A&PII: Lecture Exam2-CH.18

What are the two major blood-flow circuits, and which side of the heart pumps each?

• Right heart → pulmonary circuit: sends O₂-poor blood to lungs; O₂-rich blood returns to left heart.

• Left heart → systemic circuit: sends O₂-rich blood to body tissues; O₂-poor blood returns to right heart.

Where is the heart located?

In the mediastinum, between the lungs. About 2/3 lies left of the midsternal line

What are the approximate size and weight of the heart?

About the size of a fist and weighs less than 1 lb

What are the base, apex, and apical impulse of the heart?

• Base: broad superior/posterior portion

• Apex: pointed inferior end, formed mainly by the left ventricle

• Apical impulse: point where the heartbeat can be felt against the chest wall

What is the pericardium?

A double-walled sac surrounding the heart consisting of the fibrous pericardium and serous pericardium

What does the fibrous pericardium do?

Protects and anchors the heart and helps prevent overfilling

What are the layers of the serous pericardium?

• Parietal layer: lines inner surface of fibrous pericardium

• Visceral layer: lies directly on heart surface and is also called the epicardium

What is the pericardial cavity?

Fluid-filled space between the parietal and visceral serous pericardium. Its fluid reduces friction as the heart beats

What is pericarditis, and what is a pericardial friction rub?

Pericarditis = inflammation of the pericardium. Roughened inflamed surfaces rubbing together can produce a pericardial friction rub

What is cardiac tamponade?

Excess fluid accumulates in the pericardial cavity and compresses the heart, impairing pumping. Fluid may need to be removed

What are the 3 layers of the heart wall from superficial → deep?

Epicardium → myocardium → endocardium

What is the epicardium?

Outermost heart-wall layer; it is also the visceral layer of the serous pericardium and serves as a protective layer for the heart. It contains blood vessels, nerves, and fat.

 What is the myocardium?

Thick cardiac muscle layer responsible for the heart’s contractile pumping action

What is the cardiac skeleton and what does it do?

 Interlacing connective tissue that:

• Anchors cardiac muscle fibers

• Supports the valves and great vessels

• Helps restrict electrical impulses to specific pathwaysprovides structural support for the heart, maintains its shape, and aids in proper contraction.

What is the endocardium?

 Innermost heart-wall layer. It lines the chambers and is continuous with the endothelium of blood vessels and valves, providing a smooth surface for blood flow.

What are the four chambers of the heart?

Right atrium, right ventricle, left atrium, left ventricle.
Atria = receiving chambers; ventricles = pumping chambers

What are auricles and pectinate muscles?

• Auricles: atrial appendages that increase atrial volume

• Pectinate muscles: muscular ridges in the atria

Trace blood flow through the heart in ONE direction

 Body → venae cavae → RA → tricuspid valve → RV → pulmonary SL valve → pulmonary trunk/arteries → lungs → pulmonary veins → LA → mitral valve → LV → aortic SL valve → aorta → body. This sequence outlines how blood moves from the body to the heart and lungs, and back to the body in a single, unidirectional flow.

What is the overall function of the heart valves?

To ensure one-way blood flow by preventing backflow

What are the two Atrioventricular valves?

• Right AV = tricuspid = 3 cusps

• Left AV = mitral/bicuspid = 2 cusps

 What are chordae tendineae and papillary muscles?

Chordae tendineae attach AV valve cusps → papillary muscles. During ventricular contraction, they prevent AV cusps from everting/prolapsing into the atria. Pressure closes the valves; chordae/papillary muscles prevent them from flipping backwards

When do Atrioventricular valves open and close?

• Atrial pressure > ventricular → OPEN

• Ventricular pressure > atrial → CLOSE

• During ventricular contraction, the AV valves close to prevent backflow, and they open when atrial pressure exceeds ventricular pressure during diastole.

What are the two semilunar valves?

• Pulmonary semilunar valve

• Aortic semilunar valve
  They prevent arterial blood from flowing back into the ventricles.

When do semilunar valves open and close?

• Ventricular pressure > arterial pressure → OPEN

• Arterial pressure > ventricular pressure → CLOSE

What controls heart-valve opening and closing?

