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Chapter 21 Peripheral Circulation & Regulation • The heart is the pump that provides the major force causing blood to circulate and the blood vessels are the pipes that carry the blood to the tissues of the body and back to the heart 2 major vessel types: 1. Systemic Vessels: – Transport blood from left ventricle to the body back to right atrium 2. Pulmonary Vessels: – Transport blood from the right ventricle to the lungs back to the left atrium AP2 Chap. 21: Cardio Syst-Vessels 1 I. Functions of peripheral circulation AP2 Chap. 21: Cardio Syst-Vessels 2 I. Fxns of peripheral circulation 5 major fxns: 1. Carries blood – 2. XD’s nutrients, waste products, & gases w/tissues – – 3. Not only the nutrients & wastes but things like hormones & immune system components Helps to regulate BP – 5. Nutrients & O2 can diffuse from blood to cells Wastes & CO2 can diffuse from cells to blood Transports substances – 4. Takes blood on a roundtrip from heart to tissues back to heart Using contractions of smooth muscle to make vessels larger or smaller Directs blood flow to tissues – It can flow with purpose directing circulation to areas in need. AP2 Chap. 21: Cardio Syst-Vessels 3 VI. The dynamics of blood circulation A. Laminar & turbulent flow in vessels B. BP C. Blood flow & Poiseuille’s Law D. Critical closing pressure & Laplace’s Law E. Vascular Compliance AP2 Chap. 21: Cardio Syst-Vessels 4 VI. The dynamics of blood circulation • Just like water flowing thru pipes certain relationships effect the function of the cardiovascular system these include: – BP – Flow – Resistance – Control mechanisms of BP & blood flow AP2 Chap. 21: Cardio Syst-Vessels 5 VI. The dynamics of blood circulation A. Laminar & turbulent flow in vessels • Laminar flow: fluid in a smooth tube moves in a stream lined fashion • It flows in concentric layers. Because the outmost blood is against the stationary wall of the vessel, it moves slowest; but as the layers go inward they become faster with the innermost fasted. • Turbulent flow: when a rate of flow exceeds a critical velocity or when fluid passes a constriction, sharp turn, or rough surface. • The vibrations caused by the chaotic blood flow cause sound (Some sounds thru valves in heart or BP cuff) Abnormal sounds can signal a blocked artery Figure 21.31 Page 741 6 VI. The dynamics of blood circulation B. Blood Pressure • BP measure of the force bld exerts on the blood vessel walls • 2 main methods for measuring: – Mercury Manometer • Indirect – Cannula • Direct (tube inserted directly into the blood vessel) • Although 2 methods exist, using a stethoscope (auscultatory methods) are more practical in a clinical setting. • Korotkoff Sounds: point at which cuff loosens enough to allow for turbulent flow in the artery (represents systolic pressure #) • Diastolic Pressure #: when sounds are no longer heard Figure 21.32 Page 742 7 B. Blood Pressure VI. The dynamics of blood circulation Figure 21.31 Page 753 21.32 Figure Page 742 AP2 Chap. 21: Cardio Syst-Vessels 8 VI. Dynamics of Blood Circulation Poiseuille’s Law Laplace’s Law: • a small D in radius dramatically D’s resistance to flow thus the amount of blood flowing thru the vessel • The force acting on the wall of a blood vessel is proportional to the diameter of the vessel times BP AP2 Chap. 19: Cardiovascular Syst 9 VI. The dynamics of blood circulation C. Bld Flow & Poiseuille’s (pwah-zuh’yes) Law • Blood flow: amount of bld that moves thru a vessel in a given period – Blood flow is directly proportional to pressure differences • BP = Bld flow – Blood flow is inversely proportional to resistance • Resistance: sum of all factors that inhibit bld flow – Effected by: • D’s in viscosity • D’s in bld vessel diameter • D’s in bld vessel length • Resistance = bld flow AP2 Chap. 21: Cardio Syst-Vessels 10 VI. The dynamics of blood circulation C. Bld Flow & Poiseuille’s (pwah-zuh’yes) Law • Viscosity: resistance of a liquid to flow • Bld’s viscosity is the result of [RBC]. As hematocrit (% of total bld vol. composed of RBC’s) increases so does bld viscosity • Poiseuille’s Law states that a small D in radius dramatically D’s resistance to flow thus the amount of blood flowing thru the vessel. AP2 Chap. 21: Cardio Syst-Vessels 11 VI. The dynamics of blood circulation D. Critical Closing Pressure & Laplace’s Law • As pressure in a vessel , the force holding the vessel open , & the vessel tends to collapse. • Critical Closing Pressure: – Pressure at which the blood vessel closes and blood flow stops • Laplace’s Law: – The force acting on the wall of a blood vessel is proportional to the diameter of the vessel times BP F= force D= diameter P= pressure F=D*P • Shock (BP drops) necrosis • Aneurysm AP2 Chap. 21: Cardio Syst-Vessels 12 VI. The dynamics of blood circulation E. Vascular Compliance • Compliance: • Veins: – Tendency for blood vessel vol to as the BP • Vessels with a high compliance exhibit large increases in volume when pressure increases a small amount. (vise versa) – 24X greater compliance than arteries – Thus veins can act as storage areas (reservoirs) for blood because high compliance allows them to hold larger volume than other areas of the vascular system AP2 Chap. 21: Cardio Syst-Vessels 13 VII. Physiology of Systemic Circulation A. B. C. D. Cross sectional area Pressure & resistance Pulse Pressure Capillary XD & regulation of interstial fluid E. Fxnal characteristics of veins F. BP & FX of gravity AP2 Chap. 21: Cardio Syst-Vessels 14 VII. Physiology of Systemic Circulation • Physiological characteristics of the circulatory system are determined by: – Anatomy of circulatory system – Dynamics of blood flow – Regulatory mechanisms of the heart & blood vessels • 84% of blood resides in the systemic blood vessels – 64% in the systemic veins – 15% in systemic arteries – 5% in capillaries AP2 Chap. 21: Cardio Syst-Vessels Page 743 15 VII. Physiology of Systemic Circulation A. Cross-sectional area of blood vessels • As the diameter of blood vessels decreases their total cross-sectional area (CSA) increases and the velocity of blood flow thru them decreases Aorta= 5 cm2 cross sectional area Capillaries (each with a very small cross sectional area) The total cross sectional area of ALL capillaries = 2500 cm2 Thus the smaller vessels have more area Velocity of blood flow is greatest in the aorta but total CSA is small. Velocity of blood flow is low in capillaries, but the total CSA is large. Figure 21.33 Page 744 16 VII. Physiology of Systemic Circulation B. Pressure & resistance • BP is initially 100mmHg in the aorta ending at 0mmHg in the right atrium (high to low movement) • Decreases in arterial pressure are directly proportional to resistance. With the highest encountered at the arterioles. – When it gets there 85mmHg at the end 35mmHg – Also fairly high resistance in the capillaries Figure 21.33 Page 756 Figure 21.34 Page 745 • Low resistance in veins b/c they have a relatively large diameter. • Arteries can contract or relax changing their diameter & pressure AP2 Chap. 21: Cardio Syst-Vessels 17 VII. Physiology of Systemic Circulation C. Pulse Pressure • Pulse pressure equals the difference between the systolic & diastolic pressures – Increases when: • Stroke volume increases • Vascular compliance decreases Pg 746 Fig 21.35 • Pulse pressure waves travel thru the vascular system faster than blood flows. PP can be used to take a pulse as the artery expands with the PP waves. (radial pulse) AP2 Chap. 21: Cardio Syst-Vessels 18 VII. Physiology of Systemic Circulation D. Capillary XD & regulation of interstitial fluid