blood
_ flows in a closed loop between the heart and the organs
arteries
transport blood from the heart throughout the body
arterioles
control the amount of blood that flows through each organ
capillaries
the vessels where materials are exchanged between blood and surrounding tissue cells
veins
return blood from the tissue back to the heart
blood pressure
Force exerted by blood against a vessel wall
systolic pressure
– Peak pressure exerted by ejected blood against vessel walls during cardiac systole
– Averages 120 mm Hg
diastolic pressure
– Minimum pressure in arteries when blood is draining off into vessels downstream
– Averages 80 mm Hg
pulse pressure
the difference between systolic and diastolic pressures
Mean Arterial Pressure (MAP)
• the average driving pressure throughout the cardiac cycle=
2/3 (diastolic) + 1/3 (systolic)
arteries
• have low resistance so are rapid-transit passageways; large radius
• act as pressure reservoir due to elastic properties to provide driving force for blood when ventricle is in diastole
arterioles
• Major resistance vessels
• Have a thick layer of circular smooth muscle.
high
_ resistance produces a large drop in mean pressure between the arteries and capillaries
This decline enhances blood flow by contributing to the pressure gradient between the heart and organs
functions of arterioles when adjusted
– to variably distribute cardiac output among the organs depending on body needs'
– to help regulate arterial blood pressure
parallel flow
blood across the entire system
series flow
blood through individual organs
priority of the circulatory system
Maintaining adequate flow to the brain
hemodynamics
represents the relationship of flow, pressure and resistance
increases; decreases
- Flow is inversely related to resistance.
Resistance _ so flow _
pressure gradient
the difference in pressure between the beginning and the end of a vessel
higher; lower
blood flows from an area of _ pressure to an area of _ pressure down a pressure gradient
greater
The _ the pressure gradient the greater the flow rate through that vessel
resistance
the hindrance to blood flow through a vessel
• Based on frictional forces during blood flow.
resistance and r4
Doubling the radius reduces the resistance to 1/16th its original value and increases flow 16-fold.
intrinsic control
Tissues have mechanisms to regulate arteriole tone; affect nutrient delivery and waste removal (metabolism)
extrinsic mechanisms
exist to regulate arterioles and maintain adequate MAP; controlled by sympathetic NS.
vasoconstrictor
increased sympathetic activity
Decreased metabolism
(high oxygen, low CO2, low temperature)
(extrinsic)
vasodilation
decreased sympathetic activity
Increased metabolism (low oxygen, high CO2, high temperature)
(intrinsic)
extrinsic control
• The cardiovascular control center in the medulla adjusts sympathetic output to the arterioles.
• NE released from sympathetic nerve bring about vasoconstriction
• This change in arteriolar resistance bring about increased mean arterial pressure.
extrinsic sympathetic
control of arteriolar radius is important in regulating blood pressure
intrinsic control
• Local chemical changes associated with changes in the level of metabolic activity affect arteriole resistance
• Increased blood flow in response to enhanced tissue activity is called active hyperemia (exercising muscle)
• Can be pathological like that of inflammation
septic shock
• mediated by massive vasodilation
– Cause by dilators released from bacteria (basically)
neurogenic shock
loss of sympathetic innervation
cardiogenic shock
• hypoperfusion due to the heart itself
• Could either be low SV and/or low HR
• Resistance isn’t the problem, it’s cardiac output
capillaries
• thin-walled, small-radius, extensively branched vessels.
• Surface area for exchange is maximized
• Diffusion distance is minimized
•Large cross-sectional area results in slow blood velocity to maximize time for exchange
passive diffusion
down concentration gradients is the primary mechanism for exchanging solutes
bulk flow
determines the distribution of the ECF volume between the vascular and the interstitial fluid compartments
Individual solutes
_ are exchanged primarily by diffusion down concentration gradient
lipid
_ soluble substances pass directly through endothelial cells lining a capillary.
water
_ soluble substances pass through water-filled pores between the endothelial cells.
capillary exchange
Plasma proteins generally do not escape
bulk flow
• occurs when protein-free plasma filters out of the capillary, mixes with the interstitial fluid and then is reabsorbed.
• important in regulating the distribution of ECF between the plasma and the interstitial fluid to help maintain arterial blood pressure.
filtration
occurs when pressure inside the capillary exceeds pressure outside and fluid is pushed out through the pores
reabsorption
occurs when inward-driving pressures exceed outward pressures and net movement of fluid back into the capillaries occurs.
Capillary hydrostatic
pressure pushes fluid out of the capillary bed
Plasma colloid osmotic
pressure draws fluid back into the capillary bed
filtered; reabsorbed
Slightly more fluid is _ out of the capillaries into the interstitial fluid than is _ from the interstitial fluid back into the plasma.
lymphatic
Excess fluid left in the interstitial fluid is picked up by the _ system and returned to general circulation.