Pressure differences. Heart valves are passive; they do not actively open themselves

What produces the first and second heart sounds?

• S1 “lub” = AV valves close

• S2 “dup” = semilunar valves close

What is a heart murmur?

An abnormal heart sound produced by turbulent blood flow, often associated with an abnormal valve

What is mitral valve prolapse?

one or both cusps of the bicuspid valve bulge backward into left atrium during ventricular contraction, which may allow regurgitation/backflow

Why does the myocardium need its own coronary circulation?

Coronary circulation delivers O₂ and nutrients to the myocardium and removes its wastes

What are the major coronary arteries/branches?

• Right coronary artery → right marginal + posterior interventricular

• Left coronary artery → circumflex + anterior interventricular (LAD)

• The major coronary arteries include the right coronary artery, which branches into the right marginal and posterior interventricular arteries; and the left coronary artery, which branches into the circumflex and anterior interventricular (LAD) arteries.

What is a coronary anastomosis?

 connection between blood vessels that can provide an alternate route for blood flow, although coronary anastomoses may not adequately compensate for a major occlusion

What is the major venous drainage pathway of the myocardium?

Cardiac veins → coronary sinus → right atrium.
Recognize: great, middle, small, and anterior cardiac veins + coronary sinus

What happens when coronary circulation is blocked?

Myocardium becomes ischemic because it receives inadequate O₂

Distinguish angina pectoris from myocardial infarction (MI)

• Angina: temporary myocardial ischemia → chest pain

• MI: prolonged/severe loss of coronary blood flow → cardiac muscle death → damaged area replaced by noncontractile scar tissue

What are intercalated discs?

Connections between cardiac muscle cells containing:

• Gap junctions → electrical communication

• Desmosomes → mechanically hold cells together

What are the structural characteristics of cardiac muscle cells?

 Short, branched, striated, interconnected, usually with a central nucleus and many mitochondria

What is a functional syncytium?

Cardiac cells electrically communicate through gap junctions, allowing the myocardium to contract as a coordinated unit due to the presence of intercalated discs, which facilitate cellular connections.

 How does cardiac muscle’s SR/T-tubule system differ from skeletal muscle?

Cardiac muscle has wider but fewer T tubules, a less-developed SR, and no triads

Compare cardiac vs. skeletal muscle

Both: striated, sarcomeres, T tubules, SR, Ca²⁺ binds troponin.

Cardiac: short/branched, interconnected, central nuclei, intercalated discs, gap junctions, many mitochondria, no triads, involuntary.

Skeletal: long/unbranched, multiple peripheral nuclei, no intercalated discs, triads, voluntary

How does Ca²⁺ release differ in cardiac vs. skeletal muscle?

• Cardiac: extracellular Ca²⁺ enters → triggers additional Ca²⁺ release from SR

• Skeletal: excitation-contraction coupling relies primarily on Ca²⁺ released from SR

What are the two types of cardiac myocytes?

• Contractile cells: generate force/pumping

• Pacemaker (autorhythmic) cells: spontaneously depolarize and initiate electrical activity

 Why doesn’t the heart require nervous stimulation to initiate each heartbeat?

Pacemaker cells are autorhythmic/self-excitable and spontaneously depolarize. The ANS modifies heart rate rather than initiating every beat

What is a pacemaker potential?

 An unstable membrane potential that slowly depolarizes toward threshold, allowing pacemaker cells to repeatedly generate action potentials

What are the 3 phases of a pacemaker-cell action potential?

1. Pacemaker potential: slow Na⁺ entry → toward threshold

2. Depolarization: threshold ≈ −40 mV → Ca²⁺ channels open → Ca²⁺ IN

3. Repolarization: Ca²⁺ channels close + K⁺ channels open → K⁺ OUT

Na creeps in → Ca shoots in → K goes out.

What are the 3 phases of a contractile cardiac-cell action potential?

