Week 2

Question 1

70. List the general processes that use ATP in the working heart.

Answer 1

Cellular processes (25%) and cross-bridging to produce contractions (75%, 50% of which is due to isovolumetric contraction)

Question 2

71. State the phase of the cardiac cycle in which the most energy is expended, and which cardiac variable the amount of that energy use is most dependent upon.

Answer 2

Most energy is spent in the isovolumetric phase of contraction, cardiac afterload being a major determinant of myocardial oxygen consumption

Question 3

72. Explain what feature of the ventricular pressure-volume loop represents “stroke work,” list the two general ways that stroke work can be increased, and note which of those two mechanisms are more costly in terms of myocardial oxygen consumption.

Answer 3

Stroke work is equal to the area enclosed by the left ventricle pressure- volume loop. Stroke work is increased wither by an increase in stroke volume or by an increase in afterload, an increase in afterload being the most costly parameter to change

Question 4

73. Describe the effects of increasing heart rate and increasing myocardial contractility on the oxygen requirements of the heart, and explain which of these changes is the most efficient way to increase cardiac output.

Answer 4

Increasing heart rate and myocardial contractility increase the oxygen requirements of the heart. The most efficient way to increase cardiac output is with a low heart rate and high stroke volume.

Question 5

74. List three noninvasive techniques that are used to evaluate electrical function, valve function, and mechanical pumping action of the heart.

Answer 5

Electrocardiographic record, auscultation of the chest, echocardiography

Question 6

75. Draw a stereotypical electrocardiogram trace showing one beat of the heart, label the three major wave features, and explain what electrical events are indicated by those waves and the intervals/segments that interconnect them.

Answer 6

P wave is depolarization of the atria, the QRS complex is ventricular depolarization and T wave the ventricular repolarization; PR segment/ interval indicates the time takes for an action potential to spread through the atria and the AV node; ST segment follows the QRS complex is a phase of no rapid changes in membrane potential; the QT interval roughly approximates the duration of the ventricular myocyte depolarization and thus the period of ventricular systole

Question 7

76. Explain the electrical conventions that create Lead’s I, II, and III of Einthoven’s triangle, specifying which end of each lead is negative (reference electrode) and which end is positive (recording electrode) for each lead.

Answer 7

Lead II between right arm (-) and left leg(+); Lead I between right arm (-) and left arm (+); lead III between left arm (-) and left leg (+). When a lead registers, if charge is flowing from (-) to (+) then the lead read up will deflect upward, whereas the converse is also true

Question 8

77. Explain how a moving wave of depolarization can be represented by a net electrical dipole that can be detected by electrodes on the surface of the body, and list the two factors that determine the magnitude of the dipole.

Answer 8

A net electrical dipole describes the net direction of the charge separation on the AP wavefront, each dipole being oriented in the direction the local wave is traveling. Extracellular fluid conducts these net dipoles to be detected on the surface of the skin. The magnitude of the dipole is determined by how many cells are depolarizing at the same time as well as the consistency of the orientation between individual dipoles.

Question 9

78. Demonstrate how a net dipole simultaneously is recorded as electrical voltage in different ECG Leads, using an example where one lead shows a negative voltage difference and the other two leads show a positive voltage difference. Explain how the voltage in a given lead is affected when the dipole is oriented perpendicular or parallel to that lead.

Answer 9

the more parallel the dipole is to the lead poles, the greater the magnitude of the voltage on the trace, if the dipole is in the same orientation as – to + then it will appear positive voltage.

Question 10

79. Describe the nature of the cardiac dipole while an action potential is traveling through the AV node, and how that event appears on the ECG.

Answer 10

The P wave terminates when the depolarization reaches the non-muscular border between the atria and the ventricles and the number of individual dipoles becomes very small. The number of cells in the AV node is so small that it does not register on the EKG

Question 11

80. Draw a figure showing how the net cardiac dipole changes during the spread of depolarization through the ventricle, and show how that spread would appear when viewed by Leads I, II, and III.

Answer 11

just do it.

