CHAPTER 17

CONTROL OF CARDIOVASCULAR FUNCTION

Essentials of Pathophysiology

The left side of the heart pumps blood to the lungs.

 The venous side of the circulation contains a larger portion of the blood volume than the arterial side.

 The rate of blood flow through a vessel is affected by pressure, resistance, and vessel radius.

 The loose-fitting sac that surrounds the heart is called the myocardium.

 The rhythmic impulse of the cardiac conduction system is generated at the AV node and is known as the pacemaker of the heart.

PRE LECTURE QUIZ (TRUE/FALSE)

F

T

T

F

F

_______________ is the result of disorganized electrical activity in the atrium or the ventricle.

Cardiac _______________ is the amount of blood the heart pumps each minute and is defined by the formula SV × HR.

The _______________ are thin-walled, distensible, and collapsible vessels that are capable of enlarging and storing large quantities of blood.

The ______________ period of the cardiac cycle is marked by ventricular relaxation and filling.

The heart valve that controls the direction of blood flow from the right atrium to the right ventricle is called the _________________ valve.

PRE LECTURE QUIZ

Diastolic

Fibrillation

output

Tricuspid

veins

 

PATH OF BLOOD FLOW

Scenario: 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 deactivated

Question: How did it get there?

SIMPLIFIED PATH OF BLOOD FLOW

right heart

lungs

left heart

body

HEART ANATOMY

Lungs

QUESTION

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 (less Negative)

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

Resting membrane potential Stimulus

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

Resting membrane potential Stimulus

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

Desmosomes link cells tightly together

Gap junctions pass the electrical signal to

the next cells

HEART CONTRACTION

How 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 relax

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

Systole

What happens in isovolumetric contraction?

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 CYCLE

Discussion: Arrange these steps in the proper order:

8– Ventricles relax 4– First heart sound1– Systole 5– Semilunar valves open10–Diastole 3– AV valves close9– AV valves open 6– Semilunar valves

close2– Ventricles contract 7– 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 (R) to fluid flowº Small vessels have more resistanceº More viscous fluids have greater resistance

ΔP = Pin - Pout

Flow, F= ΔP ÷ R

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

DISCUSSION

How 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

How is this related to F=P/R ?

QUESTION

Tell whether the following statement is true or false.

In patients with hypertension (high blood pressure), peripheral resistance is increased.

(Hint: P= F x R )

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

Higher Pressure from artery

Lower Pressure of

the veins

LYMPH VESSELS CARRY TISSUE FLUID BACK TO THE VEINS Interstitial fluid not

recaptured in the capillaries enters the lymphatic system and ultimately reenters the blood at the subclavian

vein