Heart and its structure

  • Human heart is a roughly triangular structure and a muscular organ.
  • It is situated in the thoracic cavity between the two lungs.
  • One third of its part lies on the right side and two third on the left side.
  • An average human heart weighs about 300-350 grams which is about 12 cm long and 9 cm broad.
  • It is enclosed in a strong double walled membrane called pericardium.
  • The pericardium is filled with pericardial fluid that protects the heart from any shock.
  • The heart is composed mainly of the cardiac muscle.
  • Cardiac muscle is a specialized tissue that contracts automatically, powerfully and without fatigue throughout our lives.

Structure of heart

  • The human heart is four chambered structure with two auricles and two ventricles.
  • The two upper chambers are called left auricle and right auricle (atria) and the two lower chambers are called left and right ventricles.
  • A distinct transverse groove divides the heart into an anterior smaller auricular part and a posterior larger ventricular part.
  • This groove is known as the auriculo-ventricular groove or coronary sulcus.
  • The right side of the heart is completely separated from the left by septum, so there is no mixing of impure and pure blood in the heart.
  • The thickness of the walls in the different heart chambers reflects their function.
  • The atria are thin muscled; they pump blood the short distance to the ventricles directly below them.
  • The right ventricle is more heavily muscled than either of the atria as it has to force blood a much farther distance to the lungs.
  • The left ventricle has the thickest wall as it has to push blood all around the body.
  • The blood flows through the heart in one direction only. This is due to the sets of valves which close to prevent back-flow.
  • The heart consists of four valves.

A) Auricles

  • The auricles are thin walled chambers which are completely separated from each other by a thin vertical inter-auricular septum.
  • Each auricle opens into the ventricle of its own side through an auriculo-ventricular aperture.
  • Each aperture is guarded by atrio-ventricular valves (AV valves) to prevent blood from returning to the atria when the ventricles contract.
  • The right auriculo-ventricular aperture is guarded by tricuspid valve as it consists of three flaps.
  • It is also known as right atrio-ventricular valve.
  • Similarly, the left atrio-ventricular aperture is guarded by bicuspid valve or mitral valve or left atrio-ventricular valve which consists of two flaps.
  • These valves allow blood to flow from the auricle into the ventricle and prevent any back-flow of blood.
  • They are attached to walls of the ventricles through long white strands called chordae tendinae.

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B) Ventricles

  • The ventricles are thick walled chambers which are separated by thick and oblique inter-ventricular septum.
  • The left ventricle is larger and its walls are thicker than the right ventricle.
  • From the right ventricle originates a pulmonary arch or aorta which carries de-oxygenated blood to the lungs.
  • Similarly, from the left ventricle originates a systemic arch or aorta which carries oxygenated blood to various parts of the body.
  • The opening of pulmonary arch and systemic arch are guarded by semi-lunar valves.


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  • Both sets of valves have three semi-lunar (half-moon shaped) flaps.
  • These valves allow blood to flow from the ventricle into the aorta and prevent the backward flow of blood into the ventricle.
  • Valves are simply strong flaps of tissue and they cannot move on their own.
  • As blood begins to flow back, the valve is forced shut and this prevents any further back-flow.


i) https://training.seer.cancer.gov/anatomy/cardiovascular/heart/structure.html

ii) https://www.news-medical.net/health/Structure-and-Function-of-the-Heart.aspx

Heart and its structure