Chapter 16 Control of Cardiovascular Function

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 16Control of Cardiovascular

Function


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?


Simplified Path of Blood Flow

right heart

lungs

left heart

body


Heart Anatomy


Question

Tell whether the following statement is true or false.The pulmonary circulation moves blood through the left

side of the heart.


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.


The Heart Layers


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


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


Action potential


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


Action potential


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


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


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


Cardiac Muscle Firing (cont.)• During

plateau, the muscle contracts strongly

• Then the Ca2+ channels shut and it repolarizes

Threshold potential

PLATEAUAction potential

Calcium leak


Question

Which ion channels allow cardiac muscle to fire without a stimulus?

a. Na+

b. K+

c. Ca2+

d. Cl-


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).


The Cell Passes the Impulse to Its Neighbors


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


Cardiac Cycle—Diastole• Ventricles relaxed

• Blood entering atria

• Blood flows through AV valves into ventricles

• Semilunar valves are closed


Cardiac Cycle—Systole

• Ventricles contract• Blood pushes against AV valves and they

shut• Blood pushes through semilunar valves into

aorta and pulmonary trunk


Question

Which of the following statements is true about ventricular systole?

a. Atria contractb. Ventricles contractc. AV valves are opend. Semilunar valves are closed


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.


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


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


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


DiscussionHow will each of these factors affect arteriole

size and peripheral resistance?• Lactic acid • Low PO2 • Cold • Histamine• Endothelin • Heat• NO • Adenosine


Blood Pressure

BP = CO x PRBlood pressure = cardiac output × peripheral resistance


Question

Tell whether the following statement is true or false.In patients with hypertension (high blood pressure),

peripheral resistance is increased.


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).


Forces Moving Fluid In and Out of Capillaries


Lymph Vessels Carry Tissue Fluid Back to the Veins

Chapter 16 Control of Cardiovascular Function

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