Question 12

81. List the components of an idealized ECG recording that are typically isoelectric.

Answer 12

PR and ST intervals are typically isoelectric, the PR being when depolarization is traveling through the AV node and the ST interval when all the ventricular cells are in their plateau

Question 13

82. Explain why the T-wave is typically broader than, and in the same direction as, the R wave in a Lead II recording.

Answer 13

Typically the ventricular depolarization occurs in a less unified way where the dipoles created are not in a similar direction. It is in the same direction because the cells that depolarized first are the first to repolarize and therefore demonstrate a repolarization in the opposite direction (opposite direction and opposite charge mean same dipole) and same positive deflection

Question 14

83. From a sample recording of a QRS complex, be able to determine the mean electrical axis of ventricular depolarization by the method you learn in our ECG workshop.

Answer 14

Mean electrical axis: the orientation of the cardiac dipole during the most intense phase of ventricular depolarization, used to determine whether the ventricular depolarization is proceeding over normal pathways

Question 15

84. Draw a figure that shows the convention by which the angle (in degrees) of electrical axis is reported, and define left axis deviation and right axis deviation. (Note: use the ranges taught in the workshop rather than in the textbook).

Answer 15

The downward direction is designated 90+, and anywhere in the patients left hand quadrant is considered normal

Question 16

85. Describe how the augmented unipolar limb leads (aVR, aVL, and aVF) are measured, and state their orientation (in degrees) on the standard axes.

Answer 16

Between right arm and aVR, left arm and aVL and left leg and aVF, these leads describe additional “perspectives” defined by drawing a line from the center to vertices of Einthoven’s triangle with (-) in the center and (+) at the vertices the leads together can be considered a hexaxial reference system for observing the cardiac vectors in the frontal

Question 17

86. Describe how the precordial limb leads (V1-V6) are measured, and describe the electrical orientation (“view”) of each of those leads.

Answer 17

12 unipolar leads that look at the electrical system in the transverse plane, the indifferent leads are formed by electrically connecting the limb electrodes, the electrical orientation the this view is of the transverse plane with the first 6 leads forming a central point of reference

Question 18

87. List the criteria that are used to define an ECG trace as being a normal sinus rhythm with respect to the following variable: Frequency, QRS duration, PR interval duration, QT interval duration and P-wave occurrence.

Answer 18

Frequency of QRS complex is 1/s, the shape of the QRS is normal for lead II and duration is less than 120 milliseconds, each QRS complex is preceded by a P wave of proper configuration , indicating SA node origin of excitation, PR interval Is less than 200 milliseconds, indicating proper delay through AV node, the QT interval is less than half the P-T interval, indicating normal ventricular repolarization and there are no extra P waves, indicating that no AV nodal conduction block is present; deviation of ST segment from isopotential baseline is indicative of cardiac ischemia

Question 19

88. Define tachycardia and bradycardia.

Answer 19

Tachycardia, excessively fast HR limiting the time for cardiac filling between beats and bradycardia, excessively slow HR, which is inadequate to support sufficient cardiac output or decreases the coordination of myocyte contraction, which will reduce stroke volume

Question 20

Normal sinus rhythm

Answer 20

typical EKG discussed earlier

Question 21

Supraventricular tachycardia

Answer 21

occurs when the atria are abnormally excited and drive the ventricles at a very fast pace

Question 22

First degree heart block

Answer 22

the only electrical abnormality is unusually slow conduction through the AV node

Question 23

Second-degree heart block

Answer 23

some but not all atrial impulses are transmitted through the AV node to the ventricle, impulses are blocked in the AV node if the cells of the region are still in a refractory period form a previous excitation

Question 24

Third degree block

Answer 24

no impulses are transmitted through the AV node, atrial and ventricular rate are completely independent, and ventricle output can be slowed significantly

Question 25

Atrial fibrillation

Answer 25

complete loss of normally close synchrony of the excitation and resting phases between individual atrial cells, cells in different areas of the atria depolarize, repolarize and are excited again randomly ** no P wave is present, can lead to blood clots

Question 26

Right and Left bundle branch blocks

Answer 26

leads to reentrant conduction pathway, less synchronous ventricle depolarization and wider QRS complex

Question 27

Premature ventricular contraction

Answer 27

ectopic focus starts an independent ventricular contraction, often followed by a compensatory beat which can affect the filling volume of the ventricles

