2 Capillaries • Smallest. • Most abundant. • Exchange – How many?? – Why?• Exchange
3 Veins• TOWARDS• Converge.• Typically deoxygenated.
4 3 Layers of the Vascular Wall • Tunica interna• Tunica media• Tunica externa.
5 Tunica Interna/Intima • Lining.• Endothelium.• Supported by loose CT.• Only layer in capillaries.
6 Tunica Media • Primarily smooth muscle plus elastic fibers. • Most prominent layer in arteries.
7 Tunica 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?
9 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:
10 This 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?
11 Tunica Externa/Adventitia • Primarily collagen• Function?• Most prominentlayer in veins
12 Elastic Arteries• Aorta and major branches.• Act as AUXILIARY PUMPS.
62 Respiratory 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…
63 Venomotor Tone • An increase in sympathetic activity causes: – NE release on the TM of medium/large veins to…– Venous pressure to…– Venous return to…
64 Controlling MAP • Why do we need to control it? • Short term • Long term
65 Brain Centers for Short Term MAP Control • Vasomotor• Cardioinhibitory• Cardioacceleratory
66 Increased vasomotor center activity __creased sympathetic output to arteriolesVaso____________creased peripheral resistance__creased blood pressureWhat about a decrease in vasomotor activity?
67 Increased 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?
68 Increased cardioinhibitory center activity __creased parasympathetic output to heart__creased heart rate__creased cardiac output__creased blood pressureWhat about a decrease in cardioacceleratory activity?
70 Baroreceptor 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.
71 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?
72 Adrenal 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
74 Renin-Angiotensin-Aldosterone System Angiotensin II
75 Indirect Mechanism Renin-Angiotensin-Aldosterone System Angiotensin IIVasoconstrictionAldosterone &ThirstAntidiuretichormoneIncreased TPRIncreased BVIncreased BP
76 Indirect 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:
77 A 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?
78 Long Term BP Control • Achieved by the... • Primarily done by altering...
79 Long 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?
82 The Paradoxical Problem of the Vasomotor Center
83 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.
84 Local 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 ________
87 Capillary Hydrostatic Pressure • A.k.a…• What does it do?ISFCAPILLARY HP
88 Capillary Osmotic Pressure • Mostly due to…• What does it do?ISFCAPILLARY OP
89 Interstitial Hydrostatic Pressure • Usually inconsequential b/c…• What would it do?ISF HPCAPILLARY
90 Interstitial Osmotic Pressure • Usually inconsequential b/c…• What would it do?ISF OPCAPILLARY
91 Capillary Fluid Exchange • Thebalance of what 2 forces typically determines iffluid enters or exits the capillary?• Net filtration pressure
92 Capillary Filtration • If capillary HP >> capillary OP, – What kind of fluid movement will occur?ISFCAPILLARY
93 Capillary 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
96 Capillary Fluid Exchange • Capillary HP usually slightly exceeds capillary OP.• Why does this matter?