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                                Anatomy 

Heart
Summary
The heart is a muscular organ located in the middle mediastinum that pumps blood through the circulatory system. The heart is surrounded by the pericardium and is divided into four chambers: two atria and two ventricles. 
The right atrium and ventricle are often referred to as the right heart while the left atrium and ventricle are often referred to as the left heart.
 The atria and ventricles are separated by the atrioventricular valves, while the ventricles and the arterial outflow tracts of the heart (namely the pulmonary trunk and the aorta) are separated by the semilunar valves. The heart wall consists of the endocardium (innermost), the myocardium, and the epicardium. The conduction system of the heart is composed of specialized nodes and pacemaker cells that initiate and coordinate the contraction of the heart.
The right heart receives deoxygenated blood from the systemic circulation and pumps it from the systemic circulation and pumps it
through the pulmonary circulation, where it from the systemic circulation and pumps it through the pulmonary circulation, where it becomes oxygenated. The left heart then receives the oxygenated blood from the pulmonary circulation and pumps it through the blood vessels of the systemic circulation. The coronary arteries, namely the right coronary artery and the left coronary artery, arise in the root of the aorta and supply the myocardium and endocardium. The heart develops embryologically from the heart tube, which undergoes looping and septation to separate it into the four chambers.

Overview
Characteristics
1. Two ventricles and two atria, which connect the pulmonary circulation with the systemic circulation.
2. Four valves, which ensure that blood flow occurs in only one direction
3. Roughly the size of a fist
4. Weighs approx. 300–500 g
5. Surrounded by pericardium (a fibroserous, fluid- filled sac)
6. Location: in the middle mediastinum between the lungs.
7. Anterior to the heart: sternum and rib cartilage
8. Posterior to the heart Vertebral column (T5–T8)
- Esophagus
- Carina and primary bronchi
9. The upper part of the heart is at the level of the third costalcartilage.
10. The site of attachment for the venae cavae, aorta, and pulmonary trunk.
11. The lower part of the heart (cardiac apex) lies left of the sternum at the level between the fourth and fifth ribs.
Function
1. Pumps blood through the body via the circulatory system
2. ANP synthesis.

The left atrium is the posteriormost part of the heart, located directly in front of the esophagus.
It can be visualized using TEE.
 The right ventricle is the anteriormost part of the heart and is at greatest risk of injury following chest trauma.
The cardiac apex beat can typically be palpated to the left of the sternum, medial to the midclavicular line at the 4th–5th intercostal
space. In patients with dextrocardia, the orientation of the heart is inverse so the apex is located to the right of the mediastinum rather
than the left.
Heart chambers





Two atria
Separated by the interatrial septum (The fossa ovalis is visible on the septum as a small oval- shaped depression in the interatrial septum.)
Right atrium
- Receives deoxygenated blood via the superior vena cava (SVC), inferior vena cava (IVC), and the coronary veins.
- Pumps deoxygenated blood into the right ventricle
Right auricle (right atrial appendage):
- Muscular pouch that acts to increase the capacity of the atrium
- Located close to the ascending aorta
- Separated from the atrium by the terminal sulcus
- Located close to the ascending aorta
- Separated from the atrium by the terminal sulcus (sulcus terminalis) and terminal crest (crista \ terminalis).
- Common site for the development of thrombi in patients with atrial fibrillation
Left atrium
- Receives oxygenated blood from the four pulmonary veins
- Pumps oxygenated blood into the left ventricle to enter the systemic circulation
Left auricle (left atrial appendage): 
- Muscular pouch that acts to increase the capacity of the atrium
- Extends from superior aspect of the chamber in close proximity to the root of the pulmonary trunk
- Common site for the development of thrombi in patients with atrial fibrillation
Two ventricles of the heart



Right ventricle
- Receives deoxygenated blood from the right atrium
- Pumps deoxygenated blood into the pulmonary trunk as part of the pulmonary circulation.
- Left ventricle
trunk as part of the pulmonary circulation Left ventricle
- Receives oxygenated blood from the left atrium
- Pumps oxygenated blood into the aorta as part of the systemic circulation
Cardiac borders
Frontal view
Right border is formed by the right atrium
Left border is formed by the left ventricle and left atrial appendage
Inferior border is formed by the right ventricle
Superior border is formed by the atria and great vessels
Lateral view
Anterior border is formed by the right ventricle
Posterior border is formed by the left atrium and left ventricle
The cardiac borders form the cardiac silhouette on chest x-ray!
Normal chest x-ray
Heart valves

Two types of cardiac valves that differ in location and morphology
Cardiac skeleton
Consists of four fibrous rings (annuli fibrosi cordis) that surround the atrioventricular and arterial orifices
Function
- Separates atria and ventricles
- Provides anchor and structural support for the valves
- Provides electrical insulation layer between atria and ventricles
- Closure of heart valves produces heart sounds (See auscultation of the heart in cardiovascular examination for details.)
This mnemonic provides the order in which blood flows through the heart valves: Try PULling My AORTA (Tricuspidal, Pulmonary, Mitral, Aortic)!
Overview of the cardiac skeleton
Atrioventricular valves
Structure: leaflets supported by subvalvular apparatus
Valves.
Tricuspid valve: consists of three leaflets;
located between right atrium and right ventricle.