Question 28

Ventricular tachycardia

Answer 28

ventricles are beating at a high rate, often by an ectopic center (very serious condition, can lead to inefficient filling of ventricles)

Question 29

Long QT syndrome with torsades des pointes

Answer 29

a result of delayed ventricular myocyte repolarization which maybe due to inappropriate opening of sodium channels or prolonged closure of K channels during the AP plateau phase, when QT interval is greater than 50% of cycle length which can occur with ventricular electrical complexes cyclically varying in amplitude around the baseline and can deteriorate rapidly into ventricular fibrillation

Question 30

Ventricular fibrillation

Answer 30

various areas of the ventricle are excited and contract asynchronoysly

Question 31

90. Write the Fick equation and, given appropriate data, use it to calculate cardiac output.

Answer 31

tissue substance rate/ substance consumed = flow; requires invase methods to obtain measurements (venous blood requires mixing by heart to get adequate measurement

Question 32

91. Describe the echocardiography imaging technique, and explain how it can be used to determine the ejection fraction.

Answer 32

Eco uses sound waves which come in contact with substances of varying densities and the reflection of the waves off those substances are reflected back to a computer and interpreted by that computer to make an image of the heart and its vessels. Eco can be used to find the end diastolic volume, which is used to calculate ejection fraction (EF = SV/EDV)

Question 33

92. Write the equation for ejection fraction, and state the range and mean value observed in people with normal cardiac contractility.

Answer 33

EF= SV/ EDV, range 55-87% with the mean at 67%; ejection fraction is useful in estimating contractility

Question 34

93. Describe how the end-systolic pressure-volume relationship can be used to determine myocardial contractility.

Answer 34

use one of the imaging techniques to measure ESV (measured based on the insicura or rebound on the aortic valve) and measure ESP via the arterial pressure next to the aortic valve - that gives you a data point. you can draw a line from point to origin and the slope of that will give you contractility. Higher contractility = a leftward shift of the curve (like the hand on a clock going in reverse), lower c = rightward shift

Question 35

94. Draw pressure volume loops comparing the function of a normal heart, a failing heart with depressed contractility (untreated), and the failing heart after a treatment that reduces arterial blood pressure.

Answer 35

in an untreated heart, there is reduced contractility and less ability to fight the atrial pressure so that leads to reduces EF and SV(taller/skinnier curve), if you treat by decreasing arterial pressure, you will increase the pumping abilities of the heart and increase EF and SV

Question 36

95. With regard to valve function, define “stenosis” and “insufficiency,” and explain how the different effect these two abnormalities have on ventricular chamber remodeling.

Answer 36

Stenosis is narrowing (or does not open fully) of the valves and since this narrowing leads to extra force required to move fluid through the valve, it can lead to ventricular hypertrophy insufficiency relates to valves that do not close completely and leads to regurgitation of the valves, leading to a greater volume load on the ventricle. Stenoic SL valves cause increased thickness of walls of the upstream chamber; insufficient valves tend to cause an increase in “volume work” and dilation of chambers

Question 37

Aortic stenosis

Answer 37

a much greater pressure is required by the ventricular contraction to overcome the extra obstruction of the stenoic valve and would lead to a whistling sound between the lub and the dup (systolic murmur)

Question 38

Mitral stenosis

Answer 38

a much greater left atrial pressure (leading to pulmonary edema and SOB) leading to a whistling between the dup and the lub (diastolic murmur)

Question 39

Aortic insufficiency (aka regurgitation, incompetence)

Answer 39

aortic pressure falls much faster and farther than normal so it is normally low and EDV and pressure are also elevated, leads to a gurgling diastolic murmur

Question 40

Mitral insufficiency (aka regurgitation, incompetence)

Answer 40

causes an increase in left atrial pressure as excess fluid re-enters the atria from the ventricle and results in a gurgling systolic murmur (common to hear both an insufficiency and stenosis)

Question 41

97. Describe the force that causes one-way flow of blood through the peripheral vasculature.

Answer 41

The pressure difference between the aorta and vena cava is such that blood flows from high pressure to lower pressure

Question 42

98. Write the equation that determines the rate of convective transport of a substance (X) through the cardiovascular system.

Answer 42

Transport rate= flow x concentration

Question 43

99. List the four factors that determine the rate of diffusion of a substance between capillary blood in the interstitial fluid, and write them in the equation that determines diffusion rate.

