Cardiovascular
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Dr. Vince Scialli BSC 1086
REV. 7/16/08 CARDIOVASCULAR SYSTEM CIRCULATION LECTURE 4 BLOOD VESSELS ~ OVERVIEW Blood vessels are the plumbing for the body Blood vessels are NOT rigid . . . they are dynamic structures Pulsate Constrict ~ “vasoconstriction” Relax ~ “vasodilation Proliferate ~ grow & invade ~ “collateral circulation” Blood vessels are a closed delivery system Start at left heart: Aorta > Arteries ~ carry O2 blood End at right heart: Veins > Vena Cava ~ carry CO2 blood BLOOD VESSEL TYPES ARTERIES > Large Arteries > Small Arteries > Arterioles Carry “oxygenated” blood away from heart ~ high O2 Branch Out ~ from big to small VEINS < Large Veins < Small Veins < Venules (small to large) Carry “unoxygenated” blood toward heart ~ high CO2 Merge together from small to big CAPILLARIES ~ contact tissue through capillary walls Only one cell layer thick for diffusion ~ endothelium Exchange O2 & CO2 between blood & tissue ~ O2/CO2 BLOOD VESSEL WALL STRUCTURE Arteries & Veins ~ Three distinct layers 1. Tunica intima ~ tunica interna ~ inside layer Lines “lumen” of vessels ~ “opening” Endothelium ~ simple squamous & elastic tissue Continuous with endocardium Veins have flaps or “valves” that prevent back flow 2. Tunica media ~ middle smooth muscle & elastic layer Thick in arteries Thin in veins Innervated by Sympathetic NS ONLY Adrenergic Stimulation > Vasoconstriction BP Cholinergic Stimulation > Vasodilation BP Vasa Vasorum ~ blood vessels supplying wall of other blood vessels 3. Tunica externa ~ outside layer ~ collegen & elastic fibers Thin in arteries Thick in veins Capillaries ~ composed of epithelial cells only ~ single layer Tunica Interna ONLY CIRCULATORY PATHWAYS ARTERIES ~ ARTERIAL SYSTEM Systemic arteries always carry oxygenated blood ~ ↑ O2 Pulmonary arteries always carry unoxygenated blood ~ ↑ CO2 Arterial walls thicker than veins Artery walls DO NOT contain valves ~ Veins contain valves Arteries vasoconstrict ~ Veins collapse BOTH Arteries & Veins can relax ~ vasodilate Types of Arteries
Called “Conducting Arteries” . . . Close to heart Thick Tunica Externa with some elastic fibers Conduct blood from heart to smaller arteries Elasticity allows expansion & contraction as blood volumes change NOT much resistance ~ due to large diameter DO NOT Vasoconstrict ~ due to thick externa walls Maintain constant blood flow ~ “conducting” 2. MUSCULAR ARTERIES ~ MOST of arterial system Called “Distributing” Arteries ~ MOST COMMON Deliver blood to organs & skeletal muscle Small Diameter ~ more resistance > greater pressure Thick tunica media with less elastic tissue More vasoconstriction than larger elastic arteries Make up “pressure points” Can be pressed against bones to stop bleeding
