Cardiovascular Physiology Review

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

Anatomy of the Heart

Review 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

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

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