Answer 43

Variables that determine the rate of diffusion are: permeability of the membrane, surface area of exchange, the concentration gradient and the thickness of the membrane (diffusion distance)

Question 44

100. List the anatomical features of capillaries that maximize the ability to exchange substances between the blood and interstitial fluid.

Answer 44

Capillary tube walls are very thin and allow for diffusion across themselves very easily, have a small diameter, may pores and are present in huge numbers (great surface area)

Question 45

101. Contrast the diffusion pathway across capillary walls of lipid-soluble substances like O2 and CO2 with small water-soluble molecules like ions and glucose.

Answer 45

Lipid-soluble substances can diffuse across the cell wall easily (occurring at any point in the capillary wall) while polar substances have a much lesser permeability and it is proposed that they move through pores

Question 46

102. Name a class of molecules that are in high concentration in the plasma but have a very low permeability through the capillary wall.

Answer 46

Plasma proteins like albumin

Question 47

103. List three physiological roles that endothelial cells play in addition to being the barrier to exchange between the blood and ISF.

Answer 47

Epithelial cells convert certain circulating hormones to their active forms, they produce substances that are involved in blood clotting (angioplasty can kill endothelia and cause contraction) and can produce vasoactive substances that act on smooth muscle cells that surround them to influence arteriolar diameter

Question 48

104. With regard to capillary function, define “filtration” and “reabsorption.”

Answer 48

Net fluid movement out of capillaries is referred to as filtration, and fluid movement into capillaries is called reabsorption; net flow can help maintain circulating blood volume, allow intestinal fluid absorption, cause tissue edema and form saliva, sweat and urine

Question 49

105. List and describe the two categories of pressures that influence transcapillary fluid movement.

Answer 49

Both hydrostatic and osmotic pressure influence transcapillary fluid movement, hydrostatic pressure is what keeps blood moving through vessels and osmotic pressure is its opposing force, keeping plasma in the capillaries to accommodate the density of plasma proteins dissolved in the blood (specially named oncotic pressure)

Question 50

106. Write out the mathematical relationship that determines net filtration pressure at capillaries (aka, the Starling hypothesis), and define each of the 5 variables in the equation.

Answer 50

Net filtration pressure (NFP) is the tendency for fluid to move. Net filtration pressure = k[(pc-pi) (πc-πi)] Pc is the hydrostatic pressure of the intracapillary fluid, πc is the oncotic pressure of intracapillary fluid, Pi and πi are the hydrostatic and oncotic pressures for the interstitial fluid; (important variable K, fluid permeability, is close to one for leaky capillaries, and close to 0 for tight capillaries). Postive NFP means net filtration, negative NFP means net reabsorption

Question 51

107. Explain what occurs when the Starling forces are unbalanced at capillary beds, using the examples of tissue histamine release and hemorrhage-induced hypotension.

Answer 51

Normally NFP is very small ~0 with a very small net filtration. When histamine is released into the blood, it causes increased capillary permeability, which allows plasma proteins to enter the interstitial space and cause a disruption in the balance of oncotic pressure, increased diameter also means increased capillary pressure. Hemorrhage-induced hypotension would lead to greatly reduced hydrostatic pressure and also increased recovery of fluid from capillary beds

Question 52

108. Describe the anatomy and physiology of the system that prevents the accumulation of large, osmotic molecules in tissue interstitial fluid spaces.

Answer 52

The lymphatic system represents a pathway by which large molecules reenter the circulating blood. Lymph vessels are very porous and collect large particles, carried in lymph (accompanying interstitial fluid) and flows through lymph nodes before reentering the circulation via the thoracic duct (2.5L/day) Back up is exemplified in filariasis, blockage of lymph by parasite causing edema.

Question 53

109. For a series of vessels of differing diameter arranged in series, describe the relationship between flow, pressure and resistance.

Answer 53

In series, the resistances of vessels of varying diameter are additive so the equation is just slightly adjusted as Q = ΔP/ (sum of Resistances), the fluid that flows through each element in a given time must be a constant volume. Pressure will decrease over any element, and decrease the greatest when it flows through elements with the greatest resistance. Remember, given a constant flow, velocity of flow varies inversely with radius.

