Biophysics of Circulation PDF - Module 7

PHYSIOLOGY BIOPHYSICS OF CIRCULATION MODULE 7 Dr. Kristine Marie Gozos-Narceda, MD 1E, 4B...

PHYSIOLOGY BIOPHYSICS OF CIRCULATION MODULE 7 Dr. Kristine Marie Gozos-Narceda, MD 1E, 4B Systemic Circulation OUTLINE PULMONARY CIRCULATION I.​ Circulation ​ 9% of the entire blood volume of the body A.​ Systemic Circulation ​ Right side of the heart to the lungs where it is oxygenated B.​ Pulmonary Circulation and returned to the left side of the heart II.​ Role of Each Vessel in the Circulatory System A.​ Arteries ROLE OF EACH VESSEL IN THE CIRCULATORY SYSTEM B.​ Arterioles C.​ Capillaries D.​ Venules E.​ Veins III.​ Blood Volume In The Body IV.​ Cross-Sectional Areas of Vessels V.​ Equation for Velocity of Blood Flow VI.​ 3 Basic Principles of Circulatory Function A.​ Controlled to the Tissue’s Needs B.​ Cardiac Output is Sum of All Tissue Flows C.​ Arterial Pressure Regulation VII.​ Blood Flow VIII.​ Types of Blood Flow A.​ Lamina Flow/Streamline Flow B.​ Turbulent Flow IX.​ Blood Flow Principles and Laws A.​ Poiseuille’s Law Distribution of Blood In the Circulatory System (by B.​ Bernoulli’s Principle percentage) X.​ Factors Affecting Blood Flow A.​ Pressure, Length, and Radius of the Vessel ARTERIES B.​ Viscosity of Blood ​ Transfer blood under high pressure to the tissues C.​ Vascular Wall Tension ​ Has strong vascular walls and blood flows in high velocity D.​ Vascular Shear Stress ARTERIOLES REFERENCES: ​ Last small branches of the arterial system Dr. Kristine Marie Gozos-Narceda — PPT & Recorded ​ Act as a control conduit through which blood is released Lecture into the capillaries ​ Have strong muscular walls that can close the arteriole NUMBER OF PAGES: 04 walls completely or by relaxing, can dilate the vessel walls by several folds CIRCULATION ​ Can vastly alter blood flow in each tissue in response to its ​ Movement of blood in the body needs ○​ Divided into systemic and pulmonary circulation ​ Function: CAPILLARIES ○​ Transport → serve the needs of the body tissues by ​ Function: transporting: ○​ Exchange fluid nutrients, electrolytes, hormones, and ​ Nutrients to the tissues other substances between blood and interstitial fluid ​ Waste products away from the body ​ Capillary walls ​ Hormones from one part of the body to the other ○​ Thin and have numerous minute capillary pores that are ○​ Control → maintain an appropriate environment in all the permeable to water and other small molecular tissue fluids for survival and optimal function of the cells substances SYSTEMIC CIRCULATION VENULES ​ Blood starting from the left side of the heart ​ Collect blood from capillaries and gradually combine into ​ Supplies blood flow to all the tissues of the body except large veins lungs ​ AKA greater circulation or peripheral circulation VEINS ​ 84% of the entire blood volume of the body ​ Act as conduits for transport of blood from the venules back ○​ 16% is in the heart and the lungs to the heart ​ Serve as major and controllable reservoir of extra blood ○​ Even if the pressure in the venous system is low and the venous walls are thin, the vein are muscular enough to contract or expand ​ Muscular enough to contract or expand even if the venous pressure is low and the venous walls are thin Module 7 Biophysics of Circulation 1  ○​ Other parts such as kidneys and nerves help to supply the BLOOD VOLUME IN THE BODY cardiac output BLOOD VOLUME HEART 7% SYSTEMIC CIRCULATION 84% ARTERIES 13% ARTERIOLES & CAPILLARIES 7% VEINS, VENULES, AND 64% VENOUS SINUSES PULMONARY CIRCULATION 9% ARTERIAL PRESSURE REGULATION ​ Most important function of circulation occurs in capillaries ○​ Diffusion of substances back and forth between the blood and tissues, despite low blood volume in capillaries ​ Rate of blood flow through tissues is controlled mainly by the need for nutrients and the removal of waste products of metabolism ​ Circulation is divided into two: ○​ Systemic Circulation ​ Blood starts from the left