Questions and Answers
Describe the location and position of the heart.
The heart is in the thoracic cavity in the mediastinum between ribs 2-5, about 2/3 on the left side of the body. It is about the size of a fist and weighs 10 ounces.
Describe the internal and external anatomy of the heart.
External includes great vessels, vena cava, pulmonary trunk, aorta, pulmonary veins, coronary vessels, and fat. Internal includes atrium, 4 chambers, 4 valves, left ventricle, chordae tendineae, and papillary muscles.
Describe the structure of the pericardium and heart wall.
The pericardium has a fibrous layer made of dense connective tissue that anchors the heart and a serous layer that provides lubrication. The heart wall consists of the endocardium, myocardium, and epicardium.
Describe the heart valves.
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What is the difference between pulmonary and systemic circulation?
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What is the flow of blood in the heart?
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Contrast prenatal heart structure with postnatal heart structure.
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Name the major vessels of the coronary circulation.
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List the special structural and functional characteristics of cardiac muscle tissues.
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Describe the structure and function of the electrical conduction systems of the heart.
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Contrast the flow of ions underlying each phase of a cardiac pacemaker and a contractile cell action potential.
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Describe how each segment of an ECG corresponds to the electrical activity and contraction of the myocardium.
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What occurs during the ventricular filling phase?
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What happens during isovolumetric contraction?
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What occurs during isovolumetric relaxation?
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Discuss disorders related to the heart.
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Describe the relationship between heart rate (HR), stroke volume (SV), and cardiac output (CO).
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Explain the regulation of heart rate (HR), stroke volume (SV), and cardiac output (CO).
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Study Notes
Heart Location and Position
- The heart functions as a muscular pump, beating approximately 3 billion times in an 80-year lifespan.
- Located in the thoracic cavity within the mediastinum, positioned between ribs 2-5.
- Occupies 2/3 of the left side of the body, comparable in size to a fist, and weighs around 10 ounces.
Internal and External Anatomy
- External features include major vessels: vena cava, pulmonary trunk, aorta, and pulmonary veins, along with coronary vessels and surrounding fat.
- Internally, the heart consists of 4 chambers (atria and ventricles) and 4 valves, with the left ventricle being three times thicker than the right.
- Structures include chordae tendineae and papillary muscles.
Pericardium and Heart Wall Structure
- The heart is encased in a fibrous layer, which is dense connective tissue providing anchorage.
- The serous layer produces lubricating fluid to minimize friction.
- Heart wall layers from deepest to superficial include endocardium, myocardium, and epicardium.
Heart Valves
- Two atrioventricular (AV) valves separate the atria from the ventricles, supported by the fibrous skeleton to provide insulation.
- Semilunar valves differ as they lack tendinous cords.
Circulation Types
- Pulmonary circulation involves the right side of the heart pumping blood to the lungs for oxygenation.
- Systemic circulation involves the left side pumping oxygen-rich blood to the rest of the body.
Blood Flow Through the Heart
- Blood flows from the superior vena cava into the atrium, then through the pulmonary arteries to the lungs, and returns via pulmonary veins to the left atrium, eventually moving out through the aorta.
Prenatal vs. Postnatal Heart Structure
- The prenatal heart features include the foramen ovale (a hole between the right and left atria) and the ductus arteriosus (a passage connecting the pulmonary trunk to the aorta).
Coronary Circulation
- Major vessels of coronary circulation originate at the base of the aorta, with the right coronary artery (RCA) traveling alongside the superior vena cava and pulmonary trunk to the apex.
- Venous blood returns through the coronary sinus to the right atrium.
Cardiac Muscle Tissue Characteristics
- Cardiac muscle is composed of short, branched cells connected by intercalated discs, with high mitochondria content and resistance to fatigue.
Electrical Conduction System
- The heart's rhythm is managed by the electrical conduction system, with the SA node acting as the pacemaker.
- Signals progress from the SA node to the AV node, followed by the Bundle of His, and finally to the Purkinje fibers.
Cardiac Action Potentials
- Only depolarizes when stimulated; phases include rapid sodium influx, calcium influx causing a plateau, followed by potassium efflux for repolarization.
ECG and Myocardial Activity
- An electrocardiogram (ECG) monitors the heart's electrical activity, helping assess heart health, size, position, and potential damage.
Cardiac Phases: Ventricular Filling
- Passive filling occurs primarily due to pressure gradients, with additional volume contributed by atrial contraction.
- End diastolic volume (EDV) reflects the total volume in ventricles after filling.
Cardiac Phases: Isovolumetric Contraction
- Tension builds in the ventricles with no blood flow; AV valves close producing the "lub" sound.
- Blood is ejected once semilunar valves open, with a typical stroke volume of about 70 mL and end systolic volume (ESV) of around 60 mL.
Cardiac Phases: Isovolumetric Relaxation
- Pressure in the ventricle drops, leading to the closure of semilunar valves, producing the "dub" sound.
- Muscle relaxes with constant volume in the ventricles as all valves remain closed.
Heart Disorders
- Sinus rhythm represents a normal heartbeat initiated by the SA node.
- Ectopic focus occurs when a different site functions as a pacemaker, leading to arrhythmias (irregular rhythms).
- Bradycardia refers to a resting heart rate below 100 bpm, while fibrillation results in chaotic electrical activation preventing effective blood pumping, which can be fatal.
Relationship Between Heart Rate, Stroke Volume, and Cardiac Output
- Cardiac output (CO) is directly related to heart rate (HR) and stroke volume (SV) defined by the equation CO = HR x SV.
Regulation of HR, SV, and CO
- Increased venous return contributes to greater end diastolic volume (EDV), resulting in enhanced tension/stretch and subsequently stronger contractions, effectively increasing stroke volume (SV).
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Test your knowledge of the heart's location, position, and anatomy with these flashcards. Learn about the heart's role in the circulatory system and its structural features. Perfect for students of biology and health sciences.