the human heart

hope well thanks for your great support in the previous segments of this blog so in this segment of the blog i would like to talk about human heart such as its location its protection layers its function its chambers about the circulation of blood the cardiac cycle how heart excites and contracts electrocardiogram artificial pacemaker and the blue babies and the thing if you want to know anything related to biology so please let me know down in the comment section and please follow my blog you can do this on the right side below my picture to show your great support and so
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such that human is present in the center of his chest cavity between the lungs and is located behind the sternum or the breast bone such that it is protected bu the rib cage and the sternum it is surrounding by a layer known as the pericardium it is said that the size of person heart is equal to that respective person fist its average weight varies from about 250-300g
the heart is enclosed in a double membranous sac like structure in the pericardial cavity which contains the pericardial fluid that protects the heart from any type of friction and also prevents it from any kind of extension 
such that the walls of heart is composed of three principle layers that are known as the 
*the layer of heart myocardium is made up of special tissue that are known as the cardiac 
*these muscles contains myofibrils and micro-filaments of myosin and actin
*their arrangement is similar to those of skeleton muscles fibers and their mechanism of contraction is essentially the same except that they are branched cells in which the successive cells are separated by junctions known as the intercalated discs 
*the heart contracts automatically with rhythmicity under the control of autonomic nervous system of the body 
chambers of the heart 
these are four chambers in the heart of an human that are 
*two upper thin walled atria 
*two lower thick walled ventricles 
*the heart of human function of a double pump and is responsible for both pulmonary and systemic circulation 
*complete separation of deoxygenated blood (that is on the right side)and the oxygenated blood that is on the (left side) in the heart is maintained 
circulation of blood by heart
*the right atrium receives deoxygenated blood from the venae cavae from the body the blood is passed on to the right ventricle through the tricupsid value it is called ass such as it have three flaps 
*such that these cords are attached with fibrous cords called as the chordeae tendinae to the papillary muscle which are the extensions of the wall of the right ventricle 
*when the right ventricle contracts the blood is passed to the pulmonary trunk which carries blood via left and right pulmonary arteries to the lungs
*at the base of the pulmonary trunk semilunar valves are present
*after the oxygenation in the lungs the blood is brought by the pulmonary veins to the left atrium which passes the blood via the bicapsid valve (it is named so due to the presence of two flaps)to the left ventricle 
*the flaps of the bicapsid valve are similarly attached to through the chordeae tendina to the papillary muscles of the walls of the left ventricle 
*when the left ventricle contracts it pushes the blood through the aorta to all of the parts of the body except to the lungs 
*at the base of the aorta the semilunar valve is present the value of the heart controls the direction of the blood flow 
*the walls of the left ventricle is much thicker about three times to the walls of the right ventricle 
*at the base of the aorta the first pair of arteries the coronary arteries arises and supply the blood to the heart
*the aorta forms an arch and before descending down give rise to three branches that supply blood head arms and to the shoulder the aorta descends down in the chest cavity 

*it gives rise to many of the small branches in the chest wall and then passes down to the abdominal region here it give branches which supply blood to different parts of the alimentary canal kidney and to the lower abdomen 
*the aorta bifurcates into the iliac arteries each of which leads as femoral and the sciatic artery supplying blood to legs 
*the blood from the upper part of the body is collected by different veins which join to form superior vane cava which pass its blood to the right atrium 
*two iliac veins are formed by veins that collect blood from the legs and unite to form inferior vena cava 
*it receives renal vein from each of the kidney and the hepatic vein from the liver before it enters the right atrium 
*the liver receives hepatic portal vein which is formed by many of the veins that collects deoxygenated blood with absorbed food from different parts of the alimentary canal 
the cardiac cycle 
it is sequence of events which takes place during the events that take place during the completion of one heart beat 
heart beat involves three main stages that are 
relaxation cycle -diastole 
*the deoxygenated blood enters right atrium through vena cava and the oxygenated blood enters left atrium through the pulmonary veins 
*the walls of the atria and that of the ventricles are relaxed 
*as the atria are filled with blood they become distended and have more pressure than the ventricles 
*the relaxed period of heart chambers is called as the diastole 
atria contract atrial systole 
*the muscles of atria simultaneously contract when the atria are filled and distended with blood this is called as the atrial systole 
*the blood passes through the tricupsid and bicuspid valves into the two ventricles which are relaxed 
ventricles contract ventricular systole 
when the ventricle  receives blood from the atria both of the ventricles contracts simultaneously and then the blood is then pumped to pulmonary arteries and aorta 
the tricupsid and the bicuspid valve close and LUBB sound is produced 
ventricular systole ends and ventricles relax at the same time semilunar valves at the base of pulmonary artery and aorta and closes simultaneously and DUBB sound is produced 
such that LUBB DUBB can be heard with the help of the stethoscope 
*one complete heart beat consists of one systole and one diastole and last for about 0.8 seconds such that in ones life heart contracts for about 2.5 billion times without stopping
mechanism of heart excitation and contraction 
*the heart beat cycle described above starts when the sino- atrial node at the upper end of the atrium sends out an electrical impulse to the atrial muscles and causing both atria to contract 
*the sino atrial node consist of a small number of diffusely oriented cardiac fibres possessing few of the myofibrils and few never ending from the autonomic nervous system 
*impulse from the node travels to the musculature of the atrium and to an atrioventricular node from it an anti-ventricular bundles of muscle of bundle fibers propagates the regulatory impulse via excitable fibers in inter-ventricular septum to the myocardium of the ventricles 
*there is a delay of approx 0.15 seconds in conductance from the S-A node to A-V node permitting atrial systrol to be completed before ventricular systole begins 
*as the cardiac impulse passes through the heart electrical currents spread into the tissue surrounding the heart and a small proportion of these spread all the way on the surface of the body
*such that it electrodes are placed on the skin on opposite side of the heart electrical potentials generated by these currents can be recorded 
*this recording is known as the electro cardiogram which is taken by the electrocardiograph ( E.C.G ) machine 
*it helps to diagnose the abnormalities in the rhythmicity and conduction system of the heart which may be corrected by the use of the artificial pacemaker 
artificial pacemaker 
*pacemaker is responsible for initiating the impulse which trigger the heart beat rate 
*if there is some block in the flow of the electrical impulse or if the impulse initiated by S.A nodes are weak it may lead to the death of the respective person 
*so an artificial pacemaker which is an battery operated producing electrical stimulus is used 
*for example is A-V pathway is blocked the electrodes of artificial pacemaker are attached to the ventricle 
*then this pacemaker provides continued rhythmic impulse that take over the control of the ventricles 
blue babies 
*it is the failure of the interatrial foramen an opening in the inter atrial septum to close or of ductus arterious  to fully constricts results in cyanosis blueness of the skin
*this is due to the mixing of blood between the two atria and then the mixed blood is supplied to the body of the newly born babies resulting in blueness of skin thus named as the blue babies 
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