Human Heart
Once thought to be the source of feelings of love and emotion, the heart is actually the powerhouse of the Circulatory System. Rhythmic contractions of this muscular pump push blood along the blood vessels to all parts of the body, even its far extremities, and back to the heart again. The beating heart ensures that every cell of the body has an uninterrupted supply of food, oxygen, and other essentials. So powerful is the heart that it can pump the body's entire blood volume of 5 litres (8.8 pints) around the body about once every minute. On average it beats, or pumps, 70 times a minute when the body is at res, yet can increase this rate if the body is more active. Over a lifetime of 70 years, the heart beats some 2.5 billion times without tiring or stopping for a rest, thanks to the cardiac muscles in its walls.
TWO SIDES
HEART VALVES AND ONE-WAY FLOW
The direction of blood flow through the heart is maintained by valves . Massive valves, the atrio-ventricular valves, separate the upper chambers from the lower. The edges of the atrio-ventricular valves are supported by non-elastic strands, the Chordae tendinae, which are anchored to the muscular wall of the ventricle below. The atrio-ventricular valve of the right side of the heart is called tricuspid valve ; that of the left side is the bicuspid or mitral valve. Pocket-shaped valves, the semilunar valves, lie between the ventricles and the pulmonary artery and aorta. Each of these valves allows blood to flow through it in one direction only.
INTERNAL STRUCTURE OF THE HEART
The right auricle is bigger than
the left auricle. Both the auricles are thin walled. The right auricle and the
left auricle are separated from each other by a verticle septum called
interauricular septum. There is large aperture in the dorsal wall of the right
auricle. This aperture is known as sinu auricular aperture. The sinu auricular
aperture is guarded by a pair of valves. The common pulmonary vein opens in the
dorsal wall of the left auricle through a small oblique aperture devoid of any
valves. Auriculo-ventricular septum, a horizontal septum, internally separates
the two auricles from the ventricle. The right and left auricle open into the
ventricle through a single aperture called auriculo ventricular aperture. The
auriculo ventricular aperture is guarded by a four flapped valve called
auriculo ventricular valve. Several chordae tendinae are attached to the margin
of the four flaps of the auriculo ventricular valve. The chordate tendinae are
thread like chords which are attached to the muscular wall of the ventricle at
their other ends. The truncus arteriousus arises from the anterior and ventral
part of the lumen of the ventricle. The truncus anteriosus emerges and runs
forward obliquely on the ventral surface of the right auricle. There are three
semilunar valves at the proximal end in the truncus arteriosus. The basal,
broad and thick walled portion of the truncus arteriosus is known as conus
arteriosus.
The anterior, distal, thin walled
and narrow portion of the truncus arteriosus is known as venral aorta. There is
a longitudinal spinal valve in the lumen of conus arteriosus. The dorsal margin
of this valve is attached to the dorsal wall of the conus. The ventral margin
of this valve is freely suspended in the lumen. This valves divides the lumen
of conus arteriosus into a left cavum pulmocutaneum and right cavum aorticum.
The left cavum pulmocutaneum and right cavum aorticum are incompletely
separated from each other. There is an aperture of common pulmocutaneous arch
in the anterior part of the cavum pulmocutaneum. The aperture is guarded by a
valve. The blood entering the cavum pulmocataeum enters and flows through the
pulmocutaneous arches due to this type of structure. The ventral aorta divides
into two lateral aortae. Each lateral aorta is divided into two arches: a
carotid arch and systemic arch.
CARDIAC CYCLE
The function of the heart is to pump blood into the blood vessels to ensure that blood reaches all the parts of the body. This is done by the contraction and relaxation of the chambers of the heart. Contraction is called systole and relaxation is called diastole. The pumping action of heart takes place in a rhythmic pattern.
It consists of three stages:
Auricular systole or ventricular diastole
Auricular diastole or ventricular systole
Joint diastole or auricular and ventricular diastole
