Anatomy of Heart in a Nutshell

Heart:

Beating starts with 7-10 somites, 2.2 mm in length, at 23 days old.

Pericardium:

Double walled fibroserous sac which surrounds and covers the heart and roots of great vessels.

Serous pericardium is the serous lining layer: 2 layers

• Parietal layer – lines on inside of fibrous pericardium
• Visceral layer – covers outside of heart = epicardium

Fibrous pericardium – CT layer outside of the parietal serous layer, forms bulk of gross pericardial sac, fused to adjacent CT planes.

Outermost = fibrous pericardium parietal layer, deep = serous pericardium parietal layer, then have space (between parietal layer and visceral layer) then deep to space have the serous pericardium visceral layer (called visceral layer epicardium).

Pericardium has sinuses:

• Transverse pericardial sinus = behind the pulmonary trunk and aorta.  To obstruct flow, can put clamp here.
• Oblique pericardial sinus = posterior aspect of heart.

Pericardial cavity has small amount of fluid for lubrication.

Pericardial extent:

• Superiorly: fuses with adventitia of great vessels at level of sternal angle.
• Inferiorly: fuses with fascia of diaphragm
• Laterally: fuses with mediastinal pleura
• Posteriorly: fuses with adventitia of esophagus

• Blood supply:

1. Pericardiacophrenic arteries = from internal thoracic (most important to remember)
2. Musculophrenic
3. Internal thoracic (direct)
4. Esophageal arteries from aorta
5. Bronchial arteries
6. Pericardial

Innervation:

• Phrenic nerves most important
• Vagi nerves
• Sympathetic trunk

Function: Protection, prevents heart from bouncing around during beating.  Holds it in position. Contains 10-15 cc of fluid.  Prevents distension of heart once volume is used up.

If have leak of blood into pericardium: heart won’t be able to expand as needed.  If have fluid in space between 2 layers of pericardium, will restrict heart = called Cardiac Tamponade due to fluid. May put needed under xyphoid and enter pericardiumà drain blood.

Heart wall:

• Epicardium: visceral layer of the pericardium, external covering of heart
• Subepicardim: between epicardium and muscles, contains fat and major vessels to the heart.
• Myocardium: middle muscular layer, oblique fibers, torsion of chambers, major muscle.
• Endocardium: inner lining layer, composed of endothelium backed by thin CT
• Subendocardium: just outside the endocardium, contains tissues of the conducting system. Myocardial infarction starts here.  Absence of oxygen impacts this first.

Heart Base: where major vessels are located, attachment point at top. Base is slightly tilted.

Heart Apex: mainly left ventricle, is the portion that hangs free.The apex (lateral border) generally extends to mid clavicular line. Cardiac enlargement will be clear if it reaches past mid clavicular line (may extend all the way to costal cartilage).

Heart surfaces:

• Diaphragmatic surface = Posterior portion in contact with diaphragm.
• Left pulmonary surface = Obtuse margin
• Right pulmonary surface = Acute margin

Anterior surface: see R ventricle as main chamber from this view.  Coronary Sulcus = where coronary artery sits.  Projections of R and L atrium = auricles, remnants of primative atria.

Ligamentum arteriosum = important from development.

Posterior surface: left atrium in back with pulmonary veins leaving.

Left atrium is hard to visualize: can see auricle from anterior view.  If enlarged, will be able to see auricle much more clearly.

Aortic knuckle (formed in arch) will be enlarged in hypertension.

Septa:

• Interatrial septum, divides R and L atrium.  More superior septum.
• Interventricular septum, divides R and L ventricle. More inferior septum.

Right Atrium:

Crista Terminalis = ridge of muscle in roof of R Atrium.

Musculi pectinati (pectonate muscle) extend away from the crista terminalis.  These two groups are only in R. Atrium.

Fossa Ovalis: opening during development that allows blood to R atrium to shunt into L atrium while there is no pulmonary circulation.  This is closed at birth and seals over time. Begins as foramen ovalisà seals to become fossa ovalis.  The peripheral depression is the limbus of fossa ovalis.

No functioning valve between atrium and inferior vena cava, but still have a valve of inferior vena cava present in R. Atrium.  Adjacent to valve of inferior VC, have valve of coronary sinus.

Tricuspid valve also present:  requires three papillary muscles.

Left Atrium:

• Valve of foramen ovale where foramen ovale closed.
• Also have mitral valve. 2 cusps, requires two papillary muscles.

Right Ventricle:

Spetomarginal trabecula

Conus ateriosus = conical region where blood flows into pulmonary artery. (outflow track) aka infundibulum.