Resistance Vessels ~ increase/decrease resistance Deliver blood into “capillary beds in tissue Very small diameter ~ Greatest resistance DILATION > decreases resistance > increases blood flow into capillaries ----> Lowers Blood Pressure CONSTRICTION > increases resistance > decreases flow into Capillaries ----> Increases Blood Pressure Most important in regulating B.P. & flow to tissues !!! ARTERY STRUCTURE ABNORMALATIES Atheriosclerosis ~ thickening & hardening of artery walls Plaque ~ cholesterol, low density lipoproteins ~ LDL Coronary Artery Disease ~ Cerebral Strokes ~ Thrombus Aneurysm ~ bulge ~ thin weakened artery wall Can be very dangerous if in brain or in large artery Can result in catastrophic blow out ~ fatal bleeding Aortic Aneurysm ~ Fatal bleeding Brain Aneurysm ~ stroke due to hemorrhage COMMON if associated with high blood pressure CAPILLARIES Microscopic in size ~ smallest of all blood vessels Diameter is slightly larger than diameter of a single RBC Very thinned wall ~ tunica interna only ~ endothelium only MOST body tissue has a rich capillary supply Exceptions: Tendons & Ligaments ~ DON’ T BLEED Capillaries allow exchange of O2/CO2, nutrients, & hormones between blood & tissue cells thru: “Fenestrations” ~ large pores allow large particle exchange CAPILLARY BEDS ~ “Capillary Plexus” ~ “Microcirculation” Network of capillaries ~ controls flow to tissues Allow blood to flow between arterioles & venules Artery Vein O2 CO2 Arteriole Microcirculation Venule O2 CO2 metarteriole post capillary venule O2 CO2 Capillary bed O2/CO2 Thorough fare channel Mixed Blood Vasomotion ~ automatic vasoconstriction & vasodilation Arterioles ~ Most important in regulating flow to tissues & control of blood pressure Blood entering capillary beds depends on BODY NEEDS Dilation of arterioles blood flow into capillaries BP Constriction of arterioles flow into capillaries BP Causes pooling in various body parts at different times: Examples: Blood to digestive organs after a meal Blood to skeletal muscle after exercise Exercise after eating > muscle cramps VENOUS SYSTEM Systemic veins always carry unoxygenated blood ~ ↑ CO2 Pulmonary veins always carry oxygenated blood ~ ↑ O2 Types of Veins 1. VENULES ~ very small ~ flow into veins Extremely porous Fluid & white blood cells move from blood into tissue cells very easily ~ diffusion & pressure Ascites Edema Inflammation 2. VEINS Walls thinner but lumen larger than arteries Tunica externa ~ thick outer wall . . . Very thick near heart Tunica media ~ thin ~ smooth muscle ~ no constriction Expandable ~ Veins dilate & hold large volumes of blood “Capacitance Vessels” ~ expandable & can collapse Blood Reservoirs – contain 65% of body blood volume Blood pressure is much lower in veins than arteries Farthest distance from heart ~ no constriction VENOUS VALVES In veins of limbs & extremeties . . . not in body cavities Veins can move blood against gravity ~ valves & muscles Valves prevent backward flow of blood ~ Prevents pooling Valve Dysfunction: Vericose Veins & Hemorrhoids VASCULAR ANASTAMOSIS Organs receive blood from more than one arterial source Arterial anastamosis ~ artery to artery merge By-Pass Surgery ~ coronary artery anastamosis Venous anastamosis ~ veins to veins Arterio-venous anastamosis ~ arterioles to venules Collateral Circulation ~ alternative supply of blood vessels Maintains blood supply to an area when main supply is cut or blocked by a clot or injury Part of the Healing process to improve blood supply Aerobic exercise Myocardial infarct Cerebral clot Occlusion of veins is rare ~ DO NOT become blocked Tissue death is rare as a result of venous occlusion PHYSIOLOGY OF CIRCULATION HEART = PUMP ARTERIES = CONDUITS O2 ARTERIOLES = RESISTANCE VESSELS CAPILLARIES = EXCHANGE SITES O2/ CO2 VEINS = CONDUITS & BLOOD RESERVOIRS CO2 FACTORS AFFECTING CIRCULATION BLOOD FLOW . . . BLOOD PRESSURE . . . RESISTANCE 1. BLOOD FLOW ~ ml/minute VOLUME OF BLOOD FLOWING THROUGH A VESSEL, ORGAN, or ENTIRE CIRCULATION IN A GIVEN PERIOD VARIES WIDELY BASED ON ORGAN NEEDS Skeletal Muscles . . . Digestive Organs 2. BLOOD PRESSURE ~ mmHg FORCE PER UNIT AREA EXERTED ON THE WALL OF A BLOOD VESSEL BY ITS CONATINED BLOOD Defined: MEAN SYSTEMIC ARTERIAL PRESSURE IN THE LARGEST ARTERIES ~ NEAR THE HEART PRESSURE DIFFERENCE PROVIDES THE FORCE THAT KEEPS BLOOD MOVING . . . FROM HIGH PRESSURE TO LOW PRESSURE 3. RESISTANCE OPPOSITION TO BLOOD FLOW due to friction RESISTANCE -----> FLOW Causes of Resistance: 1. Blood Viscosity ~ THICKNESS OR STICKINESS H2O & BLOOD PARTICULATES PLASMA PROTEIN & LIPIDS LOW RBC’S ---> LOW VISCOSITY HIGH RBC’S ---> HIGH VISCOSITY 2. Blood Vessel Length LONGER VESSELS ---> greater RESISTANCE FAT REQUIRES MORE & LONGER VESSELS WHICH INCREASES RESISTANCE 3. Blood Vessel Diameter . . . Most Significant Factor GREATER DIAMETER ----> LESS RESISTANCE SMALLER DIAMETER ----> MORE RESISTANCE Vasoconstriction ↑↑↑ . . . Vasodilation ↓↓↓ As radius decreases by ½ ~ resistance increases 16X 4. Turbulance ~ increases resistance Fatty Plaques ~ atherosclerosis ~ cholesterol FACTORS AFFECTING BLOOD CIRCULATION KNOW RELATIONSHIPS: VESSEL DIAMETER BLOOD FLOW VOLUME BLOOD FLOW VELOCITY BLOOD PRESSURE RESISTANCE ~ most dominant factor BLOOD PRESSURE ----> BLOOD FLOW VELOCITY Vessel Diameter is the greatest resistance factor RESISTANCE ----> BLOOD FLOW VOLUME RESISTANCE ----> BLOOD PRESSURE KNOW VASODILATION VASOCONSTRICTION VESSEL DIAMETER VESSEL DIAMETER FLOW VOLUME FLOW VOLUME RESISTANCE RESISTANCE BLOOD PRESSURE BLOOD PRESSURE FLOW VELOCITY FLOW VELOCITY CARDIOVASCULAR SYSTEM CIRCULATION LECTURE 5 SYSTEMIC BLOOD PRESSURE ~ Circulatory Pressure Heart PUMP generates the “circulatory