L03. Mediastinum & Heart Part II

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Questions and Answers

What is the primary role of the annulus fibrosus in the heart?

To enhance the electrical conduction between ventricles

To transport blood between atria and ventricles

To provide attachment points for cusps and myocardium (correct)

To increase the efficiency of heart contractions

Which artery typically supplies the SA node the most effectively?

Circumflex branch

Right marginal branch

Left coronary artery

Right coronary artery (correct)

In the context of coronary artery dominance, what is indicated by a 15% occurrence?

RCA provides supply to left ventricle

LCA supplies the posterior IV branch via circumflex (correct)

Both arteries supply equally to the myocardium

Collateral circulation is established in all patients

What can be concluded about the branches of coronary arteries?

They are considered true end arteries Signup and view all the answers

Which anatomical structure is NOT included in the contents of the middle mediastinum?

Pulmonary veins Signup and view all the answers

What is the consequence of slower progression in coronary artery disease regarding the smaller arterial branches?

Their anastomoses provide functional value Signup and view all the answers

What is the primary composition of the fibrous pericardium?

Dense connective tissue Signup and view all the answers

In what position do the structures of the middle mediastinum typically sag due to gravity?

Standing Signup and view all the answers

Which statement best describes the relationship of the fibrous pericardium to the diaphragm?

It is fused with the central tendon of the diaphragm. Signup and view all the answers

Which of the following nerves accompany the pericardiacophrenic vessels in the middle mediastinum?

Phrenic nerves Signup and view all the answers

What is the primary consequence of fused valve cusps in pulmonary stenosis?

Narrowing of the outflow tract Signup and view all the answers

Which component of the heart is primarily responsible for receiving blood from the pulmonary veins?

Left atrium Signup and view all the answers

What is the function of the bicuspid valve during ventricular contraction?

To close off the left atrioventricular orifice Signup and view all the answers

Which part of the left atrium serves as the primary reservoir for blood returning from the lungs?

Smooth wall Signup and view all the answers

What is a possible clinical consequence of thrombi forming in the left atrium?

Formation of emboli that can occlude arteries Signup and view all the answers

What structure connects the papillary muscles to the tricuspid valve cusps?

Chordae tendineae Signup and view all the answers

Which component separates the inflow portion from the outflow tract in the right ventricle?

Supraventricular crest Signup and view all the answers

Which valves prevent backflow of blood into the heart chambers?

Pulmonary and tricuspid valves Signup and view all the answers

What is the primary consequence of pericardial effusion on heart function?

Prevents heart expansion and limits blood inflow. Signup and view all the answers

Which condition results in the accumulation of blood within the pericardial cavity?

Hemopericardium. Signup and view all the answers

During ventricular contraction, what action occurs to prevent the tricuspid valve from inverting?

The papillary muscles contract Signup and view all the answers

What is the primary role of the pulmonary valve?

To prevent backflow from the pulmonary trunk into the right ventricle Signup and view all the answers

What is the function of pericardiocentesis?

To drain serous fluid from the pericardial cavity. Signup and view all the answers

Which part of the right ventricle is responsible for the majority of its anterior surface?

Right ventricle wall Signup and view all the answers

Where is the apex of the heart located?

At the left inferolateral part of the left ventricle. Signup and view all the answers

What structure serves as a shortcut for the right bundle of the AV bundle to the anterior wall of the right ventricle?

Septomarginal trabecula Signup and view all the answers

During which condition does the superior vena cava (SVC) get compressed?

Hemopericardium. Signup and view all the answers

What feature characterizes the valve anatomy of the tricuspid valve?

Three cusps each associated with papillary muscles Signup and view all the answers

Which statement accurately describes cardiomegaly?

It involves the slow enlargement of the heart without compression. Signup and view all the answers

What structures enter the base of the heart?

Pulmonary veins and superior/inferior vena cava. Signup and view all the answers

Which anatomical feature is primarily located at the posterior aspect of the heart?

Left atrium. Signup and view all the answers

What are the primary components controlling heart rate and force of contractions?

Both sympathetic and parasympathetic stimulation Signup and view all the answers

In which spinal cord segments do the axons of afferent pain fibers from the heart primarily enter?

