Heart – External and Internal Features

Heart

Learning Objectives:

After reading this post you will know the:

  • Location and average dimensions of heart.
  • External features of heart.
  • Internal features of heart.
  • Structures opening into right atrium.
  • Right ventricle and right artioventricular valve.
  • Differences between right and left ventricle.
  • Applied aspect of heart – tetrology of Fallot, Dextrocardia.

 Heart – External Features 

Q. Describe heart under the following headings:

  1. Location
  2. Dimensions and weight
  3. External features

A  1.  Locationlocation of heart in middle mediastinum
         Heart lies in the middle mediastinum. 1/3rd of the heart lies to the right and 2/3rd to the left  of the midline. It lies opposite to T5- T8 vertebrae in supine position &  T6 –  T9 vertebrae in erect position.

2. DimensionsBase to apex-12cm;      Transversely– 8-9cm;      Anteroposteriorly– 6cm

     Weight: Males : 280-340 gm, Females : 230-280 gm

3. External features:The heart has:

  • An apex:
    • It is formed by the left ventricle.
    •  It lies in the fifth intercostal space 9cms. from the median plane.sternocostal surface and borders of heart
  • Three surfaces
    • Sternocostal: Is formed by right atrium, right ventricle, left auricle and left ventricle.
    • Left surface: Is formed by left auricle and left ventricle.
    • Diaphragmatic:  2/3rd is formed by  left ventricle and 1/3rd by right ventricle.
    • Posterior surface /Base: It is quadrilateral in shape.
      • 2/3rd   of base is formed by posterior surface of left atrium and 1/3rd by right atrium.
      •  It lies opposite to T5-T8 vertebra in supine position.

 

posterior and diaphragmatic surface of heart

  • Four borders
    • Superior: is formed by the two atria.
    • Inferior: Right atrium
    • Right: Mainly by right ventricle and near the apex by left ventricle.
    • Left: Is formed by left auricle and left ventricle.
  • Five sulci:
    • Atrioventricular sulcus (coronary sulcus): separates atria from ventricles.
    • Anterior interventricular sulcus: separates right and left ventricles on the sternocostal surface.
    • Posterior interventricular sulcus: separates right and left ventricles on the diaphragmatic surface.
    • Interatrial sulcus: Separates right atrium from the left atrium .
    • Sulcus terminalis: extends from the opening of  superior vena cava  to inferior vena cava and separates the rough part from the smooth part of the right atrium.

 

                 Apex beat: Is the lowermost and outermost thrust of the heart felt on the front of the chest.
                                    In adults it is felt in the left 5th intercostal space 9cm. from the median plane (just medial to the midclavicular line).
                                    In infants it is felt in the  3rd intercostal space just lateral to the midclavicular line.

 

Q. Enumerate the:

  1. Chambers of the heart
  2. Posterior relations of base of heart

A. Heart consists of four chambers

  • Right atrium : Receives the impure blood from the body and the heart itself.
  • Right ventricle: Receives the impure blood from the right atrium and outflows the blood into the pulmonary circulation through the pulmonary trunk.
  • Left atrium : Receives oxygenated blood from the lungs via pulmonary veins.
  • Left ventricle : Receives oxygenated blood from the left atrium and outflow the blood into the systemic circulation via aorta. 

chambers of heart

   Posterior relations of the Base of heart 

  • Oblique sinus of pericardial cavity
  • Right pulmonary veins
  • Oesophagus
  • Descending thoracic aorta
  • Middle four thoracic vertebrae

 Heart –  Right Atrium

Q3. Draw  labeled diagram to show the internal features of the right atrium.

Ans. Internal features of right atrium

internal features of right atrium

 

Q. Describe briefly fossa ovalis.

Ans. 1. Fossa ovalis

  • It is a shallow oval depression in the lower part of the interatrial sepyum.
  • It marks the site of the foramen ovale, an opening in the interatrial septum of the fetal heart
  • It represents septum primum
  • Limbus fossa ovalis ( free edge of septum secundum) forms the margins of fossa ovalis except inferiorly.

Q. Enumerate the veins opening into the right atrium.

A. Veins opening into the right atrium:

  1. Superior vena cava
  2. Inferior vena cava
  3. Coronary sinus
  4. Anterior cardiac veins
  5. Venae cordis minimae ( Thebesian veins)

Heart – Right Ventricle

 Q. Describe briefly the right atrioventricular orifice and tricuspid valve complex.

     Right atrioventricular orificeRight ventricle and tricuspid valve

  • Is the opening between right atrium and ventricle.
  • Is elliptical in shape and about 3cm wide.
  • Is guarded by tricuspid valve.

    Tricuspid valve complex

  • It guards the right atrioventricular orifice.
  • The complex includes:
    1. Tricuspid annulus ( a collagenous ring to which the bases of cusps are attached)
    2. Three cusps :anterior, posterior and septal.
    3. Chordae tendinae: Endothelial covered collagenous threads that connect the apical 1/3rd of the papillary muscles to the free margins and ventricular surface of the tricuspid valve complex.
    4. Papillary muscles: are conical shaped muscles , their base is attached to the walls of the ventricles and apex provide attachment  to chordate tendinae. Right ventricle has three papillary muscles:
      • Anterior
      • Posterior
      • Septal

 

Q. What is moderator band or septomarginal trabecula?

Ans.  Moderator band/Septomarginal trabecula

  • It is a specialized trabecula in the right ventricle that extends from the right side of the ventricular septum to the base of the anterior papillary muscle.
  • It carries the right branch of bundle of His.
  • It ensures the closure of right atrioventricular orifice before the systole so that there is no regurgitation of blood into the right atrium
  • It prevents over distension of right ventricle.

Heart – Differences Between Right and Left Ventricle

Q. Enumerate the differences between the right and left ventricle.

Right VentricleLeft ventricle
The walls are thinnerThe walls are 3 times thicker
In TS – the cavity is cresenteric shapeIn TS – the cavity is oval shaped
Trabeulae carneae are coarse and fewTrabeulae carneae are fine and numerous
Has three papillary musclesHas 2 papillary muscles
Chordae tendinae are few and shortChordae tindinae ar more and long
Atrioventricular orifice is guarded by tricuspid valveAtrioventricular orifice is guarded by bicuspid valve
Inlet and outlet lie at obtuse anglesInlet and outlet lie at acute angle

left and right atrium

 

Heart – Applied Aspect

Q. Give anatomical basis of :

a. Fallot’s tetrology
b. Dextrocardia

A. a. Fallot’s tetrology: Is a congenital heart anomaly which involves four anatomical abnormalities.Tetrology of Fallot
It is the most common cyanotic defect, and the most common cause of blue baby syndrome. The aorta and pulmonary artery  develop from the truncus arteriosus which is divided by a spiral septum. The spiral septum separates the aorta and pulmonary artery and it grows down and attaches to the ventricular septum. However, if the spiral septum deviates towards the right side, following will happen:

  • opening to the pulmonary would be small
  • opening to the aorta would be large
  • spiral septum would  not come in contact with the  the ventricular septum

As a result the following four defects will be present:

• Pulmonary stenosis
• Overriding aorta over the ventricular septal defect
• Ventricular septal defect
• Right ventricular hypertrophy

Right ventricular hypertrophy is a compensatory result  due to  pulmonary stenosis. As right ventricle has to work extra hard to pump blood into the pulmonary trunk, therefore it is hypertrophied

 

b. Dextrocardia Dextrocardia

it is a congenital anomaly in which the heart lies on the right
side of the thoracic cavity. This may be associated with the
reversal of all the abdominal organs , a clinical
condition known as situs inversus.

 

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