Exam 3 Kirk 7: Special Circulation (coronary and skeletal)

Question 1

_______ provide entire blood supply to the myocardium

In humans, right coronary artery is dominant in ___% of people, left cornoary artery is domanint in ___% of people and the rest is both

Answer 1

CORONARY arteries provide blood flow to the entire heart

Right coronary artery is dominant in 50%

Left is 20%

Both is 30%

Question 2

The coronary sinus carries the ______ back into the _____

The descinding branch is important because:

Answer 2

Coronary sinus dumps deoxygenated blood into the inferior vena cava so that it can go into RA

Descending branch feeds the left ventricle, and this is important because that is where a ton of heart attacks occur

Question 3

Each myocyte (cardiac cell) comes into contact with how many capillaries?

Answer 3

Each myocyte comes into contact with 3-4 coronaries

Question 4

The primary determinant of coronary blood flow is _______

Squeezing effect by contracting heart causes ______. This force is highest during early ventricular systole.

Answer 4

Primary determinant of coronary blood flow is aortic pressure (secondary determinant is the tissue pressure)

Squeezing effect by the contracting myocardium causes extravascular compression (extra coronary resistance)

Question 5

Left coronary blood flow is more influenced by ____ than right coronary blood flow. Blood flow is briefly reversed during systole.

Endocardium is most as risk for ischemia… explain why

Answer 5

Left coronary blood flow is more influenced by LV tissue pressure than right coronary blood flow is.

Endocardium is most at risk for ischemia because it is in the middle and gets squeezed the most during systole. Low diastolic pressure… severe hypotension, partial coronary occlusion, aortic stensosis.

Question 6

The highest tissue pressure occurs during _____

Thus, left coronary blood flow may actually ____

Maximual left coronary blood flow occurs in _____

Approximately 60-65% of coronary blood perfusion to LV myocardium occurs during ______

If Pdiastole falls below _____ it may cause ischemia

Increase HR decreases diastolic time, ____

Answer 6

Highest tissue pressure occurs during early systole (isovolumic contraction)

Thus, left coronary blood flow may actually reverse in early systole

Maximal left coronary blood flow occurs in early diastole when tissue pressure falls to rougly zero

60-65% of coronary perfusion to LV happens during diastole

If Pdiastole falls below 50 mmHg it may cause ischemia

If HR increase, diastole time decreases

Question 7

Sympathetic stimulation of Beta 1 causes coronary _____

Weak alpha 1 vasoconstriction from sympathetic nerves is overridden by _______

Answer 7

SNS stimulation of beta 1 causes strong coronary vasodilation due to increases in metabolism

Weak alpha 1 vasoconstriction from SNS stimulation is over-ridden by strong metabolic vasodilation

Question 8

Which part of the body maximizes their AV O2 difference?

Thus PO2 is lowest in _______

Max O2 extraction is around ____% and heart operates around _____%

Because O2 extraction is already _____, the only way to increase O2 to the heart is to ____

Answer 8

Heart maximizes AV O2 difference

PO2 is lowest in coronary circulation

Max O2 extraction is 15%, heart operates at 12%

Because O2 extraction is already at a maximum, only way to increase O2 to the heart is to increase blood flow

Question 9

The relationship between coronary blood flow and myocardial metabolic activity is ___

Increase in myocardial metabolism causes _____ coronary resistance, causing ____ coronary blood flow

High _____ metabolism in the heart makes it a large consumer of O2

Answer 9

Relationship between coronary blood flow and myocardial metabolic activity is linear

Increase in myocardial metabolism causes an decreases in coronary resistance, causing an increase in coronary blood flow

High fatty acid metabolism makes the heart a large consumer of O2

Question 10

What is cardiac work? (Equation)

Myocardial work is an approximation of ____

What kind of work consumes more oxygen: pressure or volume?

Hypertension causes _______ in oxygen consumption

Answer 10

Cardiac work = Mean arterial pressure (force) x systolic blood volume (distance)

Myocardial work is an approximation of O2 consumption

Pressure work requires more O2

Hypertension causes a disproportionate increase in O2 consumption

Question 11

Myocardial oxygen supply = ____ x ______

Answer 11

Oxygen supply = blood flow x O2 content

Question 12

Because myocardial O2 supply = blood flow x O2 content

What effects myocardial blood flow?

