Pumping organ: The Heart .
The heart of the human is located in the chest cavity. The heart is enclosed in a double membranous sac, the pericardial cavity, which contains the pericardial fluid. Pericardium protects the heart and prevents it from over extension.
The wall of the heart is composed of three layers.
(i) Pericardium (ii) Endocardium (iii) Myocardium.
The myocardium of the heart is made up of the special type of muscles, the cardiac muscles. These muscles contain myofibrils and myofilaments of myosin and actin. Their arrangement is similar to those in skeletal muscle fibers, their mechanism of contraction is essentially the same, except that they are branched cells, in which the successive cells are separated by junctions called intercalated discs. The heart contracts automatically with rhythmicity, under the control of the autonomic nervous system of the body.
There are four chambers of the heart: two upper thin-walled atria and two lower thick walled ventricles. The human heart works as a double and controls systemic circulation of the blood in all the body. Oxygenated and deoxygenated blood is completely separated through walls.
source google.com
Blood Flow PatternTrough Heart
Heart to Lungs And Back to Heart
The right atrium receives blood via venae cavae from the body. The blood is passed on to the right ventricle through a tricuspid valve.
The tricuspid valve is made up of tree flaps and these flaps are attached with fibrous cord called chordeae tedinae, to the papillary muscles which are the extension of the walls of the right the ventricle. When right ventricle contracts, the blood is passed to pulmonary trunk, which carries blood via left and right pulmonary arteries, to the lung.
At the base of the pulmonary trunk, semilunar valves are present. After oxygenation in lungs, the blood is brought by pulmonary veins in the left atrium, which passes this blood via bicuspid valve to the left ventricle.
The tricuspid valve is made up of tree flaps and these flaps are attached with fibrous cord called chordeae tedinae, to the papillary muscles which are the extension of the walls of the right the ventricle. When right ventricle contracts, the blood is passed to pulmonary trunk, which carries blood via left and right pulmonary arteries, to the lung.
At the base of the pulmonary trunk, semilunar valves are present. After oxygenation in lungs, the blood is brought by pulmonary veins in the left atrium, which passes this blood via bicuspid valve to the left ventricle.
Blood Flow from Heart to The Body.
When left ventricle contracts, it pushes the blood through the aorta to all parts of the body. At the base of aorta semilunar valves are also present. At the base of the aorta, the first pair of arteries, the coronary arteries arise and supply blood to the heart. The aorta forms an arch, and before descending down gives three branches supplying blood to head, arms and shoulders. The aorta descends down in the chest cavity giving many branches to the chest wall and then passes down to the abdominal cavity. Here it gives many branches which supply blood to different parts of the alimentary canal, kidneys and the lower abdomen. then it bifurcates into two iliac arteries. The iliac arteries supply blood to every cell of legs.
Backflow of Blood from Body to heart
The blood from all the upper part of the body is collected back by different veins, which then join to form superior vena cava; that passes its blood to the right atrium. Two iliac veins are formed by veins which collect blood from both legs and unite to from inferior vena cavae. Two Renal veins from each kidney, and hepatic vein from the liver joins inferior vena cavae before it enters the right atrium of the heart.
The Cardiac Cycle
It is the sequence of events which take place during the completion of one heart beat. Heartbeat involves three different stages.
source google.comRelaxation phase (diastole).
The deoxygenated blood enters right atrium through vena cava, and oxygenated blood enters left atrium through pulmonary veins. The walls of the atria and that of ventricles are relaxed. As the atria are filled with blood, they become distended and have more pressure than the ventricles. This relaxed period of heart chambers is called diastole.
Atria Contract (atrial systole)
The muscles of atria simultaneously contract, when the atria are filled and distended with blood, this is called atrial systole. The blood passes through tricuspid and bicuspid valves, into the two ventricles which are relaxed.
Ventricles contract (ventricular systole)
When the ventricles receive blood from atria, both ventricles contract simultaneously and the blood is pumped to pulmonary arteries and aorta. The tricuspid and bicuspid valves close, and "lubb" sound is made. Ventricular systole ends, and ventricles relax at the same time semilunar valves at the base of the pulmonary artery and aorta close simultaneously, and "dubb" sound is made. (Lubb dubb can easily be heard by using a stethoscope).
One complete heartbeat consists of one systole and one diastole and lasts about 0.8 seconds. In one's life, the heart contracts 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 right atrium sends out electrical impulses to the atrial muscles and causing both atria to contract. The sino-atrial node consists of a small number of diffusely oriented cardiac fibers, possessing few myofibrils; and few nerve endings from the autonomic nervous system.
Impulses from the node travel to the musculature of the atrium and to an atrioventricular node. From it, an atrioventricular bundle of muscle fibers propagates the regulatory impulses via excitable fibers in the interventricular septum, to the myocardium of the ventricles. There is a delay of approximately 0.15 second in conductance from S-A node to A-V node, permitting atrial systole to be completed before ventricular systole begins.
Impulses from the node travel to the musculature of the atrium and to an atrioventricular node. From it, an atrioventricular bundle of muscle fibers propagates the regulatory impulses via excitable fibers in the interventricular septum, to the myocardium of the ventricles. There is a delay of approximately 0.15 second in conductance from S-A node to A-V node, permitting atrial systole to be completed before ventricular systole begins.
How the Heart Works 3D video source youtube
Electrocardiogram (E.C.G)
As the cardiac impulse passes through the heart, electrical currents spread into the tissues surrounding the heart, and a small proportion of these spread all the way on the surface of the body. If electrodes are placed on opposite sides of the heart on skin electrical potentials generated by these currents can easily be recorded as electrocardiogram which is taken by electrocardiograph (E.C.G.) machine. It also helps to diagnose the abnormalities in the rhythmicity and conduction system of the heart which may be corrected by the use of an artificial pacemaker.
source google.com
Artificial Pacemaker
Artificial Pacemaker source google.com
A pacemaker is responsible for initiating the impulses which trigger the heart beat rate. If there is some block in the flow of the electrical impulses, or if the impulse initiated by S-A node are weak; it may lead to the death of the individual.
source google.com
So, an artificial pacemaker, which is battery operated producing electrical stimulus is used. For example, if A-V pathway is blocked, the electrodes of the artificial pacemaker are the ventricle. Then this pacemaker provides continued rhythmic impulses that take the control of the ventricles.
The Cardiovascular System source Youtube
I think the above-discussed structure and function are enough to introduce heart. If you like this, do comment to let me know about my shortcoming so that I may improve in my next blog.
orignally submitted and published here
orignally submitted and published here
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