1. Depolarization: fast Na⁺ channels open → Na⁺ IN

2. Plateau: slow Ca²⁺ channels remain open → Ca²⁺ IN; prolongs depolarization

3. Repolarization: Ca²⁺ channels close + K⁺ channels open → K⁺ OUT

Na → Ca plateau → K out

 Why is the plateau phase important?

it prolongs the cardiac action potential and contraction, producing a long refractory period

Why can’t cardiac muscle undergo tetanus?

Its absolute refractory period lasts almost as long as the contraction, preventing repeated stimulation from producing tetanic contraction. This allows the heart to relax and refill

How do cardiac and skeletal muscle action-potential/contraction durations compare?

Cardiac AP and contraction are much longer than skeletal muscle because of the cardiac plateau and long refractory period

What is the complete intrinsic conduction pathway?

 SA node → AV node → AV bundle (bundle of His) → R/L bundle branches → Purkinje fibers/subendocardial conducting network

 What does the SA node do? (Sinoatrial)

It is the heart’s normal pacemaker, located in the right atrial wall, and normally initiates each heartbeat

Why does the AV node delay the impulse?

Delays it about 0.1 sec, allowing the atria to contract before the ventricles so that blood can fill the ventricles before they contract

What is special about the AV bundle (bundle of His)?

It is the normal electrical connection between atria and ventricles and carries the impulse into the interventricular septum

 What do bundle branches and Purkinje fibers do?

Bundle branches carry impulses toward the apex; Purkinje fibers distribute excitation throughout the ventricular myocardium

In what direction does ventricular contraction proceed?

Apex → toward the atria, helping eject blood superiorly into the pulmonary trunk and aorta

 What is the pacemaker hierarchy from the lecture?

 Approximate inherent rates:
SA ≈ 100/min → AV ≈ 50/min → AV bundle/Purkinje ≈ 30/min

What is sinus rhythm?

The normal cardiac rhythm established by the SA node

What do the P wave, QRS complex, and T wave represent?

• P wave = atrial depolarization

• QRS = ventricular depolarization

• T wave = ventricular repolarization

 Atrial repolarization occurs during QRS and is hidden by it.

 What mechanical events follow the major ECG waves?

• P wave → atrial contraction follows

• QRS → ventricular contraction follows

• T wave → ventricular relaxation follows

What is an arrhythmia?

An abnormal/irregular heart rhythm caused by abnormal impulse generation or conduction

What is fibrillation?

Rapid, chaotic electrical activity producing ineffective contractions and potentially preventing effective circulation

 What does defibrillation do?

 Interrupts chaotic electrical activity so an organized cardiac rhythm can potentially resume

 Compare sympathetic vs. parasympathetic control of the heart

 Sympathetic: cardioacceleratory center → ↑ HR + ↑ contraction force
Parasympathetic: cardioinhibitory center → vagus nerve → ↓ HR

How does sympathetic stimulation increase HR?

Sympathetic stimulation → norepinephrine → β₁ receptors → pacemaker cells fire faster → ↑ HR Increased conduction and contraction strength

How does parasympathetic stimulation decrease HR?

ACh → opens K⁺ channels → hyperpolarizes pacemaker cells → slower firing → ↓ HR

What is vagal tone?

Dominant parasympathetic influence at rest. It lowers HR by about 25 beats/min; without vagal influence, HR approaches the SA node’s inherent rate of about 100/min

How do sympathetic and parasympathetic activity interact?

They have opposing effects: increased activity of one is generally accompanied by decreased activity of the other

What are tachycardia and bradycardia?

• Tachycardia: HR >100 beats/min

• Bradycardia: HR <60 beats/min; may impair circulation in nonathletes but can occur normally in endurance-trained athletes

What is the cardiac cycle?

The mechanical events associated with blood flow through the heart during one complete heartbeat, involving pressure and volume changes

What do systole and diastole mean?

• Systole = contraction 🧠 Squeeze

• Diastole = relaxation/fillingWhat are the 4 phases of the cardiac cycle in order?
  

What are the 4 phases of the cardiac cycle in order?

1. Ventricular filling

2. Isovolumetric contraction

3. Ventricular ejection

4. Isovolumetric relaxation

What happens during ventricular filling?