Question 54

110. Contrast how resistance to blood flow is determined in blood vessels arranged in parallel with how resistance to blood flow is determined in blood vessels arranged in series.

Answer 54

Resistance is calculated by adding the reciprocals of all the systems, in general, the more parallel systems that a circuit contains, the lower the overall resistance due to the increased total cross-sectional area; therefore, although an individual capillary may have a very high resistance, the overall resistance of the system will be much lower.

Question 55

111. Explain the distinction between blood flow, and blood flow velocity, using the units of each quantity to reinforce your explanation.

Answer 55

Flow will be the same at all points but the velocity varies inversely with the local cross-sectional area. Blood flow is the total volume flowing by a point in a given time (flow= volume/time) and blood flow velocity is the speed at which a fluid flows past a point (linear velocity = flow/ cross-sectional area)

Question 56

112. Describe the variation in flow velocity in the arteries, arterioles, capillaries, venules and veins.

Answer 56

Flow velocity is greatest in larger vessels such as the arteries and veins and much slower in the smaller vessel, the arterioles, venules and especially the capillaries, which is important for exchange with the blood.

Question 57

113. Describe the laminar flow pattern that occurs during blood flow in normal vessels, and explain what occurs to this pattern when blood flows through an excessively narrowed segment of a vessel; use the term “bruits” in your explanation.

Answer 57

Laminar flow in normal vessels is streamlined and orderly where the velocity profile can be described with a parabola, the speed at the edges of the vessel being the least and the speed being greatest at the center of the vessel. If liquid is forced to go through a diameter that is too small, it causes disruption of the laminar flow of the fluid, mixing the fluid traveling at different speeds and turbulent blood flow. Turbulent blood causes sounds called briuts and can be a sign of a pathological condition.

Question 58

114. Rank the following vessels according to the volume of blood they contain at any given moment in a health adult: Arteries, Arterioles, Capillaries, Venules, Veins.

Answer 58

veins and venules, arteries, capillaries, arterioles

Question 59

115. Draw a graph that shows how the mean pressure changes in the systemic circuit as blood flows through arteries, arterioles, capillaries, and veins.

Answer 59

mean pressure is greatest in arteries, decreases the most in arterioles and then decreases slowly as it returns back to the heart

Question 60

116. Draw a graph showing how the total vascular resistance varies in arteries, arterioles, capillaries and veins.

Answer 60

resistance rises moving from arteries to arterioles and the decreases until it reaches the heart, the greatest vascular resistance occurs in the arterioles

Question 61

117. Explain how the total peripheral resistance (TPR) would be different if systemic organ systems were arranged in series rather than in parallel.

Answer 61

If systemic organs were in series, their total resistance would be much greater (the resistance of the vessels would be additive) Bonus: arteriole dilation decreases pressure in the arteries and increases pressure in the capillaries, where the opposite is also true—net arteriole radius determines the TPR which is an important determinant of mean artery pressure

Question 62

118. Draw a graph the demonstrates the difference in compliance in the arterial compartment vs the venous compartment.

Answer 62

both arteries and veins are compliant (veins most compliant), which mean they are prone to stretch with applied pressure but arteries are elastic and resist the compliant stretching whereas veins are not as elastic. Compliance is change in volume over change in pressure.

Question 63

119. Describe a scenario that demonstrates the effect of high venous compliance on circulating blood volume during postural changes, and explain how active venous constriction influences that effect.

Answer 63

High venous compliance causes results in an increase in venous volume when a person goes from sitting to standing because there is greater pressure of gravity pulling blood downwards. This can greatly decrease the blood pressure. This process can be countered by active venous constriction of smooth muscle by sympathetic innervation.

Question 64

120. Describe how the elasticity of arteries contributes to blood flow in the systolic and diastolic phases of the cardiac cycle.

Answer 64

The elasticity of arteries allows them to act as a pressure reservoir (2/3 total pressure) between beats of the heart. The recoil of the arteries during diastole is what pushes blood through the vessels. Elasticity of arteries maintain a fairly stable pressure and flow of blood to the systemic circulation. With aging, there is less compliance and less elasticity so there is an increase in systolic pressure and decrease in diastolic pressure.

