Cardiac Output, Blood Flow, and Pressure

Question 1

What is cardiac output? What are its two determinants?

Answer 1

-Volume of blood pumped by each ventricle per minute

-Determined by: Heart rate (beats/min) and stroke volume (volume of blood/beat)

Question 2

Describe in detail how the parasympathetic branch of ANS modulates heart rate? Does it modulate stroke volume?

Answer 2

Parasympathetic (vagus) input = decreases heart rate
A) Innervates the SA & AV nodes & the atrium; little to the ventricles
B) Via the muscarinic cholinergic receptor and G-protein activation, AcH
increases SA node permeability to K and closes both the T-type calciium
channels and the “Funny” sodium channels, hyperpolarizing it; threshold
takes longer to reach
C) AcH hyperpolarizes the AV node
D) Decreases atrial contractile strength by shortening plateau phase

Question 3

Describe in detail how the sympathetic branch of ANS modulates heart rate & stroke volume?

Answer 3

A)Innervates the SA & AV nodes & the atrium & ventricles
B)Via beta 1 adrenergic receptors & cAMP 2nd messenger system, NE
increases both sodium “Funny” and T-type calcium channel opening which
increases rate of spontaneous depolarization
C)NE reduces AV nodal delay by enhancing the slow, inward (T-type) Ca
current
D) Via beta 1 adrenergic NE increases both atria & ventricular contraction
strength by increasing Ca influx through L-type Ca channels, Ca release from SR,
increasing myosin ATPase activity, & increasing Ca re-uptake to relax muscle faster

Question 4

What is Frank-Starling Law of the Heart?

Answer 4

-Heart normally pumps all the blood returned to it; increased venous return (end-diastolic volume) results in increased stroke volume

Question 5

What is heart failure?

Answer 5

-Inability of the cardiac output to keep pace with the body’s demands for supplies and removal of wastes

Question 6

What is the difference between backward failure & forward failure?

Answer 6

-Backward failure=blood dams up in venous system

-Forward failure=blood cannot be adequately supplied to the tissues

Question 7

What is the role of adenosine in coronary circulation?

Answer 7

-Adenosine is the control molecules for linking coronary blood flow to the oxygen requirement of the heart

Question 8

What is the difference between systolic & diastolic pressure?

Answer 8

-Systolic pressure: pressure of 120 mm Hg is developed by the contracting heart

-Diastolic pressure: pressure of 80mm Hg is the minimum pressure within the arteries as the blood is draining off into the remainder if the vessels during diastole

Question 9

What is pulse pressure?

Answer 9

-The pulse that is felt in an artery lying close to the surface of the skin is due to the difference between the systolic and diastolic pressures

Question 10

What is the formula for calculating MAP? What are the two determinants of MAP?

Answer 10

-Diastolic pressure + 1/3 pulse pressure

-Determined by cardiac output & total peripheral resistance

Question 11

What local factors would cause vasoconstriction of arterioles?

Answer 11

-Increased myogenic activity

-Increased O2 concentration or decreased CO2 concentration & other wastes

-Increased sympathetic stimulation, vasopressin, angiotensin II

-Cold

Question 12

What local factors would cause vasodilation of arterioles?

Answer 12

-Decreased myogenic activity

-Decreased O2 concentration or increased CO2 concentration and other wastes

-Decreased sympathetic stimulation, vasopressin, angiotensin II

Question 13

Does nitric oxide induce vasoconstriction or vasodilation? How about endothelin?

Answer 13

-Nitric oxide= induces relaxation of smooth muscle; vasodilation

-Endothelin= indices contraction; vasoconstriction

Question 14

What is reactive hyperemia?

Answer 14

Dilation due to occlusion

Question 15

Why is pressure autoregulation a bad way to control blood pressure?

Answer 15

Cut femoral artery = Drop in MAP –> Drop in blood flow through brachial artery <–> Brachial artery vasodilates to restore blood flow back to normal, but that increase blood loss

Question 16

What is bulk flow?