Ventricles relaxed; AV valves OPEN, SL valves CLOSED. About 80% of filling occurs passively; atrial systole supplies the final ~20%

What is EDV?

End-diastolic volume: volume in a ventricle after filling is complete, immediately before ventricular contraction

What happens during isovolumetric contraction?

Ventricles begin contracting → ventricular pressure rises → AV valves CLOSE. All valves are closed, so pressure rises but volume stays the same

 What happens during ventricular ejection?

Ventricular pressure exceeds pressure in pulmonary trunk/aorta → SL valves OPEN → blood is ejected

What happens during isovolumetric relaxation?

Ventricles relax → arterial backflow closes SL valves → all valves temporarily closed → pressure falls while volume remains unchanged

What ends isovolumetric relaxation?

When atrial pressure > ventricular pressure, AV valves open and ventricular filling begins again

phases of cardiac cycle

• early diastole = isovolumetric relaxation

• mid-late diastole = ventricular filling

• systole = isovolumetric contraction + ventricular ejection

How long is a normal cardiac cycle at ~75 bpm?

• Complete cycle ≈ 0.8 sec

• Atrial systole ≈ 0.1 sec

• Ventricular systole ≈ 0.3 sec

What is cardiac output (CO)?

 Volume of blood pumped by each ventricle per minute

 What is the cardiac-output equation?

CO = HR × SV
Example: 75 beats/min × 70 mL/beat = 5.25 L/min

What is stroke volume (SV)?

Volume of blood ejected by one ventricle per heartbeat

 What is the stroke-volume equation?

 SV = EDV − ESV
Example: 120 mL − 50 mL = 70 mL/beat

What are EDV and ESV?

• EDV: blood present before ventricular contraction

• ESV: blood remaining after ventricular contraction

What is preload?

Degree to which ventricular cardiac muscle is stretched before contraction. Increased filling/EDV increases preload

How does venous return affect preload and stroke volume?

 ↑ venous return → ↑ EDV/preload → greater stretch → stronger contraction → ↑ SV

 This is the Frank-Starling mechanism

 What is afterload?

 Pressure the ventricles must overcome to eject blood; essentially the arterial back pressure against the semilunar valves

How does hypertension affect afterload, ESV, and SV?

Hypertension → ↑ afterload → ↑ ESV → ↓ SV

What is contractility and how does increased contractility affect SV?

Contractility = strength of ventricular contraction independent of stretch.
↑ contractility → more blood ejected → ↓ ESV → ↑ SV

What three major factors regulate stroke volume?

 Preload, contractility, and afterload

 How can the body maintain CO if stroke volume falls?

By increasing heart rate, because CO = HR × SV

What factors can increase heart rate?

Sympathetic stimulation, epinephrine, thyroxine, exercise, and increased body temperature

Why are normal Ca²⁺ and K⁺ concentrations important to the heart?

They are essential for normal cardiac electrical activity and contraction; major disturbances can produce dangerous rhythm/conduction abnormalities

 What is pulmonary congestion and which side of heart failure causes it?

Left-sided heart failure → blood backs up into pulmonary circulation → pulmonary congestion, which can impair gas exchange and cause breathing difficulty

What is peripheral/systemic congestion and which side of heart failure causes it?

Right-sided heart failure → blood backs up in systemic circulation → peripheral/systemic congestion, often producing peripheral edema

What is cor pulmonale?

Right-sided heart enlargement/failure associated with high resistance/pressure in the pulmonary circulation, often secondary to lung disease

What is cardiac fibrosis?

Replacement/accumulation of fibrous connective tissue in myocardium; fibrotic tissue is noncontractile and can impair cardiac function.

What is congestive heart failure (CHF), and what causes it?

CHF occurs when the heart cannot pump blood effectively enough to meet the body’s needs.
→ Blood backs up → congestion/fluid accumulation.
Common causes: coronary artery disease/MI, chronic hypertension, and heart valve disease.

What are heart palpitations?

The sensation of being unusually aware of your heartbeat—often described as pounding, racing, fluttering, or skipped beats.
→ Can occur with changes in heart rate or rhythm