Blood Flow and Blood Pressure Flashcards
Which blood vessels alter their diameter to adjust blood supply?
Arterioles - this is an example of variable resistance
Where does the circulatory system pass from arterial to venous system?
Capillary beds
Which part of the circulatory system acts as a pressure reservoir to maintain blood flow during ventricular relaxation?
Systemic arteries
Which part of the circulatory system acts as a volume reservoir and holds most of the blood at any given time?
Systemic veins
Which vessels are elastic and why?
Arteries and veins - to accommodate high pressure blood
Which vessels have a layer of smooth muscle and why?
Arteries, arterioles, and veins
To allow for vasodilation and vasoconstriction
Metarterioles
Bypass channels for blood passing from arterioles to venules when precapillary sphincters constrict blood flow to capillaries
Precapillary sphincters
Close off capillaries in response to local signals
By what mechanism is blood returned to the heart in the venous system?
Skeletal muscle pumps and valves that prevent the back flow of blood when the muscle releases
Respiratory pump - creation of negative thoracic cavity pressure upon inhalation decreases pressure in the large central vein which increases flow in the direction of the heart
How do arteries & arterioles function as pressure reservoirs?
Expand upon ventricular contraction to store pressure in their elastic walls
Upon ventricular relaxation, elastic recoil of arteries propels blood to systemic circulation. Movement of arteries back o resting diameter increases the pressure in the arteries which pushes blood forward.
Pulse pressure
Systolic - diastolic pressure
Mean arterial pressure
Diastolic pressure - (1/3)pulse pressure
How to measure BP
Inflate cuff until blood flow stops
Release pressure in cuff until korotkoff sounds = systolic pressure
Continue releasing pressure in cuff until sounds disappear = diastolic pressure
How does blood volume affect mean arterial blood pressure?
Fluid intake increases blood volume which increases BP
Fluid loss may be passive or regulated by kidneys - lowers blood volume, decreases BP
How do changes in cardiac output affect mean arterial blood pressure?
Cardiac output = heart rate x stroke volume
Increasing cardiac output increases BP
Active hyperemia
Blood flow to capillary beds regulated by local signals such as metabolic vasodilator during exercise
Reactive hyperemia
Hyperemia that follows a period of decreased blood flow usually due to an occlusion
Metabolic vasodilators accumulate in the ECF due to an occlusion
Autonomic nervous system control of vasodilation/constriction
Arterioles have sympathetic (epi/norepi) and parasympathetic receptors (ACh)
In sympathetic signaling, the amount of epi/norepi determines whether vasoconstriction or dilation will occur. Signaling rate increases cause constriction while signaling rate decreases cause dilation.
At rest, approx. how much blood goes to the kidneys and liver/digestive tract?
20% to kidneys
25% to digestive tract and liver
How does constriction of one blood vessel affect flow in neighboring vessels?
Since total flow in a closed system must be equal, if one vessel is constricted, the other vessels compensate with higher flow rates.
Baroreceptor reflex
Sensors in carotid and aortic arteries sense pressure changes via mechanoreceptors which balances parasympathetic and sympathetic NS
Standing up shifts to sympathetic signaling —> increase in HR
Sympathetic neurons stimulate which parts of the circulatory system
SA node, ventricles, arterioles, veins
Sympathetic stimulation of arteriolar smooth muscle affects what aspect of blood pressure?
Vasoconstriction/dilation and thus peripheral resistance
Sympathetic stimulation of ventricular myocardium affects
Cardiac output
How do materials enter and exist the capillary bed?
Leaky junctions where water and small dissolved solutes bass through the basement membrane of the capillary
Transcytosis where proteins and macromolecules cross the endothelium
Fence started pores that allow larger molecules to pass through the basement membrane - kidneys, intestines
Filtration
Movement of fluid and solutes out of the blood plasma into the interstitial fluid
Absorption
Movement of fluid and solutes out of the interstitial fluid into the blood plasma
Net pressure in systemic capillaries is composed of what types of pressure?
Hydrostatic pressure - colloid osmotic pressure
Hydrostatic pressure is the pressure that forces fluid out of the capillary
Colloid osmotic pressure is the pressure of proteins within the capillary that fulls fluid into the capillary
Positive net pressure (hydrostatic pressure > colloid osmotic pressure) indicates?
Net filtration
Negative net pressure (hydrostatic pressure < colloid osmotic pressure) indicates?
Net absorption
Function of the lymphatic system
Return excess filtered fluid and proteins to the circulatory system
Take fat front he small intestine to the circulatory system
Captures and destroys pathogens with the immune system