side of the heart that supplies the body, except for the lungs ​ 84% of the entire blood volume ○​ Pulmonary Circulation ​ Blood comes from the right side of the heart to the lungs where it is oxygenated and returned to the left side of the heart ​ Usually consists of 9% of the entire blood volume ​ Nervous reflex response ​ Generally independent of either local blood flow control or CROSS-SECTIONAL AREAS OF VESSELS cardiac output control ​ Based on the table below, the cross-sectional area of veins is much larger than that of the arteries A good clinical example is when a patient undergoes ○​ Explains why the venous system has a large blood hypotension storage capacity compared to the arterial system ​ The patient has a lower cardiac output resulting in the heart pumping more blood or faster CROSS-SECTIONAL VESSEL ○​ Causing veins and arterioles constrict AREA (cm2) ​ BP is expected to rise, going back to its normal range AORTA 2.5 under normal physiologic reaction of body SMALL ARTERIES 20 ARTERIOLES 40 CAPILLARIES 2500 BLOOD FLOW VENULES 250 ​ Blood flow through a blood vessel is determined by 2 factors: SMALL VEINS 80 ○​ Pressure Difference ​ Pressure difference of blood between 2 ends of the VENAE CAVAE 8 blood vessel ​ AKA pressure gradient EQUATION FOR VELOCITY OF BLOOD FLOW ​ Push the blood flow through the vessel ​ V = F/A ○​ Vascular Resistance ○​ V = Velocity of blood flow ​ Impediment of blood flowing through the vessel ○​ F = Blood flow ​ Resistance occurs as a result of friction between ○​ A = Vascular cross-sectional area flowing of blood and intravascular endothelium all ​ Velocity of blood flow in each segment of the circulation is: along inside of the vessel ○​ Directly proportional to blood flow ○​ Inversely proportional to cross-sectional area BASIC PRINCIPLES OF CIRCULATORY FUNCTION CONTROLLED TO THE TISSUE’S NEEDS ​ Blood flow to most tissues is controlled according to the tissue’s needs OHM’S LAW ​ When tissues are active, they need an increase supply of ​ Blood flow through the vessel can be calculated using the nutrients Ohm's law ○​ Thus, they need more blood flow than when at rest Δ𝑃 F= 𝑅 wherein: During exercise, the heart will pump more blood to the body F = blood flow compared to when at rest. Δ𝑃 = pressure difference R = resistance ​ States that the blood flow is: CARDIAC OUTPUT IS SUM OF ALL LOCAL TISSUE FLOWS ○​ Directly proportional to the pressure difference ​ Heart automatically supplies all parts of the body ○​ Inversely proportional to the resistance ○​ However, it cannot solely supply everything Module 7 Biophysics of Circulation 2  TYPES OF BLOOD FLOW ○​ Inversely proportional to the radius of wall LAMINAR FLOW/STREAMLINE FLOW ​ Blood flows at a steady state through a long, smooth blood vessel ○​ It flows in streamline, with each layer of blood remain the same distance as the vessel wall ​ Central most portion of the blood stays at the centre of the vessel FACTORS AFFECTING BLOOD FLOW ​ The faster one is usually at the center, while the slower ones PRESSURE, LENGTH, AND RADIUS OF VESSEL are near the vessel wall ​ First factor to affect blood flow ​ Example: Patients at rest (normal patients) 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 (𝑃) ​ Flow (F) = 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 ​ As stated in Pouiseuille’s law, blood flow is regulated by changes in the vessel size and blood pressure, especially in turbulent flow ○​ Adjustment to the blood flow are made primarily by the varying size of the vessel TURBULENT FLOW ​ Bernoulli’s principle states that an increase in the speed of ​ Occurs when the rate of blood flow becomes too great the fluid occurs simultaneously with a decrease in pressure ​ Also occurs when: or a decrease in the fluid's potential energy ○​ Blood passes an obstruction in a vessel ○​ The smaller the blood vessel, the larger the pressure it ○​ Makes a sharp turn can apply to the blood ○​ Passes over a rough surface ​ Blood flows from areas