volume • 3 things affect the movement of fluid from the capillaries: – BP – Capillary Permeability – Osmosis • Net movement occurs from the blood vessel into the tissues. The lymphatic system removes XS tissue fluid. • Capillary XD – Mvmt of substances into & out of the capillary – Most important method used is diffusion • Nutrients, gases & hormones • Some go thru fenestrations others between the cell spaces. • Pinocytosis does a very small amount AP2 Chap. 21: Cardio Syst-Vessels 19 VII. Physiology of Systemic Circulation Fxnal Characteristics of Veins • Factors that increase venous return to the heart include: a) Increase in blood volume b) Venous tone (constriction or dilation of the veins) • BP & the effect of gravity • Hydrostatic pressure caused by gravity increases BP below the level of the heart & decreases BP above the level of the heart. Based on SNS stimulation c) Arteriole dilation AP2 Chap. 21: Cardio Syst-Vessels 20 VIII. Control of Blood Flow in the tissues A. Local control of blood flow by the tissues B. Nervous & hormonal regulation of local circulation AP2 Chap. 21: Cardio Syst-Vessels 21 VIII. Control of Blood Flow in the tissues • Blood flow to the tissues is highly controlled and matched closely to the metabolic needs of tissues. • 2 mechanisms of control are: A. Local Control • • • Fxnal characteristics of the capillary bed Autoregulation of blood flow Long-term local blood flow B. Nervous & hormonal control AP2 Chap. 21: Cardio Syst-Vessels 22 VIII. Control of Blood Flow in the tissues A. Local control of blood flow by tissues • Blood flow can vary by organ with some getting more than others with little change. • Some tissues alter blood flow based on metabolic need such as skeletal muscle at rest vs. exercising (20X more flow than at rest). • Blood serves to deliver nutrients & remove waste, but: – Skin: blood flow dissipates heat – Kidneys: eliminated metabolic waste products, regulates water balance, controls pH of body fluids – Small intestine: blood removes the nutrients for liver processing AP2 Chap. 21: Cardio Syst-Vessels 23 VIII. Control of Blood Flow in the tissues A. Local control of blood flow by tissues Fxnal Characteristics of the capillary bed • Capillaries can alter blood flow based on the conditions of the tissues they supply – Vasomotion: cyclic fluctuation of contraction & relaxation of sphincters • Vasodilator substances are prod’d as metabolism increases. They literally diffuse from the tissue to the precapillary sphincter muscles to get them to relax. Pg 751 Fig 21.37 AP2 Chap. 21: Cardio Syst-Vessels 24 VIII. Control of Blood Flow in the tissues A. Local control of blood flow by tissues Autoregulation of Blood Flow • Arterial BP can D over a wide range, but blood flow remains relatively constant. • Autoregulation is maintenance of blood flow by the tissues themselves. In the tissues: • Build-up of metabolic waste – Precapillary sphincters dilate • Blood flow increases • Nutrient & O2 supply adequate – Precapillary sphincters constrict • Blood flow decreases AP2 Chap. 21: Cardio Syst-Vessels 25 VIII. Control of Blood Flow in the tissues A. Local control of blood flow by tissues Long term regulation • Long term regulation of blood flow is matched to the metabolic needs of the tissue. • Metabolic activity in tissue increases over long term: – Diameter & # of blood vessels increase • Results in increase in local blood flow. AP2 Chap. 21: Cardio Syst-Vessels 26 VIII. Control of Blood Flow in the tissues B. Nervous & hormonal regulation of local circulation • NS control of Arterial BPimportant in the minute-tominute regulation of local circulation • SNS (vasomotor center of the medulla oblongata) controls blood vessel diameter and can be influenced by other areas in the brain. • Vasomotor Tone: state of partial contraction of