Dynamics of Blood & Lymph Flow

Dynamics of Blood Flow Departemen FisiologiFakultas Kedokteran Universitas Sumatera Utara

Introductionblood vessels are a closed system of conduits that carry blood from heart to tissues and back to heart.

Darah mengalir maju ok : pemompaan jantung, recoil diastolik dinding arteri, tekanan pada vena otot rangka selama berolahraga, dan tekanan negatif dalam rongga dada selama inspirasi.2FUNCTIONAL MORPHOLOGY

Vessel Size and Composition

Arteries & ArteriolesWalls ; outer layer (adventitia) : connective tissuemiddle layer (media) : smooth muscleinner layer (intima) : endothelium & underlying connective tissue

aorta and other large arteries contain relatively large amount of elastic tissue, arterioles contain less elastic tissue but much more smooth muscle.the muscle is innervated by noradrenergic nerve fibers, which function as constrictors, and in some instances by cholinergic fibers, which dilate the vesselsarterioles are major site of resistance to blood flow, and small changes in their caliber cause large changes in the total peripheral resistance.Capillaries

total area of all capillary walls in body exceeds 6300 m2 in adultwalls, which are about 1 um thick, are made up of a single layer of endothelial cells

the junctions between the endothelial cells permit the passage of molecules up to 10 nm in diameter.In most endocrine glands, the intestinal villi, and parts of the kidneys, the cytoplasm of the endothelial cells is attenuated to form gaps called fenestrations, are 20 to 100 nm in diameter

8Capillaries and postcapillary venules have pericytes around their endothelial cells.have long processes that wrap around the vessels; contractile and release a wide variety of vasoactive agents. Synthesize and release constituents of the basement membrane and extracellular matrix. Regulate flow through the junctions between endothelial cells, particularly in the presence of inflammation.

Kiri: kapiler yang berada di otot rangka, otot jantung dan otot polos. Celah antar sel endotel = 10 nm.Kanan : kapiler berfenestrasi krn sitoplasma menipis = 20-100 nm, terdapat di kelenjar endokrin, vili usus dan sebagian ginjal. Kapiler & venula paska kapiler mempunyai perisit di luar sel endotel, bersifat kontraktil dan melepaskan bermacam zat vasoaktif. Mengatur aliran antar celah sel endotel terutama saat peradangan.9Arteriovenous (A V) Anastomoses or Shuntshort channels that connect arterioles to venules, bypassing capillariesin fingers, palms, and ear lobes of humans and paws, earshave thick, muscular walls and are abundantly innervated, presumably by vasoconstrictor nerve fibersVenules & Veins walls are only slightly thicker than capillaries, and easily distended, relatively little smooth muscle, venoconstriction is produced by activity noradrenergic nerves to veins and by circulating vasoconstrictors such as endothelinsintima of limb veins is folded at intervals to form venous valves that prevent retrograde flowNo valves are present in the very small veins, great veins, or the veins from brain and viscera

Angiogenesis formation of new blood vessels, important during fetal life and growth to adulthood, wound healing, formation of the corpus luteum after ovulation, and formation of new endometrium after menstruation.many factors are involved in angiogenesis; protein growth factor vascular endothelial growth factor (VEGF). FLOW, PRESSURE, & RESISTANCEeffective perfusion pressure is the mean intra luminal pressure at the arterial end minus the mean pressure at the venous endR units, which are obtained by dividing pressure in mm Hg by flow in mL/sfor example, when the mean aortic pressure is 90 mm Hg and the left ventricular output is 90 mL/s, the total peripheral resistance is

Laminar Flowflow of blood in straight blood vessels, like flow of liquids in narrow rigid tubes, is normally laminar (streamline).

Laminar flow occurs at velocities up to a certain critical velocity. At or above this velocity, flow is turbulent. Laminar flow is silent, but turbulent flow creates sounds.

Aliran darah dalam pembuluh darah yang lurus, seperti aliran di pembuluh yang kaku dan sempit, secara normal adalah aliran laminar (streamline). Aliran laminar tetap terjadi pada kecepatan sampai suatu kecepatan kriis tertentu, pada kecepatan di atasnya, aliran menjadi turbulen, dan aliran laminar tidak bersuara, sedangkan aliran turbulen menimbulkan suara.15R = Re = Reynolds = densitas cairanD = diameter pebuluhV= kecepatan aliran = viskositas cairanTurbulence is also related to the diameter of the vessel and the viscosity of the blood.

Re < 2000 -> tidak terjadi turbulenRe > 3000 -> turbulen

Kemungkinan terjadinya turbulensi juga berhubungan dengan diameter pembuluh darah dan viskositas darah. Kemungkinan ini dinyatakan dengan rasio inersi (kelembaman) terhadap daya viskositas.16SHEAR STRESS & GENE ACTIVATIONThis shear stress () is proportionate to viscosity () times the shear rate (dy/dr), which is the rate at which the axial velocity increases from the vessel wall toward the lumen.

Average velocityVelocity : displacement per unit time (eg, cm/s), Flow : volume per unit time (eg, cm3/s)Velocity (v) is proportionate to flow (Q) divided by the area of the conduit (A)if flow stays constant, velocity increases in direct proportion to any decrease in A

Flow( ) is the volume that passes through a region in a unit time.

Flow through the vascular system is produced by the arterio-venous pressure difference and is proportional to the pressure difference.

Haemodynamics of Pressure and Flow

P = tekanan perfusi efektif = tekanan intralumial rata-rata di ujung arteri dikurangi tekanan rata-rata di ujung vena.19Flow rate also dependent upon resistance (R) to flow Resistance indicates how difficult it is for blood to flow between two points at any given pressure difference

F = P/R

Critical Closing PressureResistance is Dependent on DiameterResistance falls with increasing radius of the blood vessel, and increase with increasing blood viscosity.Under ideal conditions the resistance of a tube is described by Poiseuilles law.Resistance to blood flow is determined not only by radius of the blood vessels (vascular hindrance) but also by viscosity of the blood.

