Marieb Human Anatomy & Physiology Chapter 18: The Cardiovascular System - The Heart

Comprehensive practice flashcards covering Chapter 18 (The Cardiovascular System: The Heart) from Marieb Human Anatomy & Physiology, 12th Edition.

What are the two side-by-side circulation circuits supplied by the heart?

The pulmonary circuit (right side, carrying blood to and from the lungs) and the systemic circuit (left side, carrying blood to and from body tissues).

Which side of the heart receives oxygen-poor blood from body tissues and pumps it to the lungs?

The right side of the heart.

Which chambers of the heart act as receiving chambers for returning blood?

The right atrium (receives blood from systemic circuit) and left atrium (receives blood from pulmonary circuit).

Which chambers of the heart act as pumping (discharging) chambers?

The right ventricle (pumps blood through the pulmonary circuit) and left ventricle (pumps blood through the systemic circuit).

What is the approximate size and weight of the human heart?

Roughly the size of a fist, weighing less than a pound.

Where is the heart located within the thoracic cavity?

In the mediastinum between the second rib and fifth intercostal space, resting on the superior surface of the diaphragm between the sternum and vertebral column.

Where is the apical impulse of the heart palpated?

Between the fifth and sixth ribs, just below the left nipple.

How are the base and apex of the heart oriented?

The broad, flat base is directed toward the right shoulder, and the apex points toward the left hip.

What are the primary functions of the superficial fibrous pericardium?

To protect the heart, anchor it to surrounding structures, and prevent overfilling.

What are the two layers of the deep serous pericardium?

The parietal layer (lines the internal surface of the fibrous pericardium) and the visceral layer/epicardium (covers the external surface of the heart).

What fluid-filled space separates the parietal and visceral layers of the serous pericardium?

The pericardial cavity, which decreases friction during heart contraction.

What is pericarditis and what distinct sound does it cause during auscultation?

Pericarditis is inflammation of the pericardium that roughens membrane surfaces, causing a creaking sound called a pericardial friction rub.

What is cardiac tamponade and how is it treated?

A condition where excess inflammatory fluid leaks into the pericardial space and compresses the heart, limiting its pumping ability; treated by draining fluid with a syringe.

What are the three layers of the heart wall from superficial to deep?

Epicardium, myocardium, and endocardium.

What layer constitutes the bulk of the heart wall and what is its arrangement?

The myocardium, consisting of circular or spiral bundles of contractile cardiac muscle cells.

What are four functions of the fibrous cardiac skeleton within the myocardium?

It anchors cardiac muscle fibers, supports heart valves and great vessels, and limits the spread of action potentials to specific pathways.

With what tissue is the endocardium continuous?

The endothelial lining of blood vessels.

What structure separates the left and right atria, and what fetal remnant does it contain?

The interatrial septum, which contains the fossa ovalis (remnant of the fetal foramen ovale).

What groove encircles the surface junction between the atria and ventricles?

The coronary sulcus (or atrioventricular groove).

What are auricles and what is their functional significance?

Wrinkled appendages on the external surface of the atria that increase atrial volume.

Where are pectinate muscles located in the heart?

In the anterior portion of the right atrium and in the auricles of the left atrium.

What ridge separates the smooth posterior region from the pectinate anterior region in the right atrium?

The crista terminalis.

Which three systemic veins empty oxygen-poor blood into the right atrium?

The superior vena cava, inferior vena cava, and coronary sinus.

Which vessels enter the left atrium to deliver oxygenated blood?

Four pulmonary veins.

What are trabeculae carneae?

Irregular ridges of muscle marking the internal ventricular walls.

What structures project into the ventricular cavity to anchor the chordae tendineae?

Papillary muscles.

What is the primary function of the chordae tendineae?

They anchor AV valve cusps to papillary muscles, holding valve flaps closed and preventing them from everting into the atria during ventricular contraction.

Into which major vessel does the right ventricle pump blood?

The pulmonary trunk (beginning of the pulmonary circuit).

Into which major vessel does the left ventricle pump blood?

The aorta (beginning of the systemic circuit), the largest artery in the body.

How do heart valves enforce unidirectional blood flow?

By opening and closing in response to pressure changes as chambers contract and relax.

Where are the two atrioventricular (AV) valves located?

Between the atria and ventricles (tricuspid valve on the right, mitral/bicuspid valve on the left).

How many cusps make up the tricuspid valve and where is it situated?

Three cusps; located between the right atrium and right ventricle.

How many cusps make up the mitral (bicuspid) valve and where is it situated?

Two cusps; located between the left atrium and left ventricle.

Where are the two semilunar (SL) valves located?

Between the ventricles and major arteries (pulmonary semilunar valve between right ventricle and pulmonary trunk; aortic semilunar valve between left ventricle and aorta).

Why are anatomical valves unnecessary between major veins and the atria?

Because the inertia of incoming blood prevents backflow, and atrial contractions compress the venous openings.