T1 – T4/5 Signup and view all the answers

Which of the following areas is located in the traditional auscultatory area for the mitral valve?

5th intercostal space Signup and view all the answers

What effect does sympathetic stimulation have on the nodal tissue of the heart?

Increases heart rate and contractility Signup and view all the answers

Which statement correctly describes the cardiac plexus?

Includes both parasympathetic and sympathetic fibers Signup and view all the answers

How does parasympathetic stimulation affect the heart?

Decreases heart rate, conserving energy Signup and view all the answers

Which vessels are contained within the pericardial sac?

Ascending aorta and pulmonary trunk Signup and view all the answers

What phenomenon describes the perception of heart pain in areas outside the heart?

Referred cardiac pain Signup and view all the answers

Which structure primarily receives blood from the great cardiac vein, middle cardiac vein, and small cardiac vein?

Coronary sinus Signup and view all the answers

What initiates the electrical impulses that regulate the heartbeat?

SA node Signup and view all the answers

Where do the lymphatics of the myocardium primarily drain?

Inferior tracheobronchial lymph nodes Signup and view all the answers

What phase of the cardiac cycle begins with the closure of the aortic and pulmonary valves?

Diastole Signup and view all the answers

Which characteristic is true of the AV node compared to the SA node?

It is smaller and located near the coronary sinus opening. Signup and view all the answers

During which part of the cardiac cycle do the atrioventricular valves close?

During systole after ventricular contraction begins Signup and view all the answers

What structure provides collateral circulation to the myocardium?

Smallest cardiac veins Signup and view all the answers

What is the primary function of the cardiac impulse-conducting system?

To initiate spontaneous contraction of the heart muscle Signup and view all the answers

What role does the fibrous trigone play in the structure of the heart?

It helps maintain the integrity of valves and provides muscle attachment points. Signup and view all the answers

How does the left coronary artery primarily contribute to the heart's blood supply?

It primarily supplies the anterior and lateral aspects of the heart. Signup and view all the answers

What is a key characteristic of the branches of the coronary arteries?

They function as end arteries with minimal collateral circulation. Signup and view all the answers

Which clinical condition is characterized by sudden occlusion of a major coronary artery?

Myocardial infarction (MI) Signup and view all the answers

What percentage of individuals typically exhibit a dominant left coronary artery system?

15% Signup and view all the answers

What is the significance of a single coronary artery?

It often arises directly from the right aortic sinus. Signup and view all the answers

What is the common outcome of atherosclerosis affecting the coronary arteries?

Coronary insufficiency leading to ischemic heart disease. Signup and view all the answers

What anatomical feature separates the atrial musculature from the ventricular musculature?

The annulus fibrosus Signup and view all the answers

Study Notes

Right Ventricle

Forms the largest part of the anterior surface and inferior border of the heart
Contains irregular muscular elevations called trabeculae carneae
Papillary muscles, attaching to the ventricular wall on one end, connect to chordae tendineae on the other end, which attach to the cusps of the tricuspid valve
- There are three papillary muscles: anterior, posterior, and septal
The septomarginal trabecula, or moderator band, is a specialized trabecula that bridges the inferior interventricular septum to the anterior papillary muscle base.
- It acts as a shortcut for the right bundle of the AV bundle to the anterior wall of the right ventricle
The conus arteriosus is a smooth-walled outflow tract to the pulmonary trunk.
- The pulmonary valve is located at its apex
The supraventricular crest separates the muscular inflow part from the smooth-walled conus arteriosus (outflow)

Tricuspid Valve

Closes off the right atrioventricular orifice during ventricular contraction
Consists of three cusps: anterior, septal, and posterior
The base of each cusp is secured to a fibrous ring that maintains the shape of the atrioventricular orifice
The free margins of the cusps are attached to chordae tendineae
The cusps project into the ventricle and open the valve while the right ventricle fills
Papillary muscles contract during ventricular contraction, pulling the cusps closed and preventing backflow into the right atrium

Pulmonary Valve

Closes the outflow tract between the right ventricle and pulmonary trunk
Consists of three semilunar cusps: left, anterior, and right, forming pocket-like sinuses
After ventricular contraction, the sinuses fill with blood, forcing the cusps closed and preventing backflow into the right ventricle