Answer 16

-Determines volume between the vascular & interstitial fluid compartments

Question 17

What is colloid osmotic pressure?

Answer 17

-Part of osmotic pressure contributed by large molecules, such as colloid proteins, and act as a pull on fluid back into the capillary

Question 18

What determines the amount of blood in the veins vs. the amount returned to the heart?

Answer 18

-Venous capacity=the volume of blood that the veins can accommodate

-Venous return=the volume of blood entering each atrium per minute

Question 19

What determines venous capacity?

Answer 19

-Distensibility of the veins

-Any externally applied pressure=skeletal muscle contraction decreases capacity and increases venous pressure; it also empties “segments” of the vein to counteract gravity

Question 20

How can distensibility of the veins be changed? How is this different from arterioles?

Answer 20

-Sympathetic activity: induces vasoconstriction which decreases the volume capacity of the veins; this also increases venous pressure which increases the blood flow back to the heart

-Arteriole vasoconstriction reduces flow due to higher resistance

Question 21

What factors modulate venous return?

Answer 21

1. Cardiac contraction pressure gradient
2. Sympathetic activity increases flow as previously mentioned
3. Skeletal muscle activity increases flow as previously mentioned
4. Venous valves serve as one way stops = once blood has traveled “one segment”
   back to the heart, it can’t go back
5. Respiratory activity = lower pressure in the chest vs the extremities
6. Cardiac suction = Contraction of the ventricles creates a favorable pressure gradient to move blood into the atria

Question 22

Describe baroreceptor reflex for maintaining blood pressure.

Answer 22

1. Most important mechanism for short-term regulation
2. Adjustment of cardiac output & total peripheral resistance
3. The key baroreceptors are located in the carotid sinus & aortic arch
   A) Both are sensitive to changes in both MAP & PP
4. When pressure increases - receptor potential increases - increases AP firing in
   afferent neuron; reverse for a decrease in pressure
5. Impulses integrated in the cardiovascular control center of the medulla
6. Appropriate sympathetic & parasympathetic responses

Question 23

What is hypertension? What is the difference between primary & secondary hypertension?

Answer 23

-Blood pressure above 140/90 mm Hg

-Primary: 90% causes unknown

-Secondary: 10% caused by a known or primary pathological problem

Question 24

What is the difference between cardiovascular, renal, endocrine, & neurogenic hypertension?

Answer 24

1. Cardiovascular hypertension due to atherosclerosis
2. Renal hypertension caused by an increase in overall blood volume due to:
   A) Reduced blood flow to kidneys (atherosclerosis)
   B) Increased salt retention
3. Endocrine hypertension
   A) Pheochromocytoma - adrenal medulla tumor - excess E/NE
   B) Conn’s syndrome - increased aldosterone (induces salt retention) secretion
   by the adrenal cortex
4. Neurogenic hypertension
   A) Defect in nervous control - receptors & center
   B) If there is a reduction in blood flow to the brain

Question 25

What is hypotension? What is orthostatic hypotension?

Answer 25

-Blood pressure below 100/60 mm Hg (heart is too weak

-Shift from lying down to upright position; reflexes inadequate= blood pools in the veins=pressure drops

Question 26

What is circulatory shock?

Answer 26

-Tissues cannot be maintained due to low blood pressure

Question 27

What are the 4 types of circulatory shock?

Answer 27

1. Hypovolemic shock = fall in blood volume; hemorrhage, vomiting
2. Cardiogenic shock = weakened heart; inability to pump blood
3. Vasogenic shock = widespread vasodilation due to substances
   A) Septic - massive infection; vasodilator substances released by bacteria
   B) Anaphylactic - allergic reaction; histamine released
4. Neurogenic shock - loss of sympathetic vascular tone resulting in vasodilation.
   Induced by PAIN! OUCH!