PSIO 241 CH 10

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.