiting frequency change with response to pressure?
- Increased firing of AP due to elevated MAP.
- Decreased firing rate of AP due to reduced MAP
How can PT help to challenge the strength of the baroreceptor reflexes?
slow positional changes
What are some potential causes of hypotension?
- Hemorrhage
- Decreased cardiac contractility
- Strong emotion
- Massive release of endogenous substances (allergic reaction)
Why is the skeletal muscle pump in the LE’s important?
It reduces the effects of gravity (pressure) and aids in return of blood to heart.