pressure” Difference in pressure between the base of the AORTA & the entrance to the RIGHT ATRIUM via vena cava Average Circulatory Pressure ~ 100 mgHg Depends on: Arterial Pressure ~ 120 mmHg Capillary Pressure ~ 20 to 40 mmHg Venous Pressure ~ 0 to 20 mmHg PRESSURE IS GREATEST CLOSE TO THE PUMP ~ Heart PRESSURE GRADIENT FLOW FROM HIGH TO LOW PUMP . . . CREATES FLOW RESISTANCE . . . CREATES PRESSURE AORTA ~ 120 mm Hg ARTERIES ~ 120 mm Hg ARTERIOLES ~ 60 mm Hg CAPILLARIES ~ 40 - 20 mm Hg (most critical) VENULES ~ 20 mm HG VEINS ~ 10 mm Hg VENA CAVA ~ 1-5 mm Hg RIGHT ATRIUM 0 ARTERIAL PRESSURE ~ “BLOOD PRESSURE” It is what we Actually Measure in determining Blood Pressure Blood Pressure Dependent on TWO Factors
2. VOLUME OF BLOOD FORCED INTO ARTERIES BLOOD PRESSURE RISES & FALLS WITH EACH BEAT . . . as measured in arteries nearest the heart SYSTOLIC PRESSURE PRESSURE produced in arteries AFTER each left ventricular contraction AVERAGE ~ 120 mm Hg DIASTOLIC PRESSURE PRESSURE remaining in AORTA & major ARTERIES during DIASTOLE ~ Ventricular filling /heart relaxed AORTIC SEMI-LUNAR VALVES CLOSED Prevents back flow into left ventricle Maintains a lower arterial pressure in diastole Keeps blood flowing when heart is not pumping AVERAGE ~ 80 mm Hg Normal blood pressure = 120/80 = Systolic/Diastolic PULSE PRESSURE SYSTOLIC minus DIASTOLIC PRESSURE AVERAGE ~ 120mm Hg – 80 mm Hg = 40mm Hg Factors Increasing Pulse Pressure INCREASED STROKE VOLUME ~ systolic pressure INCREASED CONTRACTILITY ~ systolic pressure ATHEROSCLEROSIS ~ resistance MEAN ARTERIAL PRESSURE ~ “The Real Pressure” AVERAGE PRESSURE THAT PROPELS BLOOD TO ALL TISSUE DURING CARDIAC CYCLE Lower than SYSTOLIC but higher than DIASTOLIC DIASTOLE lasts longer than SYSTOLE ~ 2/3 to 1/3 Know MAP = Diastolic Pressure + 1/3 Pulse Pressure How to Calculate EXAMPLE: Systolic pressure = 120 Diastolic pressure = 80 Pulse Pressure = 40 MAP = 80 + 40/3 = 93 mm Hg NOTE: BOTH MAP & PULSE PRESSURE DECREASES WITH INCREASING DISTANCE FROM THE HEART ---> systolic pressure CAPILLARY PRESSURE ~ “Capillary Hydrostatic” Pressure BEGINNING CAPILLARY BED PRESSURE ~ 40 mm Hg END CAPILLARY BED PRESSURE ~ 20 mm Hg LOW CAPILLARY BED PRESSURE is DESIRABLE Capillary Walls very fragile ~ only one cell layer thick HIGH PRESSURE ----> RUPTURE Nose Bleeds ~ mixed O2/CO2 blood Capillaries very permeable ~ pushes fluid out of capillaries HIGH PRESSURE ----> EDEMA EDEMA ~ abnormal accumulation of fluid in tissue Pulmonary Edema ~ LEFT SIDED FAILURE Accumulation in lungs Peripheral Congestion ~ edema/ascites RIGHT SIDED FAILURE Accumulation in abdomen & tissue Arterioles are most critical in regulating blood flow to tissues & controlling of blood pressure CAPILLARY BLOOD FLOW BLOOD FLOW THROUGH CAPILLARY BEDS IS SLOW & INTERMITTENT . . . NOT STEADY FLOW IS FROM HIGH PRESSURE