Chapter 8- Heart

THE CARDIAC SKELETON

- Fibrous CT - Rings imbedded in myocardium around each of valve orifices (Annulus Fibrosus) - Some CT fibers extend into each valve cusp

CONDUCTING SYSTEM OF THE HEART:

- Inherent Rhythmicity - Inherent Rhythmicity • For these contractions to occur in an orderly sequence and coordinated manner, there must be some type of controlling system • Cardiac muscle fibers have the ability to contract in the absence of innervation - Atria » 40 - 60 contractions/min - Ventricles » 20 contractions/min

The Right Ventricle

- Occupies most of the sternocostal surface of the heart from the AV sulcus to the anterior interventricular sulcus. Its wall is much thicker than the wall of the atrium and about 1/3 as thick as the wall of the left ventricle. -Pumps blood through the PULMONARY ORIFICE (VALVE) to the pulmonary trunk and then on to the lungs.

clinical of Right atrium

- Patent Foramen Ovale (PFO) • Actual openings between atria can exist. atria can exist. • Morecommonly(≈25%of pop.) - Probe Patent Foramen Ovale » Membranes overlap to close foramen ovale but fail to fuse » Can pass probe obliquely between atria

CONDUCTING SYSTEM OF THE HEART Summary:

- SA Node initiates impulse • Spreads throughout both atria • Converge on AV Node via three "Internodal Pathways" - AV Node distributes impulses to AV Bundle • Spreads to right and left bundle branches • Spreads to Purkinje Fibers throughout walls of ventricles • Transmission of the cardiac impulse through the heart, showing the time of appearance (in fractions of second) of the impulse in different parts of the heart.

CONDUCTING SYSTEM OF THE HEART regions

- Sinuatrial Node (SA Node) - Atrioventricular Node (AV Node) - Atrioventricular Bundle (AV Bundle of His) - Purkinje Fibers

right atrium

-Receives deoxygenated blood from the entire body, including the heart, from the superior and inferior venae cavae and the coronary sinus and pumps the blood through the RIGHT ATRIOVENTRICULAR (TRICUSPID) ORIFICE (FIG. 8) into the right ventricle. -Developed from the right half of the sinus venosus and the right half of the primitive atrium. As a result the interior of the right atrium is divided into two parts by the CRISTA TERMINALIS:

SULCUS TERMINALIS

1) An external landmark of the right atrium. It is a shallow groove which marks the position of the CRISTA TERMINALIS on the internal surface of the right atrium

Atrioventricular (coronary) sulcus (groove) contains: (both anterior and posterior parts)

1) Anteriorly: a) Right Coronary Artery, b) A tributary of the Small Cardiac Vein, c) Circumflex Branch of the Left Coronary Artery, d) Part of Great Cardiac Vein. 2) Posteriorly a) Coronary Sinus, b) Terminal part of the Great Cardiac Vein, c) Circumflex Branch of the Left Coronary Artery, d) Right Coronary Artery.

INTERVENTRICULAR SEPTUM (left ventricle)

1) Possesses a large lower muscular part and a thin, oval upper membranous part. As we will see in Human Embryology each part is of a different embryological origin. 2) The membranous part is the usual site of ventricular septal defects which are the most common of all congenital cardiac defects. The membranous part of the septum also lies in close relation to the right atrium.

Posterior Interventricular sulcus (groove) contains:

1) Posterior Interventricular (Descending) Branch of the Right Coronary Artery. 2) Middle Cardiac Vein.

Auricular appendages:

1) The Right Auricle a) A cone-shaped muscular pouch of the superior portion of the right atrium. It lies against the root of the aorta and covers the first portion of the right coronary artery. 2) The Left Auricle a) A muscular out-pouching of the left margin of the left atrium. The left auricle is directed anteriorly and overlaps the root of the pulmonary trunk. 3) The auricles represent remnants of the embryological primitive atria.

right atrium is divided into two parts by the CRISTA TERMINALIS:

1) The part from the sinus venosus is smooth-walled and is called the SINUS VENARUM. It receives the OPENINGS of the CORONARY SINUS and the SUPERIOR and INFERIOR VENAE CAVAE. 2) The part from the primitive atrium is rough-walled with ridges called MUSCULI PECTINATI and includes the RIGHT AURICLE.

