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Home
NEET Biology
Structure of Heart

Structure of Heart

The heart is a muscular organ that pumps blood throughout the body, supplying oxygen and nutrients to tissues and removing carbon dioxide and waste products. It is a key component of the circulatory system and is located in the thoracic cavity, between the lungs, slightly tilted to the left. 

1.0Location of the heart

  • The heart is present in the thoracic cavity, in space mediastinum (between both the lungs). 
  • The heart is slightly tilted to the left. 

2.0Weight of the Heart 

  • Adult Male:- 300 gms. 
  • Adult Female:- 250 gms.

Size 

Shape

Origin

Clenched fist (12 × 9 × 6 cm)

Pear shaped 

Mesodermal 

3.0Coverings and Layers of Heart

The heart is protected by a double walled membranous bag.

Coverings and Layers of Heart


Epicardium 

Myocardium

Endocardium 

Layer

Outermost

Middle 

Innermost layer

Origin 

Mesodermal 

Mesodermal

Mesodermal

Made up of

Simple squamous epithelium

Cardiac muscles which are striated but involuntary 

Simple squamous epithelium

Layers of the coverings of the heart

Significance of Pericardial Fluid 

  • The pericardial fluid acts as a shock absorber.
  • Pericardial fluid provides frictionless movements between two pericardial membranes (parietal & visceral). 

4.0Structure of Heart

Chambers of Heart

Our heart has four chambers: two relatively small upper chambers called atria or auricles and two larger lower chambers called ventricles. 

Chambers of Heart

Septa of Heart

  • A thin, muscular wall called the interatrial septum separates the right and the left atria, whereas a thick-walled interventricular septum separates the left and the right ventricles. 
  • A thick fibrous tissue also separates the atrium and the ventricle of the same side called the atrioventricular septum. 
  • However, each septum is provided with an opening through which the two chambers on the same side are connected. 

Septa of Heart

Vessels and Valves of Heart

  • The opening between the right atrium and the right ventricle is guarded by a valve formed of three muscular flaps or cusps, the tricuspid valve, whereas a bicuspid or mitral valve guards the opening between the left atrium and the left ventricle. 
  • The semilunar valves provide the openings of the right and left ventricles into the pulmonary artery and the aorta. 

Significance of Valves in Heart 

  • The heart's valves allow blood to flow only in one direction from the atria to the ventricles and from the ventricles to the pulmonary artery or aorta. 
  • These valves prevent any backward flow. 

Significance of Chordae Tendineae and Papillary Muscles 

  • Chordae tendineae and papillary muscles prevent the reverse opening of AV valves (Tricuspid and bicuspid) at the time of ventricular systole (contraction of ventricles). 

5.0Conducting System of Heart

Types of heart on the basis of source of Heart Beat

Neurogenic Heart 

Myogenic Heart

Heart beat is entirely controlled by nervous supply 

Heart beat originates from a muscular tissue. Such a heart is called myogenic heart (Auto excitable heart).

Example : Arthropods and some annelids

Example : Mollusca and vertebrates

  • The entire human heart is made of cardiac muscles. The walls of the ventricles are much thicker than those of the atria because the ventricles have to supply blood to various parts of the body.   
  • A specialized cardiac musculature called the nodal tissue is also distributed in the heart. A patch of this tissue is present in the right upper corner of the right atrium called the sino-atrial node (SAN). 
  • Another mass of this tissue is seen in the lower left corner of the right atrium, close to the atrioventricular septum, called the atrioventricular node (AVN). 
  • Three bundles of muscle fibres connect the AV node and SA node, called internodal pathways.
  • A bundle of nodal fibres, the atrioventricular bundle (AV bundle), continues from the AVN, which passes through the atrioventricular septa to emerge on top of the interventricular septum and immediately divides into a right and left bundle. 
  • These right and left bundles with AV bundles are known as the Bundle of HIS. 
  • These branches give rise to minute fibres called Purkinje fibres throughout the ventricular musculature of the respective sides.
  • These fibres and right and left bundle branches are called the Purkinje system. 
  • The nodal musculature can generate action potentials without external stimuli; it is auto-excitable. Our heart normally beats 70-75 times a minute (on average 72 beats/minute). 
  • SA node (Pacemaker of the heart) (Generate a maximum number of action potentials, i.e., 1 to 72 beats per minute. 
  • Atrio-ventricular node (AVN). Present at the lower left corner of the right atrium close to the (atrioventricular septum) (Reserve pacemaker of heart pacesetter of the heart). 
  • Correct Pathway : SA node → Inter nodal pathway → AV node → AV bundle → Bundle branches → Purkinje fibers

Number of Beats Per Minute 

  • SA Node 70-75
  • AV Node 40-60
  • Purkinje fibers 20-35

Table of Contents


  • 1.0Location of the heart
  • 2.0Weight of the Heart 
  • 3.0Coverings and Layers of Heart
  • 4.0Structure of Heart
  • 4.1Chambers of Heart
  • 4.2Septa of Heart
  • 4.3Vessels and Valves of Heart
  • 5.0Conducting System of Heart

Frequently Asked Questions

The heart consists of four chambers (two atria and two ventricles), valves, arteries, veins, and a network of blood vessels. It is divided into the right and left sides, each with its distinct function.

The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs for oxygenation through the pulmonary arteries. This process is part of pulmonary circulation.

The left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body through the aorta. This is part of the systemic circulation.

The heart has an electrical system that controls the heartbeat. The sinoatrial (SA) node in the right atrium is the heart's natural pacemaker. It generates electrical impulses that trigger the heart's contraction, ensuring a coordinated heartbeat.

The left ventricle is the most powerful chamber of the heart. It pumps oxygen-rich blood through the aorta to all parts of the body. Its thick muscular walls allow it to generate the force needed for systemic circulation.

The walls of the left ventricle are thicker because it must pump blood to the entire body, which requires greater force. In contrast, the right ventricle only pumps blood to the nearby lungs.

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