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Questions and Answers
Which layer of the heart is responsible for the actual contraction of the heart muscle?
Which layer of the heart is responsible for the actual contraction of the heart muscle?
- Endocardium
- Myocardium (correct)
- Pericardium
- Epicardium
What is the primary function of the pericardial sac?
What is the primary function of the pericardial sac?
- To facilitate blood flow into the heart
- To produce hormones for heart regulation
- To encase and protect the heart from trauma and infection (correct)
- To maintain blood pressure in the arteries
Which valve is located between the right atrium and right ventricle?
Which valve is located between the right atrium and right ventricle?
- Pulmonic Semilunar Valve
- Tricuspid Valve (correct)
- Aortic Semilunar Valve
- Bicuspid (Mitral) Valve
Where does the left ventricle pump oxygenated blood to?
Where does the left ventricle pump oxygenated blood to?
Which structure serves as the main pacemaker of the heart?
Which structure serves as the main pacemaker of the heart?
What is the function of the semilunar valves in the heart?
What is the function of the semilunar valves in the heart?
What structures receive deoxygenated blood from the body?
What structures receive deoxygenated blood from the body?
How much fluid is typically found in the pericardial space?
How much fluid is typically found in the pericardial space?
What initiates and sustains a heart rate of 40 to 60 beats per minute if the SA node fails?
What initiates and sustains a heart rate of 40 to 60 beats per minute if the SA node fails?
Which heart sound is produced when the atrioventricular valves close?
Which heart sound is produced when the atrioventricular valves close?
What is the normal heart rate range for sinus rhythm?
What is the normal heart rate range for sinus rhythm?
What does stimulation of sympathetic nerve fibers primarily release that affects heart rate?
What does stimulation of sympathetic nerve fibers primarily release that affects heart rate?
Which arteries supply blood to the left atrium and parts of the left ventricle?
Which arteries supply blood to the left atrium and parts of the left ventricle?
What is the potential heart rate of Purkinje fibers when both the SA and AV nodes fail?
What is the potential heart rate of Purkinje fibers when both the SA and AV nodes fail?
Which hormone plays a role in regulating blood pressure by influencing blood volume?
Which hormone plays a role in regulating blood pressure by influencing blood volume?
Which condition may lead to a third heart sound (S3) in an individual under 30 years of age?
Which condition may lead to a third heart sound (S3) in an individual under 30 years of age?
What happens to heart rate when arterial pressure decreases?
What happens to heart rate when arterial pressure decreases?
What structure is responsible for the spread of depolarization through the ventricles?
What structure is responsible for the spread of depolarization through the ventricles?
What effect does sympathetic stimulation have on cardiac contractility?
What effect does sympathetic stimulation have on cardiac contractility?
Which structure continues as a bundle after the AV node?
Which structure continues as a bundle after the AV node?
Which artery supplies the anterior wall of the left ventricle?
Which artery supplies the anterior wall of the left ventricle?
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Study Notes
Heart Anatomy and Layers
- Located in the mediastinum; the heart is composed of three layers:
- Epicardium: Outermost layer
- Myocardium: Middle layer and main contracting muscle
- Endocardium: Innermost layer lining the chambers and valves
Pericardial Sac
- Protects the heart from trauma and infection, consisting of two layers:
- Parietal pericardium: Tough outer membrane attaching to the sternum, vertebrae, and diaphragm
- Visceral pericardium: Thin inner layer closely adhering to the heart
- Pericardial space contains 5 to 20 mL of fluid for lubrication and cushioning
Heart Chambers
- Four chambers:
- Right atrium: Receives deoxygenated blood from the body via superior and inferior vena cava
- Right ventricle: Pumps blood to lungs via pulmonary artery
- Left atrium: Receives oxygenated blood from lungs through four pulmonary veins
- Left ventricle: Largest and most muscular, pumps oxygenated blood into systemic circulation via the aorta
Heart Valves
- Four valves divided into two groups:
- Atrioventricular valves: Tricuspid (right) and Mitral (bicuspid, left) prevent backflow into atria during ventricular contraction
- Semilunar valves: Pulmonic (between right ventricle and pulmonary artery) and Aortic (between left ventricle and aorta) prevent backflow into ventricles during relaxation
Electrical Conduction System
- Sinoatrial (SA) Node: Primary pacemaker, located at junction of superior vena cava and right atrium, generates impulses at 60-100 beats per minute
- Atrioventricular (AV) Node: Located in lower aspect of atrial septum; can sustain heart rate of 40-60 beats if SA node fails
- Bundle of His: Continuation of AV node in interventricular septum, branches into right and left bundle branches that lead to Purkinje fibers
- Purkinje Fibers: Conduct impulses through ventricles; can act as pacemaker at 20-40 beats per minute if both SA and AV nodes fail
Coronary Arteries
- Right coronary artery supplies right atrium, right ventricle, inferior left ventricle, and nodes
- Left coronary artery branches into:
- Left anterior descending (LAD): Supplies anterior wall of left ventricle and septum
- Circumflex artery: Supplies left atrium and lateral/posterior walls of left ventricle
- Blockages can lead to myocardial infarction (MI)
Heart Sounds
- S1: First heart sound, loudest at apex, marks closure of atrioventricular valves
- S2: Second heart sound, loudest at base, marks closure of semilunar valves
- S3: Possible sign of decreased ventricular wall compliance; may be normal in individuals under 30
- S4: Indicates resistance to ventricular filling due to conditions like cardiac hypertrophy
Heart Rate
- Normal sinus heart rate: 60-100 beats per minute
- Sinus tachycardia: Rate over 100 beats per minute
- Sinus bradycardia: Rate below 60 beats per minute
- Rapid heart rate reduces filling time; very fast rates decrease cardiac output
Autonomic Nervous System
- Sympathetic stimulation increases heart rate and contractility via norepinephrine release
- Parasympathetic stimulation decreases heart rate and contractility via acetylcholine release
Blood Pressure Control
- Baroreceptors in aortic arch and carotid sinuses detect arterial pressure changes
- Increased arterial pressure suppresses heart rate; decreased pressure triggers heart rate increase and vessel constriction
- Stretch receptors in vena cava and right atrium respond to changes in blood volume, influencing heart rate and pressure
- Antidiuretic hormone (ADH) regulates blood volume and pressure; renin-angiotensin system also affects blood pressure
Vascular System
- Arteries transport oxygenated blood from the heart; arterioles control blood flow to capillaries
- Capillaries facilitate nutrient and fluid exchange; venules collect blood from capillaries to veins
- Veins return deoxygenated blood to the right heart; valves aid in blood return against gravity
- Lymphatics drain tissue and return fluid to bloodstream
Cardiac Markers
- Troponin: Three proteins; Troponin I indicates myocardial injury, rising within 3 hours and lasting 7-10 days; normal: Troponin I < 0.35 ng/mL
- High-sensitivity Troponin (hsTnT): Detects troponins early (60-90 minutes) after injury; speeds triage for potential MI
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