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Questions and Answers
What is included in the contents of the middle mediastinum?
What is included in the contents of the middle mediastinum?
Which boundary is not associated with the anterior mediastinum?
Which boundary is not associated with the anterior mediastinum?
What characterizes the anterior mediastinum?
What characterizes the anterior mediastinum?
Which structure is part of the pericardium?
Which structure is part of the pericardium?
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What is the relationship of the anterior mediastinum to the diaphragm?
What is the relationship of the anterior mediastinum to the diaphragm?
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What causes the first heart sound, commonly referred to as 'lub'?
What causes the first heart sound, commonly referred to as 'lub'?
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What is one of the primary functions of the fibrous skeleton of the heart?
What is one of the primary functions of the fibrous skeleton of the heart?
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Which structure separates the atria from the ventricles?
Which structure separates the atria from the ventricles?
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What is the function of the fibrous rings in the fibrous skeleton of the heart?
What is the function of the fibrous rings in the fibrous skeleton of the heart?
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Which of the following structures contains the anterior interventricular artery?
Which of the following structures contains the anterior interventricular artery?
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What role does the fibrous skeleton of the heart serve regarding electrical impulses?
What role does the fibrous skeleton of the heart serve regarding electrical impulses?
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Which heart sound is associated with the closure of the aortic and pulmonary valves?
Which heart sound is associated with the closure of the aortic and pulmonary valves?
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Which sulcus separates the two ventricles of the heart?
Which sulcus separates the two ventricles of the heart?
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What forms the largest part of the anterior surface of the heart?
What forms the largest part of the anterior surface of the heart?
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What separates the inflow part from the outflow part of the right ventricle?
What separates the inflow part from the outflow part of the right ventricle?
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How many papillary muscles are present in the right ventricle?
How many papillary muscles are present in the right ventricle?
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Which structure prevents backflow of blood in the right ventricle during contraction?
Which structure prevents backflow of blood in the right ventricle during contraction?
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From which area does the inflow part of the right ventricle receive blood?
From which area does the inflow part of the right ventricle receive blood?
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Which of the following statements about trabeculae carneae is accurate?
Which of the following statements about trabeculae carneae is accurate?
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What is the function of tendinous cords in the right ventricle?
What is the function of tendinous cords in the right ventricle?
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The right ventricle's outflow tract leads to which major vessel?
The right ventricle's outflow tract leads to which major vessel?
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What is the primary role of the sinoatrial (SA) node in the conduction system?
What is the primary role of the sinoatrial (SA) node in the conduction system?
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Where is the atrioventricular (AV) node located?
Where is the atrioventricular (AV) node located?
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What effect does the sympathetic nervous system have on the sinoatrial (SA) node?
What effect does the sympathetic nervous system have on the sinoatrial (SA) node?
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What structure serves as the bridge between the atrial and ventricular myocardium?
What structure serves as the bridge between the atrial and ventricular myocardium?
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Which part of the conduction system extends into the walls of the ventricles?
Which part of the conduction system extends into the walls of the ventricles?
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How does the impulse generated by the SA node travel to the AV node?
How does the impulse generated by the SA node travel to the AV node?
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What is the average rate at which the sinoatrial (SA) node gives off impulses?
What is the average rate at which the sinoatrial (SA) node gives off impulses?
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What initiates the conduction process in the cardiac conduction system?
What initiates the conduction process in the cardiac conduction system?
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What percentage of people exhibit codominance in the branching of coronary arteries?
What percentage of people exhibit codominance in the branching of coronary arteries?
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Which of the following is NOT a vein that drains into the coronary sinus?
Which of the following is NOT a vein that drains into the coronary sinus?
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What typically characterizes the pain associated with myocardial infarction?
What typically characterizes the pain associated with myocardial infarction?
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Which factor does NOT influence the severity of ischemia during a coronary artery occlusion?
Which factor does NOT influence the severity of ischemia during a coronary artery occlusion?
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How does the coronary sinus primarily drain the heart?
How does the coronary sinus primarily drain the heart?
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What role do anastomoses play in the coronary arterial system?
What role do anastomoses play in the coronary arterial system?
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What consequence does an occlusion of a major coronary artery usually have?
What consequence does an occlusion of a major coronary artery usually have?
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In which part of the heart do approximately two-thirds of the heart's venous drainage occur?
In which part of the heart do approximately two-thirds of the heart's venous drainage occur?