SIZE AND SHAPE of the heart

1. A normal heart usually weighs 200 - 400 g. It is roughly pyramidal in shape and somewhat larger than a closed fist. 2. The wall of the heart

surface of the heart:

1. ANTERIOR (STERNOCOSTAL) SURFACE 2. DIAPHRAGMATIC (INFERIOR) SURFACE 3. BASE OF THE HEART (POSTERIOR SURFACE)

Grooves of the heart:

1. ATRIOVENTRICULAR (CORONARY) SULCUS (GROOVE) 2. ANTERIOR INTERVENTRICULAR SULCUS (GROOVE) 3. POSTERIOR INTERVENTRICULAR SULCUS (GROOVE) 4. Auricular and Sulcus terminals

Heart valves positions:

1. PULMONARY VALVE a. Lies at the left 3rd costosternal articulation. 2. AORTIC VALVE a. Lies slightly below and medial of the Pulmonary Valve. 3. LEFT ATRIOVENTRICULAR (BICUSPID/MITRAL) VALVE a. Located just to the left of the midline opposite the 4th costosternal articulation. 4. RIGHT ATRIOVENTRICULAR (TRICUSPID) VALVE a. Located near the midsternal region opposite the 4th or 5th intercostal space.

Position of the heart:

1. The heart and roots of the great vessels occupy the pericardium. 2. The heart is not centered in the median plane, but lies approximately 2/3 of its mass to the left and 1/3 to the right. 3. Related anteriorly (i.e., anterior to the heart) to the sternum, costal cartilages, and ribs. 4. The heart lies obliquely in the chest with the APEX (see below) directed downward and to the left and the BASE (see below) directed superiorly and posteriorly.

Chambers of the heart:

1. The right Atrium 2. the right ventricle 3. the left atrium 4. the left ventricle

SURFACE ANATOMY AND SURFACE PROJECTIONS OF THE HEART:

1. the apex 2. left border 3. superior border 4. right border 5. inferior diaphragmatic border

CHORDAE TENDINEAE (right ventricle)

Attaching the apices of the papillary muscles to the three cusps of the tricuspid valve are small tendinous bands. The papillary muscles of the heart neither open nor close the atrioventricular valves. Contraction of the papillary muscles function to stabilize the cusps of the tricuspid valves (via chordae tendineae) preventing the valve cusps from everting during ventricular contraction thereby insuring complete closure of the tricuspid valve and preventing blood from being forced back into the right atrium. Paralysis of a papillary muscle due to ischemia or rupture of the chordae tendineae results in valvular incompetence, a situation that can lead to severe or fatal cardiac failure.

SInus (right ventricle)

Behind each cusp (i.e., between each cusp and the vessel wall) is a slight dilatation of the vessel wall

Anterior interventtricular sulcus (groove) contains:

Contains: 1) Anterior Interventricular (Descending) Branch of the Left Coronary Artery. 2) Great Cardiac Vein.

2 sounds of the heart:

During each cardiac cycle the heart produces two sounds which are often described as "lubb-dubb". The first heart sound, the "lubb", has a longer duration and a lower frequency than the second heart sound (the "dubb"). The first heart sound is called "S1" and the second heart sound "S2". S1 results from the almost simultaneous closure of the mitral and tricuspid valves (the mitral valve closes first). S2 results from the near-simultaneous closure of the aortic and pulmonary valves (the aortic valves closes first). Consequently, each heart sound possesses two components.

TRICUSPID VALVE sound:

Just to the left of the lower end of the body of the sternum over the left 5th intercostal space (LLSB = lower left sternal border).

PULMONARY VALVE sound:

Over the 2nd intercostal space just to the left of the sternum (2ICS-LSB = second intercostal space, left sternal border).

AORTIC VALVE sound:

Over the 2nd intercostal space just to the right of the sternum (2ICS-RSB = second intercostal space, right sternal border).

BICUSPID VALVE sound:

Over the apex of the heart (i.e., left 5th intercostal space, just medial to the mid- clavicular line). Where the "Lubb" sound of the "lubb - dubb" heart beat is heard.

Sinuatrial Node (SA Node)

Small mass of specialized muscle cells in right atrium at superior end of crista terminalis and to right of SVC • "Pacemaker" - Fastestspontaneousrateof depolarization - Initiatesimpulsesthat spread through the muscle fibers of both atria causing them to contract - Inmostpeople,SAnode gives off impulses » 70times/min(70- 80) [innervation intact] » 100 times/min (without nerve input)

lunula (right ventricle)

The free margin of the cusps on either side of the nodule

the heart

The heart is a muscular pump involved in the movement of blood through the systemic, coronary (actually a part of the systemic circulation), and pulmonary circulations.

CHORDAE TENDINEAE (left ventricle)

The left ventricle has two papillary muscles, an anterior and a posterior attached to the cusps of the bicuspid valve by:

Superficial parts of the Heart.

