2Capillaries • Smallest. • Most abundant. • Exchange – How many?? – Why?• Exchange
3Veins• TOWARDS• Converge.• Typically deoxygenated.
43 Layers of the Vascular Wall • Tunica interna• Tunica media• Tunica externa.
5Tunica Interna/Intima • Lining.• Endothelium.• Supported by loose CT.• Only layer in capillaries.
6Tunica Media • Primarily smooth muscle plus elastic fibers. • Most prominent layer in arteries.
7Tunica Media • Smooth muscle tone • Regulated by: – Metabolites – Hormones– Sympathetic vasomotorneurons.
8• Vasomotor neurons constantly release NE onto TM smooth muscle. – What does the NE do?– Why have a constant release?
9Increased 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:
10This gentleman has fatty plaques in his lower leg 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?
11Tunica Externa/Adventitia • Primarily collagen• Function?• Most prominentlayer in veins
12Elastic Arteries• Aorta and major branches.• Act as AUXILIARY PUMPS.
62Respiratory Pump Pressure in thoracic veins will… Deep InspirationThoracic volume will…Pressure in thoracic cavity will…Pressure in thoracic veins will…Blood flow into thoracic veins andtowards the heart will…
63Venomotor Tone • An increase in sympathetic activity causes: – NE release on the TM of medium/large veins to…– Venous pressure to…– Venous return to…
64Controlling MAP • Why do we need to control it? • Short term • Long term
65Brain Centers for Short Term MAP Control • Vasomotor• Cardioinhibitory• Cardioacceleratory
66Increased vasomotor center activity __creased sympathetic output to arteriolesVaso____________creased peripheral resistance__creased blood pressureWhat about a decrease in vasomotor activity?
67Increased cardioacceleratory center activity __creased sympathetic output to heart__creased heart rate and stroke volume__creased cardiac output__creased blood pressureWhat about a decrease in cardioacceleratory activity?
68Increased cardioinhibitory center activity __creased parasympathetic output to heart__creased heart rate__creased cardiac output__creased blood pressureWhat about a decrease in cardioacceleratory activity?
70Baroreceptor Reflex • Frequency of these impulses is proportional • Baroreceptors signals thecardiac and vasomotorcenters via CN IX and X.• Frequency of theseimpulses is proportionalto MAP.• Cardiac and vasomotorcenters adjust theiroutput accordingly.
71Demonstrating 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?
72Adrenal Medullary Mechanism • Release epinephrine (and asmall amt of NE) in responseto:– Large drops in MAP.– Increases in physical activity.– Stressful situations.
73• How would activation of the adrenal Adrenal Medullary Mechanism• How would activation of the adrenalmedulla affect:–HRSVCOPRBP
74Renin-Angiotensin-Aldosterone System Angiotensin II
75Indirect Mechanism Renin-Angiotensin-Aldosterone System Angiotensin IIVasoconstrictionAldosterone &ThirstAntidiuretichormoneIncreased TPRIncreased BVIncreased BP
76Indirect Mechanism Renin-Angiotensin-Aldosterone System • In response to a fall in MAP, renin releaseby the kidney would:• In response to a rise in MAP, renin releaseby the kidney would:
77A 25yo woman complains to her doctor of headaches 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?
78Long Term BP Control • Achieved by the... • Primarily done by altering...
79Long Term BP Control ____________ _________BP Large increase in BP urine formationurine output____________blood volume_________BP
80• As we go from theaorta to thebillions ofcapillaries, whathappens to thetotal cross-sectional area?• What happens tothe velocity ofblood flow?
81• As we go from thebillions ofcapillaries to thevenae cavae, whathappens to thetotal cross-sectional area?• What happens tothe velocity ofblood flow?
83Local 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.
84Local Regulation of Blood Flow Tissue temp. ____WorkingMuscle TissueTissue CO2 levels ___Tissue O2 levels ___Arteriolesserving tissuevaso________Lactic acid levels _________bloodflow to tissueCO2 _______Lactic acid _______Heat _______O2 ________
87Capillary Hydrostatic Pressure • A.k.a…• What does it do?ISFCAPILLARY HP
88Capillary Osmotic Pressure • Mostly due to…• What does it do?ISFCAPILLARY OP
89Interstitial Hydrostatic Pressure • Usually inconsequential b/c…• What would it do?ISF HPCAPILLARY
90Interstitial Osmotic Pressure • Usually inconsequential b/c…• What would it do?ISF OPCAPILLARY
91Capillary Fluid Exchange • Thebalance of what 2 forces typically determines iffluid enters or exits the capillary?• Net filtration pressure
92Capillary Filtration • If capillary HP >> capillary OP, – What kind of fluid movement will occur?ISFCAPILLARY
93Capillary Reabsorption • If capillary HP << capillary OP,– What kind of fluid movement will occur?ISFCAPILLARY
94• Is capillary HP constant?? • Is capillary OP constant?? Capillary Fluid Exchange• Is capillary HP constant??• Is capillary OP constant??PressureArterial endVenous endDistance along the capillary
95• 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?PressureArterial endVenous endDistance along the capillary
96Capillary Fluid Exchange • Capillary HP usually slightly exceeds capillary OP.• Why does this matter?