Flashcards in Medical Physiology Block 3 Week 1 Deck (29):
Describe how blood passes through the heart & circulation in a complete circuit.
The circulatory system uses one circuit for exchange of gases with the external milieu and another circuit for exchange of nutrients and non-gaseous wastes; We can divide the vascular system into a high-pressure part (extending from the contracting left ventricle to the systemic capillaries) and a low-pressure part (extending from the systemic capillaries, through the right side of the heart, across the pulmonary circulation and left atrium, and into the left ventricle; the flow of blood through the heart is into the right atrium from the venous blood, into the right ventricle, in the pulmonary circulation, into the left atrium, into the left ventricle, and out of the aorta into the systemic circulation
Describe how parallel arrangement (vs. series) of the circulatory system allows independent regulation of blood flow in organs.
Flow = change in pressure / resistance; for elements that are in series, the resistance summates and is greater than a single resistive element; for elements that are in parallel, the resistance is the reciprocal of the combined resistance (lowering the total resistance)
How does radius, length, & fluid viscosity affect flow; what defines an ideal tube?
increased radius increases flow; increased tube length decreases flow; increased fluid viscosity decreases flow; (these three parameters change the resistance of the system); an ideal tube is small, rigid, uniform, and straight
What is the effect of non‐ideal variables on blood flow such as: transmural & hydrostatic pressure, varying vessel compliance/radius, & the pulsatile nature of the heart pumping?
transmural pressure is the difference between the intravascular pressure and the tissue pressure (transmural pressure governs vessel diameter; P in the vessel - tissue pressure; increase in tissue pressure increases resistance and decreases flow); gravity produces a hydrostatic pressure difference between two points whenever there is a difference in height (Δ h) (the reference point is the heart; increase in pressure for the lower extremity and decrease in pressure for upper extremity); the change in pressure accompanying a change in volume is greater if the compliance of a vessel is lower (C = change in volume/change in pressure); flow in the circulation follows an AC circuit diagram (pulsatile nature of the heart)
Explain how viscosity, vessel size, & flow rate drive laminar vs. turbulent flow.
turbulent flow occurs where there is low viscosity (anemia), large radius, and large velocity (high cardiac output)
How can blood pressure, blood flow & cardiac volume be measured using either direct vs. indirect & invasive vs. non‐invasive methodologies?
Indirect: sphygmomanometer- inflation of the bag by means of a rubber squeeze-bulb to a pressure level above the expected systolic pressure occludes the underlying brachial artery and halts blood flow downstream. The pressure in the cuff, measured by means of a mercury or aneroid manometer, is then allowed to slowly decline; The most direct way of measuring blood pressure is through a catheter, inserted into an artery, connected to a strain gauge on a flexible diaphragm, with signal amplification coinciding with a recorder (The measuring apparatus consists of an arterial cannula connected to tubing containing a continuous column of saline which conducts the pressure wave to the transducer, or flexible diaphragm); ultrasonic methods are also widely used transcutaneously on surface vessels in humans; Electromagnetic flowmeters (most invasive) rely on the idea that the movement of blood through an electromagnetic field induces a voltage that is perpendicular to the magnetic field and the axis of blood flow
What are the components of whole blood and what are their functional roles?
If you spin down a sample of blood containing an anticoagulant for ∼5 minutes at 10,000 g , the bottom fraction contains formed elements —RBCs (or erythrocytes), WBCs (leukocytes, which include granulocytes, lymphocytes, and monocytes), and platelets (thrombocytes) (WBCs and platelets form a whitish gray layer—the buffy coat). The top fraction is blood plasma; Principal plasma proteins are albumin, fibrinogen, globulins, and other coagulation factors
Describe the myeloid stem cell and its role in hematopoiesis
the common myeloid progenitor produces megakaryocytic (platetlets), erythroid (RBC), granulocytic, and monocytic lineages; RBC production is stimulated by the growth factor erythropoetin
Describe the components of the CBC and what they measure.
the number of red blood cells (RBC count), the number of white blood cells (WBC count), the total amount of hemoglobin, the hematocrit, average red blood cell size (mean corpuscular volume; ratio of hematocrit to red blood cells), hemoglobin amount per red blood cell (mean corpuscular hemoglobin; ratio of hemoglobin to red blood cells), the amount of hemoglobin relative to the size of the cell (hemoglobin concentration) per red blood cell (mean corpuscular hemoglobin concentration; ratio of hemoglobin to hematocrit), and the red cell distribution width (standard deviation of the mean corpuscular volume)
What is the major physiologic role of red blood cells?
The RBC performs three major tasks: (1) carrying of O2 from the lungs to the systemic tissues, (2) carrying of CO2 from tissues to the lungs, and (3) assisting in the buffering of acids and bases.