Middle Mediastinum

Located within the inferior mediastinum, between the transverse thoracic plane (level of the sternal angle and intervertebral disc of T4/T5 vertebra) and the diaphragm
Contents include:
- Pericardium
- Heart
- Roots of great vessels (ascending aorta, pulmonary trunk, SVC)
- Arch of azygos vein
- Main bronchi
- Phrenic nerves accompanied by pericardiacophrenic vessels
The levels of viscera within the middle mediastinum can vary depending on the patient's position (supine vs. standing)

Pericardium

Lies deep to the mediastinal parietal pleura
Composed of two layers:
- External sac: Fibrous pericardium
  - Outer layer of dense connective tissue
  - Bound to the central tendon of the diaphragm
  - Fused with the tunica adventitia of great vessels (at the level of the sternal angle)
  - Anteriorly attached to the sternum by sternopericardial ligaments
- Internal sac: Serous pericardium
  - Consists of two layers: parietal pericardium (fused to fibrous pericardium) and visceral pericardium (epicardium)
  - The pericardial cavity is a potential space between the parietal and visceral pericardium, filled with a small amount of serous fluid

Clinical Notes: Pericardium

The fibrous pericardium, being tough and inelastic, protects the heart against abrupt overfilling.
- Pericardial effusion, the leaking of fluid from pericardial capillaries into the pericardial cavity, can lead to extensive fluid build-up, preventing the heart from expanding and limiting blood inflow to the ventricles, resulting in cardiac tamponade due to the unyielding fibrous sac.
Cardiomegaly, the slow increase in heart size, allows for enlargement to occur without compression.
Hemopericardium, the entry of blood into the pericardial cavity (e.g., from a stab wound or weakened area of the heart muscle after a heart attack), can lead to heart compression, circulatory failure, and SVC compression, engorging veins in the face and neck.
Pericardiocentesis, the drainage of serous fluid from the pericardial cavity, relieves cardiac tamponade.

Heart

Serves as two muscular pumps propelling blood to the body
Approximately the size of a clenched fist
The right side receives low-oxygen blood from the SVC/IVC and sends it to the pulmonary trunk for oxygenation
The left side receives high-oxygen blood from the pulmonary veins and sends it to the aorta for systemic distribution
The right and left atria are receiving chambers
The right and left ventricles are discharging chambers

External Anatomy of the Heart

Located posterior to the sternum, costal cartilages, and medial ends of ribs 3-5 on the left side
Sits obliquely, with approximately 2/3 to the left and 1/3 to the right of the median plane
Apex:
- Left inferolateral part of the left ventricle
- Posterior to the left 5th intercostal space (8-9 cm from the midsternal line)
- Directed downward and to the left ~45 degrees from the median plane
- More anteriorly located than the base
Base:
- Posterior aspect of the heart
- Mainly composed of the left atrium
- Faces posteriorly toward the vertebral bodies of T6-T9
- Between the bifurcation of the pulmonary trunk and the coronary groove

The great veins enter the base of the heart:

The pulmonary veins enter the right and left sides of the left atrium
The SVC/IVC enter the upper and lower ends of the right atrium, respectively

Clinical Notes: External Anatomy

Pulmonary stenosis:
- Valve cusps fuse, narrowing the pulmonary valve
- Infundibular pulmonary stenosis: conus arteriosus is underdeveloped, restricting right ventricular outflow

Left Atrium

Derived embryologically from two structures: a smooth wall and a muscular portion
The posterior half receives blood from four pulmonary veins, having smooth walls.
The smaller muscular auricle is in the anterior half, with no distinct structure to separate it from the smooth-walled portion.
The interatrial septum forms part of the anterior wall.
- A thin area/depression called the valve of the foramen ovale is present.
- Is the probe patent in your cadaver?
Blood passes from the left atrium to the left ventricle through the left atrioventricular orifice.
- It is closed during ventricular contraction by the bicuspid valve.
Blood entering the left ventricle from the left atrium moves forward toward the apex
Clinical importance: Thrombi (immobile blood clots) form on the wall of the left atrium. When they detach, they become emboli (mobile clots) and can occlude an artery

