Anatomy and Physiology: Heart Layers

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Questions and Answers

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?

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?

Pulmonic Semilunar Valve

Tricuspid Valve (correct)

Aortic Semilunar Valve

Bicuspid (Mitral) Valve

Where does the left ventricle pump oxygenated blood to?

To the body via the aorta Signup and view all the answers

Which structure serves as the main pacemaker of the heart?

Sinoatrial (SA) Node Signup and view all the answers

What is the function of the semilunar valves in the heart?

To prevent backflow into the ventricles during relaxation Signup and view all the answers

What structures receive deoxygenated blood from the body?

Right atrium via vena cava Signup and view all the answers

How much fluid is typically found in the pericardial space?

5 to 20 mL Signup and view all the answers

What initiates and sustains a heart rate of 40 to 60 beats per minute if the SA node fails?

AV node Signup and view all the answers

Which heart sound is produced when the atrioventricular valves close?

First heart sound (S1) Signup and view all the answers

What is the normal heart rate range for sinus rhythm?

60 to 100 beats per minute Signup and view all the answers

What does stimulation of sympathetic nerve fibers primarily release that affects heart rate?

Norepinephrine Signup and view all the answers

Which arteries supply blood to the left atrium and parts of the left ventricle?

Circumflex artery Signup and view all the answers

What is the potential heart rate of Purkinje fibers when both the SA and AV nodes fail?

20 to 40 beats per minute Signup and view all the answers

Which hormone plays a role in regulating blood pressure by influencing blood volume?

Antidiuretic hormone Signup and view all the answers

Which condition may lead to a third heart sound (S3) in an individual under 30 years of age?

Normal physiological variation Signup and view all the answers

What happens to heart rate when arterial pressure decreases?

Heart rate increases Signup and view all the answers

What structure is responsible for the spread of depolarization through the ventricles?

Purkinje fibers Signup and view all the answers

What effect does sympathetic stimulation have on cardiac contractility?

Increases contractility Signup and view all the answers

Which structure continues as a bundle after the AV node?

Bundle of His Signup and view all the answers

Which artery supplies the anterior wall of the left ventricle?

Left anterior descending artery Signup and view all the answers

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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Description

This quiz explores the anatomy and physiology of the heart, focusing on its structure and components, including the three heart wall layers: epicardium, myocardium, and endocardium. Additionally, it covers the protective role of the pericardial sac and its two layers. Test your knowledge on these critical aspects of cardiac anatomy!