OVERVIEW OF CIRCULATION...Principles of circulation 1. Rate of blood flow is controlled by the...
Transcript of OVERVIEW OF CIRCULATION...Principles of circulation 1. Rate of blood flow is controlled by the...
OVERVIEW OF CIRCULATIONDr. Sumaira Iqbal
Learning Objectives
•By the end of lecture student should be to:• Explain types of circulation•Comprehend the principles of circulation• Explain structure and function of various
components of circulation• Explain blood flow dynamics• Summarize vascular circuits
Why circulation is needed????
• To transport nutrients
• To remove wastes
• To transport hormones
• To maintain homeostasis
Circulation– Percentage of Blood Volume
•Pulmonary circulation 16%• Heart 7%• Pulmonary vessels 9%
• Systemic circulation 84%• Arteries 13%• Veins 64%• Arterioles & capillaries 7%
Principles of circulation
1. Rate of blood flow is controlled by the tissue need
• Active tissue require more blood
• Control their own blood flow
• Cardiac output can be increased only 4-7 times
2. Maintenance of cardiac output
• Heart as automaton, amount of blood comes to it is returned
• Cardiac output increase from 5L/min to 25L/min
Principles of circulation
3. Control of arterial pressure
• Blood flow cannot be increased to all organs at a time
• Balance is maintained by less supply to dormant organs
• When blood pressure falls, nervous reflexes elicit:• Increase in force of contraction
• Constriction of arterioles and venules
BLOOD VESSELSARTERIES
• Elastic vessels
• Strong vascular wall
• Transport of blood from heart to tissues under high pressure
• Pressure reservoir
• Systolic and diastolic pressure --- 120/80 mmHg
• Mean arterial pressure --- 93 mmHg
• Leads to arterioles
BLOOD VESSELS
WINDKESSEL EFFECT:
• Interaction between stroke volume, compliance of vessels and resistance of vessels for account of arterial pressure waveform
• Recoiling effect of aorta and elastic arteries convert pulsatile flow in to continuous flow in capillaries
• Aorta and large arteries act as a SECOND PUMP
BLOOD VESSELS
ARTERIOLES
• Major resistance vessels
• Control conduit– release blood into capillaries
• Thick smooth muscle layer --- thick tunica media
• Under nervous control • Vasoconstriction
• Vasodilation
• Under humoral control• NO, angiotensin, endothelin, prostacyclin
BLOOD VESSELS
CAPILLARIES
• Single layered vessels
• Minimum diameter (5-20 micron)
• Site of exchange of nutrients and waste materials
• Maximum cross sectional area
BLOOD VESSELS
VEINS
• Accounts for 64% blood volume
• Compliant vessels
• Capacitance vessels
• Least pressure --- 10 mmHg
Blood Flow Dynamics
BLOOD FLOW
Volume of blood that passes through in a given point of time
Normal blood flow
5000-6000ml/min
• Total circulation 5000-6000ml/min OR 100ml/sec
Pressures In Systemic And Pulmonary Circulation
PRESSURE VALUE (mmHg)
Pulmonary Systemic
Systolic 25 120
Diastolic 8 80
Mean pressure 16 100
Capillary pressure 7 17
Right atrial pressure 2 (left atrial) 0 (right atrial)
Blood Flow Dynamics
• Blood flow is determined by OHM’S LAW
F=ΔP/R (ml/min or L/min)
Where • ΔP= P2-P1
i.e. pressure difference between two ends of vessel• R is the vascular resistance
• Flow is directly proportional to pressure difference and inversely proportional to resistance offered
• Contraction of heart is the main driving force for the flow
Resistance
• Resistance—hindrance caused by friction between the moving molecules and stationary vessel wall.
• Conductance is reciprocal to resistance
• Resistance is said to be 1 PRU if flow is 1ml/sec and pressure difference is 1mmHg
Blood Flow Dynamics
• Resistance --- hindrance depends upon• Radius of vessel• Length of vessel• Viscosity of blood– friction developed between molecules
when they slide over each other
• Inversely related to fourth power of radius
R∝1/r4
if radius doubles, resistance becomes 1/16th
Blood Flow Dynamics
• Control of blood flow
• In severe vasoconstriction TPR becomes 4 PRU
• In vasodilation TPR becomes 0.2 PRU
• Vasodilation• Decreased resistance• Increased blood flow
• Vasoconstriction• Increased resistance• Decreased blood flow
Total Peripheral Resistance
• Resistance in entire circulatory system is known as total peripheral resistance OR Total resistance offered by all the systemic vasculature
• Resistance in pulmonary vasculature is about 1/7th of systemic vessels
• Total pulmonary vascular resistance is 0.14 PRU
Blood Flow Dynamics
POISEUILLE’S LAW
Interrelation between flow(F), radius(R), pressure difference (ΔP), viscosity (πη) and length (L)
F= πΔPr4/8ηL
F ∝ r4
F ∝ 1/η
• Flow is primarily altered by radius of vessel
Blood Flow Dynamics
• VASCULAR CIRCUITS• Parallel vascular circuits
• Series vascular circuits
Blood Flow Dynamics
SERIES VASCULAR CIRCUIT
• Arteries, arterioles, capillaries, venules and veins are arranged in series
• Individual resistance is less than total resistance
Blood Flow Dynamics
PARALLEL VASCULAR CIRCUIT
• Within a vascular segment vessel of one type lie in parallel arrangement
• Total resistance is less than individual resistance
• Like arteries arise from aorta in parallel
• Capillaries arise from arteries in parallel
Parallel Vascular Circuit
BENEFITS• Distribution of blood to various organs
• Every organs receives fresh blood
• Each organ control its blood supply
• Total blood flow is the sum of individual flow
• Amputation/ removal of organ• Increases TPR
• Decreases cardiac output
Blood Flow Dynamics
• Types of blood flow
• Streamline/laminar blood flow
• Turbulent blood flow
Blood Flow Dynamics
STREAMLINE/LAMINAR BLOOD FLOW
• Flow at a steady rate
• Each layer remain at a same distance from vessel wall
• Do not produce sounds
Blood Flow Dynamics
TURBULENT BLOOD FLOW
• Flow in all directions
• Produce eddy currents
• Produce sounds like korotokoff’s sounds, bruit etc
• Reynold’s number• Measure the tendency of turbulence
• Re= v.d.ρ/η
v(flow velocity), d(vessel diameter), ρ(blood density) and η(blood viscosity)
THANK YOU