Left Ventricle

Forms most of the heart base
Longer than the right ventricle, with the thickest layer of myocardium
Lies anterior to the left atrium and forms the apex
Makes up nearly all of the left surface/border and diaphragmatic surface
Has a thicker layer of myocardium than the right ventricle since arterial pressure is higher in the systemic circulation compared to the pulmonary circulation
Contains trabeculae carneae, papillary muscles, and chordae tendineae associated with the bicuspid valve.
Blood flows from the apex of the ventricle toward the base during ventricular contraction, entering the aorta

Bicuspid Valve

Closes off the left atrioventricular orifice during ventricular contraction
Consists of two cusps: anterior and posterior
The base of each cusp is secured to a fibrous ring that maintains the shape of the atrioventricular orifice
The free margins of the cusps are attached to chordae tendineae
The cusps project into the ventricle and open the valve while the left ventricle fills
Papillary muscles contract during ventricular contraction, pulling the cusps closed and preventing backflow into the left atrium

Aortic Valve

Closes the outflow tract between the left ventricle and the aorta
Consists of three semilunar cusps: right, left, and posterior, forming pocket-like sinuses
After ventricular contraction, the sinuses fill with blood, forcing the cusps closed and preventing backflow into the left ventricle

Internal anatomy of the Heart

Atrial septum
Ventricular septum
4 fibrous rings
- Right and left fibrous trigone: areas of thickened connective tissue between the rings
The fibrous rings maintain the integrity of the openings they surround, provide attachment points for cusps and myocardium, separate the atrial from ventricular musculature, and act as a partition of dense connective tissue to electrically isolate the atria from the ventricles, leaving the AV bundle as the single connection between the two groups of myocardium.

Coronary Vasculature

Arterial blood supply to the heart:
- Right coronary artery
  - Supplies the SA node (60%), AV node (80%), right atrium, most of the right ventricle, part of the left ventricle, and part of the interventricular septum
  - Branches: SA nodal branch, right marginal branch, AV nodal branch, and posterior interventricular artery
- Left coronary artery
  - Supplies the SA node (40%), left atrium, most of the left ventricle, part of the right ventricle, and most of the interventricular septum
  - Branches: SA nodal branch, anterior interventricular artery, circumflex branch, and left marginal branch

Clinical Notes: Coronary Vasculature

Variations of coronary arteries:
- Normally, there is a 50/50 blood supply contribution from the LCA and RCA.
- In 15% of cases, the LCA is dominant, with the posterior interventricular branch arising off of the circumflex.
- A single coronary artery can occur.
- The circumflex can arise directly from the right aortic sinus.
- An accessory coronary artery can occur in 4% of cases.
The branches of coronary arteries are considered end arteries, supplying myocardium without functional overlap. However, smaller branches do anastomose, and the functional value of this is apparent in slowly progressive coronary artery disease.

Heart Anatomy

The heart is located in the middle mediastinum, within the pericardial sac
The fibrous pericardium is a tough, fibrous sac that encloses the heart
The fibrous pericardium helps to maintain the integrity of the openings it surrounds and provides attachment points for cusps and myocardium.
The fibrous pericardium separates atrial from ventricular musculature
The fibrous pericardium serves as a partition of dense connective tissue to electrically isolate the atria from the ventricles, leaving the A/V bundle as the single connection between the two groups of myocardium.

Coronary Vasculature

Right coronary artery supplies: right atrium, most of right ventricle, part of left ventricle, part of IV septum, SA node (60%), AV node (80%)
- SA nodal branch supplies the SA node
- Right marginal branch supplies the right border of the heart
- AV nodal branch supplies the AV node
- Posterior IV artery supplies the posterior interventricular artery
Left coronary artery supplies : left atrium, most of left ventricle, part of right ventricle, most of IV septum, SA node (40%)
- SA nodal branch supplies the SA node
- Anterior IV artery supplies the anterior interventricular artery
- Circumflex branch supplies the posterior surface
- Left marginal branch branches off the circumflex and supplies the left ventricle
Clinical Importance: Variations of coronary arteries:
- Normally, there is a 50/50 blood supply contribution from LCA & RCA
- In 15% of cases, LCA is dominant, and the posterior IV branch comes off the circumflex
- In some cases, there is a single coronary artery
- In some cases, the circumflex arises directly from the right aortic sinus
- In 4% of cases, an accessory coronary artery is present
End Arteries: Branches of coronary arteries are considered end arteries, but smaller branches anastomose and functional value of this is apparent in slowly progressive coronary artery disease
Clinical Importance: Myocardial infarction (MI) is a major artery that is suddenly occluded by an embolus, myocardium in that region becomes infarcted. MI is an area of myocardium that is necrotic. Atherosclerosis of coronary arteries → coronary insufficiency → ischemic heart disease; often characterized by angina pectoris (pain in substernal region and down medial side of the left arm and forearm).

