Heart Essay Research Paper HEARTThe human heart

9 September 2017

Heart Essay, Research Paper

Heart Essay Research Paper HEARTThe human heart Essay Example


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. 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.


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.


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.


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.

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