Question 65

121. Describe the technique for measuring systolic and diastolic blood pressure with a blood pressure cuff (sphygmomanometer) and stethoscope, explaining the relationship between cuff pressure, blood vessel patency, and the arterial pressure profile.

Answer 65

Stethoscope is placed over the brachial artery of the arm. A cuff is inflated until it reaches pressures well over the systolic pressure, which collapses the vessels in the arm. Air is bled from the cuff until the it reaches a pressure equal to the systolic pressure, the vessels will be partially patent and produce Korotkoff sounds due to turbulent flow of the partially occluded vessels. When the pressure in the cuff reaches systolic pressure or below, no sounds can be heard over the brachial artery, as the vessels are again fully patent.

Question 66

122. Starting with the basic equation relating blood flow to pressure and resistance (Q=∆P/R), derive the fundamental equation of cardiovascular physiology underlying how mean arterial blood pressure is determined (not calculated or measured, but determined).

Answer 66

Flow defined in the whole circuit is equal to cardiac output, change in pressure is analogous to difference between mean arterial pressure and central venous pressure (~0) and resistance is analogous to total peripheral resistance. This equation can be represented by CO= Mean arterial pressure/ TPR. Rearranged, mean arterial blood pressure is determined by the product of cardiac output and total peripheral resistance.

Question 67

123. Given systolic and diastolic blood pressure, calculate the mean arterial blood pressure.

Answer 67

Mean arterial pressure is approximately equal to diastolic pressure plus one third of the difference between systolic and diastolic pressures; Mean arterial pressure = CO x TPR. All changes in mean arterial pressure result from changes in either CO or TPR (Mean aterial pressure = Pd + 1/3 (Ps-Pd))

Question 68

124. Define “pulse pressure,” and list the variables that influence the magnitude of the pulse pressure.

Answer 68

Arterial pulse pressure is the systolic pressure minus the diastolic (difference in pressure between when the heart is contracting and when it is relaxed). Variables that affect pulse pressure include: pressure of a vessel determined by the vessel’s volume and compliance. Pulse pressure is calculated by dividing stroke volume by compliance. Increase in pressure during systole is proportional to the stroke volume and inversely proportional to compliance

Question 69

125. Draw and explain a graph that demonstrates the factors underlying the typical difference in pulse pressure between a 20-year-old and a 70-year-old patient.

Answer 69

Pulse pressure increases due to decreased compliance, plain old arterial pressure and volume can increase with age but not due to artery compliance but rather to arteriole changes that increase TPR

Question 70

126. Name the type of blood vessel in which regulation of smooth muscle contraction controls the distribution to different tissues to match their individual physiological needs.

Answer 70

arterioles

Question 71

127. Name the type of blood vessel in which regulation of smooth muscle contraction controls the distribution of blood volume and cardiac filling.

Answer 71

veins and venules

Question 72

128. Name the type of blood vessel that has no smooth muscle associated.

Answer 72

capillaries

Question 73

129. Define “vascular tone.”

Answer 73

Term that characterizes the general contractile state of a vessel or a vascular region, arteriolar tone implies a decrease in arteriolar vessel diameter and venous tone causes increased cardiac filling

Question 74

130. Describe the basal tone of the vasculature in a resting individual (is it low, intermediate, or high?) and explain the functional reason for this typical state.

Answer 74

Intermediate. Basal tone exists somewhere between complete relaxation and maximum contraction which establishes a baseline from which arteriolar tone can be regulated as well as contributing to arterial blood pressure (via TPR)

Question 75

131. Explain the effect of local tissue oxygen levels on arteriolar tone in systemic organs.

Answer 75

In nearly all vascular beds, exposure to low oxygen reduces arteriolar tone and vasodilation

Question 76

132. List the chemical alterations that occur in metabolically active tissue that can regulate the tone of arteriolar smooth muscle.

Answer 76

Tissue levels of carbon dioxide, H+ and K+ due to increased metabolism cause arteriolar dilation. Tissues may also release adenosine (from ATP), which is a potent vasodilator agent.

Question 77

133. Detail the mechanism by which endothelial cells influence the tone of adjacent arteriolar smooth muscle, and list some chemical agents known to activate this pathway.

