PSIO 241 CH 10

_ flows in a closed loop between the heart and the organs

transport blood from the heart throughout the body

control the amount of blood that flows through each organ

the vessels where materials are exchanged between blood and surrounding tissue cells

return blood from the tissue back to the heart

Force exerted by blood against a vessel wall

– Peak pressure exerted by ejected blood against vessel walls during cardiac systole

– Averages 120 mm Hg

– Minimum pressure in arteries when blood is draining off into vessels downstream

– Averages 80 mm Hg

the difference between systolic and diastolic pressures

• the average driving pressure throughout the cardiac cycle=

2/3 (diastolic) + 1/3 (systolic)

• 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

• Major resistance vessels

• Have a thick layer of circular smooth muscle.

_ 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

– to variably distribute cardiac output among the organs depending on body needs'

– to help regulate arterial blood pressure

blood across the entire system

blood through individual organs

Maintaining adequate flow to the brain

represents the relationship of flow, pressure and resistance

- Flow is inversely related to resistance.

Resistance _ so flow _

the difference in pressure between the beginning and the end of a vessel

blood flows from an area of _ pressure to an area of _ pressure down a pressure gradient

The _ the pressure gradient the greater the flow rate through that vessel

the hindrance to blood flow through a vessel

• Based on frictional forces during blood flow.

Doubling the radius reduces the resistance to 1/16th its original value and increases flow 16-fold.

Tissues have mechanisms to regulate arteriole tone; affect nutrient delivery and waste removal (metabolism)

exist to regulate arterioles and maintain adequate MAP; controlled by sympathetic NS.

increased sympathetic activity

Decreased metabolism

(high oxygen, low CO2, low temperature)

(extrinsic)

decreased sympathetic activity

Increased metabolism (low oxygen, high CO2, high temperature)

(intrinsic)

• 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.

control of arteriolar radius is important in regulating blood pressure

• 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

• mediated by massive vasodilation

– Cause by dilators released from bacteria (basically)

loss of sympathetic innervation

• hypoperfusion due to the heart itself

• Could either be low SV and/or low HR

• Resistance isn’t the problem, it’s cardiac output

• 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

down concentration gradients is  the primary mechanism for exchanging solutes

determines the distribution of the ECF volume between the vascular and the interstitial fluid compartments

_ are exchanged primarily by diffusion down concentration gradient

_ soluble substances pass directly through endothelial cells lining a capillary.

_ soluble substances pass through water-filled pores between the endothelial cells.

Plasma proteins generally do not escape

• 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.

occurs when pressure inside the capillary exceeds pressure outside and fluid is pushed out through the pores

occurs when inward-driving pressures exceed outward pressures and net movement of fluid back into the capillaries occurs.

pressure pushes fluid out of the capillary bed

pressure draws fluid back into the capillary bed

Slightly more fluid is _ out of the capillaries into the interstitial fluid than is _ from the interstitial fluid back into the plasma.

Excess fluid left in the interstitial fluid is picked up by the _ system and returned to general circulation.