Pulmonary valve present

Trabeculae carnea: similar to crista terminalis, but only present in ventricles.

Left Ventricle:

Has three papillary muscles and attached cordae tendineae to anchor mitral valve.

Heart Valves:

• Between R atrium and R ventricle = Tricuspid valve, 3 cusps. Right AV valve.
• Between L atrium and L ventricle = mitral valve, 2 cusps. Less valuable.  Left AV valve.
• AV valves= have Cordae Tendoneae (attached to fibrous ring)  that attach papillary muscles which hold valve in place during contraction.
• Semilunar valves separate L ventricle and aorta / and right ventricle and Pulmonary trunk.
• Aortic valve closes the aorta and also consists of three semilunar valves / cusps.
• Pulmonary valve: closes the orifice of the pulmonary trunk, which consists of three semillunar valves / cusps.

Semilunar valves do not have associated papillary muscles.

• Left side: has 2 papillary muscles (anterior and posterior) which correspond to each of the two cusps.
• Conus Arteriosus (AKA infundibulum) = separates two valves as blood enters / exits ventricle.
• On aortic side of aortic valve, have opening for coronary artery within cusps.

Heart sounds:

• First sound “lub” = S1, closure of AV valves.
• Dub = S2, closure of semilunar valves
• No sounds associated with valves opening
• Have systole between S1 and S2
• Diastole between S2 and next S1.
• Systole = contraction of heart
• Diastole = relaxation / dilation of the heart.
• When inhale / exhale, can change speed of blood.
• During inspiration, greater separation between 2 sounds of S2 (closure of aortic vs pulmonary valves).

Conducting system:

• Sinuatrial node (SA node) = pacemaker

• • Located along upper end of sulcus terminalis, near the Superior VC
  • Initiates heartbeat
  • Supplied by both sympathetic and parasympathetic nerves

• Atrioventricular node = located in interatrial septum adjacent to osteium of coronary sinus
• Atrioventricular bundle (bundle of His) = extends from the AV node along the IV septum, made up of purkinje fibers.AV bundle: divides into right and left bundle branches in the septum (near the junction of membranous and muscular part of septum)

Circulation of blood:

Left ventricle→oxy blood through aortic valve→aorta→system→ deoxy blood enters via vena cava→into R atrium→through tricuspid valve into R ventricle→through pulmonary valve into pulmonary trunk (veins)→to lungs to oxy→to L atrium via pulmonary arteries→ from left atrium through mitral valve→back to L ventricle.

In Left side: blood entering is almost parallel to blood leaving.  Cusp acts as a curtain to keep blood flow.

If you receive 100 ml into Right atrium→100 will enter R ventricle→ will have 100 eventually in circulation.  Have back up of blood in heart defects.

If Left ventricle fails, will have back up in R atrium and back up in lung. Have pulmonary edema.

If Right ventricle fails, have distended neck veins, lower extremity edema, distended liver.

Skeleton of heart = Fibrous rings which act as conducting system.

• Fibrous CT to which valves and muscle of heart are attached
• Support and rigidity
• Serves as electrical insulator preventing conduction between atria and ventricles.

Myocardial architecture: spiral fibers allow most efficient means of contraction.

Coronary arteries:

1. Right coronary artery = in sulcus, originates from aorta, goes to back of heart giving off several branches.
2. Left coronary artery = starts as stem from aorta and bifurcates into a. circumflex branch and b. anterior interventricular branch.

If heart is Right dominant = right coronary artery gives posterior interventricular branch. Most people (80%) are right dominant.  20% have posterior interventricular branch given by left coronary artery.

Left dominant: posterior part of heart supplied by circumflex.

During diastole, blood passes into coronary artery as relaxation would try to backflow blood into ventricle.

Cardiac veins: Very superficial, may be removed with fat.

Coronary sinus = dilation in coronary sulcus in back of heart.  All veins of heart drain into coronary sinus.  Receives blood from:

1. Great cardiac vein→ directly into coronary sinus.  Starts as anterior interventricular vein.  Is in the front of the heart, runs along circumflex and LAD.
2. Small cardiac vein coming from atrium
3. Middle cardiac vein is in the back

Nerve supply:

Vagus nerve gives off deep cardio plexus: 2 parts- sympathetic (speed up heart) and parasympathetic (slow down heart).  In between, find cardiac ganglia in surface of atrium, serves as relay system.  Very close to SA node.

Referred pain: sensory nerves in heart are from same nerve as some portions of skin. Pain location depends on which fibers are in crisis. When women have heart attack, pain is like stomachache.  Men- pain is from left arm.

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