Cardiovascular System Anatomy and Physiology

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 16:

Anatomy and Physiology of the Cardiovascular System

Chapter 16:

Anatomy and Physiology of the Cardiovascular System


Cardiac Muscle FibersCardiac Muscle Fibers


Contractile Elements Inside a SarcomereContractile Elements Inside a Sarcomere


Characteristics of Cardiac TissueCharacteristics of Cardiac Tissue

• Automaticity: Pacemaker cells generate their own action potential.

• Conductivity: Cardiac cells receive the electrical signal and pass it from one cell to another.

• Contractility: Cardiac muscle shortens because of depolarization.

• Excitability: Cardiac tissue responds to a stimulus and generates an action potential.

• Rhythmicity: Cardiac cells generate an action potential at a regular rate.


QuestionQuestion

Which of the following terms describes the cardiac tissue function of the sinoatrial node?

A. Excitability

B. Automaticity

C. Conductivity

D. Contractility


AnswerAnswer

B. Automaticity

Rationale: Automaticity is the ability of pacemaker cells to spontaneously make an action potential and depolarize. Excitability is the ability of a cardiac cell to respond to a stimulus and depolarize. Conductivity is the ability of cardiac tissue to respond to a stimulus and generate an action potential. Contractility is the ability of cardiac muscle cells to respond to depolarization by shortening.


Electrical Events That Occur in the Myocardial CellElectrical Events That Occur in the Myocardial Cell


The Resting Membrane Potential of Myocardial CellThe Resting Membrane Potential of Myocardial Cell

• Inside of the myocardial cell is more negative (-80 mV) compared to the outside of the cell because of ionic pumps.

– Determined by concentration of ions on both sides of cell membrane

– Ion transport proteins in cell membrane need ATP.

• Resting state is the time the heart is in diastole.


Cardiac Action PotentialCardiac Action Potential


Electrical Conduction SystemElectrical Conduction System


Comparison of Electrical and Mechanical Events During One Cardiac CycleComparison of Electrical and Mechanical Events During One Cardiac Cycle


Measuring Cardiac FunctionMeasuring Cardiac Function

CO = HR (beats/min) x SV (L/beat)

Normal adult range: 4 to 8 L/min

CI = CO (L/min)

BSA (m)

Normal adult range: 2.8 to 4.2 L/min


Effects of the Autonomic Nervous System on the Heart and Vascular SystemEffects of the Autonomic Nervous System on the Heart and Vascular System

Receptor Type Effects

Alpha-1 Vasoconstriction of blood vessels, increased BP, increased contractility of heart

Alpha-2 Decreased BP (reduced norepinephrine)

Beta-1 Increased heart rate, increased heart contraction

Beta-2 Dilation of arteries

Muscarinic receptors Decreased HR, decreased force of contraction


Role of the Aortic Reflex and Bainbridge Reflex on Heart RateRole of the Aortic Reflex and Bainbridge Reflex on Heart RateAortic Reflex Effects Adjust HR to BP

Bainbridge Effects Adjust HR to Handle Venous Return

Rise in BP causes decrease in HR Increase in venous return causes increase in HR

Decrease in BP causes increase in HR

Decrease in venous return causes decrease in HR


Starling’s Law of the HeartStarling’s Law of the Heart


Coronary ArteriesCoronary Arteries


Coronary Artery Blood Supply for Cardiac Muscle and Conduction SystemCoronary Artery Blood Supply for Cardiac Muscle and Conduction System


QuestionQuestion

A client is diagnosed with a 95% occlusion of the right coronary artery (RCA). Which area of the heart’s conduction system is most likely to be affected?

A. Bundle branches

B. Sinoatrial (SA) node

C. Atrioventricular (AV) node

D. Purkinje fibers


AnswerAnswer

C. Atrioventricular node

Rationale: The RCA supplies the AV node in 90% of hearts. The left anterior descending (LAD) supplies the bundle branches. The left circumflex supplies the SA node in 45% of hearts and the AV node in 10% of hearts. The Purkinje fibers are supplied by all of the coronary arteries.


QuestionQuestion

A 19-year-old client with supraventricular tachycardia has a heart rate in the 160s. The client complains of chest pain. The chest pain is most likely a result of which of the following?

A. A decrease in diastolic time

B. A decrease in atrial kick

C. Coronary artery disease

D. Decreased oxygen demand


AnswerAnswer

A. A decrease in diastolic time

Rationale: The coronary arteries receive blood flow when the aortic valve is closed (ventricular diastole). Tachycardia decreases diastolic time, resulting in decreased blood flow to the coronary arteries. Chest pain occurs from the decreased coronary perfusion. It is unlikely that a 19-year-old patient has coronary artery disease causing the chest pain. Atrial fibrillation can lead to a loss in atrial kick that would decrease the cardiac output. Tachycardia would lead to increased cardiac workload and increased oxygen demand.


Central Venous Pressure (CVP)Central Venous Pressure (CVP)

• Defined as pressure of the blood measured in mm Hg in the thoracic vena cavae before the entry into the right atrium

– CVP is increased when there is an increase in the blood volume; increase due to Valsalva maneuver, change from standing to supine position, or decrease in pumping action of heart

– CVP is decreased when there is a decrease in blood volume

– Normal range is 3 to 6 mm Hg


Influences on Blood PressureInfluences on Blood Pressure

• Neuroregulation

– Autonomic nervous system

• Hormonal influences

– Renin-angiotensin system

• Hypercapnia/hypoxia

– Vasomotor center

• Unbound calcium in tunica media

– Calcium channel blockers

Cardiovascular System Anatomy and Physiology

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