Answer 77

Tissue levels of carbon dioxide, H+ and K+ due to increased metabolism cause arteriolar dilation. Tissues may also release adenosine (from ATP), which is a potent vasodilator agent.

Question 78

134. Detail the mechanism by which shear stress influences vascular smooth muscle tone.

Answer 78

Blood flow related shear stresses also stimulate NO production. Shear stress is normally detected by cilia on cells to measure flow over the cell.

Question 79

135. Describe the myogenic response of vascular smooth muscle, and explain how it could be adaptive in cases where cardiovascular disturbances alter vascular transmural pressure.

Answer 79

After vessel is stretched (by transmural pressure) passively stretch receptors (debated) inherent to the muscle cause the vessel to actively contract (myogenic response). Myogenic response is fundamentally important factor in determining the basal tone of arteries and local flow response

Question 80

136. Define “active hyperemia,” explain when it occurs, and describe the underlying mechanism.

Answer 80

In organs with highly variable metabolism, blood flow response to metabolic rate. For example, skeletal muscle blood flow increases within seconds of the onset of muscle exercise and returns to control shortly after. Underlying mechanisms could include local metabolic vasodilator feedback on arterial smooth muscle.

Question 81

137. Define “reactive (post-occlusion) hyperemia,” explain when it occurs, and describe the underlying mechanism.

Answer 81

Greater than normal blood flow that occurs transiently after the removal of any restriction that has caused a period of lower than normal blood flow. Lower than normal blood flow causes dilation during occlusion and when flow is restored it is excessive for needs and gradually comes down. Both local metabolic and myogenic mechanism may be mechanisms involved.

Question 82

138. Define “autoregulation,” describe the underlying mechanisms, and explain the general function of this phenomenon in maintaining homeostasis.

Answer 82

Except in active and reactive hyperemia, nearly all organs tend to keep their blood flow constant despite variations in arterial pressure. Autoregulatory mechanisms operate in the opposite direction in responses to change in arterial pressure. Mechanisms include vasodilator factor washout, myogenic response, and opposing increased tissue pressure Corrections can slightly overshoot set point and create new set points.

Question 83

139. Describe the distribution of sympathetic vasoconstrictor nerves to the vasculature, and explain the global role they play in cardiovascular regulation.

Answer 83

Sympathetic vasoconstrictor nerves are the backbone of the system for controlling TPR and thus are essential participants in regulating blood pressure. These neural fibers innervate arterioles in all systemic organs. Greater firing of these nerves creates greater tone while less than baseline firing creates vasodialation

Question 84

140. Name the principal neurotransmitters and receptor-type that mediate the function of sympathetic vasoconstrictor nerves.

Answer 84

Sympathetic fibers release norepinephrine which binds to a1- adrenergic receptors on smooth muscle cells. (preganglionic fibers use acetylcholine on nicotinic receptors to propagate signals)

Question 85

141. Differentiate the phenomenon of neurogenic vascular tone from that of basal vascular tone.

Answer 85

Neurogeneic vascular tone is due to the tonic firing of sympathetics that is a component of the their normal baseline state of contraction.

Question 86

142. List some examples of the few tissues that receive parasympathetic vasodilator nerves.

Answer 86

Parasympathetic vasodilator nerves that release achetylcholine are present in the vessels of the brain and heart but their influence seems to be inconsequential. Parasympathetic are present in the vessels of the salivary glands, pancreas, gastric mucosa and external genitalia that allow for vasodialation

Question 87

143. Discriminate between the vascular effects of norepinephrine, moderate levels of circulating epinephrine, and high levels of circulating epinephrine; explain the receptor-mechanisms.

Answer 87

Moderate levels of epi cause vasodialation via B2 where as high levels of epi cause vasoconstriction via a1. (more details&raquo_space; )Moderate levels of NE and Epi activate cardiac a1 receptors to cause vasoconstriction and sometimes also B2 adrenergic receptors that mediate vasodialation. B2 receptors are more sensitive to EPi than a1 and moderately increased level of circulating epi can cause vasodilation, where as higher level cause a1 receptor mediated constriction

Question 88

144. Describe the source, stimulus for secretion, and circulatory effects of vasopressin.

Answer 88

ADH is released by poster pituitary gland in response to low blood volume and or high extracellular fluid osmolarity by decreasing water secretion. Vasopressin affects are very potent

Question 89

145. Describe the vascular effect of angiotensin II.

Answer 89

Angiotension II regulates aldosterone release from the adrenal cortex to balance salt and is also a very important vasoconstrictor agent; synthesized in response to low blood volume

Question 90

146. Differentiate the general effect of venous constriction from the general effect of arteriole constriction on the function of the cardiovascular system.

