Pumping Organ-The Heart
Structure and actions:
The heart of humans 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,prevents it from over extension.
WALL OF HEART:-
The wall of the heart is composed of three layers.
MUSCLES OF HEART:-
Myocardium of the heart is made up of special type of muscles,the cardiac muscles.
These muscles contain myofilaments of myosin and actin.
ARRANGEMENT OF MUSCLES:
Their arrangement is similar to those in skeletal muscle fibres,and their mechanism of contraction is the same,except that they are branched cells, in which the successive cells are separated by junctions called "intercalated discs".
CONTRACTION OF HEART:
The heart contracts automatically with rhythmicity,under the control of the autonomic nervous system of the body.
CHAMBERS OF HEART:
There are chambers of the heart : two upper thin-walled atria ,and two lower thick walled ventricles.
HOW HEART FUNCTIONS :
Human heart function as a double pump,and is responsible for pulmonary and systemic circulation.Complete separation of deoxygenated blood(right side) and oxygenated blood(left side), in the heart,is mentained.
CIRCULATION OF DEOXYGENATED BLOOD;
The right atrium receives deoxygenated blood via venae cavae from the body.The blood is passed on to right ventricle through tricuspid valves(called so because it has three flaps).
- ARRANGEMENT OF FLAPS:
These flaps are attached wirh fibrous cords called chordeae tendinae,to the papillary muscles which are extensions of the wall of right ventricle.When right ventricle contracts the blood is passed to pulmonary trunk,which carries blood via left and right pulmonary arteries ,to the lungs.At the base of pulmonary trunk ,semilunar valves are present .
CIRCULATION OF OXYGENATED BLOOD:
After oxygenation in lungs the blood is brought by pulmonary veins to the left atrium which passes this blood via bicuspid valves to the left ventricle.The flaps of bicuspid valve are similarly attached through chordae tendinae,to papillary muscles of the wall of left the ventricle.When the left ventrical contracts it pushes the blood through aorta to all parts of the body(except lungs). At the base of aorta semiluar valves are also present.The valves of the heartcontrol the direction of flow of the blood.The wall of left ventricle is thicker than that of the right ventrical.
ARTERIES ARISE FROM AORTA:
At the base of aorta first pairs 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 the head,arms and shoulders.The aorta dascends down in the chests cavity.It gives many small branches to the chest walll and then passes down to the abdominal region.Here it gives branches,which supply blood to different parts of alimentaery canal,kidneys and the lower abdomen.The aorta bifurcates into iliac arteries,each of which suppying blood to legs
Collection of deoxygenated blood by different veins:
The blood from the upper part of the body is collected by different veins,which join to form superior vena cava;which pass its blood to the right atrium.two lliac veins are formed by veins which collect blood from legs,and unite to from inferior vena cava.
VEINS RECEIVES BY INFERIOR VENA CAVA:
IT RECEIVES RENAL VEIN FROM EACH KIDNEY;AND HEPATIC VEIN FROM THE LIVER,BEFORE IT ENTERS THE RIGHT ATRIUM.The liver receives hepatic portal vein which is formed by many veins collecting deoxygented blood with absorbed food from different parts of alimentary canal.
THE CARDIAC CYCLE:
It is the sequence of events which take place during the completion of one heart beat.Heart beat involves three distinct stages:
- RELAXATION PHASE-DIASTOLE
- ATRIA CONTRACT-ATRIAL SYSTOLE
- VENTRICLES CONTRACT-VENTRICULAR SYSTOLE
One complete heart beat consists of one systole and one dastole,and lasts for about 0.8seconds.In one's life,heart contracts about 2.5 billion times,without stopping.
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