Anatomy of the Heart

note: Visualization is key in understanding anatomy. Please use an 3D anatomy atlas on your browser or buy one in the play/applestore. I will not add pictures because you have to look at pictures/atlas next to this text. It is much handier!

location

  • within the middle ^^mediastinum^^

= middle cavity of thorax; contains heart, pericardium, vessels to & from the heart & lungs, trachea & oesophagus

  • heart extends obliquely from ^^2nd rib to the 5th intercostal space^^

  • anterior to vertebrae, post to sternum

  • flanked by 2 lungs

  • rests on diaphragm

  • 2/3 of its mass lies to the LHS of the midsternal line

pericardium

= covering of the heart; double-walled sac; contains a film of lubricating serous fluid

2 layers

  • ==fibrous pericardium:==
  1. dense CT (connective tissue)
  2. protects and anchors heart to the surrounding
  3. prevents overfilling of heart: during fluid build-up in pericardial cavity. it inhibits effective pumping (cardiac tamponade)
  • ==serous pericardium:==

= one continuous sheet with 2 layers

  • ==parietal layer:== lines the internal surface of the fibrous pericardium
  • ==visceral layer/ Epicardium:== lines the external heart surface

layers of heart wall

  1. epicranium: visceral layer of serous pericardium
  2. myocardium: contracting heart muscle
  3. endocranium: lines heart chambers, prevents blood clotting within heart, barrier btw 02 hungry myocardium and blood (coronary system)

Connective Tissue

1 forms a network of connective tissue fibres (collagen&elastin) within the myocardium

2 anchors cardiac muscle fibers

3 reinforces the myocardium

2 parts: septum + rings

septum:

flat sheets separating atriums, ventricles and L&R heart sides

electrically isolates L&R heart sides; CT = non-conductive → important for cardiac cycle

(interatrial septum/ atrioventricular septum/interventricular system)

==rings:==

rings around great vessel enterances and valves

stop stretching under pressure

Chambers and associated great vessels

2 atrias superior

  • thin walled receiving chambers
  • on the back and superior aspect of heart
  • each have a small, protruding appendage called Auricles: increase atrial volume
  • septal area: CT dividing L&R atria → site of Foetal Shunt Foramen ovale

Right atrium:

smooth internal %%post%%. wall - veins drain into it

ridged internal %%ant%%. wall - due to msc bundles called Pectinate mscs

blood enters via 3 veins: sup & inf vena cava + coronary sinus (collects blood draining myocardium)

Left atrium

smooth internal post&ant wall

blood enters via 4 pulmonary veins (O2 blood)

2 ventricles inferior

  • thick, muscular discharging chambers
  • pump of the heart
  • crossbars of flesh line the internal walls: papillary muscles; play a role in valve function

Right Venticle

most of heart´s ant surface

thinner → responsible for pulmnary circulation

blood leaves ventricle via pulmonary trunk

Left Ventricle

thicker: responsible for systemic circulation

blood leaves ventricle via Aorta

Landmarks of Heart

  1. coronary sulcus, atrioventricular groove
    • encircles junction btw atria and ventricles like a crown → corona
    • origin of coronary arteries (R&L), coronary sinus & great cardiac vein
  2. ant interventricular sulcus
    • origin of ant interventricular artery
    • separates R&L ventricles anteriorly
    • continues as post interventr sulcus
  3. post interventricular sulcus
    • continuation of ant interventr sulcus
    • separates the R&L ventricles posteriorly

Pathway of blood through the heart

  • R side of heart pumps blood through the pulmonary circulation (to lungs & back to the L side of heart)

  • blood flowing through pulm. circuit: gains 02 and loses C02 → color change blue-red

  • L side of heart pumps blood to all body tissues and back to the R heart

  • via systemic circuit: loses 02 and picks up CO2 → color change red-blue

Coronary circulation

  • myocardium´s own blood supply
  • shortest circulation in the body
  • arteries lie in epicranium, prevents contractions inhibiting bloodflow

Arterial supply: encircle heart in coronary sulcus

  • Aorta: L&R coronary arteries

  • Left coronary arteries has 2 branches

    1. ant interventricular art, LAD left ant descending artery
    • follows ant interventricular sulcus
    • supplies blood to interventr septum & ant walls of both ventricles
    1. circumflex artery
    • follows coronary sulcus aka AV groove
    • supplies LA and post walls of LV

  • Right coronary artery has 2 branches (T-junction):

    1. marginal artery serves the myocardium lateral RHS of the heart
    2. post interventricular art: supplies post ventricular walls; anastomoses w ant interventr art

Venous supply: collected by cardiac veins

1 great cardiac vein in ant interV sulcus

2 middle cardiac vein in post interV sulcus

3 small cardiac vein along R inf margin which empties into RA

Heart Valves

function: ensure uni-directional bloodflow through heart

2x atrioventricular (AV, cuspid) valves;

  • located at the 2 AV junctions
  • prevents backflow into atria during contractions of Ventricles
  • attached to each valve flap are chordae tendinae = tendonous cords “heart strings”
    • anchor cusps to papillary muscles protruding from ventricular walls
    • papillary mscs contract before the V to take up the slack in the chordaw tendinae
    • prevent inversion of vales under ventr contraction
  • Right AV Valve: tricuspid valve, 3 flexible cusps (flasps of endocardium + CT)
  • Left AV Valve: Mitral/ bicuspid valve

2x semilunar Valves (SL)

  • guard the bases of the lage arteries issuing from the ventricles

  • each consists of 3 pocket-like cusps resembling a crescent moon (semilunar=half moon)

  • open under ventricular pressure

  • pulmonary valve: brtw R ventricle and pulmonary trunk

  • aortic valve: btw L ventricle and aorta

valve sound:

  1. lub: sound of a cuspid valve closing
  2. dupp: sound of a semilunar valve closing

where to listen:

  • sound of aortic semilunar valve are heard in 2nd intercostal space at the R sternal margin
  • sounds of pulmonary semilunar valve areheard in 2nd intercostal space at L sternal margin
  • sounds of mitral valve are heard over heart apex, in 5th intercostal space, in line with middle of clavicle
  • sounds of tricuspid valve are typically heard in R sternal margin of 5th intercostal space

Relations

  • R+L phrenic nerves (C3,4,5) pass anterior to lung root
  • R+L vagus (x) pass posterior to lung root