TO LOW PRESSURE CAPILLARY EXCHANGE ~ Occurs by DIFFUSION SOLUTES ~ “Diffuse” ~ HIGH TO LOW SOLUTE CONC. OXYGEN & CARBON DIOXIDE NUTRIENTS ~ AA, GLUCOSE, LIPIDS METABOLIC WASTES OTHER IONS ~ Na+, Ca+, K+ FLUID Moves ~ HIGH TO LOW PRESSURE LOW SOLUTE TO HIGH SOLUTE CONC. ~ via OSMOSIS DEPENDS ON: HYDROSTATIC PRESSURE PRESSURE INSIDE Capillary vs. CELL PRESSURE ~ pushes fluid out of capillaries into tissues COLLOID OSMOTIC PRESSURE ~ Draws in H2O Solutes carry H2O with them by OSMOSIS Net Filtration Pressure ~ difference between net (NFP) hydrostatic pressure & net osmotic pressure VENOUS BLOOD PRESSURE NO PULSATION ~ pressure too low ~ from 20 mmHg to 0 BEGINNING VENOUS PRESSURE ~ 20 mm Hg at capillaries END VENOUS PRESSURE ~ 0 mm Hg at Rt. Atrium FACTORS AIDING VENOUS RETURN Small PRESSURE GRADIENT = 20 to NEAR 0 mm Hg PRESSURE GRADIENT is too small to allow adequate return to heart by itself GRAVITY will allow some blood to flow from head & neck back to the heart while standing or sitting Respiratory Pump ~ (pressure/volume relationship) Breathing action sucks blood upward toward Heart Inhaling ---> increased abdominal pressure ---> squeezes local veins ---> forcing blood toward heart Inhaling ---> decreased chest cavity pressure --> thoracic veins to expand ---> speeds blood entry into right atrium Muscular Pump Skeletal muscle contraction ---> milking action of blood toward heart & prevents blood pooling Valves in extremity veins prevent flow back MAINTAINING BLOOD PRESSURE PHYSIOLOGIC FACTORS ~ INFLUENCE PRESSURE CARDIAC OUTPUT ----> BP BLOOD VOLUME ----> BP PERIPHERAL RESISTANCE ----> BP BLOOD = CARDIAC X PERIPHERAL PRESSURE OUTPUT RESISTANCE SV Constriction HR Dilation Volume Viscosity Vessel Length NEURAL . . . HORMONAL . . . RENAL CONTROLS COMPENSATES for changes in Blood Pressure SHORT TERM CONTROL ~ Neural & Hormonal Mechanisms AFFECT PERIPHERAL RESISTANCE ~ VASOMOTOR Involves: Brain Stem . . . Heart . . . Blood Vessels LONG TERM CONTROL ~ Hormonal & Renal Mechanisms AFFECT BLOOD VOLUME & FLUID RETENTION Involves: Adrenals . . . Kidney . . . Posterior Pituitary SHORT TERM CONTROLS of Blood Pressure “AFFECTS ARE IMMEDIATE & SHORT-ACTING” CONTROLS PERIPHERAL RESISTANCE by controlling vessel diameter NEURAL Mechanisms Sympathetic NS controls peripheral resistance ALTERS VESSEL DIAMETER Constriction ~ INCREASES blood pressure Dilation ~ LOWERS blood pressure ALTERS BLOOD FLOW TO MEET TISSUE DEMANDS Digestion ~ shunts blood from skeletal muscle to digestive organs . . . “cramps” Exercise ~ shunts blood from digestive organs to skeletal muscle Skin Vasodilation ~ shunts blood from internal organs to skin to loose body heat Skin Vasoconstriction ~ shunts blood from skin to internal organs to retain heat NEURAL & HORMONAL Control Mechanisms VASOMOTOR CENTER ~ MEDULLA OBLONGATA Rapid “REFLEX” response to changes in blood pressure Adrenergic Stimulation ----> Adrenaline Released Increases heart rate & myocardial contraction Potent “peripheral” Vasoconstriction HIGH BRAIN CENTERS ~ Hypothalamus ~ Cerebral Cortex Blood Pressure changes sensed in Medulla >>> relays stimuli to higher brain centers >>> Gives us awareness ONLY . . . but NO conscious control Generalized “fight or flight” sympathetic response CHEMORECEPTORS ~ chemical detectors Detect blood & CSF changes in . . . O2, CO2, & H+ LOCATED IN: Aortic Bodies ~ in AORTIC ARCH Carotid Bodies ~ in NECK ARTERIES O2, pH, CO2 ---> STIMULATES VASOMOTOR Reflex Center in Medulla Increases Heart Rate & Myocardial Contraction & Vasoconstriction > > > INCREASES BLOOD PRESSURE BARORECEPTORS ~ detect ARTERIAL pressure changes LOCATED IN: CAROTID SINUSES AORTIC SINUSES An INCREASED Arterial Pressure ----> Triggers Reflex Stretches receptors ---> impulses to medulla oblongata ----> Sympathetic inhibiton ----> VASODILATION ----> Parasympathetic Stimulation ----> SLOWS HR Results in ----> LOWER Cardiac Output & LOWER BP A DECREASED Arterial Pressure ----> Triggers Reflex Stretches receptors ----> Impulses to medulla oblongata ----> Sympathetic Stimulation ----> Faster HR, increased myocardial contractility & consriction Results in ----> HIGHER Cardiac Output & HIGH BP CAROTID SINUS REFLEX ~ “ISCHEMIC REFLEX” Prevents fainting during rapid posture changes PROTECTS BLOOD SUPPLY TO BRAIN Stimulates sympathetic nervous system Lose capability with age ~ causes syncopy ~ fainting RENAL & HORMONAL REGULATION ~ Long Term Control KIDNEY RETAINS or EXCRETES H2O IN RESPONSE TO BLOOD PRESSURE CHANGES . . REGULATES BLOOD VOLUME RENAL Autoregulation Increased blood volume & pressure increases blood flow to kidney which increases urine formation (Nervousness) Decreased blood volume or pressure decreases renal blood flow which reduces urine formation “RENIN-ANGIOTENSIN-ALDOSTERONE MECHANISM” DROP BLOOD PRESSURE ----> Kidneys release RENIN RENIN becomes Angiotensin I in blood Angiotensin I becomes Angiotensin II POTENT VASOCONSTRICTOR ~ ↑ B P Angiotensin II ----> Adrenals release of ALDOSTERONE ----> NA+ REABSORPTION & H2O RETENTION ----> INCREASED BLOOD VOLUME & BLOOD PRESSUE ERYTHROPOIETIN Large BP drop stimulates release by kidney EPO stimulates release of RBC’s from bone marrow INCREASES VOLUME & VISCOSITY OF BLOOD OTHER HORMONAL CONTROL MECHANISMS ADRENAL MEDULLA HORMONES ~ catecholamines INCREASES BLOOD PRESSURE Norepinephrine ----> VASOCONSTRICTION Epinephrine ----> INCREASED CARDIAC OUTPUT ----> VASOCONSTRICTION ANTI-DIURETIC HORMONE ~ ADH ~ “vasopressin” Secreted By POSTERIOR PITUITARY INCREASES BLOOD PRESSURE WATER RETENTION > INCREASED BLOOD VOLUME CAUSES VASOCONSTRICTION If SEVERE FLUID LOSS OR DROP IN BLOOD PRESSURE ATRIAL NATRIUETIC PEPTIDE ~ secreted by HEART LOWERS BLOOD PRESSURE ANTAGONIZES ALDOSTERONE INCREASES Na+ EXCRETION IN KIDNEYS WATER LOSS > DECREASED BLOOD VOLUME CAUSES VASODILATION BLOCKS ADH & CATECHOLAMINE RELEASE “TISSUE PERFUSION” ~ BLOOD FLOW THROUGH TISSUES
