Arteries

• AWAY

• Branch

• Typically oxygenated.

Capillaries

• Smallest.

• Most abundant.– How many??

– Why?

• Exchange

Veins

• TOWARDS

• Converge.

• Typically deoxygenated.

3 Layers of the Vascular Wall

• Tunica interna

• Tunica media

• Tunica externa.

Tunica Interna/Intima• Lining.

• Endothelium.

• Supported by loose CT.

• Only layer in capillaries.

Tunica Media

• Primarily smooth muscle plus elastic fibers.

• Most prominent layer in arteries.

Tunica Media

• Smooth muscle tone

• Regulated by:

– Metabolites

– Hormones

– Sympathetic vasomotorneurons.

• Vasomotor neurons constantly release NE onto TM smoothmuscle.– What does the NE do?

– Why have a constant release?

Increased NE release by a vasomotor neuron causes:

– Tunica media smooth muscle tone to:

– Vessel diameter to:

– Resistance to blood flow in the vessel to:

– Blood flow thru the vessel to:

This gentleman has fatty plaques in his lowerleg arteries.

How do you think they affect blood flow?

How does that relate to his facialexpression?

His doctor recommends that the sympatheticnerves to those arteries be cut.

Why?

Tunica Externa/Adventitia

• Primarily collagen

• Function?

• Most prominentlayer in veins

Elastic Arteries

• Aorta and major branches.

• Act as AUXILIARY PUMPS.

• Regional distribution

• Significant layer

Muscular Arteries

• Smallest.

• May or may not have an externa.

• Highly innervated by vasomotor neurons.

Arterioles

• Regulation of blood pressure and flow.

• Easy to change the diameter.– How would you do it?

– Why would you want to?

Arterioles

Capillaries

• Smallest.

• Thin walls

• Billions

• Function?

• Almost everywhere.

Continuous capillaries––––

Most common and least permeable.No endothelial “holes”Intercellular clefts.Abundant in…

Fenestrated capillaries– Endothelial “holes”– Intercellular clefts– Found in…

Sinusoidal capillaries.––––

Most permeable and least common.Big endothelial “holes”Intercellular clefts.Can have macrophages in theirlining. Why?

– Found in…

Why are capillaries organized into beds?

What tissues will have high densities of capillary beds?

What determines whether thesphincters are open or closed?

What do precapillary sphincters do?

Vascular shunt vs.True capillaries

If you were running,

1. Precapillary sphincters in your biceps femoris would …

2. Precapillary sphincters in your large intestine would…

Veins

• All 3 tunics.

• TE is the largest.

• Thin walls

• Large lumens.

• Low resistance

• High compliance

Veins

• Smooth muscle toneprevents too muchdistention.

• Capacitance vessels/Bloodreservoirs.

• 65%

Veins

• Low pressure vessels.

• Contain valves.– What do they do?– Where are they needed?

Venous Sinuses

• Thin-walled veins made of endothelium only.

Blood Flow

• Volume per time.

• Flow thru systemic circuit = cardiac output.

• Flow to individual organs varies.– How is this achieved?

Blood Pressure

• Force per unit area exerted onthe vessel wall by blood.

• Millimeters of mercury (mmHg).

• All vessels

Resistance

• Opposition to flow

• Measure of friction.

• Peripheral resistance.

• Direction!

While this guy is running,

- the resistance of the arteriolesof his quadriceps needs to…

- the resistance of arterioles inhis colon needs to…

Sources of Resistance

• Blood viscosity.

• Total vessel length.

• Vessel radius.

Viscosity

• Viscosity resistance.

• Can you drink one of these witha straw?

• What makes it challenging?

• What are the major contributors to bloodviscosity?

• Does viscosity change often in a healthyperson?

• An increase in plasma EPO will causeresistance to…

Total Vessel Length

• Length resistance.

• Does total vessel length change in a normal person?

A B

• Which tube has greater intrinsic resistance?

• As total vessel length increases, resistance will…

• As total vessel length decreases, blood flow will…

Vessel Radius

• (1/radius4) resistance

• Does vessel radius change in a normal healthyperson?

• Which vessels?

• How is the change achieved?

Which tube has the greater intrinsic resistance?

What layer of the vessel wall has the greatest effect onvessel resistance?

a.

b.

c.

Interna

Media

Externa

A B

Resistance (length)(viscosity)

(radius)4

Which tube has the LEAST resistance?

Which tube has the GREATEST resistance?

FLOW PRESSURE GRADIENTRESISTANCE

• As resistance decreases, flow will…

• As the pressure gradient increases, flow will…

• Which does the heart influence more: pressuregradient or resistance?

Blood Pressure• Why do all blood vessels have a BP?

• Which vessel do we usually care about?

• Where is systemic BP the highest?

• Where is systemic BP the lowest?

Arterial Blood Pressure Model

• What would happen to AP if the amount of bloodpumped into the arteries increased?

• Thus, arterial pressure varies directly with…

• What would happen to AP if the resistance in thearterioles went up?

• Thus, arterial pressure varies directly with…

• What would happen to AP if there was more bloodin the entire system?

• Thus, arterial pressure varies directly with…

Systolic Blood Pressure

Diastolic Blood Pressure

• What creates it?

• How/Where do you measure it?

• What’s its relationship to heart rate?

Pulse

Pulse Pressure

• Change in arterial pressure caused by ventricularsystole.

• Varies directly with…

• PP = SBP – DBP.

Mean Arterial Pressure (MAP)• Arterial BP fluctuates. Why?

• MAP is the pressure driving blood flow.

• MAP is a weighted average of SBP and DBP.

• MAP = ⅔DBP + ⅓SBP

• MAP = DBP + ⅓PP

Mean Arterial Pressure (MAP)

Capillary Blood Pressure• Low BP.

