Heart Essay Research Paper HEARTThe human heart
Heart Essay, Research Paper
The human bosom is a specialised, four-chambered musculus that maintains BLOOD flow in the CIRCULATORY
SYSTEM. Located in the thorax, it lies left of the organic structure & # 8217 ; s midplane, above and in contact with the
stop. It is situated instantly behind the sternum, or breastbone, and between the lungs, with its
apex tilted to the organic structure pit & # 8217 ; s left side. In most people the vertex can be felt during each bosom
contraction. At remainder, the bosom pumps about 59 milliliter ( 2 oz ) of blood per round and 5 cubic decimeter ( 5 qt ) per minute,
compared to 120-220 milliliter ( 4-7.3 oz ) per round and 20-30 cubic decimeter ( 21-32 qt ) per minute during exercising. The grownup
human bosom is about the size of a fist and weighs about 250-350 gram ( 9 oz ) .
Blood supplies nutrient and O to the cells of the organic structure for their life demands and removes the waste
merchandises of their chemical procedures.
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It besides helps to keep a consistent organic structure temperature, circulate
endocrines, and fight infections. The encephalon cells are really dependent on a changeless supply of O. If the
circulation to the encephalon is stopped, decease ensues shortly. Since bosom onslaughts are the number-one cause
of decease in the United States, the bosom gets a great trade of attending.
The function of the bosom was long considered a enigma and frequently given elevated importance. Some thought it
was the place of the psyche. Others thought it was the centre of love, bravery, joy, and unhappiness. Primitive
adult male must hold been cognizant of the pulse and likely recognized the bosom as an organ whose malfunction
could do sudden decease.
The Hippocratic De Corde, which likely dates from the clip of ARISTOTLE, describes the building of
the bosom & # 8217 ; s valves. LEONARDO DA VINCI made keen drawings of the bosom, but it was non until the
publication of William HARVEY & # 8217 ; s De Motu Cordis ( 1628 ) that the bosom & # 8217 ; s specific function in relation to
circulation was widely understood.
STRUCTURE AND FUNCTION OF THE HUMAN HEART
The bosom & # 8217 ; s wall has three parts. Muscle tissue, or myocardium, is the in-between bed. The interior bed, or
endocardium, that lines the interior of the bosom musculus consists of a thin bed of endothelial tissue
overlying a thin bed of vascularized connective tissue. The exterior of the bosom, the visceral pericardium, is in
intimate contact with the pericardium ; this serous membrane is a closed pouch covering the bosom musculus & # 8217 ; s
outside wall. Within the pouch, a little sum of fluid reduces the clash between the two beds of
tissue. In add-on to muscular and connective tissue, the bosom musculus contains changing sums of fatso
tissue, particularly on the exterior. Both anatomically and functionally, the bosom is divided into a left
and a right half by the cardiac septum. Each half contains two separate infinites: the atrium ( pl. atria ) ,
or auricula atrii, and the ventricle. The upper reservoirs, or roll uping Chamberss, are the thin-walled atria,
and the lower pumping Chamberss are the thick-walled ven!
tricles. The entire thickness of the ventricular walls is about three times that of the atria ; the wall of
the bosom & # 8217 ; s left half is about twice every bit thick as that of the right half. The thickness of the
bosom musculus varies from 2 to about 20 millimeters ( 0.1 to 0.8 in ) . This thickness is correlated with the upper limit
force per unit area that can be attained in each chamber.
Flow OF BLOOD THROUGH THE HEART
The right atrium receives oxygen-poor blood from two major venas: the superior and inferior vein cava,
which enter the atrium through separate gaps. From the right atrium the blood passes through the
tricuspid valve, which consists of three flaps, or cusps, of tissue. This valve directs blood flow from
the right atrium to the right ventricle. The tricuspid valve remains unfastened during diastole, or ventricular
filling ; nevertheless, when the ventricle contracts, the valve closes, sealing the gap and preventing
backflow into the right atrium. Five cords attached to little musculuss ( papillose musculuss ) on the
ventricles & # 8217 ; interior surface prevent the valves & # 8217 ; flaps from being pushed backward. From the right ventricle
blood is pumped through the pneumonic, or semilunar, valve, which has three half-moon-shaped flaps, into
the pneumonic arteria. This valve prevents backflow from the arteria into the right ventricle. From the
pneumonic arteria, blood is pumped to the lungs, where it gives up ca!
rbon dioxide and receives O, and so is returned to the bosom & # 8217 ; s left side through four pulmonary
venas ( two from each lung ) to the left atrium and so through the mitral valve, a two-flapped valve besides
called a premolar valve, to the left ventricle. As the ventricles contract, the mitral valve prevents
backflow of blood into the left atrium, and blood is driven through the aortal valve into the AORTA, the
major arteria, which supplies blood to the full organic structure. The pneumonic valve, like the aortal valve, has a
semilunar form and a unidirectional map.
The blood supply to the bosom musculus is furnished chiefly by the CORONARY ARTERIES, which originate from
the aorta instantly after the aortal valve. These vass pass through the fatty tissue beneath the
pericardium and so ramify out into the bosom musculus.
The coronary venas transport the deoxygenated blood from the bosom musculus to the right atrium. The
bosom & # 8217 ; s energy supply is about wholly dependent on these coronary vass. Merely the tissues lying
straight beneath the endocardium receive a sufficient sum of O from the blood within the pits
of the bosom.
Regulation OF THE HEARTBEAT
The bosom musculus pumps the blood through the organic structure by agencies of rhythmical contractions ( systole ) and
dilations ( diastole ) . The bosom & # 8217 ; s left and right halves work about synchronously. When the ventricles
contract ( systole ) , the valves between the atria and the ventricles near, as the consequence of increasing
force per unit area, and the valves to the pneumonic arteria and the aorta unfastened.