Determined by VOLUME & VELOCITY of Blood Flow VOLUME AT REST EXERCISE BRAIN 13% 4% HEART 4% 4% KIDNEYS 20% 3% ABDOMINAL ORGANS 24% 3% SKELETAL MUSCLE 20% 71% VELOCITY VELOCITY IS INVERSELY PROPORTIONAL TO CROSS SECTIONAL AREA OF THE BLOOD VESSEL BLOOD FLOWS FASTEST WHERE THE TOTAL CROSS SECTIONAL AREA IS SMALLEST INDIVIDUAL CAPILLARY HAS SMALL LUMEN BUT TOTAL CROSS SECTION AREA OF CAPILLARY BED IS VERY LARGE TOTAL CROSS SECTIONAL AREA FLOW SPEED AORTA 250 cm sq FASTEST ARTERIES 500 cm sq FAST ARTERIOLES 3000 cm sq SLOW * * * CAPILLARIES 4500 cm sq SLOWEST VENULES 3000 cm sq SLOW VEINS 500 cm sq FAST * * * SLOW CAPILLARY FLOW ALLOWS ADEQUATE TIME FOR EXCHANGES TO BE MADE CIRCULATORY IMBALANCES ~ (May Not be Covered in Lecture) HYPOTENSION ~ LOW BLOOD PRESSURE SYSTOLIC PRESSURE DROPS BELOW < 100 mm Hg ACUTE HYPOTENSION ~ MOST common DUE TO: DROP IN BLOOD VOLUME & PRESSURE -----> CIRCULATORY SHOCK ~ SYSTEM SHUTDOWN Hypovolemic ~ large volume loss ~ Hemorrhage Anaphylaxis ~ system vasodilation ~ Histamine Cardiogenic ~ heart failure ~ inadequate circulation Vascular ~ damaged vessels, dilation, aneurisms Septic ~ bacterial toxins IMMEDIATE THERAPY: IV FLUIDS TO REPLACE VOLUME ~ TRANSFUSIONS CHRONIC HYPOTENSION DUE TO: “THIN” BLOOD ~ LOW VISCOSITY POOR NUTRITION & ANEMIA LOW PROTEIN ~ low hemoglobin ORTHOSTATIC HYPOTENSION ~ OLD AGE Loss of Carotid Sinus SYMPATHETIC RESPONSE LOW BLOOD PRESSURE & DIZZINESS FAINTING WHEN STAND UP . . . BLOOD POOLS HYPERTENSION ~ HIGH BLOOD PRESSURE SYSTOLIC PRESSURE > 140 mm Hg (BORDERLINE) DIASTOLIC PRESSURE > 90 mm Hg (now > 85) NORMAL INCREASES: FEVER EXERCISE & EXCITEMENT EMOTIONAL UPSET CHRONIC HYPERTENSION ~ MOST COMMON High Stress for Years > INCREASE VESSEL RESISTANCE SLOWLY STRAINS HEART & DAMAGES VESSELS “SILENT KILLER” HEART FAILURE RENAL FAILURE ATHEROSCLEROSIS STROKE Causes: DIET ~ NA+, FAT, CHOLESTEROL OBESITY ~ LONGER VESSEL LENGTH AGE ~ > 40 STRESS & SMOKING ~ NICOTINE is a vasoconstrictor PRIMARY HYPERTENSION ~ NO SPECIFIC CAUSE IN 90% RACE ~ BLACKS > WHITE HEREDITARY ~ FAMILIES AGING EFFECTS ON CARDIOVASCULAR SYSTEM HEART CHANGES REDUCTION IN MAXIMUM CARDIAC OUTPUT CHANGES IN CONDUCTION CAPABILITIES REDUCTION IN ELASTACITY OF FIBROUS SKELETON PROGRESSIVE ATHEROSCLEROSIS RESTRICTS CORONARY CIRCULATION ~ ↑ Resistance DAMAGED CARDIAC CELLS REPLACED BY SCAR TISSUE VESSEL CHANGES WALLS LOOSE ELASTICITY LESS TOLERANT TO SUDDEN PRESSURE CHANGES MORE PRONE TO ANEURYSM FORMATION CALCIUM DEPOSITS ON WEAKENED VESSEL WALLS INCREASED RISK OF STROKE OR INFARCTION PRONE TO THROMBI FORMATION ~ ATHEROSCLEROSIS The remaining