The surface of the heart is marked by sulci, or grooves, that overlie the internal septae which separate the chambers of the heart:

PAPILLARY MUSCLES (right ventricle)

The trabeculae carneae are continuous with conical muscular projections from the wall of the right ventricle. Three in the right ventricle: 1. anterior papillary muscle 2. posterior papillary muscle 3. septal papillary muscle

Anterior papillary muscle (right ventricle, papillary)

a) Largest of the three papillary muscles. b) Originates off the sternocostal wall.

Posterior papillary muscle (right ventricle, papillary)

a) May consist of several parts. b) Originates off the diaphragmatic wall.

Septal papillary muscle (right ventricle, papillary)

a) Usually small and multiple. b) Originates off the interventricular septum.

Posterior Interventricular sulcus (groove):

a. Continuous with the anterior interventricular sulcus near the apex of the heart.

Atrioventricular (coronary) sulcus (groove)

a. Encircles the heart. b. Indicates the division of the atria from the ventricles. c. As a result of the position of the heart it is oriented almost vertically behind the sternum.

The wall of the heart consists of:

a. Epicardium: the outermost layer - consists of the visceral pericardium. b. Myocardium: the middle layer - composed of cardiac muscle. c. Endocardium: The innermost layer - consists of a layer of endothelium.

INFERIOR (DIAPHRAGMATIC) BORDER

a. Formed almost entirely by the acute margin (Margo Acutis) of the RIGHT VENTRICLE. b. Indicated by a line drawn from the right 6th costal cartilage to the apex.

diaphragmatic (inferior) surface

a. Formed by both ventricles (mainly the left). b. Rests on the diaphragm which separates it from the liver and the stomach. c. The POSTERIOR INTERVENTRICULAR SULCUS (see below) separates the ventricles.

right border of the heart:

a. Formed by the superior vena cava, the RIGHT ATRIUM, and the inferior vena cava. b. Indicated by a line drawn from the right 3rd costal cartilage to the right 6th costal cartilage.

apex of the heart:

a. Formed by the tip of the LEFT VENTRICLE. b. Located in the left 5th intercostal space, just medial to the mid-clavicular line. c. The site is recognized as the position of the "heart beat".

anterior (sternocostal) surface

a. Formed mainly by the right ventricle and the right atrium. b. The ATRIOVENTRICULAR (CORONARY) SULCUS (see below) separates the atria from the ventricles. c. The ANTERIOR INTERVENTRICULAR SULCUS (see below) separates the right ventricle from the left ventricle. d. The left atrium is not visible anteriorly as it forms the base of the heart.

left border of the heart:

a. Formed mostly by the obtuse margin (Margo Obtusus) of the LEFT VENTRICLE. b. Indicated by a line drawn from the apex to the left 2nd costal cartilage. c. On X-ray the left border of the cardiovascular silhouette is formed by the aortic arch, the pulmonary trunk, the left auricle, and the left ventricle.

left atrium

a. Forms most of the base of the heart and lies directly posterior to the right atrium. b. It is the most posterior chamber of the heart. c. Since it is derived primarily from the pulmonary veins, its interior is smooth except for a few MUSCULI PECTINATI in the left auricle. d. It receives the four pulmonary veins (two left, two right or two superior, two inferior). e. The interatrial septum on the left atrial side also demonstrates the remnant of the foramen ovale (may also be called the FOSSA OVALIS).

left ventricle

a. Forms the apex of the heart and most of its left border and diaphragmatic surface. b. The internal structure is similar to the right ventricle in that TRABECULAE CARNEAE and PAPILLARY MUSCLES are present. However, there is no moderator band. c. Its wall is about three times as thick as that of the right ventricle. d. One reason for the thicker walls is that the TRABECULAE CARNEAE are more dense.

Anterior interventtricular sulcus (groove):

a. Marks the location of the interventricular septum anteriorly which separates the right and left ventricles. b. Lies perpendicular to the AV sulcus. c. Extends inferiorly, from just to the right of the apex, superiorly to just slightly to the left of the pulmonary trunk.

superior border of the heart:

a. The location of the great vessels of the heart. b. Formed by both the RIGHT and LEFT ATRIA. c. Indicated by a line drawn from the left 2nd costal cartilage to the right 3rd costal cartilage.

base of the heart (posterior) surface

a. The most superior part, separated from the diaphragmatic surface by the AV SULCUS. b. It is called the base because it is opposite the "apex". c. Formed by the atria (mainly the left). d. The great vessels enter and leave the heart at its base.

SURFACE PROJECTION OF VALVE SOUNDS (I.E., AUSCULATORY AREAS):

because of the auditory carrying capacity of fluids the AUSCULATORY AREAS are located distal to their actual location and are best heard when a stethoscope is placed in the following areas:

nodule (right ventricle)

each cusps possesses a nodule (a fibrocartilaginous thickening of the center of the free margin of each cusp) which come together during closure of the valve to prevent the tendency of the central portions of the cusps to pull away from one another.

