Function of Circulatory System
The function of circulatory system in all living organisms are basically the same. These are follows:
- Transport respiratory gases- It transports oxygen from respiratory surface to tissue and carbon dioxide from the tissues to the respiratory surface.
- Transport of metabolic waste products- It transports various metabolic waste products produced from different tissues to the organs from where they are removed out from the body.
- Transport of digested food substances- It absorbs and transports the digested foods from the site of absorption to the different organs of body for storage, oxidation or synthesis of the stuffs of body.
- Transport of chemical messengers- It transports the chemical messengers like hormones from site of their origin to target organs.
- Temperature regulation - It regulates the temperature by distributing the heat produced in one part of the body to different parts there by equalizing the body temperature.
- Transport of metabolic intermediates- The circulatory fluid carries various intermediate compounds produced in metabolic reactions from one tissue to another for their further metabolism. For example, lactic acid is produced as an intermediate compound in respiration and is carried from muscle to the liver for its oxidation.
- Protection against diseases- The circulatory fluid like blood contain phagocytic leukocytes that engulf and kill harmful microorganisms. Leukocytes also produce antibodies.
Types of Heart
Depending upon their mode of contraction,two kinds of hearts are-
(a) Myogenic hearts: The hearts in which the wave of contraction starts in the muscle fibres of heart (nodule tissue ) are said to be myogenic hearts.e.g. human heart.
(b) Neurogenic hearts: The hearts in which contraction wave takes its origin from nerve cells or group of such cells are said to be neurogenic hearts.e.g. frog's heart.
Types of Circulatory System: Two types of circulatory systems are -
(1) Closed type of Circulatory system : Blood circulates throughout the body through a closed vessel from the heart and returns back to the heart.e.g. all vertebrates.
(2) Open type of Circulatory system : Blood circulates throughout the body through a open cavity like coelom or other spaces like lacunae or sinuses.e.g. all invertebrates except annelids.
Structure of Human Heart
Location - A human heart is a triangular an muscular organ located in thoracic cavity between the lungs. The human heart is about 12 cm in length n 250 gms in weight.
External structure
Heart is a conical muscular organ, enclosed and protected in a double walled pericardium. The cavity between two pericardial membranes is filled with pericardial fluid that prevents the heart from the shocks, mechanical injury and also free movements of the heart.
Human heart is a four chambered organ, having two auricles (atria) and two ventricles. Right auricle and right ventricles are the chamber for the impure blood whereas the left auricle and left ventricle are for the pure blood. There is no mixing of pure and impure blood in the heart.
Auricles
Auricles are thin walled chambers. the left auricle is smaller than right auricle. right auricle receives the venous (impure0 blood through an opening of two precavals, one post-caval and coronary sinus. Left auricle receives oxygenated blood from lungs by opening of two pairs of pulmonary veins.
Ventricles - Ventricles are thick walled. The left ventricle is somewhat longer and about three times thicker than the right ventricle. Right ventricle receives the impure blood from right auricle whereas the left ventricle receives pure blood from left auricle.
Pulmonary trunk and aorta- The pulmonary trunk arises from the right ventricle. It divided into left and pulmonary arteries that carry deoxygenated blood to the lungs. Similarly, an aorta arises from the left auricle. The aorta gives off three branches- innominate, left common carotid and left subclavian.
Internal structure of heart
The internal structure of human heart has following parts-
Auricles- Auricles are thin walled chambers separated by inter-auricular septum. Right auricle receives the venous (impure) blood through an opening of two precavals, one post caval and coronary sinus.
The opening is venacava is guarded by eustachian valve. The coronary sinus has coronary valve. In the right auricle adjoining the inter-auricular septum, an oval depression, the fossa ovalis is present which communicates two auricles during the foetal life, but in the adult it persists only as a depression. Left auricle receives oxygenated blood from lungs through four openings of pulmonary veins.
Bicuspid and tricuspid valves – The auricles and ventricles are separated by the auriculo- ventricular septum. Each auricle opens into its corresponding ventricle through an auriculo- ventricular aperture. These apertures are guarded by flaps or valves which open only in the ventricle and prevent the back flow of the blood. The left auriculo- ventricular aperture is guarded by bicuspid valve or mitral valve (2 flaps). Similarly, the right auriculo- ventricular aperture is also guarded by tricuspid valve (3 flaps).
These valves are attached to the walls of the ventricles by means of tendons or fibrous chords called chordae tendinae. It s main function is to hold the flaps or valves and thus not allowing valves to enter in auricles during powerful ventricular contractions.
Ventricles – Ventricles are thick walled, separated by thick and oblique inter- ventricular septum. The left ventricle is somewhat longer and thicker than right ventricle. The walls of ventricles have many muscular ridges or projections called columnae carneae. It divides the cavity of ventricles into smaller spaces, known as fissures. Right ventricle receives the impure blood whereas the left ventricle receives the pure blood. Due to the contraction of ventricles, the blood is pumped forcefully to the different parts of the body.
Semilunar valves- Right ventricle pumps the impure blood to the lungs through the pulmonary aorta for its purification or oxygenation. Similarly, the left ventricle pumps the pure blood to all parts of body through aorta. These openings are guarded by three Semilunar valves which prevents he blood from returning to the ventricle once forced out.
Blood supply to the heart: a pair of coronary arteries supplies pure blood to the heart. A series of coronary veins collect impure blood from heart and joins to from coronary sinus which opens into the right auricle.
Blood circulation through the heart
There are two separate chambers for oxygenated and deoxygenated blood. The right auricle and right ventricle are the chambers for deoxygenated blood whereas left auricle and left ventricle are for oxygenated blood. There is no any chance of mixing of blood. The circulation of blood in the body is as follows –
(i) Circulation begins with the right auricle that receives deoxygenated blood from the body (except the lungs) through two main vessels;
(a) Pre-cavals- It collects the impure blood from the head and upper parts of the body.
(b) Post -caval- It collects impure blood from the lower body parts.
(ii) Due to the contraction of right auricle, blood is pumped into the right ventricle.
(iii) When the right ventricle contracts, deoxygenated blood is forced through a set of Semilunar valves into the pulmonary artery which carries blood to lungs for purification.
(iv) After the blood gets oxygenated in lungs, it is returned to the left auricle through the right and left pulmonary veins. From there blood is passed into the left ventricle.
(v) As the left ventricle is contracts, oxygenated blood is pumped forcely through the aorta and distributed to all parts of the body.
fig: Course of circulation of blood
