0 explain the structure of human heart
Answers
The human heart is pinkish about the size of a fist and weighs approx. 300 gms, the weight in females being about 25% lesser than the males.
It is a hollow, highly muscular, cone-shaped structure located in the thoracic cavity above the diaphragm in between the two lungs.
It is protected by rib cage. The narrow end of the triangular heart is pointed to the left side, during working this end gives a feeling of the heart being on the left side.
Location of Heart :-
Heart is right in the centre between the two lungs and above the diaphragm in the ribcage. The narrow end of the roughly triangular heart is pointed to the left side and during working the contraction of the heart is most powerful at this end giving a feeling of the heart being on the left side.
External Structure:
The heart is surrounded by two layered tissue membrane called pericardium. The space between the two layers is filled with fluid called pericardial fluid. This fluid protects the heart from external pressure, push, shock and reduces friction during the heart beat and facilitates free heart contraction.
Internal Structure:
The heart is composed of outer pericardial, middle myocardial and inner endocardial layers, which correspond to tunica adventitia, tunica media and tunica internal respectively of the blood vessels layers. The heart consists of four chambers. The two thin walled auricles which are upper chambers (right and left). Right and left auricles are separated from each other by an inter-auricular septum.
Right auricle receives deoxygenated blood from the body parts by anterior and posterior vena cava. The two thick walled lower chamber (right and left) are called ventricles. Right and left ventricles are separated by an inter-ventricular septum. The walls of left ventricle are much thicker as it supplies blood to large distance and up to the brain against gravity. The left ventricle has chordae tendinae and papillary muscles which prevent tricuspid and bicuspid valves from being pushed into auricles at the time of ventricular contraction.
Blood Vessels Entering and Leaving the Heart:
1. (a) Superior vena cava:
It brings deoxygenated blood from anterior body parts (head, neck, chest and arms) to the right auricle.
(b) Posterior vena cava:
It brings deoxygenated blood from posterior or lower body parts i.e. abdomen and legs to the right auricle.lt is the largest vein.
2. Pulmonary artery:
It arises from right ventricles and carries deoxygenated blood to the lungs for oxygenation.
3. Pulmonary vein:
It arises from each lung and brings oxygenated blood from lungs to left auricle.
4. Aorta:
It arises from left ventricles and carries oxygenated blood to supply it to all body parts. Abdominal aorta is the largest artery.
5. Coronary arteries:
There are two coronary arteries right and left, arising from the base of aorta and supply blood to heart muscles, (blockage at these arteries result a myocardial infraction or heart attack).
Valves in the Heart:
1. Right atrio-ventricular valve (Tricuspid valve)-Located at the opening between right auricle and right ventricle.
2. Left atrio-ventricular valve (“Mitral” or bicuspid valve)-Located at the similar way between left auricle and left ventricle.
3. Pulmonary semi-lunar valve: Present at the opening of right ventricle into pulmonary artery.
4. Aortic Semi-Lunar Valve: Located at the point of origin of aorta from left ventricle.
Pacemaker tissues of the Heart:
Certain tissues in the heart, concerned with the initiation (generation of impulse) and propagation (conduction) of the heart beat, are called “Pace- Maker” tissue, such as:
1. Sino Atrial Node (S.A. Node):
It is located at the junction of superior vena cava with right auricle it initiates and maintains the myocardial activity and its rhythmicity, (called pace maker of heart).
2. Atrio-Ventricular Node (A.V. Node):
Located posteriorly on right side of the interatrial septum near coronary sinus, in the destruction of S.A. Node. The function of pace maker can be taken up by the A.V. Node.
3. Bundle of HIS:
Starts from A.V. Node along interventricular septum at the top. Impulses travel along bundle of HIS on to ventricles.
4. Purkinje Fibers:
Located at the terminal divisions of right and left branch of the bundle of HIS. Purkinje fibers transmit the impulse at a fast velocity of 4 mts/sec.
auricles due to this deoxygenated blood rushes from veins to right auricle and oxygenated blood through pulmonary vein in to left auricle.