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Blood Vessels-Chps. 14-19 Powered by the pumping action of the heart Heart ArteriesElastic muscular Arterioles Capillaries Venules veins • Transporting nutrients and oxygen to the tissues • Transporting waste products away from the tissues • Transporting hormones Lecture outline I. Review anatomy of vessels A. Arteries B. Elastic C. Muscular D. Arterioles- resistance vessels E. Capillaries- exchange vessels F. Veins- capacitance vessels II. Ohm’s law is flow = change in pressure/ resistance A. Blood Flow i. Laminar vs. turbulent B. Pressure- blood pressure i. Mean arterial pressure (MAP) ii. Central venous pressure iii. Pulse pressure C. Resistance i. Factors of resistancePoiseuille’s law III. Getting to know “Flow” better A. Velocity B. Control of flow i. Autoregulation ii. Nervous system iii. Endocrine-kidney (unit 4) IV. Exchange of extracellular fluid- the microcirculation A. Starling Forces i. Capillary hydrostatic pressure ii. Interstitial hydrostatic pressure iii. Capillary colloid osmotic pressure iv. Interstitial colloid osmotic pressure B. Lymphatic drainage C. Causes of edema 2 • Branch and diverge • Blood away from heart • Walls have 3 tunics Arteries – Tunica intima-simple squamous endothelium – Tunica media-circular sheets of smooth muscle (vasodilation and vasoconstriction- diameter controlled by local factors and sympathetic NS) – Tunica adventitiaconnective tissue with collagen and elastin in longitudinal arrangement 3 Arteries • Elastic- largest arteries near heart – Low resistance – More elastin interspersed with the tunica media – Can distend and recoil back to pump blood (maintain blood pressure) • Muscular– Supply organs – Can regulate diameter of artery to control blood supply to organ – Thick tunica media with more smooth muscle – External and internal elastic lamina. 4 Arterioles • Smallest arteries“resistance arteries” • THICK tunica media- little compliance • Diameter controlled by local factors (intrinsic) and sympathetic division (extrinsic) and long-term factors (hormones) • Metarterioles- just upstream of capillary beds. • Precapillary sphincterscontrols blood reaching capillary bed. 5 Capillaries • Smallest blood vessels • Single layer of endothelial cells and basal lamina • Renew interstitial fluid- pick up wastes, drop off nutrients, etc. • Most cells only 20-30 µm away • Over 10 billion of them. 6 Types of Capillaries • Continuous – Most common and least permeable – Intercellular clefts and transcellular cytosis allows for exchange of molecules – Abundant in skin and muscle • Fenestrated – “Holes” in the endothelial membrane – Found in kidney • Sinusoidal/ discontinuous – Most permeable and least common – Big ‘holes” in endothelial membranes – Big clefts between cells – Liver, spleen, and bone marrow especially 7 Veins • Volume reservoir- “capacitance vessels” (60-70%) of blood • Have vasomotor control. • Valves in abdominal veins prevent backflow • Skeletal muscle “pump” and respiratory pump 9 Vascular Distensibility= is the fractional increase in volume for each mmHg rise in pressure times original volume- veins are 8x more distensible 0 mmHg Artery Vein 100 mmHg 100 ml 800 ml In hemodynamics, it’s more valuable to know the total quantity of blood that can be stored in a given portion of the circulation for each mmHg pressure rise. 10 Capacitance = increase in volume/increase in pressure The capacitance of veins is 24 times that of arteries. Ohm’s Law • Q=P/R • Flow (Q) through a blood vessel is determined by: • 1) The pressure difference (P) between the two ends of the vessel – Directly related to flow • 2) Resistance (R) of the vessel – Inversely related to flow • Can you rearrange the equation above and solve for P? Solve for R? 11 Blood Flow (L/min) • Blood flow is the quantity of blood that passes a given point in the circulation in a given period of time. • Unit of blood flow