Heart Anatomy: Chambers, Surfaces & Features

Heart - Overview

• The heart serves as a pump circulating blood to big vessels, it's a hollow and muscular organ
• The heart position puts it in the middle mediastinum inside the pericardium
• Two-thirds of the heart lie to the left of the median plane and one-third to the right
• Weighing approximately 250-300 grams, the heart is slightly larger than a closed fist on average
• Percussion and echocardiography are used to assess living heart dimensions
• The heart contains a total of four chambers: there are two atria situated on the left and right, and two ventricles found on the left and right
• The shape of the heart can be described as conical

Surface Anatomy

• Base (posterior surface) exists
• Apex exists
• The axis runs from the base to the apex and is directed downwards, forwards, and to the left
• There exist two: sternocostal (or anterior) and diaphragmatic (or inferior)
• There exist four, including the superior, inferior, right, and left

External Features - Base

• The posterior surface of the heart forms the base.
• The base faces backward and to the right
• Atria mostly form the base, specifically the left atrium
• The upper border has the right and left pulmonary arteries running along it
• The lower border has the coronary sulcus, containing the coronary sinus and circumflex artery
• The superior end has the SVC and inferior end has the IVC which enter the right atrium
• The middle four thoracic vertebrae (5th to 8th) are related and separation occurs via:
• The oblique sinus of the serous pericardium
• Fibrous pericardium posterior wall
• The 2 left & right pulmonary veins which enter at the left & right sides of the left atrium
• The oblique vein of the left atrium to open into coronary sinus
• The descending thoracic aorta, esophagus, azygos vein, and thoracic duct (posterior mediastinum structures)

External Features - Apex

• Lowermost and leftmost point of the heart
• Directed downwards, forwards, and to the left
• The left ventricle exclusively forms the apex
• Sits in the left 5th intercostal space, situated medially to the midclavicular line, approximately 3½ inches (9 cm) from the median plane
• The left lung and pleura are its relations

Surfaces

• The sternocostal (anterior) surface is convex and bounded by the 4 borders of the heart
• The right ventricle primarily forms the sternocostal (anterior) surface
• Each surface includes coronary (A-V) sulcus division into an atrial portion and a ventricular section
• The right atrium & its auricle and the left auricle form the atrial part
• The ventricular part includes the right ventricle (right 2/3) and the left ventricle (left 1/3)
• Anterior thoracic wall shows the sternum and 2nd-6th costal cartilages
• The borders of the two pleurae and lungs split it from the anterior thoracic wall, save for the cardiac notch region
• Anterior mediastinum contents exist
• Pericardium exists
• Diaphragmatic (inferior) surface: rests on the diaphragm's central tendon and is limited posteriorly by the coronary sulcus
• Its left two-thirds are made up of the left ventricle, and its right one-third includes the right ventricle
• Two ventricles are separated by the inferior interventricular groove
• Base of pericardium, central tendon of the diaphragm separate it from the left lobe of the liver and fundus of the stomach

Borders - Upper

• The atrial part mainly forms this section through the left atrium
• It is hidden anteriorly by the ascending aorta and pulmonary trunk roots
• The right and left pulmonary arteries run on it

Borders - Lower

• The right ventricle primarily forms this including a small part near the left ventricle's apex,
• It extends from the IVC opening into the right atrium to the apex of the heart

Borders - Left

• Slightly convex, it's formed mainly via the left ventricle and in smaller measure via its upper smaller part to the auricle
• It relates to the pericardium, left phrenic nerve and pericardiaco-phrenic separates it from the left lung and pleura

Borders - Right

• This is slightly convex and the right atrium is its only component
• SVC extends above and IVC opening lies below
• This related to the pericardium, right phrenic nerve, and pericardiaco-phrenic that separate it from the right lung and pleura

Grooves or Sulci - Atrio-ventricular (Coronary Groove)

• Separates the two atria and two ventricles by a circle around the heart

Grooves or Sulci - Interventricular Grooves

• Divides ventricles into anterior and inferior surfaces

Chambers of the Heart - Atria

• Atrial wall thickness averages 3 mm
• The interatrial septum separates the two atria
• Each atrium includes a projecting auricle