O2 demand?

Answer 12

Myocardial blood flow: diastolic perfusion pressure and coronary vascular resistance

O2 demand: afterload/ wall tension, HR and contractility

Question 13

What increases O2 consumption in the heart?

Answer 13

Increase O2 consumption:

decrease in compliance

increased sympathetic activity

Na/K pump inhibitors

Question 14

Myocardial ischemia results from an _____ between oxygen supply and oxygen demand

Excessive O2 demand is _______ a cause of primary ischemia (usually perfusion)

Answer 14

Myocardial ischemia results from an inbalance in supply and demand

Excessive O2 demand is never a primary cause of ischemic, it’s usually perfusion

Question 15

Explain coronary steal:

What happens when the heart compensates and avoids coronary steal

Answer 15

Under certain conditions, an increase in blood flow in one region of the heart can cause a decrease in another region

Question 16

Explain what happens in coronary steal in decompensated situations (when coronrary steal does happen)

Answer 16

Question 17

What are the clinical manifestations of coronary steal?

Aka how do doctors find out that its happening

Answer 17

Exercise induced ischemia (stress test)

If too old to exercise, they administer adenosine (vasodilator)

Question 18

In resting human, __% of cardiac output goes to skeletal muscle, this is because skeletal muscle makes up ____% of body mass

Skeletal muscle has the ____ vascular bed in the body

Noncontracting state, muscle blood flow is ______ (ml/min for 100g).

Skeletal muscle blood flow can increase ___ during exercise due to ____

Answer 18

20% of cardiac output goes to skeletal muscle (skeletal muscle makes up 40% of body mass)

Skeletal muscle has largest vascular bed in the body (important in regulating blood pressure)

Noncontracting state: 3 mL/min per 100g (much less than brain and kidneys)

Skeletal muscle flow can increase 20x during exercise

Question 19

Define active hyperemia

Skeletal muscle has a very large _____ , indicating that is has high _____

At resting state, _____ dominate, whereas during muscle contraction ______ dominate

Answer 19

Active hyperemia: increase in blood flow due to increase in metabolic activity

Skeletal muscle has a very large flow reserve, indicating high degree of vascular tone

At resting state, vasoconstrictors dominate, whereas during muscle contraction, vasodilator influences dominate to increase O2 to muscle tissues and remove metabolic waste build up

Question 20

The reduction of vascular resistance during dynamic exercise results from _____, depsite the increase in central sympathetic nerve activity

Answer 20

Reduction of vascular resistance during dynamic exercise results from local metabolic control, despite the increase in central nervous activity

SO it vasodilates instead of vasoconstricts

Question 21

What happens to blood flow during isometric contraction>

Answer 21

Isometric contraction: you actually cut off blood flow

During isometric exercise, vascular resistance increases and cardiac output rises, thus there is an increase in arterial pressure

Question 22

How does muscle contraction help with venous return?

Answer 22

Muscle contraction pumps blood out of muscle veins

contraction compresses veins, you get an increase in venous return

Muscle extraction acts as a secondary pump

Question 23

Explained what happens during inspiration and expiration in terms of venous return

Answer 23

Inspiration: decrease pleural pressure, increase abdominal pressure, compressing veins there and increases venous return (reduces pressure in right atrium as well)

Expiration: increase pleural pressure, decreased abdominal pressure, opposite

Increased inspiration rate during exercise causes increased venous return overall

Question 24

Skeletal muscle is primarily innervated by _____

NE binds to ___ receptors causing ____

Blood flow through skeletal muscle vessels can also stimulate release of ___ causing ______.

THis mechanism along with _____ is responsible for active hyperemia during exercise.

Answer 24

Skeletal muscle is innervated by sympathetic adrenergic fibers

NE binds to alpha receptors causing vasoconstriction

Blood flow through skeletal muscle vessels can also stimulate release of NO causing vasodilation

This mechanism along with metabolic activity is responsible for active hyperemia during exercise