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Study Notes
### Inferior Mediastinum
- Divided by the pericardial sac
- Anterior mediastinum
- Middle mediastinum
- Posterior mediastinum
Anterior Mediastinum
- Smallest subdivision of the mediastinum
- Continuous with the superior mediastinum
- Limited inferiorly by the diaphragm
- Consists of loose connective tissue, fat, lymphatic vessels, lymph nodes, and internal thoracic vessels
- Contains the inferior part of the thymus in infants and children
Middle Mediastinum
- Contains the pericardium, heart and the roots of great vessels
- Ascending aorta
- Pulmonary trunk
- Superior vena cava (SVC)
Pericardium
- Fibroserous sac surrounding the heart and the roots of the great vessels
- Composed of two layers: outer fibrous pericardium and inner serous pericardium
Heart Sounds
- Two heart sounds are audible with a stethoscope:
- First sound (“lub”): Caused by the closure of the tricuspid and mitral valves
- Second sound (“dub”): Caused by the closure of the aortic and pulmonary valves
Fibrous Skeleton of the Heart
- Dense, fibrous connective tissue forming four rings with interconnecting areas between the atria and ventricles
- Cardiac muscle fibers are anchored to the fibrous skeleton
- Forms a complex framework:
- 4 fibrous rings surrounding the orifices of the valves
- Right and left fibrous trigone
- Membranous parts of the interatrial and interventricular septa
Functions of the Fibrous Skeleton
- Keeps the orifices of the AV and semilunar valves patent and prevents over distention
- Provides attachments for the leaflets or cusps of the valves
- Provides attachment for the myocardium
- Acts as an electrical “insulator,” separating the myenterically conducted impulses of the atria and ventricles
Internal Partitions of the Heart
- Divide the heart into four chambers: two atria and two ventricles
- Produce surface or external grooves: sulci
- Coronary sulcus / AV groove: Separates the atria from the ventricles
- Contains the right coronary artery, small cardiac vein, coronary sinus, and the circumflex branch of the left coronary artery
- Anterior and posterior interventricular sulci: Separate the two ventricles
- Anterior interventricular sulcus: Contains the anterior interventricular artery and the great cardiac vein
- Posterior interventricular sulcus: Contains the posterior interventricular artery and the middle cardiac vein
Right Ventricle
- Forms the largest part of the anterior surface of the heart
- Outflow tract leads to the pulmonary trunk: conus arteriosus (infundibulum)
- Contains irregular muscular elevations: trabeculae carneae
- Thick muscular ridge: supraventricular crest
- Separates the muscular wall of the inflow part from the smooth wall of the conus arteriosus
Papillary Muscles and Chordae Tendineae
- Papillary muscles contract before the right ventricle to tighten the tendinous cords, drawing the cusps together and preventing blood backflow
- Inflow part of the ventricle receives blood from the right atrium through the right AV (tricuspid) orifice
- Trabeculae carneae are numerous muscular, irregular structures in the inflow part of the right ventricle
- Papillary muscles attach to tendinous cords (chordae tendineae), which connect to the free edges of the tricuspid valve cusps
- Three papillary muscles in the right ventricle:
- Anterior papillary muscle: Largest, arises from the anterior wall, attaches to the anterior and posterior cusps of the tricuspid valve
- Posterior papillary muscle: Smaller than the anterior muscle, arises from the inferior wall, attaches to the posterior cusp of the tricuspid valve
- Septal papillary muscle: Arises from the interventricular septum, attaches to the anterior and septal cusps of the tricuspid valve
- Tendinous cords attach to the anterior, posterior, and septal cusps of the tricuspid valve
Interventricular Septum (IVS)
- Strong, obliquely placed partition between the right and left ventricles
- Consists of muscular and membranous parts
- Codominance (branches of both the right and left coronary arteries reach the crux of the heart) occurs in approximately 18% of people
- In some people, the circumflex branch arises from the right aortic sinus
- Approximately 4% of people have an accessory coronary artery
Coronary Collateral Circulation
- Branches of coronary arteries are generally considered functional end arteries (lacking sufficient anastomoses)
- Anastomoses exist between branches of coronary arteries, subepicardial or myocardial, and extracardiac vessels
- Anastomoses between the terminations of the right and left coronary arteries occur in approximately 10% of normal hearts.
Clinical: Coronary Artery Disease
- Occlusion of a major coronary artery leads to myocardial infarction (cell death)
- Severity depends on the size and location of the affected artery and whether the blockage is complete
- Partial blockages cause angina (pain) during or after exercise
- Cardiac pain is typically a deep central sternal pain radiating into the left arm and neck
- Severity of ischemia and infarction depends on the rate of occlusion or stenosis and the development of collateral channels
Venous Drainage of the Heart
- About 2/3 of the heart is drained by the coronary sinus, located posteriorly
- Coronary sinus opens into the right atrium
- Veins that drain into the coronary sinus:
- Great cardiac vein: Accompanies anterior interventricular artery
- Middle cardiac vein: Accompanies posterior interventricular artery
- Small cardiac vein: Accompanies right marginal artery
- Posterior left ventricular vein
Conduction System of the Heart
- Consists of nodes and networks of specialized cardiac muscle cells organized into four components:
- Sinoatrial node (SA)
- Atrioventricular node (AV)
- Atrioventricular bundle with its right and left bundle branches
- Subendocardial plexus of conduction cells (Purkinje fibers)
- Initiated by nodal tissue and propagated by cardiac striated muscle cells
- SA node is located anterolaterally at the junction of the SVC and right atrium
- SA node is the pacemaker of the heart: initiates and regulates impulses for heart contractions at approximately 70 times per minute
- SA node is stimulated by the sympathetic nervous system to accelerate heart rate and inhibited by the parasympathetic nervous system
- AV node is located in the posteroinferior region of the interatrial septum
Impulse Conduction through the Conduction System
- Impulse generated by the SA node passes through the walls of the right atrium
- Impulse is propagated by myogenic conduction, transmitting from the SA node to the AV node
- AV node then distributes the signal to the ventricles through the AV bundle
- AV bundle passes from the AV node through the fibrous skeleton of the heart and along the membranous part of the IVS
- AV bundle divides into right and left bundles at the junction of the membranous and muscular parts of the IVS
- Subendocardial branches (Purkinje fibers) extend into the walls of the respective ventricles
Summary of Impulse Generation and Conduction
- SA node initiates an impulse that is rapidly conducted to cardiac muscle fibers in the atria, causing them to contract
- Impulse spreads by myogenic conduction, rapidly transmitting from the SA node to the AV node
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Description
Test your knowledge on the inferior mediastinum and its subdivisions, including the anterior, middle, and posterior mediastinum. This quiz covers key components such as the pericardium, heart sounds, and anatomical structures. Perfect for anyone studying anatomy or cardiovascular physiology!