is usually expressed as milliliters (ml) or Liters (L) per minute. • Overall flow in the circulation of an adult is 5 liters/min which is the cardiac output. • CO= HR X SV • 70 b/min x 70 ml/beat =4900ml/min 12 Characteristics of Blood Flow • Blood usually flows in streamlines with each layer of blood remaining the same distance from the wall, this type of flow is called laminar flow. – When laminar flow occurs, the velocity of blood in the center of the vessel is greater than that toward the outer edge creating a parabolic profile. Laminar flow Blood Vessel 13 Laminar Vs. Turbulent Blood Flow Causes of turbulent blood flow: • high velocities • sharp turns in the circulation • rough surfaces in the circulation • rapid narrowing of blood vessels Turbulent flow • Laminar flow is silent, whereas turbulent flow tend to cause murmurs. • Murmurs or bruits are important in diagnosing vessels stenosis, vessel shunts, and cardiac valvular lesions. 14 Effect of Wall Stress on Blood Vessels Turbulent flow increases resistance and wall stress Nitric oxide released by endothelial cells to reduce the stress Aortic Aneurysm Atherosclerosis 15 Blood Pressure— The driving force • Blood pressure (hydrostatic pressure) is the force exerted by the blood against any unit area of vessel wall. Stephen Hales 1733 • Measured in millimeters of mercury (mmHg). A pressure of 100 mmHg means the force of blood was sufficient to push a column of mercury 100mm high. • All vessels have it – but we’re usually addressing arteries when we refer to it. 16 Ejected Blood contracted When the LV contracts more blood enters the arterial system than gets pushed onward. This causes the arteries to stretch and pressure within them to rise. The highest pressure achieved is known as the systolic pressure. 17 Recoil of the elastic artery relaxed As the LV relaxes, the stretched arterial walls recoil and push the contained blood onward through the system. As they recoil, the amount of blood contained decreases as does pressure. The lowest pressure achieved just before the next contraction is the diastolic pressure. 18 Mean Arterial Pressure (MAP) FLOW = arterial - venous pressure (P) resistance (R) • Is an average, but not a simple arithmetic average • Heart spends longer in diastole than systole • Value is significant- why? • The difference between the mean arterial pressure and the pressure in the venous system drives the blood through the capillary beds. • MAP= .4 (systolic) + .6 (diastolic)= 96mmHg • Venous pressure is about 2mmHg 100 mmHg A 0 mmHg R = .1mmHg/ml/min FLOW = 1000 ml/min 100 mmHg B 20 mmHg R = .1mmHg/ml/min FLOW = 800 ml/min 19 Central Venous Pressure • Pressure in the right atrium is called central venous pressure. • determined by the balance of the heart pumping blood out of the right atrium and flow of blood from the large veins into the right atrium. • normally 0 mmHg, but can be as high as 20-30 mmHg. More vigorous heart contraction (lower CVP). Less heart contraction (higher CVP) Factors that increase CVP: increased blood volume increased venous tone (peripheral pressure) dilation of arterioles decreased right ventricular function Skeletal and respiratory pumps • • • Figure 15-9; Guyton and Hall 20 Arterial Pulsations and Pulse Pressure • The height of the pressure pulse is the systolic pressure (120mmHg), while the lowest point is the diastolic pressure (80mmHg). • The difference between systolic and diastolic pressure is called the pulse pressure (40mmHg). Systolic Pressure } Pulse Pressure Diastolic Pressure 21 Factors Affecting Pulse Pressure • Stroke volume —increases in stroke volume increase pulse pressure, conversely decreases in stroke volume decrease pulse pressure. • Arterial compliance —decreases in compliance increases pulse pressure; increases in compliance decrease pulse pressure. Figure 15-5; Guyton and Hall 22 Stroke volume Cardiac output Systolic Pressure } Pulse Pressure Mean