BISC 104 - Physio Ex_Exercise 5 - Cardiovascular Dynamics

BISC 104 - Physio Ex_Exercise 5 - Cardiovascular Dynamics -...

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T he cardiovascular system is composed of a pump—the heart—and blood vessels that distribute blood containing oxygen and nutrients to every cell of the body. The principles governing blood flow are the same physical laws that apply to the flow of liquid through a system of pipes. For example, one very elementary law in fluid mechanics is that the flow rate of a liquid through a pipe is directly proportional to the difference between the pressures at the two ends of the pipe (the pressure gradient ) and inversely proportional to the pipe’s resistance (a measure of the degree to which the pipe hinders or resists the flow of the liquid): Flow 5 pressure gradient/resistance 5D P/R This basic law applies to blood flow as well. The “liquid” is blood, and the “pipes” are blood vessels. The pressure gradient is the difference between the pressure in arteries and that in veins that results when blood is pumped into ar- teries. Blood flow rate is directly proportional to the pressure gradient, and in- versely proportional to resistance. Recall that resistance is a measure of the degree to which the blood vessel hinders or resists the flow of blood. The main factors governing resistance are 1) blood vessel radius, 2) blood vessel length, and 3) blood viscosity. Radius. The smaller the blood vessel radius, the greater the resistance, due to frictional drag between the blood and the vessel walls. Contraction, or vasocon- striction, of the blood vessel results in a decrease in the blood vessel radius. Lipid deposits can cause the radius of an artery to decrease, preventing blood from reaching the coronary tissue and result in a heart attack. Alternately, relaxation, or vasodilation, of the blood vessel causes an increase in the blood vessel radius. As we will see, blood vessel radius is the single most important factor in deter- mining blood flow resistance. Length. The longer the vessel length, the greater the resistance—again, due to friction between the blood and vessel walls. The length of a person’s blood vessels change only as a person grows; otherwise, length generally remains constant. Viscosity. Viscosity is blood “thickness,” determined primarily by hematocrit the fractional contribution of red blood cells to total blood volume. The higher the Cardiovascular Dynamics 5 EXERCISE OBJECTIVES 1. To understand the relationships among blood flow, pressure gradient, and resistance 2. To define resistance and describe the main factors affecting resistance 3. To describe Poiseuille’s equation and how it relates to cardiovascular dynamics 4. To define diastole, systole, end systolic volume, end diastolic volume, stroke volume, isovolumetric contraction, and ventricular ejection 5. To describe Starling’s Law and its application to cardiovascular dynamics 6. To design your own experiments using the lab simulation for pump me- chanics 7. To understand what is meant by the term compensation 63
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hematocrit, the greater the viscosity. Under most physiological
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BISC 104 - Physio Ex_Exercise 5 - Cardiovascular Dynamics -...

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