Chapter 16 Control of Cardiovascular Function
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Transcript of Chapter 16 Control of Cardiovascular Function
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Chapter 16Control of Cardiovascular
Function
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Path of Blood FlowScenario:• You inject a medication into the client’s arm• Within a few minutes, some of that drug has reached the client’s liver and is being deactivatedQuestion:• How did it get there?
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Simplified Path of Blood Flow
right heart
lungs
left heart
body
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Heart Anatomy
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Question
Tell whether the following statement is true or false.The pulmonary circulation moves blood through the left
side of the heart.
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Answer
FalseRationale: The right side of the heart pumps blood to the
lungs through the pulmonary arteries, where gas exchange takes place. The left side of the heart is considered systemic circulation because blood is pumped to all body tissues.
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The Heart Layers
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The Basics of Cell Firing
• Cells begin with a negative charge: resting membrane potential
• Stimulus causes some Na+ channels to open
• Na+ diffuses in, making the cell more positive
Threshold potential
Resting membrane potential Stimulus
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The Basics of Cell Firing (cont.)• At threshold
potential, more Na+ channels open
• Na+ rushes in, making the cell very positive: depolarization
• Action potential: the cell responds (e.g., by contracting)
Threshold potential
Resting membrane potential Stimulus
Action potential
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The Basics of Cell Firing (cont.)• K+ channels open• K+ diffuses out,
making the cell negative again: repolarization
• Na+/K+ ATPase removes the Na+ from the cell and pumps the K+ back in
Threshold potential
Resting membrane potential Stimulus
Action potential
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Cardiac Muscle Firing
• Cells begin with a negative charge: resting membrane potential
• Calcium leak lets Ca2+ diffuse in, making the cell more positive
Threshold potential
Resting membrane potential Calcium
leak
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Cardiac Muscle Firing (cont.)• At threshold
potential, more Na+ channels open
• Na+ rushes in, making the cell very positive: depolarization
• Action potential: the cell responds (e.g., by contracting)
Threshold potential
Resting membrane potential
Action potential
Calcium leak
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Cardiac Muscle Firing (cont.)• K+ channels open• K+ diffuses out,
making the cell negative again, but Ca2+ channels are still allowing Ca2+ to enter
• The cell remains positive: plateau
Threshold potential
PLATEAU
Action potential
Calcium leak
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Cardiac Muscle Firing (cont.)• During
plateau, the muscle contracts strongly
• Then the Ca2+ channels shut and it repolarizes
Threshold potential
PLATEAUAction potential
Calcium leak
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Question
Which ion channels allow cardiac muscle to fire without a stimulus?
a. Na+
b. K+
c. Ca2+
d. Cl-
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Answer
c. Ca2+
Rationale: In the SA and AV nodes, resting cardiac muscle cells have open Ca2+ channels. This allows Ca2+ to leak into the cells, making them more positive (the cells reach threshold this way without the need for a stimulus).
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The Cell Passes the Impulse to Its Neighbors
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Heart ContractionHow would each of the following affect heart contraction:
• A calcium channel blocker
• An Na+ channel blocker
• A drug that opened Na+ channels
• A drug that opened K+ channels
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Cardiac Cycle—Diastole• Ventricles relaxed
• Blood entering atria
• Blood flows through AV valves into ventricles
• Semilunar valves are closed
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Cardiac Cycle—Systole
• Ventricles contract• Blood pushes against AV valves and they
shut• Blood pushes through semilunar valves into
aorta and pulmonary trunk
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Question
Which of the following statements is true about ventricular systole?
a. Atria contractb. Ventricles contractc. AV valves are opend. Semilunar valves are closed
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Answer
b. Ventricles contractRationale: During ventricular systole, the ventricles
contract. Because blood is being forced from the ventricles, semilunar valves must be open and AV valves closed. The atria are in diastole (relaxation) during ventricular systole.
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Cardiac CycleDiscussion:• Arrange these steps in the proper order:
– Ventricles relax – First heart sound– Systole – Semilunar valves open– Diastole – AV valves close– AV valves open – Semilunar valves close– Ventricles contract – Second heart sound
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Pressure, Resistance, Flow
• Fluid flow through a vessel depends on:– The pressure difference between ends of the vessel
º Pressure pushes the fluid throughº Pressure keeps the vessel from collapsing
– The vessel’s resistance to fluid flowº Small vessels have more resistanceº More viscous fluids have greater resistance
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Pressure, Resistance, Flow of Blood• Blood flow through a vessel depends on:
– Heart creating pressure difference between ends of the vessel• Heart pushing the blood through• Blood pressure keeping the vessels open
– The vessel’s resistance to fluid flow• Constricting arterioles increasing resistance• Increased hematocrit increasing resistance
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DiscussionHow will each of these factors affect arteriole
size and peripheral resistance?• Lactic acid • Low PO2 • Cold • Histamine• Endothelin • Heat• NO • Adenosine
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Blood Pressure
BP = CO x PRBlood pressure = cardiac output × peripheral resistance
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Question
Tell whether the following statement is true or false.In patients with hypertension (high blood pressure),
peripheral resistance is increased.
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Answer
TrueRationale: In hypertension, blood vessels are
constricted/narrowed. Smaller vessels increase resistance (it’s harder to push the same amount of fluid/blood through a tube that has become smaller).
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Forces Moving Fluid In and Out of Capillaries
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Lymph Vessels Carry Tissue Fluid Back to the Veins