Venous Drainage

The heart drains via the coronary sinus (primary) and anterior cardiac veins → right atrium (secondary)
The coronary sinus receives the great cardiac vein, middle and small cardiac veins
The left posterior vein and left marginal vein → coronary sinus
Smallest cardiac veins – capillary beds of myocardium → atria (provide collateral circulation to musculature)

Lymphatic Drainage

Myocardium and subepicardial connective tissue → subepicardial lymphatic plexus
The lymphatic plexus travels along the coronary groove → ends in inferior tracheobronchial lymph nodes

Conducting System of Heart

The impulse-conducting system coordinates the cardiac cycle
The impulse-conducting system consists of cardiac muscle cells & highly specialized conducting fibers for initializing impulses and conducting them through the heart
Nodal tissue initiates heartbeat & coordinates contractions
- SA node:
  - Impulse 70x/min
  - Pacemaker of heart
  - Located just deep to epicardium, junction of SVC & right atrium
- AV node:
  - Smaller collection of nodal tissue
  - Just posteroinferior of interatrial septum, near coronary sinus opening

Cardiac Cycle

The cardiac cycle is the complete movement of the heart; the period from the beginning of one heartbeat to the beginning of the next.
The cardiac cycle consists of diastole (ventricular filling) and systole (ventricular emptying).
- Diastole:
  - The aortic and pulmonary valves close
  - The atrioventricular valves open during early stages of diastole
  - Atrial contraction occurs during the final moments of diastole
- Systole:
  - The atrioventricular valves (tricuspid and mitral) close very soon after systole begins
  - The aortic and pulmonary valves open during systole

Innervation of the Heart:

Cardiac Plexuses
- Located anterior to bifurcation of the trachea, posterior to the ascending aorta, superior to the bifurcation of the pulmonary trunk
- The Autonomic division of the PNS is only in the atria to any specific degree and very little in ventricles. It is therefore directly responsible for regulating heart rate and force of atrial contraction and no direct effect on ventricles.
- Sympathetic stimulation of the nodal tissue increases heart rate and the force of cardiac contractions
- Parasympathetic stimulation slows the heart rate, saving energy
- Branches from both parasympathetic and sympathetic contribute to the cardiac plexus
- Visceral afferents from the heart are also part of the cardiac plexus

Clinical Importance: Cardiac Pain

The heart is insensitive to touch and temperature
Ischemia can stimulate pain endings in the myocardium
Pain fibers enter spinal cord segments T1 – T4/5, especially on the left side
Referred cardiac pain is a phenomenon whereby stimuli originating in the heart is perceived as pain arising from a superficial body part – e.g., skin on the medial aspect of left upper limb

Auscultatory Areas of the Heart

The traditional valve areas are not the anatomical positions of the valves, but where they are best heart based on sound projections related to blood flow
- Aortic valve area: 2nd right intercostal space
- Pulmonic valve area: 2nd left intercostal space
- Mitral valve area: 5th intercostal space
- Tricuspid valve area: left lower sternal border

Great Vessels

The pulmonary trunk is contained within the pericardial sac, along with the ascending aorta.
The pulmonary trunk arises from the conus arteriosus and divides into left and right pulmonary arteries between TV5-TV6
The ascending aorta originates at the aortic orifice and moves superiorly to the level of the 2nd right costal cartilage, where it enters the superior mediastinum and becomes the arch of the aorta.

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Description

This quiz explores the anatomy and functions of the right ventricle and the tricuspid valve in the human heart. Participants will learn about important structures such as papillary muscles, trabeculae carneae, and the conus arteriosus. Test your knowledge on how these components work together to facilitate proper blood flow and heart function.