When the ventricles become flaccid during diastole a
nd the force per unit area decreases, the contrary procedure takes
topographic point: through the valves between the atria and the ventricles, which are now unfastened once more, blood is drawn
from the atria into the ventricles, and the valves to the pneumonic arteria and the aorta near.
At the terminal of diastole the atria besides contract and therefore assist to make full the ventricles. This is followed by
systole. The electrical stimulation that leads to contraction of the bosom musculus originates in the bosom
itself, that is, in the sinoatrial node ( SA node ) , or pacesetter. This node, which lies merely in forepart of
the gap of the superior vein cava, measures no more than a few millimetres. It consists of bosom
cells that emit regular urges. Because of this self-generated discharge of the fistula node, the bosom
musculus is automated, and a wholly stray bosom can contract on its ain, every bit long as its metabolic
procedures remain integral. The electrical stimulation from the SA node becomes propagated on a regular basis over the
musculus cells of both atria and reaches the auriculoventricular node ( AV node ) , which lies on the boundary line
between the atria and the ventricles. The stimulation continues into the package of His. This bundle returns
for about a centimetre and so divides into a left and a right!
bundle subdivision. The two bundle subdivisions lie along the two sides of the bosom & # 8217 ; s septum and so continue
toward the vertex. The little side subdivisions that come off are the Purkinje fibres, which conduct the
stimulation to the musculus cells of the bosom & # 8217 ; s ventricles.
The Purkinje fibres differ from the cardiac musculus cells and carry on the stimulations more quickly. However,
the AV node conducts the stimulation comparatively easy. As a consequence, the bosom Chamberss contract on a regular basis
and equally during systole, and ventricular contraction does non co-occur with that of the atria ; so the
pumping map is well-coordinated. Potentially, the whole conductivity system is able to dispatch
spontaneously and can take over the map of the SA node. The rate at which the cells of the SA node
discharge under normal fortunes is externally influenced through the autonomic nervous system, which
sends nerve subdivisions to the bosom. Through their stimulatory and repressive influences they determine the
attendant bosom rate. In grownups at remainder this is between 60 and 74 beats a minute. In babies and immature
kids it may be between 100 and 120 beats a minute. Tension, effort, or febrility may do the rate of
a healthy bosom to change between 55 and 200 beats a minu!
The end product of the bosom is expressed as the sum of blood pumped out of the bosom each minute: the
bosom minute-volume ( HMV ) . This is the merchandise of the bosom rate and the shot volume ( SV ) , the sum
of blood pumped out of the bosom at each contraction.
Development OF THE HEART
The Black Marias of crude craniates seemingly had merely one atrium and one ventricle. Since their organic structure
temperature and metabolic rate fluctuated with the environmental temperature, they did non necessitate as
efficient a circulatory system as mammals and birds. The two-chamber bosom is retained by modern fish,
but oxygen-rich blood does non blend with oxygen-poor blood, because the blood is aerated at the gills and
goes straight into systemic circulation, non to the bosom. As the crude lung evolved in amphibious vehicles,
two circulative systems arose. The job of blending oxygenated and deoxygenated blood was resolved in a
figure of amphibious vehicles such as the FROG, in which the individual atrium is divided into two separate Chamberss.
Therefore there is merely a little commixture of the bloods in these three-chambered Black Marias. This version appears
to assist the toad when it is under H2O, since the tegument provides O when the lungs can non be used. In
SIRENS a partial division takes topographic point in the ventricle!
every bit good.
As animate beings became larger and more active on land, they needed more force per unit area to supply faster flow. The
sides of the bosom were separated when a septum formed to split the ventricle into two Chamberss. Birds
and mammals have wholly separate Chamberss and have more blood per tissue weight and more force per unit area,
because the tissues of birds and mammals ( warm-blooded craniates ) require a changeless perfusion of
oxygen-rich blood in order to keep their high metabolic rates and changeless organic structure temperature.
The closing of the bosom valves and the contraction of the bosom musculus produce sounds that can be heard
through the thoracic wall by the unaided ear, although they can be amplified by agencies of a STETHOSCOPE.
The sounds of the bosom may be represented as lubb-dupp-pause-lubb-dupp-pause. The lubb sound indicates
the shutting of the valves between the atria and ventricles and the catching ventricles ; the dupp sound
indicates the shutting of the semilunar valves. In add-on, there may besides be cardiac mutters, particularly
when the valves are unnatural. Some bosom mutter, nevertheless, may besides happen in healthy individuals, chiefly
during rapid or marked cardiac action. The survey of bosom sounds and mutters furnishes valuable
information sing the status of the bosom musculus and valves. The bosom sounds are recorded with
the assistance of sensitive mikes ( phonocardiography ) , so that anomalousnesss of the bosom or the valves can be
analyzed. The conductivity of the contraction stimulation can!
besides be recorded on the organic structure surface by an ELECTROCARDIOGRAPH. This measures the differences in
possible ( in microvolts ) that exist between a figure of fixed points on the limbs and the chest wall.
The EKG ( EKG, ECG ) that is obtained in this manner furnishes information about the
beat of the bosom, the conductivity of the stimulation, and the status of the bosom musculus. Other methods
that have been devised to analyze the bosom are the mechanical recording of the pulse,
echocendiography and radioisotopes, X-ray analysis of the bosom & # 8217 ; s signifier and motions, and X-ray contrast
surveies of the blood flow through the bosom and the coronary vass.