Pressure Total Peripheral resistance Stroke volume Diastolic Pressure Time HR x SV = CO = MAP/ TPR MAP= (0.4 SP) + (0.6 DP) PP= SP- DP Arterial compliance 23 Damping of Pulse Pressures in the Peripheral Arteries What’s an anatomical reason for why the pressure fluctuation disappears here? • The intensity of pulsations becomes progressively less in the smaller arteries. • The degree of damping is proportional to the resistance of small vessels and arterioles and the compliance of the larger vessels. •Elastic arteries: • large radii, low resistance, some pressure reservoir •Muscular arteries •Smaller radii •Little more resistance •More pressure reservoir •Arterioles •Thick tunica media vs. radius •major pressure reservoir Figure 15-6; Guyton and Hall 24 Blood Pressure Profile in the Circulatory System Pulmonary veins Capillaries Large veins 40 Small veins 60 Venules 80 Capillaries Pressure (mmHg) 100 Pulmonary arteries 120 20 0 Systemic Pulmonary Circulatory pressure- averages 100mmHg Arterial blood pressure-100-35mmHg Capillary pressure- 35mmHg at beginning and 10-15mmHg at end Venous pressure-15-0mmHg •Large pressure drop across the arteriolar-capillary junction 25 Resistance R = ΔP = mmHg Q ml/min • Resistance is the impediment to blood flow in a vessel. • Can not be measured directly How Would a Decrease in Vascular Resistance Affect Blood Flow? FLOW = Conversely, P RESISTANCE FLOW = P RESISTANCE Therefore, flow and resistance are inversely related! 26 Resistance makes a difference for the two sides of the heart! • Let’s say the CO (flow) is roughly 100ml/sec (easier math). • To calculate systemic resistance vs. pulmonary resistance we need to know pressure differences. • Pulmonary resistance is 16-2/100 • Systemic resistance is 100/100 • So, CO is same on each side of heart (has to be!), but right side generates less pressure due to lower resistance (1/7th than systemic). 100 mmHg 16 mmHg 2mmHg 0mmHg R = ΔP = mmHg Q ml/min 27 Factors of Resistance Poiseuille’s Law = Q =_Pr4 8l • Blood viscosity • Total vessel length • Vessel diameter • Resistance (length)(viscosity) (radius)4 28 Viscosity • What are the major contributors to blood viscosity? • As viscosity increases, resistance will… • An increase in plasma EPO will cause resistance to… Figure 14-11; Guyton and Hall Figure 14-12; Guyton and Hall 29 Total Vessel Length • Longer the vessel.....more opportunity for resistance. Radius 30 So, lets review: Blood Flow is volume flowing/time • Ohm’s Law • Blood Flow (Q) = Δ P/ R Blood flow in center is fastestbecause that is the area of least resistance P1 P2 • Increase pressureincrease blood flow • Decrease resistanceincrease blood flow • Increase resistancedecrease blood flow ΔP= P1-P2 • • • As resistance decreases, flow will… As the pressure gradient increases, flow will… Which does the heart influence more: pressure gradient or resistance? – – – – Vessel diameter Viscosity length Turbulence (usually result of an occlusion reducing vessel diameter unevenly) 31 Flow (amount of blood/time) MUST be the same through vessels in series! If a pipe’s diameter changes over its length, a fluid will flow through narrower segments faster than it flows through wider segments because the volume of flow per second must be constant throughout the entire pipe. Flow (volume/time) vs. velocity (distance/time) are NOT synonyms! 