What is an incompetent (insufficient) valve?

A defective valve that fails to close completely, allowing blood to backflow and forcing the heart to repump the same blood.

What is valvular stenosis?

A condition where stiff valve flaps constrict the opening, forcing the heart to exert greater force to pump blood.

How do the wall thickness and workload of the left ventricle compare to the right ventricle?

The left ventricle wall is three times thicker than the right wall because it pumps against much higher pressure and resistance in the longer systemic circuit.

What are the cross-sectional shapes of the right and left ventricular cavities?

The right ventricle cavity is crescent-shaped, while the left ventricle cavity is round (cylindrical).

What is coronary circulation?

The functional blood supply of the heart tissue itself; it is the shortest circulation in the body.

Where do the left and right coronary arteries originate?

From the base of the aorta.

What are the two major branches of the left coronary artery and what do they supply?

Anterior interventricular artery (LAD), supplying the interventricular septum and anterior ventricular walls; circumflex artery, supplying the left atrium and posterior left ventricular wall.

What are the two major branches of the right coronary artery and what do they supply?

Right marginal artery, supplying the right atrium and most of the right ventricle; posterior interventricular artery, supplying the posterior ventricular walls.

When is coronary arterial blood delivered to the myocardium?

Intermittently, during ventricular diastole (when the heart muscle is relaxed).

What fraction of the body's blood supply goes to the heart at rest relative to its body weight?

The heart receives $\frac{1}{20}$ of the body's blood supply while representing only $\frac{1}{200}$ of total body weight.

Which cardiac vein lies in the anterior interventricular sulcus?

The great cardiac vein.

Which cardiac vein lies in the posterior interventricular sulcus?

The middle cardiac vein.

Into which heart chamber does the coronary sinus drain?

The right atrium.

What is angina pectoris?

Thoracic pain caused by a temporary deficiency in blood delivery to the myocardium, resulting in weakened cardiac cells.

What occurs during a myocardial infarction (MI)?

Prolonged coronary arterial blockage causes death of myocardial cells, which are replaced by noncontractile scar tissue.

What specialized junctions connect individual cardiac muscle cells end-to-end?

Intercalated discs.

What functions do desmosomes and gap junctions serve within intercalated discs?

Desmosomes prevent cells from separating during contraction; gap junctions allow ions to pass from cell to cell, electrically coupling the myocytes.

What is a functional syncytium in cardiac tissue?

The behavior of the entire myocardium as a single, coordinated contraction unit due to electrical coupling via gap junctions.

What volume percentage of cardiac cells is occupied by mitochondria?

$25-35\%$ (providing high fatigue resistance).

How do T tubules in cardiac muscle differ structurally from those in skeletal muscle?

Cardiac T tubules are wider, less numerous, enter the cell once per sarcomere at the Z discs, and lack triads or terminal cisterns.

What proportion of cardiac myocytes are contractile vs pacemaker cells?

About $99\%$ are contractile cells and about $1\%$ are specialized pacemaker cells.

What is automaticity (autorhythmicity)?

The ability of cardiac pacemaker cells to spontaneously depolarize and trigger action potentials for the entire heart without nervous system input.

Why can tetanic contractions NOT occur in cardiac muscle?

Because cardiac muscle has a very long absolute refractory period (nearly as long as the contraction itself, ~200 ms), allowing time for relaxation and chamber filling.

What role does extracellular $Ca^{2+}$ play in cardiac excitation-contraction coupling?

Extracellular $Ca^{2+}$ enters through slow $Ca^{2+}$ channels in the sarcolemma, triggering $Ca^{2+}$-sensitive channels in the sarcoplasmic reticulum to release stored $Ca^{2+}$.

What percentage of $Ca^{2+}$ required for cardiac contraction is released from the sarcoplasmic reticulum?

$80-90\%$ (triggered by extracellular $Ca^{2+}$ influx).

Why can cardiac muscle NOT function long without a continuous oxygen supply?

Because cardiac muscle relies almost exclusively on aerobic cellular respiration for ATP production.

What happens to the $Ca^{2+}$ that enters cardiac myocytes from the ECF during relaxation?

It is pumped back out of the cell into the extracellular fluid.

What is the pacemaker potential?

An unstable resting membrane potential in cardiac pacemaker cells that continuously and slowly depolarizes toward threshold.

Which ion channel events cause the slow pacemaker potential depolarization?

Opening of slow $Na^+$ channels and closing of $K^+$ channels.

At what threshold voltage do voltage-gated $Ca^{2+}$ channels open in cardiac pacemaker cells?

At approximately $-40\,mV$.

Which ion flux causes the rising depolarization phase of a cardiac pacemaker action potential?

Influx of $Ca^{2+}$ through opened voltage-gated $Ca^{2+}$ channels.

Which ion flux restores resting membrane potential during pacemaker repolarization?