material will not be covered in lecture ~ Reference Only TISSUE PERFUSION AUTO REGULATION Constant Dilation/Constriction of Capillaries regulates local blood flow Due to CHANGES in DIAMETERS of ARTERIOLES FEEDING CAPILLARY BEDS METABOLIC CONTROLS RESPONSE TO NUTRIENTS, O2 & CO2 VASODILATION OF ARTERIOLES ----> INCREASES PERFUSION VASOCONSTRICTION ----> DECREASES PERFUSION MYOGENIC CONTROLS LOW PERFUSION ----> DEATH OF TISSUE ~ Necrosis High PERFUSION ----> RUPTURED VESSELS ~ nose bleeds REACTIVE HYPEREMIA ~ Local Redness & Swelling DRAMATIC INCREASE IN BLOOD FLOW INTO TISSUE AFTER BLOCKAGE OR INJURY ANGIOGENESIS ~ COLLATERAL CIRCULATION NEW ARTERIOLES DEVELOP ~ COLLATERAL CIRCULATION EG. CORONARY ~ Heart Attacks HIGH ALTITUDE CONDITIONS UNIQUE TISSUE PERFUSION ~ (Not Covered in Lecture- Reference Only) SKELETAL MUSCLE EXTREMELY VARIABLE WITH MUSCLE ACTIVITY HYPEREMIA: FLOW INCREASES DIRECTLY WITH METABOLIC ACTIVITY AND O2 REQUIREMENT CHOLINERGIC RECEPTORS ----> STIMULATE VASODILATION BLOOD FLOW CAN INCREASE 10X DURING EXERCISE BLOOD DIVERTED FROM SKIN & DIGESTIVE ORGANS BRAIN TOTAL BLOOD FLOW TO BRAIN REMAINS CONSTANT 750 ml/min BRAIN NEURONS TOTALLY INTOLLERANT OF ISCHEMIA CEREBRAL EDEMA > DEATH BRAIN IS MOST METABOLIC ACTIVE ORGAN IN BODY BRAIN IS LEAST ABLE TO STORE ESSENTIAL NUTRIENTS GLUCOSE VERY RESPONSIVE TO CO2 INCREASE & H+ DECREASE VERY SENSITIVE TO CHANGES IN ARTERIAL PRESSURE FAINTING OR “SYNCOPE” IF MAP < 60 mm Hg CEREBRAL EDEMA IF MAP > 160 mm Hg Transient Ischemic Attacks ~ TIA’s Cerebro-vascular Accident ~ CVA ~ stroke UNIQUE TISSUE PERFUSION ~ (Not Covered in Lecture ~ Reference Only) SKIN BLOOD FLOW THROUGH THE SKIN
WHEN BODY TEMPERATURE INCREASES > SYMPATHETIC STIMULATION IS INHIBITED > VASODILATION OF SKIN VESSELS WHEN BODY TEMPERATURE DECREASES > SYMPATHETIC STIMULATION > VASOCONSTRICTION OF SKIN VESSELS LUNGS PULMONARY CIRCULATION VERY SHORT LOW PRESSURE SYSTEM ~ SYSTOLIC = 24 mm Hg DIASTOLIC = 8 mm Hg ARTERIAL VESSELS STRUCTURED LIKE VEINS THINNER WALLS – LARGER LUMEN AUTOREGULATION IS OPPOSITE SYSTEMIC CIRCULATION LOW BLOOD O2 > VASOCONSTRICTION TO ALLOW MORE O2 TO MOVE INTO BLOOD HIGH BLOOD O2 > VASODILATION TO ALLOW O2 TO MOVE OUT OF BLOOD UNIQUE TISSUE PERFUSION ~ (Not Covered in Lecture ~ Reference Only) HEART WHEN VENTRICLES CONTRACT, CORONARY VESSELS BECOME COMPRESSED ----> BLOOD FLOW THROUGH THE MYOCARDIUM STOPS BLOOD FLOW TO THE MYOCARDIUM OCCURS WHEN THE HEART IS IN DIASTOLE OR RELAXED ABNORMALLY FAST HEARTBEAT REDUCES THE ABILITY OF THE MYOCARDIUM TO RECEIVE ADEQUATE O2 CARDIAC CELLS USE 65% OF O2 CARRIED TO IT COMPARED TO 25% FOR NON-CARDIAC CELLS 25% of Cardiac Cell is Mitochondria 2% of Skeletal Muscle cell is Mitochondria Blood Vessels & Circulation ~ Chapter 21~ Yüklə 178,85 Kb. Dostları ilə paylaş:
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