Chambers of the Heart - Right Atrium

• Receives non-oxygenated blood from body via S.V.C., I.V.C. & Coronary Sinus
• Includes a tricuspid valve that includes 3 cusps in order to admit 3 fingers which leads toward the right ventricle
• Sits anterior and to the right relative to the left atrium
• Forms the right border of the heart & part of the anterior surface and base
• Relations:
• Anteriorly and on the right: right lung, pleura, pericardium, right phrenic nerve & pericardio-phrenic artery
• Posteriorly: left atrium and 2 right pulmonary veins
• Left side: related to the ascending aorta and pulmonary trunk
• Overlaps the of ascending aorta

Chambers of the Heart - Left Atrium

• Receives oxygenated blood through 4 pulmonary veins
• Has a mitral valve which contains 2 cusps while admitting 2 fingers to lead towards the left ventricle
• Sits posterior and tot he left side of thr right atrium
• Forms a main part of upper border and base
• Relations:
• Anteriorly: Transverse sinus of pericardium separates left atrium from the ascending aorta and Pulmonary trunk
• Posteriorly: Oblique sinus of the pericardium separates the left atrium from the posterior mediastinum components
• Occupies left aspect ot pulmonary trunk during overlap

Septal Wall

• The interatrial septum is smooth
• The fossa ovalis lies in the inferior septum above the orifice of IVC
• The fossa ovalis: Remains of the foramen ovale of the embryo
• The annulus ovalis forms margins of the fossa ovalis and the border of the septum

Orifices

• The S.V.C. orifice in the superior posterior wall is free of valves
• The I.V.C. includes valve in the inferior part of the posterior wall to direct blood flow toward foramen ovale and the left atrium
• The coronary sinus orifice on the left side contains a valve to guard it between it and the tricuspid valve

Chambers of the Heart - Ventricles

• Divided by the interventricular septum marked anteriorly/inferiorly
• The interventricular septum includes convex anterior (right) portions and concave posterior (left) portions

Interventricular Septum - Parts

• Membranous section: Thin, serves the upper/posterior septum for separating L/R ventricles and the right atrium
• Muscular section: Separates ventricles for the thick, larger lower

Ventricles Differences - Right Ventricle

• Positioned anterior and to the right of the left ventricle
• It has 3 walls: anterior, inferior, and left (septal)
• Anterior walls form the sterno-costal surface and inferior walls forms the diaphgramatic
• Convext left sepal walls curve to a cavity creating a cresent outline in section
• Forms lower part of border, not including apex

Ventricles Differences - Left Ventricle

• Positioned posterior and to the left of the right ventricle
• It has 3 walls: anterior, inferior, and right (septal)
• Inferior: 2/3 of diaphragmatic surface and Anterior: sterno-costal surface
• Concave right septal towards cavity with circular cross- section
• Forms most of left border (except apex) and some lower border

Ventricles Thickness

• RV: 9mm
• LV: 27mm (3x thicker)

Right Ventricle - Features

• Inflow (rough lower portion) includes:
• Trabeculae carnae (thick and muscular ridges) which are few and coarse
• Moderator band (Septomarginal trabecula): prevents overdistension, and transmits the heart branch
• Papillary muscles include those which are connect to apex via tendinae and surfaces
  • 3 papillary muscles: -a-Anterior attaches from the anterior walls -b- Posterior attaches to inferior wall -c-Septal muscles and rises from an irregular septum -Small

Left Ventricle- Features

• Absent: Multiple and fine trabeculae carnae
• Only 2 papillary tendinae from anterios and posterior which are cordae and surfaces are large