Efflux of $K^+$ through opened voltage-gated $K^+$ channels after $Ca^{2+}$ channels close.

What is the precise sequence of excitation through the intrinsic cardiac conduction system?

Sinoatrial (SA) node $\rightarrow$ Atrioventricular (AV) node $\rightarrow$ Atrioventricular (AV) bundle $\rightarrow$ Right and left bundle branches $\rightarrow$ Subendocardial conducting network (Purkinje fibers).

Where is the sinoatrial (SA) node located and what is its intrinsic impulse rate?

Located in the right atrial wall inferior to the entrance of the superior vena cava; generates impulses at about $75\text{ beats/min}$ (sinus rhythm).

Where is the atrioventricular (AV) node located and how long does it delay impulse transmission?

Located in the inferior interatrial septum above the tricuspid valve; delays the impulse by about $0.1\,s$.

Why is the $0.1\,s$ delay at the AV node physiologically critical?

It allows the atria to contract and completely empty blood into the ventricles before ventricular contraction begins.

What is the intrinsic firing rate of the AV node in the absence of SA node input?

$40-60\text{ beats/min}$.

What structure provides the ONLY electrical connection between the atria and ventricles?

The atrioventricular (AV) bundle (bundle of His).

Where are the right and left bundle branches located?

In the interventricular septum.

In what direction does ventricular contraction proceed when initiated by the subendocardial conducting network?

From the apex upward toward the atria, pushing blood up toward the semilunar valves.

What is the inherent firing rate of the AV bundle and Purkinje fibers without AV node input?

About $30\text{ beats/min}$.

How long does total impulse propagation take from SA node initiation to complete ventricular depolarization?

$0.22\,s$.

What is an arrhythmia?

An irregular heart rhythm caused by defects in the intrinsic conduction system.

What is fibrillation and how is it treated clinically?

Rapid, irregular, uncoordinated myocardial contractions that halt effective circulation; treated with defibrillation (electrical shock) to reset sinus rhythm.

What heart rhythm results if the SA node fails and the AV node takes over as pacemaker?

Junctional rhythm ($40-60\text{ beats/min}$).

What causes extrasystoles (premature contractions)?

An ectopic focus (hyperexcitable region of the heart) firing action potentials faster than the SA node, often induced by caffeine or nicotine.

What is a heart block and how is it managed?

An AV node defect that impairs impulse conduction from atria to ventricles; managed with an artificial pacemaker.

Which medullary autonomic center increases heart rate and force of contraction?

The cardioacceleratory center (via sympathetic nerves).

Which medullary autonomic center decreases heart rate and via which cranial nerve?

The cardioinhibitory center, via parasympathetic signals carried by the vagus nerve.

What ion influx triggers the rapid rising depolarization phase in contractile cardiac muscle cells?

$Na^+$ influx through fast voltage-gated $Na^+$ channels.

Which ion flux produces the plateau phase in contractile cardiac muscle action potentials?

$Ca^{2+}$ influx through slow $Ca^{2+}$ channels while most $K^+$ channels remain closed.

Which ion flux causes repolarization in contractile cardiac cells?

$K^+$ efflux through opened voltage-gated $K^+$ channels following $Ca^{2+}$ channel inactivation.

How do action potential duration and contraction duration compare between cardiac and skeletal muscle?

In cardiac muscle, APs last $200+\,ms$ producing contractions of $200+\,ms$; in skeletal muscle, APs last $1-2\,ms$ producing twitches of $15-100\,ms$.

What electrical event in the heart causes the P wave on an electrocardiogram (ECG)?

Atrial depolarization (initiated by the SA node).

What electrical events correspond to the QRS complex on an ECG?

Ventricular depolarization (preceding ventricular contraction) and simultaneous, masked atrial repolarization.

What electrical event causes the T wave on an ECG?

Ventricular repolarization.

What period does the P-R interval represent on an ECG?

The time from the start of atrial depolarization to the start of ventricular depolarization.

What state of the myocardium corresponds to the S-T segment on an ECG?

The entire ventricular myocardium is completely depolarized (myocytes in plateau phase).

What period is measured by the Q-T interval on an ECG?

The beginning of ventricular depolarization through ventricular repolarization.

What condition might be indicated by enlarged R waves on an ECG?

Enlarged ventricles.

What condition is indicated by an elevated or depressed S-T segment on an ECG?

Cardiac ischemia.

What risk is associated with a prolonged Q-T interval on an ECG?

It indicates a repolarization abnormality that increases the risk of ventricular arrhythmias.

What electrocardiogram abnormality is shown in this trace?

Second-degree heart block, where the AV node fails to conduct some SA node impulses, resulting in more P waves than QRS waves (typically two P waves per QRS wave).

What ECG pattern is depicted in this tracing?

Normal sinus rhythm.

What do the terms systole and diastole mean?

Systole refers to the period of myocardial contraction; diastole refers to the period of myocardial relaxation.