CIRCULATORY SYSTEM
The flow of fluid in the body is called circulation and the structure concerned constitute the circulatory.
FUNCTION:
1)Transport of respiratory gases:
The circulatory System transports oxygen from respiratory surface to tissue and carbon dioxide from tissue to respiratory surface.
2)Transport of metabolic waste product:
The circulatory system transport various metabolic waste products produced from different tissues to the organs from where they are removed from the body.
3)Transport of digested food substance:
The circulatory System transports and absorbs the digested foods from the site of absorption to different organs of body for storage,oxidation or synthesis of the stuffs of body.
4)Transport of chemical messenger:
The circulatory System transports the chemical messengers like hormones from site of their origin to target organs.
5)Temperature regulation:
The circulatory System regulates the temperature by distributing the heat produced in one part of body to different parts there by equalizing the body temperature.
TYPES OF CIRCULATORY SYSTEM:
1)Closed type of circulatory system:
Blood circulates throughout the body through a closed vessel from the heart and returns to the heart.
eg: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.
eg.all invertebrates except annelida
STRUCTURE AND WORKING MECHANISM OF HEART:
Human heart is cone shaped,hollow muscular structure that lies in the thoracic cavity above the diaphragm and in between two lungs.Heart is completely enclosed with a thin walled double layered pericardium.Between the double layered membrane,pericardial fluid is found which protects the heart from friction and keep the heart moist.It also protect the heart from mechanical injuries.
Human heart is four chambered organ with two auricles and two ventricles.The transverse groove distinctly separates the heart into anterior auricular part and posterior ventricular part which is the largest part of the heart.The auricles are thin walled separated from each other by an inter auricular septum whereas the ventricles are thick walled separated from each other by an oblique inter ventricular septum.In the upper region of right auricle,near the precaval opening there is presence of Sinu Auriculo node or SA node through which heart beat starts and is also called as natural pacemaker of heart.The right and left auricles open into their respective ventricles through Auriculo ventricular aperture.The right Auriculo ventricular aperture is guarded by tricuspid valve while the left auriculo ventricular aperture is guarded by bicuspid or mitral valve.These valve are attached with papillary muscles of columnae cornae of the ventricles through chordae tendinae,which prevent the valves from being pushed into auricles at the time of ventricular contraction.The precavals and post caval open into the right auricle through separate openings.Two pulmonary vein open in the left auricle by a common opening.A pulmonary trunk arises from the right ventricle which carry deoxygenated blood to the lungs for oxygenation.An aortic trunk arises from left ventricle which carries oxygenated blood to the different parts of the body.The opening of pulmonary and aortic trunk is guarded by three semilunar valve.
WORKING OF HEART:
The heart collects the blood through both the auricles and distributes it through the ventricles,The action of heart includes the contraction and relaxation of auricles and ventricles.The rhythmic contraction and relaxation of heart is know as heart beat.The contraction of heart is known as systole and the relaxation of heart is known as diastole.The contraction and relaxation of different parts of heart take place in a definite order.Auricles and ventricles contract alternately.
The right auricles receive the deoxygenated blood from the body through two main vessel :the precavals(collect the impure blood from the head and upper parts of the body)And post cavals(from lower part). Impure blood is pumped into right ventricle due to contraction of right auricle.When the right ventricle contract,deoxygenated blood is pushed through pulmonary artery to the for purification.The left auricle receives pure blood from the right and left pulmonary veins.The blood is passed through the corresponding left ventricles.The left ventricle contracts as a result of which aorta pumps oxygenated blood and sent to different parts of the body.
ORIGIN OF HUMAN HEART BEAT:
The rhythmic contraction and relaxation of heart is known as heart beat.The heart beat begins in the tiny island of tissue in the upper region of right auricle at the point of precaval opening called Sinu auricular node or SA node.This region is also called the natural pacemaker as Heartbeat initiated from it.A wave of contraction(Systole)originates from the region and spreads to both auricles which causes its contraction.At the posterior part of right auricle i.e at the junction of right auricle and venticle,a tissue called auricula ventricular node or AV node is present which picks the wave of contraction propagated by SA node.Av node divide into left and right branches that extends the wall of ventricles on corresponding side and reach upto the apex called Bundle of His.This fibre form the network which spread on the entire wall of ventricle called Purkinge fibre.The excitation wave from AV node spreads along Bundle of His and Purkinge fibres ,and thus excites the muscle of ventricles to contract simultaneously.
HUMAN HEART SOUNDS:
Heart sounds are the sounds that are produced due to certain closure of the valves of heart.It is accomplished by two heart sounds.The first heart sound indicates the beginning of Ventricular systole.It is also called LUBB.It is produced due to the closer of Auriculo ventricular valve.The second sound or DUBB indicates the end of ventricular systole and beginning of its diastole.It is produced due to closure of semilunar valve.
First sound----Second sound----pause
First sound----Second sound----pause
TYPES OF HEART:
1)Myogenic heart:
The heart in which wave of contraction starts from muscle fibres of hearts are said to be Myogenic Heart.
Eg:Human heart
2)Neurogenic Heart:
the hearts in which wave of contraction starts from nerve cells or group of such cells are said to be neurogenic heart.
Eg:Cray fish heart
ARTIFICIAL PACE MAKER:
When the sinu auricular node becomes defective or damaged the heart beat becomes irregular and abnormally slow downs.This problem can be rectified by surgical grafting of an instrument known as Artificial pacemaker.It was first implanted by Chardack in 1960.The implanted pacemaker raises the heart beat rate to normal.The pacemaker is made of pulse generator and an electrode.The pulse generator is a sealed box containing lithium halide cells to generate power for more than ten years and an electric circuit to regulate the heart beat rate.The electrode is a fine metallic string which is connected to the pulse generator.Its special tip remains in contact with the interior right ventricle.
The pacemaker is placed under the collar bone below the skin by a simple operation.A pacemaker can be replaced or removed easily.
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