AORTIC VALVE (left ventricle)

has three semilunar cusps: a right, left, and posterior. Above the three cusps are dilations called the aortic sinuses (of Valsalva). These sinuses, as with the pulmonary valve, prevent the cusps from sticking to the walls of the vessel. The cusps of the aortic valve also possess nodules and lunulae (see Pulmonary Valve above). The right and left coronary arteries take origin from the right and left aortic sinuses.

LEFT ATRIOVENTRICULAR (BICUSPID/MITRAL) VALVE (left ventricle)

has two cusps: an anterior and a posterior. Both cusps receive chordae tendineae from both papillary muscles.

SA nodes initiate:

impulse • Spreads throughout both atria • Converge on AV Node via three "Internodal Pathways"

SEPTOMARGINAL TRABECULA (MODERATOR BAND) (right ventricle)

is a bridge of myocardium that crosses from the interventricular septum to the base of the ANTERIOR PAPILLARY MUSCLE (see below) and carries the right branch of the ATRIOVENTRICULAR BUNDLE OF HIS (see below).

The RIGHT ATRIOVENTRICULAR (TRICUSPID) VALVE (right ventricle)

is oval and about 4 cm wide (longest diameter) or about 3 fingers width. Composed of 3 fibrous cusps which are thick where they are attached and thin at the free edges. The cusps are attached to a ring composed of dense connective tissue embedded in the myocardium around the orifice. This ring is called the ANNULUS FIBROSUS and makes up part of the fibrous cardiac skeleton. The cusps of the tricuspid valve include an anterior, septal, and posterior cusp.

AORTIC VESTIBULE (left ventricle)

is that portion of the left ventricular cavity just inferior to the aortic valve.

The SULCUS TERMINALIS (right atrium)

is the external landmark separating the sinus venosus from the primitive atrium.

The CONUS ARTERIOSUS (right ventricle)

is the funnel-shaped, smooth-walled, superior part of the right ventricle that gives origin to the pulmonary trunk. Because of its funnel shape, it is also called the infundibulum. It lies directly anterior to the root of the aorta.

Internally the CRISTA TERMINALIS (right atrium)

is the line of separation.

The FOSSA OVALIS (right atrium)

on the interatrial septum is a remnant of the fetal FORAMEN OVALE. The tissue forming the floor of the fossa ovalis is derived from the septum primum. The LIMBUS FOSSAE OVALIS is a muscular ridge around the fossa ovalis (derived from the septum secundum-

SUPRAVENTRICULAR CREST (right ventricle)

prominent ridge of the myocardium. separates the conus from the rest of the right ventricle, which has a trabeculated appearance from the many ridges of myocardium, or TRABECULAE CARNEAE, that line its walls.

The PULMONARY VALVE (right ventricle)

which is at the apex of the conus arteriosus, also has three cusps, which are called semilunar cusps: anterior, right, and left. Behind each cusp (i.e., between each cusp and the vessel wall) is a slight dilatation of the vessel wall called a sinus. These sinuses prevent the cusps from sticking to the wall and failing to close. In addition, each cusps possesses a nodule (a fibrocartilaginous thickening of the center of the free margin of each cusp) which come together during closure of the valve to prevent the tendency of the central portions of the cusps to pull away from one another. The free margin of the cusps on either side of the nodule is called the lunula. The pulmonary valve is also attached to an annulus fibrosus.

AV node divided:

• Divides into right and left bundle branches (crura) which straddle muscular part of interventricular septum. - Right Bundle Branch sends impulses to: » Interventricular septum » Anterior papillary muscle (right ventricle) » Wallofrightventricle (via Purkinje )

THE CARDIAC SKELETON FUNCTION:

• Insures competency of valves - Reinforcement of valve orifices - Provideattachmentfor cusps - Reinforcement of cusps • Insures coordination of myocardial contractions - Provideattachmentsites for cardiac muscle fibers - Insulates the electrical activity of atrial musculature from that of ventricular musculature

Atrioventricular Node (AV Node)

• Slender strand of specialized conducting muscle fibers that arise from AV node and runs anteriorly to membranous part of interventricular septum, lies just inferior to septal cusp of tricuspid valve. • Small mass of specialized muscle cells in right atrium at posteroinferior part of interatrial septum, just superior to opening of coronary sinus • Gives off impulses: - 40 - 60 times/min

CONDUCTING SYSTEM OF THE HEART consists of:

• Specialized muscle tissue that generates and distributes electrical impulses - These electrical impulses stimulate cardiac muscle fibers to contract. - Specialized muscle tissue » ↓Myofibrils ↑Gapjunctions » ↑Glycogen