What are the normal white blood cells circulating in blood and what are their relative differential count?
neutrophils- 60% (digestive elements); lymphocytes- 30% (immune system; B & T cells); monocytes- 6% (phagocytosis and antigen-presenting); eosinophils- 3% (viral and parasitic response); basophils- 1% (source of IL-4 which stimulates B lymphocytes to produce IgE antibodies); neutrophils, basophils, and eosinophils are granulated; monocytes mature in the bone marrow outside the vascular system
What is “tenase” and “prothrombinase”?
factors IXa and VIIIa together with calcium and negatively charged phospholipids form a trimolecular complex called tenase (converts factor X to factor Xa); factors Xa and Va, together with calcium and phospholipids, form a trimolecular complex called prothrombinase (cleaves prothrombin into thrombin)
What is unique about the vitamin K dependent blood coagulation proteins
phospholipid bound zymogens (proenzyme)
What are the proteins of the fibrinolytic system and what is their role?
After plug formation, fibrinolysis—the breakdown of stable fibrin—breaks up the clot in a more general process known as thrombolysis; The process of fibrinolysis begins with the conversion of plasminogen to plasmin, catalyzed by one of two activators: tissue-type plasminogen activator or urokinase-type plasminogen activator.
What are three major anticoagulant proteins and where do they function?
protein C (cofactor S; inactivates factors Va and VIIIa (tenase and prothrombinase); antithrombin III (inhibits Xa and thrombin); thrombomodulin (removes thrombin from circulation; can bind protein C); tissue factor pathway inhibitor (binds to trimolecular complex of tissue factor VIIa and calcium; extrinsic pathway)
What does the activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) measure?
APTT- intrinsic system and common pathway; PT- Extrinsic system and common pathway; TT- fibrinogen only
What are some of the protein involved in arterial thrombosis?
Fibrinogen, homocysteine, antiphospholipid protein, lipoprotein A, and factor VII
What proteins are involved in venous thrombosis?
protein C, protein S, antithrombin (anti-coagulants)
Describe the mechanical movement of the heart throughout the cardiac cycle.
During isovolumic contraction the left ventricle initially twists in a clockwise direction due to shortening of endocardial fibers (as viewed from the apex: inferior left portion of the heart); During diastole, epicardial fibers are stretched before the endocardial fibers (Epicardial fibers generate more mechanical torque than endocardial fibers)
Calculate stroke volume and ejection fraction.
SV = EDV-ESV; ejection fraction = SV/EDV
Describe the pressure volume relationship of the left ventricle.
Point A- opening of mitral valve; AB- increase in volume, decrease in pressure (lowest ventricular pressure at B); BC (increase in volume and modest increase in pressure; C- closure of mitral valve; CD- no change in volume with pressure increasing up to aortic pressure; D- opening of aortic valve; DE- decrease in volume and pressure increases to its highest at point E (also the commencement of muscle relaxation); EF- decrease in volume (less than DE) and decrease in pressure; point F- end systolic volume and closure of the aortic valve; FA- volume stays the same as pressure decreases (eventually the mitral valve opens again at point A)
Calculate the work performed by the heart and the energy the heart generates.
W = pressure-volume work + kinetic energy (total external work) + tension heat; Ventricular wall tension increases with increasing aortic pressure (majority of the energy consumption of the heart)
Identify differences in excitation contraction coupling mechanisms between skeletal and cardiac muscle cells
Force generation in cardiac muscle is dependent on calcium, cooperative (three states: blocked, closed, open), and modulated by phosphorylation
Describe the length tension relation for cardiac and skeletal muscle.
Increasing sarcomere length in cardiac muscle decreases interfilament distance increases the affinity of Troponin C for calcium. Increases cross-bridge binding and increases calcium sensitivity of force generation
Explain the effects of phosphorylation of troponin C on thin filament activation.
Troponin I phosphorylation by PKA (near TnC regulatory site) decreases the affinity of Tnc for calcium (relaxation)
Describe Starling’s Law and draw a ventricular performance curve.
Cardiac muscle shortening velocity is related to preload (increases with increasing preload), decreases by increases in afterload (resistance), and shortening velocity in isometric conditions is zero; A ventricular performance curve shows, on the y-axis, stroke work (P • δ V), which includes Starling's systolic pressure (itself an estimate of muscle tension), plotted against left atrial pressure, which corresponds to Starling's end-diastolic volume (itself an estimate of muscle length).
Define contractility, and diagram how changes in contractility affect left ventricular pressure through the cardiac cycle.
Factors that increase myocardial contractility increase [Ca 2+]i , either by opening Ca 2+ channels, inhibiting Na-Ca exchange, or by inhibiting the Ca 2+ pump—all at the plasma membrane; End Systolic Pressure Volume Relationship curve becomes steeper and shifts to the left with positive inotropic agents (ESPVR is increased with increased beta-adrenergic stimulation)
How does review of red blood cell morphology help in medical diagnosis?
Knowing the average size of red blood cells and their hemoglobin concentration with physiologic conditions helps classify anemias