• Why is this good? (Think about the structure of acapillary.)

Venous Blood Pressure

• Even lower BP.

• Very small gradient.

What is responsible for venous return?

• Remaining force imparted by ventricular systole.

• Gravity.

• Skeletal muscle pump.

• Respiratory pump.

• Venomotor action.

Skeletal Muscle Pump

Respiratory PumpDeep Inspiration

Thoracic volume will…

Pressure in thoracic cavity will…

Pressure in thoracic veins will…

Blood flow into thoracic veins andtowards the heart will…

Venomotor Tone

• An increase in sympathetic activity causes:– NE release on the TM of medium/large veins to…

– Venous pressure to…

– Venous return to…

Controlling MAP

• Why do we need to control it?

• Short term

• Long term

• Vasomotor

• Cardioinhibitory

• Cardioacceleratory

Brain Centers for Short Term MAP Control

Increased vasomotor center activity

__creased sympathetic output to arterioles

Vaso__________

__creased peripheral resistance

__creased blood pressure

What about a decrease in vasomotor activity?

Increased cardioacceleratory center activity

__creased sympathetic output to heart

__creased heart rate and stroke volume

__creased cardiac output

__creased blood pressure

What about a decrease in cardioacceleratory activity?

Increased cardioinhibitory center activity

__creased parasympathetic output to heart

__creased heart rate

__creased cardiac output

__creased blood pressure

What about a decrease in cardioacceleratory activity?

Baroreceptor Reflex

Baroreceptor Reflex

• Baroreceptors signals thecardiac and vasomotorcenters via CN IX and X.

• Frequency of theseimpulses is proportionalto MAP.

• Cardiac and vasomotorcenters adjust theiroutput accordingly.

Demonstrating the Baroreceptor Reflex

• Take the subject’s radial pulse.

• Find the carotid pulse point and GENTLY presson it.

• What will happen to the radial pulse?

• Why?

Adrenal Medullary Mechanism

• Release epinephrine (and asmall amt of NE) in responseto:– Large drops in MAP.

– Increases in physical activity.

– Stressful situations.

–

–

–

–

–

HR

SV

CO

PR

BP

Adrenal Medullary Mechanism

• How would activation of the adrenalmedulla affect:

Renin-Angiotensin-Aldosterone System

Renin

Angiotensin II

Indirect Mechanism

Vasoconstriction Aldosterone & Thirst

Antidiuretichormone

Increased TPR

Increased BV

Increased BP

Renin-Angiotensin-Aldosterone System

Angiotensin II

• In response to a fall in MAP, renin releaseby the kidney would:

• In response to a rise in MAP, renin releaseby the kidney would:

Indirect MechanismRenin-Angiotensin-Aldosterone System

A 25yo woman complains to her doctor ofheadaches and blurred vision. Her blood pressure is200/130 mmHg. After the BP has been reduced,investigations are made to find the cause of theproblem. It’s discovered that her left renal artery isnarrowed.

Why would this cause the rise in BP?

Long Term BP Control

• Achieved by the...

• Primarily done by altering...

____________blood volume

_________BP

Long Term BP Control

Large increase in BP

____________urine formation

____________urine output

• As we go from theaorta to thebillions ofcapillaries, whathappens to thetotal cross-sectional area?

• What happens tothe velocity ofblood flow?

• As we go from thebillions ofcapillaries to thevenae cavae, whathappens to thetotal cross-sectional area?

• What happens tothe velocity ofblood flow?

The Paradoxical Problem of theVasomotor Center

Local Regulation of Blood Flow

• Autoregulation - adjustment of blood flow toeach tissue according to its immediate needs.

• Surplus or deficiency of local chemicalsinfluences local vessel diameter and blood flow.

WorkingMuscle Tissue

Tissue CO2 levels ___

Tissue O2 levels ___

Arteriolesserving tissuevaso________

Lactic acid levels ___

______bloodflow to tissue

CO2 _______

Lactic acid _______

Heat _______ O2 ________

Local Regulation of Blood Flow

Tissue temp. ____

Capillary Exchange

• Btwn blood plasmaand tissue fluid.

• Nutrients, wastes,signaling molecules

• FLUID

Capillary Fluid Exchange

• 4 forces– Capillary osmotic pressure.

– Capillary hydrostatic pressure.

– Interstitial osmotic pressure.

– Interstitial hydrostatic pressure.

Capillary Hydrostatic Pressure

• A.k.a…

• What does it do?

ISF

CAPILLARY HP

Capillary Osmotic Pressure

• Mostly due to…

• What does it do?

ISF

CAPILLARY OP

Interstitial Hydrostatic Pressure

• Usually inconsequential b/c…

• What would it do?

ISF HPCAPILLARY

Interstitial Osmotic Pressure

• Usually inconsequential b/c…

• What would it do?

ISF OPCAPILLARY

Capillary Fluid Exchange

• Thebalance of what 2 forces typically determines iffluid enters or exits the capillary?

• Net filtration pressure

Capillary Filtration

• If capillary HP >> capillary OP,

– What kind of fluid movement will occur?

ISFCAPILLARY

Capillary Reabsorption

• If capillary HP << capillary OP,

– What kind of fluid movement will occur?

ISFCAPILLARY

Pressure

Capillary Fluid Exchange• Is capillary HP constant??

• Is capillary OP constant??

Distance along the capillaryArterial end Venous end

Pressure

Capillary Fluid Exchange

• At which end of the capillary is filtration likely to occur?

• At which end is reabsorption likely to occur?

Distance along the capillaryArterial end Venous end

Capillary Fluid Exchange

• Capillary HP usually slightly exceeds capillary OP.

• Why does this matter?