Chapter 19 – Heart (Saladin, 7th ed.)

Flashcards cover key concepts from Chapter 19: anatomy of the heart, circulation pathways, heart wall layers, valves, blood flow, coronary circulation, cardiac muscle physiology, conduction system, ECG, cardiac cycle, and cardiac output/regulation.

What structures are included in the cardiovascular system?

The heart and blood vessels.

What additional component makes the circulatory system different from the cardiovascular system?

The blood.

What is the primary function of the pulmonary circuit?

To carry oxygen-poor blood from the right side of the heart to the lungs for gas exchange and return it oxygen-rich to the heart.

What is the primary function of the systemic circuit?

To supply oxygenated blood from the left side of the heart to all body tissues and return it deoxygenated to the heart.

Which side of the heart pumps oxygen-rich blood?

The left side (systemic circuit).

Where is the heart located?

In the mediastinum between the lungs.

What is the base of the heart?

The wide, superior portion where large vessels attach.

What is the apex of the heart?

Its tapered inferior end that tilts left.

Approximately how big and heavy is an adult heart?

About the size of a fist; ~10 oz, 3.5 in wide at base, 5 in from base to apex.

What are the two layers of the pericardium?

The parietal pericardium (fibrous + serous layers) and the visceral pericardium (epicardium).

State two functions of the pericardium.

Allows friction-free beating and limits excessive expansion while anchoring the heart.

How much fluid normally fills the pericardial cavity?

5–30 mL of pericardial fluid.

What is pericarditis?

Painful inflammation of the pericardial membranes.

Name the three layers of the heart wall.

Epicardium, myocardium, and endocardium.

What travels through the epicardium’s adipose tissue?

Coronary blood vessels.

What is the fibrous skeleton of the heart and give one function.

A framework of collagen & elastic fibers that provides structural support and electrical insulation between atria and ventricles.

How many chambers does the heart have and what are they called?

Four: right & left atria (receiving) and right & left ventricles (pumping).

Which external groove separates atria from ventricles?

The atrioventricular (coronary) sulcus.

What are pectinate muscles and where are they found?

Internal ridges of myocardium in the right atrium and auricles.

What are trabeculae carneae and what is their presumed function?

Internal ridges in ventricles that may prevent walls from sticking together during contraction.

Name the right and left atrioventricular valves.

Right—tricuspid valve; Left—mitral (bicuspid) valve.

What structures prevent AV valve cusps from prolapsing into atria?

Chordae tendineae anchored to papillary muscles.

Where is the pulmonary semilunar valve located?

Between the right ventricle and pulmonary trunk.

When do AV valves open?

During ventricular relaxation when ventricular pressure falls below atrial pressure.

When do semilunar valves open?

During ventricular contraction when ventricular pressure exceeds arterial pressure.

Trace the basic blood flow pathway starting at the right atrium.

Right atrium → right ventricle → pulmonary trunk → lungs → pulmonary veins → left atrium → left ventricle → aorta → systemic circulation → venae cavae → right atrium.

Approximately what percent of cardiac output goes to coronary circulation?

About 5 % (≈250 mL min⁻¹).

List the two major branches of the left coronary artery (LCA).

Anterior interventricular branch and circumflex branch.

List the two main branches of the right coronary artery (RCA).

Right marginal branch and posterior interventricular branch.

What is collateral circulation (arterial anastomosis) and why is it important?

Alternative routes of blood flow that help protect the myocardium from ischemia during arterial blockage.

During which phase of the cardiac cycle is coronary blood flow greatest and why?

During ventricular diastole, because myocardial relaxation and backflow in the aorta open the coronary artery orifices.

What causes angina pectoris?

Transient ischemia of cardiac muscle from partial coronary obstruction leading to anaerobic fermentation and lactic acid buildup.

Define myocardial infarction (MI).

Death of myocardium resulting from long-term coronary obstruction; often presents with crushing chest pain and may cause lethal arrhythmias.

Into which large vein does most coronary venous blood drain?

The coronary sinus, which empties into the right atrium.

Describe three structural features of cardiocytes.

Short, branched, striated cells with one central nucleus and abundant glycogen.

What are intercalated discs?

Specialized junctions connecting cardiocytes containing interdigitating folds, desmosomes (mechanical), and gap junctions (electrical).

Why is the entire atrial or ventricular myocardium often called a functional syncytium?

Gap junctions allow ions to flow so the tissue acts as a single coordinated unit.