32 If capillaries have such a small diameter, why is the velocity of blood flow so slow? Aorta >Arterioles> Small veins >Capillaries We need slow blood flow in the capillaries—the exchange vessels 33 Control of blood flow through vessels- Why is this important? • Perfusion vs. ischemia vs. hypoxia vs. anoxia vs. infarction • Tissue Perfusion Dependent on: – Cardiac output – Peripheral resistance – Blood pressure • Regulation of perfusion dependent on: – Autoregulation (Acute, local, intrinsic) – Neural mechanisms (acute) – Endocrine mechanisms (longterm) http://www.flometrics.com/services/artery/ 34 Autoregulation the automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirements at any instant even over a wide range of arterial pressures Working Muscle Tissue active hyperemia: when tissues become active, blood flow increases. Tissue temp. rises Tissue CO2 levels rise Tissue O2 levels fall Arterioles serving tissue vasodilate and precapillary sphincters relax Lactic acid levels rise Aka: intrinsic metabolic vasodilation Increased blood flow to tissue CO2 removed Now arterioles will vasoconstrict and precapillary sphincters contract Lactic acid removed Heat removed O2 delivered 35 Autoregulation of Blood Flow to specific tissues • Vasodilator agents Histamine Nitric oxide Elevated temperatures Potassium/hydrogen ions Lactic acid Carbon dioxide Adenosine/ ADP • Vasoconstrictors Norepinephrine and epinephrine Angiotensin Vasopressin (ADH) Thromboxane 36 Other ways to ultimately change blood flow throughout the body is to change Pressure and Resistance Arterial Pressure = Cardiac Output x Total Peripheral Resistance Short term BP control- nervous 37 Long Term BP control- hormonal Brain Centers involved in Short Term BP Control • Vasomotor – Adjusts peripheral resistance by adjusting sympathetic output to the arterioles • Cardioinhibitory- transmits signals via vagus nerve to heart to decrease heart rate. (parasympathetic) • Cardioacceleratory/ contractility-sympathetic output 38 Vasomotor control: Sympathetic Innervation of Blood Vessels • Sympathetic nerve fibers innervate all vessels except capillaries and precapillary sphincters (precapillary sphincters follow local control) • Innervation of small arteries and arterioles allow sympathetic nerves to increase vascular resistance. Figure 18-2; Guyton and Hall • Large veins and the heart are also sympathetically innervated. 39 Anatomy of the Baroreceptors • spray type nerve endings located in the walls of the carotid bifurcation called the carotid sinus and in the walls of the aortic archpressoreceptors that respond to stretch. • Signals from the carotid sinus are transmitted by the glossopharyngeal nerves . • Signals from the arch of the aorta are transmitted through the vagus into the NTS. • Important in short term regulation of arterial pressure. – They are unimportant in long term control of arterial pressure because the baroreceptors adapt. Figure 18-5; Guyton and Hall 40 Response of the Baroreceptors to Arterial Pressure Figure 18-7; Guyton and Hall Constrict Common Carotids Pressure at Carotid Sinuses Arterial Pressure Constrictors • Baroreceptors respond to changes in arterial pressure. • As pressure increases the number of impulses from carotid sinus increases which results in: 1) inhibition of the vasoconstrictor 2) activation of the vagal center 41 Figure 18-5; Guyton and Hall Functions of the Baroreceptors • Maintains relatively constant pressure despite changes in body posture. Supine Standing Decrease Venous return Sympathetic Nervous Activity Decrease Cardiac Output Vasomotor Center Sensed By Baroreceptors Decrease Arterial Pressure 42 BP rises Detected by baroreceptors in aortic arch & carotid sinus Info sent to cardiac and vasomotor centers Decreased vasomotor activity Decreased NE release on arterioles Vasodilation Decreased PR Increased cardioinhibitory activity Increased vagus activity Decreased BP Increased ACh release on heart Decreased cardioacceleratory activity Decreased CO Decreased NE release on heart Decreased SV and HR Carotid and Aortic Chemoreceptors • Chemoreceptors are chemosensitive cells sensitive to oxygen lack, CO2 excess, or H ion excess. • Chemoreceptors are located in carotid bodies near the carotid bifurcation and on the arch of the aorta. • Activation of chemosensitive receptors results in excitation of the vasomotor center. O2 CO2 pH Figure 18-5; Guyton and Hall Chemoreceptors VMC Sympathetic activity BP 44 Nervous control also found in the