Right Ventricle - Orifices

• Tricuspid guards it on the right AV
• Pulmonary guards it

Left Ventricle - Orifices

• Mitral guards it
• Aortic guards it

Fibrous Skeleton

• The fibrous framework is made up of dense collagenous bundles surrounding the heart orifices
• Components include right and left atrioventricular rings which contain a right ring (larger / weaker) and and make 8 shaped cusps to attach
• Fibrous rings exist near Pulmonary and aoritc orificies and attach them Right and left fibrous trigones: Includes right (large) and left (small) masses of tissue

Function of Fibrous Skeleton

• Attachement of myocardial fibers/cusps
• Prevents heart deformation while acting as electric insulator between atria/ventricles

Conducting System

• Coordinates contractions (electric rhythmic cardiac impulses )
• The system is formed of specialized cardiac muscle fibers
• Includes the sino-atrial (pacemaker / crescent 10-20 / autonomic) and atrio-ventricular
• Passes to ventricles with Atrio and muscular is only connection to transmit
• It passes to membranes and reaches septums through endos to spread
• The right travels septums deep and has moderators towards fibers
• Left travels as septum while faces cavity towards apex

How Ventricles Contract

• Below upwards

Arterial Blood Supply

• Coronary arteries supply the heart in sulci similar to a crown

Right Coronary Artery Points

• Runs in sinus to give marginal, turns, then anastomes to branch
• Branch has veins to border heart and makes supply toward ventricle
• Inferior ends in groove along side veins ends left where it creates septum

Right Coronary Small Branches

• Right atrium/ventricle, SA, and AV nodes

Left Coronar Small Branchess

• Branch to aterior septum supplies atrium and ventricles

Coronary Differences

• Left artery supply the right artery structures and atrium has only 1 branch instead of both
• Anastomoses are few when arteries exists - blockage is high

Clinical Anatomy Notes

• Anastomoses between R/L coronary arteries exists(atheletes get here), but are commonly poor • Occlussion: sudden lack of blood causing myocardial infraction Left heart side imaging requires catheters diagnostic via arteries

Venous Flow

• Involves a valve controlled Sinus (3cm / short ) of short veins within
• Receives heart wall + atrium+ventricles via branches
• The cardiac ends middle near apex and and passes close towards atrium to follow to the left atends of sinus (receives veins), it is here receives its parts the vein
• Finally the small ones runs across borders towards right

Venae Cordis Minimae

• Exist and open within atrium sides

Pericardium

• Fibro-serous sac surrounding heart containing base that attached the trunk, while apex points up connecting veins
• Is within medium extending 2nd up to 6th cartilage with posterior connecting 5th-8th vertebrae

Components

• Includes fibrous exterior and interior sac/membrane, where inner has seruous liquid to fill it

Fibrous pericardium

• Formed tough, inelastic, strong tissue to create the boundaries
• It involves 4 surface shapes that are conincal with base is faces diaphragm and its side, and the apex to superior trunks

Layers of Pericadium

• Parietal: the inner fibrous part that is serous toward side and heart as they meet root of vessels, making part known as the epicardium
• Visceral: This also has potential space/cavity towards the sides and lungs. which acts to make the oblique sinus of left part

Features

• Anteriorly, ligaments support sides where 2/pulmo and nerve seperate
• The heart and the two extension tubes create 2 sinuses: one anterior and psterior, with each surrounding the ends, vessels, and interior layers

Sinuses Reaching Points

• Reaching points includes the aorta and the trunks
• Each are transverse pathways connecting each side A finger acts can traverse the transverse path around veins

Layers Boundaries Points

• Oblique (serous with parietal touching sinus) makes blind receess
• Anterior lies to the heart
• Posterior lies towards structures
• Top sealed from visceral layers
• Inferior runs into to lung tissue
• Can be reached in space between the lungs

Pericadium Arteries and Nerves

• Artery is from internal area towards aortas
• The veins involves are azygos
• Nervy is the heart that controls all
• Visceral is similar with 3,5, somatic sensation near lungs (functions towards movement of esophagus near trunk by moving sinus and movement

Diseases

• Inflammation, fluid buildup due to issues or injury towards percardium with the ability affect sounds, tamponade or blood

Surgical Significance

• Catheter is useful for open procedures where lungs support fixity