The cardiovascular system

·         The cardiovascular represents “Cardio” means Heart; to ensure constant circulation of blood and “Vascular” means Blood Vessel; through which the blood flows.

·         The heart is pumped by two circulation systems;

1.      The pulmonary circulation


2.      The systemic circulation 

Fig. 02: Blood circulation 

The heart and Homeostasis

·         The heart contributes homeostasis by pumping blood through blood vessels to the body to deliver oxygen and nutrients and removes wastes.

Some key facts

·         The heart beats 1,00,000 times every day.

·         35 million beats/year, 2.5 billion/average lifetime.

·         The heart pumps blood through on estimated 1,20,000 km. of blood vessels.

·         During sleeping the heart pumps about 5 liters of blood to the lungs and same to the rest of the body. In a day pumps about 14,000 liters and in a year 5 million liters of blood pumped.

·          The scientific study of heart is called cardiology

·         Homeostasis: A state of steady internal, physical and chemical condition maintained by living system.

Anatomy of heart

·         The heart is a rough cone shaped hollow muscular organ, about 10 cm long and is about the size of the owner’s fist.

·         The weight of the adult male heart is 310gm and female heart is 225gm.

·         The heart is lies in the thoracic cavity in the mediastinum.

Organ associated with the heart

·         Inferiorly         : Apex

·         Superiorly        : Aorta, Superior Vena Cava, Pulmonary artery, and Pulmonary veins

·         Posteriorly       : Esophagus, Descending aorta, Inferior Vena Cava, Trachea, Left and

  Right Bronchus, and Thoracic vertebrae

·         Laterally          : The lungs

·         Anteriorly        : Sternum, Ribs, and Intercostal Muscle.

Fig. 02: Organ associated with the heart






·         The inner most layer of the heart.

·         It lines cavities and valve of the heart.

·         Structurally: loose connective tissue and simple squamous connective tissue.

Connective tissue

1.      Subendothelial connective tissue

·         Loose connective tissue rich in elastic fibre and collagen fibre.

2.      Dense connective tissue

·         Rich in collagen fibre

·         Middle layer of the heart

·         The myocardium is composed if cardiac muscle and is an involuntary striated muscle.

·         This layer is responsible for contraction of the heart.

·         The outermost layer and is made up two sac.

·         The outer sac consists of fibrous tissue and the inner of a continuous double layer of serous membrane.



Fig. 03: The heart wall 

Structure of heart 

Fig. 04: Internal structure of the Heart 


·         The walls of the heart consist of cardiac muscle called myocardium.

·         The heart consist of 4 chambers are lined with endocardium.

·         The upper chambers of the heart are right and left atria (Atrium).

·         The atria are relatively thin wall and are separated by a wall called interatrial septum.

·         The lower chambers of the heart are right and left ventricles, which have thicker walls and are separated by the interventricular septum.

Right atrium

·         The blood from the body is returned to the right atrium by the two major caval veins.

·         Blood from upper limbs is carried by superior vena cava whereas, blood from the lower body is carried by inferior vena cava.

·         From the right atrium, blood will flow through the atrioventricular valve (AV Valve) / Tricuspid valve into the right ventricle.

·         The tricuspid valve is made of three flaps (cups) of endocardium and connective tissue.

·         The main purpose of the valves is to prevent backflow of the blood.

Left atrium

·         The left atrium receive blood from the lungs by pulmonary veins.

·         This blood will then flow into the left ventricle through left atrioventricular valve / Mitral valve / Bicuspid valve.

·         It prevents backflow of blood from the left ventricle to the left atrium.

Right ventricle

·         Contraction of right ventricle, the tricuspid valve closes and the blood is pumped to the lungs through pulmonary artery.

·         The flow of blood from right ventricle to pulmonary artery is regulated by pulmonary semilunar valve.

Left ventricle

·         Thicker than the right ventricle.

·         The left ventricle pumps blood to the body through aorta, the largest artery of the body.

·         Aortic semilunar valve opened by the force of contraction of left ventricle, which also closes the mitral valve and prevent the back flow of blood.


·         The deoxygenated blood from upper limbs drains into right atrium through superior vena cava and lower limbs blood through inferior vena cava into the right atrium.

·         This blood passes into the right ventricle via right atrioventricular valve (tricuspid valve) and from there is pumped into pulmonary artery or trunk.

·         The opening of pulmonary artery is guarded by the pulmonary valve, formed by semilunar valve/cups. This valve prevents the backflow of blood into the right ventricle when ventricular muscle relaxes.

·         The pulmonary artery divided into left and right pulmonary artery, which caries venous blood to the lungs where exchange of gases takes place (CO2 and O2).

·         Two pulmonary veins from each lung carry oxygenated blood back to the left atrium.

·         The blood then passes through the left atrioventricular valve into the left ventricle and from there it is pumped into the aorta (the first arty of the general circulation).

·         The opening of the aorta is guarded by the aortic valve formed by three semilunar cups.

Arterial supply

·         The right and left coronary artery which split from aorta just distal to the aortic valve, supply the heart with arterial blood.

·         Coronary artery receives about 5% of blood pumped from the heart.

·         Coronary artery then forming a vast network of capillaries.

 Venous drainage

·         A number of cardiac veins that joins to form the coronary sinus, which open into the right atrium. The remainder passes directly into the heart chambers through little venous channels.


SA node

·         Sinoatrial node is a small mass of specialised cells lies in the wall of the right atria near opening of superior vena cava.

·         It regulates electrical impulses, maintain depolarization (60-80 beats/min) is followed by repolarization.

·         Also called pacemaker of the heart.

·         Firing of the SA node triggers atrial contraction.

AV node

·         Atrioventricular node is a small mass of neuromuscular tissue is situated in the wall of the atrial septum near the atrioventricular valves.

·         Transmit electrical current into the ventricles.

·         The action starts when the atrial finish contracting before the ventricle starts.

·         Act as secondary pacemaker function when SA node not working properly (40-60 beats/min).

Bundle of His

·         It is a mass of specialised fibre that originated from the atrioventricular node.

·         The AV bundle crosses the fibrous ring that separates atria and ventricle.

·         It is divides into right and left bundle branches.

·         Within the ventricular myocardium the branches break up into fine fibres called purkinje fibres.

·         AV bundle, Bundle branches and purkinje fibres transmit electrical impulses from A-V node to the apex of the myocardium (Ventricular contraction).


·         It influenced by autonomic nerve (sympathetic and parasympathetic) originated in the cardiovascular centre in the medulla oblongata.

·         Vagus nerve (parasympathetic) supply mainly the SA and AV nodes and atrial muscle (Decrease heart rate↓).


·         Sympathetic nerve supplies the SA and AV nodes and the myocardium of atria and ventricles (Increase heart rate↑).

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