Where R= resistanceh= viscosityr= radiusl= lengthHalving the radius of an arteriole increases resistance by 16 fold.Factors affecting resistanceVascular resistance (largest impact) friction between blood and vessel walls related to blood vessel diameter (and length)The narrow arterioles (and capillaries) generate the largest vascular resistance

vasoconstriction: contraction to reduce diameter

vasodilation: relaxation to enlarge diameter22Factors affecting resistanceViscosity The thicker the liquid the more resistance it creates Blood is thicker than water therefore has higher resistance (presence of cells, proteins)Plasma is about 1.8 times as viscous as water, whereas whole blood is 3-4 times as viscous as water.

Viscosity of BloodThe viscosity of whole blood is dependent on the haematocrit.

Anaemia can reduce blood viscosity.

Polycythaemia increases the haematocrit, blood viscosity and resistance.

viscosity increases are seen in diseases in plasma proteins such as the immunoglobulins and in hereditary spherocytosis (red blood cells are abnormally rigid)

24Factors affecting resistanceTurbulenceBlood flow is laminar Faster flow at centre, slowest near vessel wallIncreased turbulent flow occurs at very high flow rates or as a result of vascular disease Occurs normally during blood flow between chambers (characteristic sound)Higher turbulent flow increases resistance (and elevated BP required to maintain flow can further damage walls)

Resistance Along the Vascular System

Resistance is greatest in arterioles.

Total resistance is controlled by arteriolar resistance.

Arterioles control perfusion through organs and the distribution of cardiac output.

Arterial and Venous Compliance (Capacitance)Veins are more compliant than arteries.

Veins act as capacitance vessels

The blood volume stored in veins is regulated by veno-constriction.DQ=CDP Q = blood volumeC = compliance P = pressureSejumlah besar darah dapat ditambahkan ke dalam sistem vena sebelum vena teregang mencapai suatu titik tertentu ketika penambahan volume lebih lanjut akan sangan meningkatkan tekanan vena.27Pressure and Volume in the Circulation

Pressure is pulsatile in the arteries but steady in the capillaries and veins.

Pressure falls along the circuit with the greatest fall across arterioles.

Volume is greatest in the venous system. At any time most of the blood is in veinsVelocity and Area in the Vascular System

Total cross-sectional area of the vascular system is greatest in the capillaries and lowest in the large vessels.

Because flow is constant the blood velocity is fastest in the large vessels and slowest in capillaries.

A erythrocyte spends 0.5 to 1 second in the capillaries.Law of Laplace tension in the wall of a cylinder (T) is equal to the product of the transmural pressure (P) and the radius (r) divided by the wall thickness (w).T =Pr/w

Tekanan transmural : tekanan di dalam siliner dikurangi tekanan di luar silinder, tetapi karena tekanan jaringan rendah, maka tekanan tersebut dapat diabaikan sehingga P sama dengan tekanan di dalam organ berongga.30Arterial Pressure Pulse pressure, the difference between the systolic and diastolic pressures (SP DP), is normally about 50 mm Hg (120 80 mmHg)Mean pressure is the average pressure throughout the cardiac cycle, equals diastolic pressure plus one-third of the pulse pressure= DP + 1/3 (PP)Effect of Gravity Pressure in any vessel below heart level is increased and in any vessel above heart level is decreased by the effect of gravity.Besarnya efek gravitasi-hasil kali densitas darah, akselerasi akibat gravitasi, dan jarak vertikal di atas atau di bawah jantung 0,77 mmHg/cm pada densitas darah normal.Jadi pada orang dewasa berdiri, bila tekanan arteri rata-rata setinggi jantung adalah 100 mmHg, tekanan rata-rata arteri besar di kepala ( 50 cm di atas jantung) adalah 62 mm Hg (100 - [0.77 50]) dan tekanan arteri besar di kaki (105 cm di bawah jantung) adalah 180 mm Hg (100 + [0.77 105]).32Methods of Measuring Blood PressureAuscultatory MethodPalpation Method

Manset Riva-Rocci33Active & Inactive CapillariesIn active tissues, metarterioles and precapillary sphincters dilate, is due to action of vasodilator metabolites formed in active tissue and a decrease activity of sympathetic vasoconstrictor nervesIn resting tissues, most of capillaries are collapsed, and blood flows through the thoroughfare vessels from the arterioles to the venules

VENOUS CIRCULATIONVenous flow is aided by heartbeat, increase in negative intrathoracic pressure during each inspiration, and contractions of skeletal muscles that compress the veins (muscle pump)Heartbeat, during systole contribute venous return especially at rapid heartbeatThoracic Pump, during inspiration intrapleural pressure falls from -2.5 to -6 mm Hg, drop in venous pressure during inspiration aids venous returnMuscle Pump, Rhythmic contractions of the leg muscles while the person is standing serve to lower the venous pressure in the legs to less than 30 mm Hg by propelling blood toward the heart. In patients with varicose veins because their valves are incompetent, may develop stasis and ankle edema

Measuring Venous PressureCentral venous pressure can be measured directly by inserting a catheter into the thoracic great veins. Peripheral venous pressure correlates well with central venous pressure in most conditionsPerkiraan tekanan vena sentral, dengan mengukur distensi vena jugularis eksterna pada waktu pasien berbaring dengan kepala sedikit di atas jantung.Jarak vertikal antara atrium kanan dan tempat vena yg kolaps (tempat dgn besar tekanan nol) adalah tekanan vena dalam mm darah.Thank You

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