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
STRUCTURE OF HEART (THE HEART WALL)
· The inner most layer of the heart.
· It lines cavities and valve of the heart.
· Structurally: loose connective tissue and simple squamous 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.
· 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.
· 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.
· 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.
· 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.
BLOOD FLOW THROUGH THE HEART
· 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.
· 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.
· 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.
· 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.
· 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).
NERVE SUPPLY TO THE HEART
· 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↑).
Hi….!! My name is Smrutiranjan Dash, From Odisha, India. Professionally I am Assistant Professor at The Pharmaceutical College, Barpali, Odisha, department of Pharmacology.