Mitral valve (bicuspid valve): consists of two
leaflets; located between left atrium and left ventricle
Subvalvular apparatus
Chordae tendineae: fibrous cords that support the AV valves and connect them to the papillary muscles.
Papillary muscles :(two in the left ventricle; three in the right ventricle).
- Derive from the myocardium
- Extend from the anterior and posterior ventricular walls and the septum.
- Have apices that are attached to the chordae tendineae
- Contract during systole and thereby tighten the chordae tendineae: prevent prolapse of valve leaflets and regurgitation into the atria when pressure rises during ventricular contraction.

This mnemonic provides the rule of twos and threes for the atrioventricular valves: The tricuspid valve has three leaflets and is located on the right side, as is the three-lobed right lung.
The bicuspid (mitral) valve has two leaflets and is on the right side, as is the three-lobed right lung.
The bicuspid (mitral) valve has two leaflets and is located on the left side, as is the two-lobed left lung!

Semilunar valves
- Structure: three crescent-shaped cusps without subvalvular apparatus.
Valves
Pulmonary valve: located between right ventricle and pulmonary trunk.
Aortic valve: located between left ventricle and aorta (consists of three leaflets and the aortic sinuses).
Anatomy of the heart and adjacent large vesselsLocalization of heart valvesValve plane of the heart.

          Coronary arteries
The left and right coronary arteries arise from the root of the aorta and supply the heart muscle with arterial blood.
Coronary arterial dominance
- Right-dominant (∼ 85% of the population):
posterior descending artery (PDA) supplied by the RCA
- Left-dominant (∼ 8% of the population): PDA  supplied by the left circumflex artery (LCX)
- Codominant (balanced; ∼ 7% of people): PDA supplied by both RCA and LCX.
Coronary blood flow peaks during early diastole at a point when the pressure differential between the aorta and the ventricle is the greatest (see left ventricular pressure-volume diagram.).

Coronary arteries:
1. Left coronary artery (LCA).
Source : Arises from left aortic sinus of ascending aorta.
Important branches:
a. Left anterior descending artery (LAD): descends between right and left ventricles on anterior surface of heart (in the anterior interventricular sulcus) towards cardiac apex → gives off several
diagonal branches on its course.
b. left cercumflex artery : cources left around the heart in the coronary sulcus towards the posterior aspect, ending before the posterior interventricular sulcus -give off left marginal branch .
   Supply the posterolateral left atrium and ventricle , anteriolateral papillary muscle 1n 40% of the population supply the SA node  , In left dominant and codominant circulation it gives rise to the PDA to supply the posterior .

2. Right coronary artery (RCA):
Source: Arises from right aortic sinus of the ascending aorta
Important branches:
a. Various branches
Supply majority of right atrium and ventricles.
b. Right marginal artery: courses along the diaphragmatic border (acute margin) of the heart.
Supply the tateral right ventricle and cardiac apex.
c. Posterior descending artery (PDA): descends between right and left ventricles on posterior surface of heart (in the posterior interventricular sulcus) towards cardiac apex
- Can also originate from the LCX or LCX and RCA (in left-dominant and codominant circulation).
Supply 
-  posterior ⅓ of the interventricular septum.
- Posteroinferior aspect of heart
- Posteromedial papillary muscle
d. Atrioventricular nodal artery: supply AV node (in a left dominant circulation AV node supply by the LCA). 

c. Sinoatrial nodal artery: supply the SA node.

Important note :
The LAD is the most commonly occluded coronary artery and is often referred to as the “widow maker” due to the high mortality rate associated with LAD infarction.
The RCA usually supplies the heart's conduction system (sinus and AV node) so that stenosis or occlusion of this vessel often leads to cardiac arrhythmias!.

Venous drainage
Coronary sinus
- Largest vein of the heart, into which all other coronary veins drain
- Lies in the left posterior atrioventricular groove
- Drains into the right atrium between the IVC orifice and the right atrioventricular orifice
- Veins draining into coronary sinus (coronary orifice and the right atrioventricular orifice
- Veins draining into coronary sinus (coronary veins):
- Left side of the heart: great cardiac vein and posterior cardiac vein(s)
- Right side of the heart: small cardiac vein and middle cardiac vein

Lymphatics
The lymphatics of the heart drain into the anterior mediastinal nodes and the tracheobronchial nodes.
Innervation :
Somatic nervous system :by the phrenic nerve and it is function that Sensory innervation of the pericardium.
Sympathetic nervous system : By Cardiac plexus
Function :
↑ Heart rate (positive chronotropy)
↑ Contractility (positive inotropy)
↑ Conduction velocity (positive dromotropy)
↑ Contractility (positive inotropy)
↑ Conduction velocity (positive dromotropy)
Coronary artery dilation.

Parasympathetic nervous system: By the vagal nerve.
Function :
↓ Heart rate (negative chronotropy)
↓ Contractility (negative inotropy)
↓ Conduction velocity (negative dromotropy).


Structures of cardiac conduction system


Definition: collection of nodes and specialized conduction cells that initiate and coordinate contraction of the heart muscle.
Components:
Sinoatrial node (SA node): in the upper wall of the right atrium (at the junction where the SVC enters)
Atrioventricular node (AV node): within the AV septum (superior and medial to the opening of the coronary sinus in the right atrium)
Atrioventricular bundle (bundle of His): directly below the cardiac skeleton within the membranous part of the interventricular septum
below the cardiac skeleton within the membranous part of the interventricular septum.
Purkinje fibers (modified myocytes): terminal conducting fibers in the subendocardium
See conducting system of the heart in cardiac
physiology for more details.


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