Answer 90

Veins are normally in their dilated state and vasodilators usually have little effect coming form upstream. Because of their thin walls, they are much more susceptible to physical forces ie. External compression is an important determinant of venous volume, which is especially true of veins in skeletal muscle. Constriction of peripheral veins raises central veous pressure and contributes to increased cardiac output. Smooth muscle tone in veins can be increased by sympathetic signaling

Question 91

147. With regard to venous function, define “skeletal muscle pump” and explain its role and its mechanism.

Answer 91

Rhythmic contraction of skeletal muscle can cause pumping action of the blood through the valves of veins and helps return blood to the heart during exercise

Question 92

148. List organs in which blood flow is strongly regulated by local metabolic factors, and list other organs in which blood flow is strongly regulated by sympathetic nerve activity.

Answer 92

Strongly regulated by local metabolic factors: brain, heart muscle and skeletal muscle; strongly regulated by sympathetic nerve activity: kidneys, splanchnic organs and skin

Question 93

149. State the approximate percentage range of oxygen extracted from the blood flowing through the coronary vasculature in a resting individual, and explain how homeostasis is maintained when cardiac metabolism is elevated, as in exercise.

Answer 93

Myocardium extracts 70-75% of the oxygen in the blood that passes through it, which is more than any other organ. Increases in myocardial oxygen consumption must be accompanied by appropriate increases in coronary flow, most believe it is the release of adenosine that induces this change

Question 94

150. Describe how coronary vascular resistance changes during systole and diastole, and the implications for blood flow to the endocardial and epicardial myocardium during the cardiac cycle.

Answer 94

The endocardium of the left ventricle is exposed to intraventricular pressure while epicardial surface is exposed only to intrathoracic pressure, systolic compressional forces on coronary vessels are greater in the endocardial layer of the left ventricular wall than in the epicardial layers. Endocardial layers usually make up for this flow during systole, but not when coronary flow is restricted.

Question 95

Why does power lifting exercise sometimes lead to myocardial infarction

Answer 95

thick walls + compression + high HR = No flow

Question 96

Explain the paradox of neural influence on coronary flow

Answer 96

although sympathetic vasoconstrictor neurons exist to cardiac vessels, when sympathetic firing increaes heart rate and contractility, metabolic change causes net vasodilation

Question 97

152. Explain the different effect on blood flow and central venous pressure of rhythmic skeletal muscle contraction/relaxation vs sustained, tetanic contractions of skeletal muscles.

Answer 97

Rhythmic contractions can increase venous return from exercising skeletal muscle increasing cardiac output, but with strong sustained skeletal muscle compressional forces can actually stop muscle blood flow. Blood displaced from skeletal muscle into the central venous pool is an important factor in the hemodynamics of strenuous whole body exercise.

Question 98

153. Explain the relative importance of brain blood flow in terms of the overall function of the cardiovascular system.

Answer 98

Interruption of cerebral blood flow for more than a few seconds leads to unconsciousness; in all situations, measures are taken to preserve adequate blood flow to the brain. Local control dominates and auto regulates blood flow

Question 99

154. List the mechanisms by which cerebral blood flow is regulated.

Answer 99

Cerebral blood is regulated almost entirely by local mechanisms. Flow is auto-regulated very strongly and is little affected by changes in arterial pressure unless it falls below about 60mmHg. Cerebral activity in discrete regions is not constant but closely follows the local neuronal activity. Blood CO2 is very influential in blood flow to the brain, high CO2 leads to cerebral vasodilation.

Question 100

155. Explain how hyperventilation causes changes in blood flow that can result in dizziness/confusion/fainting.

Answer 100

Confusion and dizziness are direct results of cerebral vasoconstriction. It appears that this constriction is closely related to the changes in the extracellular H+ due to excess CO2 being blown off.