Why is cardiac muscle highly resistant to fatigue?

It relies almost exclusively on aerobic metabolism, has many mitochondria, and seldom uses anaerobic pathways.

What fuels can cardiac muscle use and in what approximate proportions?

Fatty acids 60 %, glucose 35 %, ketones/lactate/amino acids 5 %.

List the components of the cardiac conduction system in order.

SA node → atrial myocardium → AV node → AV bundle (bundle of His) → right & left bundle branches → Purkinje fibers → ventricular myocardium.

Where is the SA node located and what is its function?

In the right atrium near the superior vena cava; it is the pacemaker that sets heart rate.

What is the primary role of the AV node?

It is the electrical gateway to the ventricles, delaying the impulse to allow ventricular filling.

What is the AV (His) bundle and where does it travel?

Conductive fibers that leave the AV node, enter the interventricular septum, and split into bundle branches toward the apex.

What do Purkinje fibers do?

Distribute the electrical impulse rapidly through the ventricular myocardium for coordinated contraction.

How do sympathetic nerves affect the heart?

They increase heart rate and contraction strength by releasing norepinephrine onto β-adrenergic receptors.

How do parasympathetic (vagal) nerves affect the heart?

They slow heart rate by releasing acetylcholine that hyperpolarizes SA and AV nodal cells.

Define systole and diastole.

Systole—contraction phase; Diastole—relaxation phase (usually referring to ventricles).

What is a normal adult sinus rhythm at rest?

About 70–80 beats per minute (bpm).

If the AV node becomes the pacemaker, what heart rate results?

A nodal rhythm of 40–50 bpm.

What membrane potentials define the SA node pacemaker potential and threshold?

It drifts from –60 mV to the threshold of –40 mV before firing.

Name the three phases of a cardiocyte action potential.

Rapid depolarization, plateau, and repolarization.

Why does cardiac muscle have a long absolute refractory period (~250 ms)?

To prevent tetanus and ensure time for ventricular filling between beats.

Match each ECG wave with its event.

P wave—atrial depolarization; QRS complex—ventricular depolarization; T wave—ventricular repolarization.

What produces heart sound S1 (‘lubb’)?

Closure of AV valves and associated turbulence at the start of ventricular systole.

List the four phases of the cardiac cycle in order.

Ventricular filling, isovolumetric contraction, ventricular ejection, isovolumetric relaxation.

What is a typical end-diastolic volume (EDV) in each ventricle?

About 130 mL.

Define stroke volume (SV).

The volume of blood ejected by one ventricle in one beat; SV = EDV – ESV (≈70 mL).

What is a typical ejection fraction at rest?

Approximately 54 % of EDV.

Give the formula for cardiac output and its average resting value.

CO = heart rate × stroke volume; ~5 L min⁻¹ in an adult at rest.

Define tachycardia and bradycardia.

Tachycardia: resting HR >100 bpm; Bradycardia: resting HR <60 bpm.

What is a chronotropic agent?

Any factor that changes heart rate (positive increases, negative decreases).

Describe the cellular mechanism by which norepinephrine raises heart rate.

NE activates β-adrenergic receptors → cAMP → opens Ca²⁺ channels → faster depolarization & quicker repolarization, speeding the SA node.

How does acetylcholine slow the heart?

It opens K⁺ channels in nodal cells, hyperpolarizing them and lengthening the time to reach threshold.

State the Frank–Starling law of the heart.

Stroke volume is proportional to end-diastolic volume: the more the myocardium is stretched, the stronger it contracts.

Define preload.

The initial stretching (tension) of ventricular myocardium just before contraction (related to venous return).

Define contractility and name one positive inotropic agent.

The strength of contraction for a given preload; examples of positive agents: calcium, catecholamines, digitalis.

Define afterload and explain how hypertension affects it.

The sum of forces opposing ventricular ejection; hypertension raises afterload, reducing stroke volume.

How does regular aerobic exercise affect the heart?

It increases cardiac output, causes ventricular hypertrophy, and raises cardiac reserve allowing a lower resting heart rate.

What is coronary artery disease (CAD)?

A narrowing of coronary arteries, usually due to atherosclerotic plaque buildup, that reduces myocardial blood flow.

List two unavoidable and two preventable risk factors for CAD.

Unavoidable: heredity, aging, male sex. Preventable: smoking, obesity (others: inactivity, diet, stress).