heartBainbridge Reflex • Prevents damming of blood in veins, atria and pulmonary circulation. • Increase in atrial pressure increases heart rate. • Stretch of atria sends signals to VMC via vagal afferents to increase heart rate and contractility. Atrial Stretch Vagal afferents Vasomotor Center Heart rate Contractility 45 The Microcirculation-chapter 16 • Important in the transport of nutrients to tissues. • Site of waste product removal. • Over 10 billion capillaries with surface area of 500-700 square meters perform function of solute and fluid exchange. Figure 16-1; Guyton and Hall 46 Most substances are exchanged via diffusion Concentration differences across capillary enhances diffusion. 47 Determinants of Net Fluid Movement across Capillaries-Starling forces Figure 16-5; Guyton and Hall • Capillary hydrostatic pressure (Pc)-tends to force fluid outward through the capillary membrane. (30 mmHg arterial; 10mmHg venous- average 17.3mmHg) • Interstitial fluid hydrostatic pressure (Pif)- opposes filtration when value is positive (but it’s not positive-- due to lymphatic drainage! – 3mmHg). 48 Determinants of Net Fluid Movement across Capillaries-Starling forces Figure 16-5; Guyton and Hall • Plasma colloid osmotic pressure ( c)- opposes filtration causing osmosis of water inward through the membrane – Colloid osmotic pressure of the blood plasma. (28mmHg) – 75% from albumin; 25% from globulins • Interstitial fluid colloid pressure ( if) promotes filtration by causing osmosis of fluid outward through the membrane – Colloid osmotic pressure of the interstitial fluid. (8mmHg) – 3gm% 49 Net Forces in Capillaries Filtration= Kf X (Pc- Pif - c + if) mmHg Mean forces tending to move fluid outward: Mean Capillary pressure Negative interstitial free fluid pressure Interstitial fluid colloid osmotic pressure TOTAL OUTWARD FORCE 17.3 3.0 8.0 28.3 Mean force tending to move fluid inward: Plasma colloid osmotic pressure TOTAL INWARD FORCE 28.0 28.0 Summation of mean forces: Outward Inward NET OUTWARD FORCE 28.3 28.0 0.3 Net filtration pressure of .3 mmHg which causes a net filtration rate of 2ml/min for entire body (2-4 liters/day!) 50 If capillary BP is greater than capillary OP, there will be net movement of fluid out of the capillary. Capillary BP Filtration Pressure Capillary OP Reabsorption If capillary BP is less than capillary OP, there will be net movement of fluid into the capillary. Arterial end Venous end Distance along the capillary Filtration= Kf X (Pc- Pif - c + if) • Lymphatic vessels collect lymph from loose connective tissue – Fluid flows only toward the heart – Collect excess tissue fluid and blood proteins and carry to great veins in the neck – All three tunics – NO pump! – Valves! • contains plasma, water, ions, sugars, proteins, gases, amino acids- is colorless, but low in protein compared to blood • Lymph can contain hormones, bacteria, viruses, cellular debris, traveling cancer cells, macrophages 2ml/min Excess tissue fluid is returned to the blood vessels via the lymphatic system! 52 Causes of Edema • Excessive accumulation of tissue fluid. • Edema may result from: – High arterial blood pressure. – Venous obstruction. – Leakage of plasma proteins into interstitial fluid. – Valve problems – Cardiac failure – Decreased plasma protein. – Obstruction of lymphatic drainage. ElephantiasisWuchereria bancrofli I would see your homework packet and study page 303 of Guyton and Hall! 53 Unbalanced Ventricular Output 54 Unbalanced Ventricular Output 55 Hypertension ISF formation capillary BP Starvation Lack of dietary protein Histamine capillary permeability in plasma albumin Vasodilation capillary OP ISF formation capillary BP ISF formation 56 Burn/crush injury capillary permeability Backup of blood in pulmonary circuit Cap OP pulmonary capillary BP ISF formation ISF formation L. Ventricle failure Decreased blood flow in systemic circuit systemic capillary BP ISF formation 57