Chapter017

Chapter 17

Control of Cardiovascular Function

Chapter 17

Control of Cardiovascular Function

Path of Blood FlowPath 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 FlowSimplified Path of Blood Flow

right heart

left heart

Heart AnatomyHeart Anatomy

Question Question

Tell whether the following statement is true or false:

The pulmonary circulation moves blood through the left side of the heart.

Answer Answer

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 LayersThe Heart Layers

The Basics of Cell FiringThe 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.)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.)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 Cell FiringCardiac Cell 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

Cardiac Muscle Firing (cont.)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

• 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

• During plateau, the muscle contracts strongly

• Then the Ca2+ channels shut and it repolarizes

Threshold potential

PLATEAUAction potential

Calcium leak

Question Question

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

a. Na+

c. Ca2+

d. Cl-

Answer Answer

c. Ca2+

In the S-A node and A-V node, 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).

Heart ContractionHeart Contraction

How would each of the following affect heart contraction:

• A calcium-channel blocker

• A Na+ channel blocker

• A drug that opened Na+ channels

• A drug that opened K+ channels

Cardiac Cycle—DiastoleCardiac Cycle—Diastole

• Ventricles relaxed

• Blood entering atria

• Blood flows through AV valves into ventricles

• Semilunar valves are closed

Cardiac Cycle—SystoleCardiac Cycle—Systole

• Ventricles contract

• Blood pushes against AV valves and they shut

• Blood pushes through semilunar valves into aorta and pulmonary trunk

Question Question

Which of the following statements is true about ventricular systole?

a. Atria contract

b. Ventricles contract

c. AV valves are open

d. Semilunar valves are closed

Answer Answer

b. Ventricles contract

During ventricular systole, the ventricles contract. Because blood is being forced from the ventricle, semilunar valves must be open and AV valves, closed. The atria is in diastole (relaxation) during ventricular systole.

Cardiac CycleCardiac Cycle

Discussion:

• 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, FlowPressure, Resistance, Flow

• Fluid flow through a vessel depends on:

– The pressure difference between ends of the vessel

º Pressure pushes the fluid through

º Pressure keeps the vessel from collapsing

– The vessel’s resistance to fluid flow

º Small vessels have more resistance

º More viscous fluids have greater resistance

Pressure, Resistance, Flow of BloodPressure, 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:Discussion:

How will each of these factors affect arteriole size and peripheral resistance?

• Lactic acid • Low PO2

• Cold • Histamine

• Endothelin • Heat

• NO • Adenosine

Blood PressureBlood Pressure

BP = CO x PRBlood Pressure = Cardiac Output × Peripheral Resistance

Question Question

Tell whether the following statements is true or false:

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

Answer Answer

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).

Lymph Vessels Carry Tissue Fluid Back to the VeinsLymph Vessels Carry Tissue Fluid Back to the Veins

Chapter017

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