blood vessels • NS is responsible for routing the flow of blood & maintaining BP • SNS action potentials stimulate adrenal medulla to release epi & norepi which cause vasoconstriction of most blood vessels (Skeletal muscle is opposite) AP2 Chap. 21: Cardio Syst-Vessels Figure 21.38 pg 752 27 IX. Regulation of Mean Arterial BP A. Short term regulation B. Long term regulation AP2 Chap. 21: Cardio Syst-Vessels 28 IX. Regulation of Mean Arterial BP • MAP: proportional to cardiac output times peripheral resistance MAP= CO * PR or HR * SV * PR Heart rate = HR Stroke volume= SV • Thus an increase in CO, PR, HR, or SV increases MAP or vise versa • 2 major control systems to maintain homeostasis: A. Short term • Respond quickly but can’t maintain for longer than a few days B. Long term • Primarily mechanisms that influence kidney fxn AP2 Chap. 21: Cardio Syst-Vessels 29 Regulation of MAP • Short Term reg of BP – Baroreceptor Reflex – Adrenal Medullary Mechanism – Chemoreceptor Reflexes – CNS Ischemic Response • Long Term reg of BP – Renin-angiotensinaldosterone Mechanism – ADH mechanism – Atrial Natriuretic Mechanism – Fluid Shift Mechanism – Stress relaxation response AP2 Chap. 21: Cardio Syst-Vessels 30 Baroreceptor Reflex • Minute to minute monitoring of small changes in BP that respond quickly Figure 21.39 pg 754 AP2 Chap. 21: Cardio Syst-Vessels 31 Baroreceptor Reflex Figure 21.40 Page 755 AP2 Chap. 21: Cardio Syst-Vessels 32 Adrenal Regulatory Mechanism • Physical activity/ stress • Stimulation of Medulla oblongata Figure 21.41 Page 756 – Signal to SNS to adrenal medulla • Releases Epi & norepi • Result: – Increased HR, SV, vasoconstriction of blood vessels to skin & viscera, and vasodilatation of blood vessels to heart AP2 Chap. 21: Cardio Syst-Vessels 33 Chemoreceptors Figures 21.42 Page 757 AP2 Chap. 21: Cardio Syst-Vessels 34 Chemoreceptors Figure 21.43 Page 758 AP2 Chap. 21: Cardio Syst-Vessels 35 CNS Ischemic Response • Elevation of BP in response to lack of blood flow to the medulla oblongata – Causes high CO2 & low pH levels • Responds to emergency situations where brain is starving for O2 • Vasomotor center is stimulated stimulates vasoconstriction systemic BP rises (provided blood vessels are intact) AP2 Chap. 21: Cardio Syst-Vessels 36 Regulation of MAP • Short Term reg of BP – Baroreceptor Reflex – Adrenal Medullary Mechanism – Chemoreceptor Reflexes – CNS Ischemic Response • Long Term reg of BP – Renin-angiotensinaldosterone Mechanism – ADH mechanism – Atrial Natriuretic Mechanism – Fluid Shift Mechanism – Stress relaxation response AP2 Chap. 21: Cardio Syst-Vessels 37 Long term regulation • Regulation of the [ ] & volume of blood by the kidneys, mvmt of fluid across blood vessel walls, & alterations in the volume of the blood vessels. • Response is in minutes but maintenance can last for hours, days, longer AP2 Chap. 21: Cardio Syst-Vessels 38 Renin-angiotensin-aldosterone Mechanism Figure 21.44 Page 760 •Decreased BP detected by kidney, results in renin secretion •Result: •Vasoconstriction •Increased H2O absorption •Decreased urine volume •Maintains BP AP2 Chap. 21: Cardio Syst-Vessels 39 Vasopressin (ADH) mechanism Figure 21.45 pg. 761 Increases in osmolarity of blood or decreases in BP result in ADH secretion. Increases H2O reabsorption by kidney, & large amounts result in vasoconstriction. Helps maintain BP AP2 Chap. 21: Cardio Syst-Vessels 40 Summary of control of BP long term mechanisms Page 764 Figures 21.46 41 Long term regulation of BP Fluid Shift mechanism • Causes fluid to move from the interstitial spaces into the capillaries in response to a decrease in BP. • Attempt to maintain blood volume Stress-relaxation response • An adjustment of smooth muscles of blood vessels in response to change in blood volume. AP2 Chap. 21: Cardio Syst-Vessels 42