Arteries • AWAY • Branch • Typically oxygenated.

Capillaries • Smallest. • Most abundant. • Exchange – 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 vasomotor neurons.

• Vasomotor neurons constantly release NE onto TM smooth muscle. – 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 lower leg arteries. How do you think they affect blood flow? How does that relate to his facial expression? His doctor recommends that the sympathetic nerves to those arteries be cut. Why?

Tunica Externa/Adventitia • Primarily collagen • Function? • Most prominent layer in veins

Elastic Arteries • Aorta and major branches. • Act as AUXILIARY PUMPS.

Muscular Arteries • Regional distribution • Significant layer

Arterioles • 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?

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 their lining. Why? – Found in…

Why are capillaries organized into beds? What tissues will have high densities of capillary beds?

What do precapillary sphincters do? What determines whether the sphincters are open or closed? 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 tone prevents too much distention. • Capacitance vessels/Blood reservoirs. • 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 on the 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 arterioles of his quadriceps needs to… - the resistance of arterioles in his colon needs to…

Sources of Resistance • Blood viscosity. • Total vessel length. • Vessel radius.

Viscosity • Viscosity resistance. • Can you drink one of these with a straw? • What makes it challenging?

• What are the major contributors to blood viscosity? • Does viscosity change often in a healthy person? • An increase in plasma EPO will cause resistance to…

Total Vessel Length • Length resistance. • Does total vessel length change in a normal person?

• 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 healthy person? • Which vessels? • How is the change achieved?

Which tube has the greater intrinsic resistance? What layer of the vessel wall has the greatest effect on vessel resistance? a. b. c. Interna Media Externa

Resistance  (length)(viscosity) (radius)4

Which tube has the LEAST resistance? Which tube has the GREATEST resistance?

FLOW  PRESSURE GRADIENT RESISTANCE

• As resistance decreases, flow will… • As the pressure gradient increases, flow will… • Which does the heart influence more: pressure gradient 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 blood pumped into the arteries increased? • Thus, arterial pressure varies directly with…

• What would happen to AP if the resistance in the arterioles went up? • Thus, arterial pressure varies directly with…

• What would happen to AP if there was more blood in the entire system? • Thus, arterial pressure varies directly with…

Systolic Blood Pressure

Diastolic Blood Pressure

Pulse • What creates it? • How/Where do you measure it? • What’s its relationship to heart rate?

Pulse Pressure • Change in arterial pressure caused by ventricular systole. • 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.

Mean Arterial Pressure (MAP) • MAP = ⅔DBP + ⅓SBP • MAP = DBP + ⅓PP

Capillary Blood Pressure • Low BP. • Why is this good? (Think about the structure of a capillary.)

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 Pump Pressure in thoracic veins will… Deep Inspiration Thoracic volume will… Pressure in thoracic cavity will… Pressure in thoracic veins will… Blood flow into thoracic veins and towards 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

Brain Centers for Short Term MAP Control • Vasomotor • Cardioinhibitory • Cardioacceleratory

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 • Frequency of these impulses is proportional • Baroreceptors signals the cardiac and vasomotor centers via CN IX and X. • Frequency of these impulses is proportional to MAP. • Cardiac and vasomotor centers adjust their output accordingly.

Demonstrating the Baroreceptor Reflex • Take the subject’s radial pulse. • Find the carotid pulse point and GENTLY press on it. • What will happen to the radial pulse? • Why?

Adrenal Medullary Mechanism • Release epinephrine (and a small amt of NE) in response to: – Large drops in MAP. – Increases in physical activity. – Stressful situations.

• How would activation of the adrenal Adrenal Medullary Mechanism • How would activation of the adrenal medulla affect: – HR SV CO PR BP

Renin-Angiotensin-Aldosterone System Angiotensin II

Indirect Mechanism Renin-Angiotensin-Aldosterone System Angiotensin II Vasoconstriction Aldosterone & Thirst Antidiuretic hormone Increased TPR Increased BV Increased BP

Indirect Mechanism Renin-Angiotensin-Aldosterone System • In response to a fall in MAP, renin release by the kidney would: • In response to a rise in MAP, renin release by the kidney would:

A 25yo woman complains to her doctor of headaches and blurred vision. Her blood pressure is 200/130 mmHg. After the BP has been reduced, investigations are made to find the cause of the problem. It’s discovered that her left renal artery is narrowed. Why would this cause the rise in BP?

Long Term BP Control • Achieved by the... • Primarily done by altering...

Long Term BP Control ____________ _________BP Large increase in BP urine formation urine output ____________ blood volume _________BP

• As we go from the aorta to the billions of capillaries, what happens to the total cross- sectional area? • What happens to the velocity of blood flow?

• As we go from the billions of capillaries to the venae cavae, what happens to the total cross- sectional area? • What happens to the velocity of blood flow?

The Paradoxical Problem of the Vasomotor Center

Local Regulation of Blood Flow • Autoregulation - adjustment of blood flow to each tissue according to its immediate needs. • Surplus or deficiency of local chemicals influences local vessel diameter and blood flow.

Local Regulation of Blood Flow Tissue temp. ____ Working Muscle Tissue Tissue CO2 levels ___ Tissue O2 levels ___ Arterioles serving tissue vaso________ Lactic acid levels ___ ______blood flow to tissue CO2 _______ Lactic acid _______ Heat _______ O2 ________

Capillary Exchange • Btwn blood plasma and 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 HP CAPILLARY

Interstitial Osmotic Pressure • Usually inconsequential b/c… • What would it do? ISF OP CAPILLARY

Capillary Fluid Exchange • Thebalance of what 2 forces typically determines if fluid enters or exits the capillary? • Net filtration pressure

Capillary Filtration • If capillary HP >> capillary OP, – What kind of fluid movement will occur? ISF CAPILLARY

Capillary Reabsorption • If capillary HP << capillary OP, – What kind of fluid movement will occur? ISF CAPILLARY

• Is capillary HP constant?? • Is capillary OP constant?? Capillary Fluid Exchange • Is capillary HP constant?? • Is capillary OP constant?? Pressure Arterial end Venous end Distance along the capillary

• At which end of the capillary is filtration likely to occur? Capillary Fluid Exchange • At which end of the capillary is filtration likely to occur? • At which end is reabsorption likely to occur? Pressure Arterial end Venous end Distance along the capillary

Capillary Fluid Exchange • Capillary HP usually slightly exceeds capillary OP. • Why does this matter?