Heart Anatomy

The heart measures approximately:

• 12 cm long

• 9 cm wide

• 6 cm thick

• about the size of your fist

• “cone” shaped

The heart lies:

• in the middle of the thoracic cavity

  • “middle mediastinum”

• posterior to the sternum

  • slightly to the left of center

• just superior to the diaphragm

• medial to the lungs

The heart lies anterior to the:

• trachea

• esophagus

• descending Aorta

• vertebral column

The base of the heart:

• “top” of the heart

• at 2nd intercostal space

The apex of the heart:

• “bottom” of heart

• points to the left

• formed predominately by LV

  • RV helps contribute

• “apical pulse”

  • detected on some pt’s

  • located at 5th intercostal space

Surfaces of the Heart

• Anterior / Frontal / Sternocostal

• Inferior / Diaphragmatic

• Left / Posterior

Anterior / Frontal / Sternocostal surface of the Heart

Made of RV

Inferior / Diaphragmatic surface

• Made of:

  • LV

  • 1/3 of RV

    • as if looking up from below

Left / Posterior surface of Heart

Made of LV free wall

The Pericardium

• double-layered, membranous, protective sac

• Layers:

  • Serous/Visceral/Epicardium

  • Parietal

Serous/Visceral/Epicardium layer

• inner layer of pericardium

  • actual outer layer of heart wall

• does “pericardial reflection”

Parietal layer

• outer layer of pericardium

• fibrous, tough

Pericardial space

• a “potential” space

  • between the 2 layers of pericardium

• serous layer secretes fluid

  • lubricates to protect against friction

  • 20 cc’s is a normal amount

• helps heart respond to pressure changes

Layers of Heart Wall:

1. Epicardium

2. Myocardium

3. Endocardium

Epicardium AKA:

• visceral pericardium

• serous pericardium

Epicardium

Outermost, thin layer of heart

Myocardium

• heart muscle

• thickest layer

• contains:

  • cardiac muscle fibers

    • cause heart contraction

  • conductive system

  • receives blood supply for contraction

Endocardium

• innermost layer

• smooth layer of CT (endothelial cells)

  • lines chamber of heart

  • covers valves

  • continuous with innermost layer of large blood vessels

    • synonymous w/ Tunica Intima

      • same protective properties

Heart chambers:

• 2 Atria

• 2 Ventricles

2 Atria

• receiving chambers

  • RA receives blood from systemic circulation
    LA receives blood from pulmonary circulation

• upper chambers

• thin walled

• low pressure

• fill during ventricular systole

What separates the right and left atria?

Interatrial septum (IAS) → consists of myocardium

2 Ventricles

• lower chambers

• receive blood from atria

• pumping chambers

• high pressure

• separated by interventricular septum (IVS)

  • consists of myocardium

• fill during diastole

Atrioventricular (AV) Valves

• separates atrium from ventricle

  • Tricuspid (TV)

    • right heart

  • Mitral (MV)

    • left heart

• prevents back flow of blood into atria during systole

• attached to fibrous connective tissue strands

  • Chordae tendineae

Chordae tendineae

• extend from A-V valves to projections of myocardium found on vent wall

  • Papillary M’s

Semilunar (SL) Valves

• separates ventricle from corresponding great artery

  • Pulmonic (PV)

    • right heart

  • Aortic (AoV)

    • left heart

• prevents back flow from of blood into ventricle during diastole

Order of Blood Flow through the Heart:

1. Right Atrium

2. Tricuspid valve (TV)

3. Right Ventricle (RV)

4. Pulmonic Valve (PV)

5. Lungs

6. Pulmonary V’s

7. Left Atrium (LA)

8. Left Ventricle (LV)

9. Aortic valve (AoV)

10. Aortic Root

Right atrium (RA) receives unoxygenated blood from:

• SVC

• IVC

• Coronary sinus

  • receives blood from intracardiac circulation

Right Ventricle (RV)

• ejects blood through Right Ventricular Outflow Tract (RVOT)

  • RVOT aka: infundibulum

Pulmonic Valve (PV)

• Open to Main Pulmonary A (MPA)

  • bifurcates into L and R pulm A’s

    • only A’s in the body to contain unO₂ blood

Lungs

exchange of O₂ and CO₂ occurs at capillary level

Pulmonary Veins

• oxygenated blood returned to the heart via 4 pulm V’s

• only veins in the body to carry O₂ blood

Left Ventricle (LV)

• highest pressure chamber

• 3x thicker than RV

• ejects blood through Left Ventricular Outflow Tract (LVOT)

  • area 1 cm before AoV

Aortic Root (Sinus of Valsalva)

• dilated area

• Coronary A’s originate here

  • first branch of Asc Ao

    • LMCA and RCA

Cardiac Cycle

• changes in pressure cause blood to flow from chamber to chamber

  • cause valves to open and close

• pressure change in response to contraction and relaxation

  • Systole

  • Diastole

Systole

• contraction and emptying phase

• pressure increases

Diastole

• relaxation and filling phase

• pressure decrease

Cardiac Cycle using ventricular phase as reference:

• LV fills during diastole

  • atria squeeze and empty

  • AV valves open / SL valves close

• LV empties during systole

  • atria relax and receive blood

  • AV valves closed / SL valves open

• CA’s fill during diastolic portion of cycle

Atrial Kick

• during diastole, about 2/3 of the atrial blood flows passively from the atria into the ventricles

• w/ atrial contraction, atrial blood is actively pushed from the atria from ventricles

• after A-kick

  • LV phase is called end diastole (LVED)

End Diastole (LVED)

• end stage of relaxation and filling of LV

  • maximal dimension of LV is reached

The Coronary Arteries

• sit like a “crown” on the heart

• feed the heart muscle itself

  • part of intracardiac circulation

• first branch of Asc Ao

  • Coronary A’s originate at Sinus of Valsalva

    • dilated portion called Aortic Root

RCA and Branches:

1. Posterior Descending

2. Right Marginal (A-V nodal)

   • portion of Myocardium supplied:

     • RA

     • RV

     • inferior walls of LV

     • upper 1/3 of IVS

       • basal septum

RCA and branches supply these portions of Conduction system:

• AV node

  • 90% of pop

• SA node

  • 55% of pop

• prx potion of bundle of HIS

• posterior division of Lt bundle branch (LBB)

LMCA and Branches

1. Anterior Descending (LAD)

2. Circumflex (LCX)

   • Each artery supplies:

     • LAD

       • ant surface of LV

       • portion of RV

       • lower 2/3 of IVS

         • mid and apical septum

     • LCX

       • LA

       • lateral wall of LV

LMCA and branches supply these portions of the conduction system:

• AV node

  • 10% of pop

• SA nod

  • 45% of pop

• all bundle branches

Coronary Sinus

• part of the intracardiac circulation

• (unO₂) Venous blood from the heart drains into the Coronary sinus

  • then returns to the RA

• enters posteriorly

  • near floor of RA

The following drain into the Coronary sinus:

• Great Cardiac Vein

  • drains LAD and LCX

• Middle Cardiac Vein

  • drains posterior descending CA (RCA)

• Small Cardiac Vein

• Thebesian Veins

  • any of the smallest cardiac veins