of high pressure to areas of low ​ Blood flows crosswise in a vessel and along the vessel, pressure, except in certain situations usually forming whirls of blood called Eddy currents ○​ Similar to whirlpools that can be seen in a rapidly flowing river at a point of obstruction BLOOD FLOW PRINCIPLES AND LAWS VISCOSITY OF BLOOD POISEUILLE’S LAW ​ Viscosity depends on the: ​ Explains how blood flow is regulated by changes in blood ○​ Hematocrit → mostly vessel size and blood pressure, especially in turbulent flow ​ Increased hematocrit = increased blood viscosity ​ Blood vessels are not rigid but are elastic ○​ Plasma protein concentration ○​ Adjustments in the blood flow are made primarily by the ○​ Protein types in the plasma varying size of the blood vessels ​ Other factors that affect plasma protein concentration and the ​ Rate of blood flow: types of protein in plasma have less effect than the ○​ Directly proportional to pressure difference in blood hematocrit vessel and to 4th power of the radius of vessel ○​ Indirectly proportional to length of the vessel and ​ Blood flow resistance is determined by the radius of blood viscosity of blood vessel and viscosity of blood ​ Patients with a heart attack caused by a blockage are given blood thinners to make the blood less viscous ○​ Makes blood flow smoother VASCULAR WALL TENSION ​ Tension on the blood vessel wall develops in response to transmural pressure gradients ○​ Causes vascular, smooth muscle and endothelial cells to stretch in all directions 𝑟 ​ Law of Laplace: 𝑇 = △𝑃 x ℎ Where: 𝑇 = tension △𝑃 = pressure gradient 𝑟 = radius of the blood vessel ℎ = wall thickness BERNOULLI’S PRINCIPLE ​ Explains why larger blood vessels exposed to higher ​ Key concept in fluid dynamics, which relates pressure, pressures, such as the aorta, must have stronger walls to speed, and height withstand higher levels of tension and are generally ​ States that an increase in the speed of a fluid occurs reinforced with fibrous bands of collagen simultaneously with a decrease in pressure or a decrease ​ In contrast, capillaries have a much smaller radius and in the fluid's potential energy therefore are exposed to much lower tension, permitting them ​ Inward pressure that is exerted by the vessel wall on the to withstand pressures in some organs, such as kidneys blood is: ○​ Directly proportional to the tensional stress in the vessel wall Module 7 Biophysics of Circulation 3  VASCULAR SHEAR STRESS SUBTOPIC I VASCULAR SHEAR STRESS ​ Frictional force or drag on the endothelium 𝑟 ​ 𝑇 = △𝑃 x ℎ Where: 𝑇 = tension △𝑃 = pressure gradient 𝑟 = radius of the blood vessel ℎ = wall thickness ​ Shear stress ○​ As blood flows, it creates a frictional force on the individual cells lining the blood vessels ​ Proportional to the flow velocity and viscosity of the blood ​ Inversely related to the radius QUESTION ANSWER 1. What is the function of circulation? a.​ To transport nutrients to the tissues b.​ Transport waste products c.​ Functions to maintain an appropriate D environment in all the tissue fluids for survival and optimal function of the cells d.​ All of the above 2. What part of the circulation functions to transport blood under high pressure to the tissues? a.​ Arteries A b.​ Arterioles c.​ Veins d.​ Capillaries 3. What part of the circulation functions as control conduits through which blood is released into the capillaries? a.​ Arteries B b.​ Arterioles c.​ Veins d.​ Capillaries 4. What part of the circulation functions to exchange fluid, nutrients, electrolytes, hormones, and other substances between blood and interstitial fluid? D a.​ Arteries b.​ Arterioles c.​ Veins d.​ Capillaries 5. What vessel has a large storage capacity? a.​ Venous System A b.​ Arterial System c.​ Lymphatic System​​ A 75-year-old female experienced chest pain. Turbulent She consulted a physician and was noted to blood have ischemia on 12L ECG. What type of blood flow flow does the patient have? Module 7 Biophysics of Circulation 4