The Human Heart And Functions Essay

While the free essays can give you inspiration for writing, they cannot be used 'as is' because they will not meet your assignment's requirements. If you are in a time crunch, then you need a custom written term paper on your subject (the human heart and functions)
Here you can hire an independent writer/researcher to custom write you an authentic essay to your specifications that will pass any plagiarism test (e.g. Turnitin). Waste no more time!

Abstract:

Dorland's Illustrated Medical Dictionary defines the

heart as "the viscus of cardiac muscle that maintains

the circulation of the blood". It is divided into

four cavities; two atria and two ventricles. The left

atrium receives oxygenated blood from the lungs. From

there the blood passes to the left ventricle, which

forces it via the aorta, through the arteries to

supply the tissues of the body. The right atrium

receives the blood after it has passed through the

tissues and has given up much of its oxygen. The

blood then passes through the right ventricle into

the lungs where it gets oxygenated. There are four

major valves in the heart; the left atrioventricular

valve (also known as the mitral or bicuspid valve),

the right atrioventricular valve (tricuspid), aortic

valve, and the pulmonary valve. The heart tissue

itself is nourished by the blood in the coronary

arteries.

Position of the Heart Within the Body:

The heart is placed obliquely in the chest. The two

atria are directed upwards and backwards to the right and

are at the level of the fifth through the eight dorsal

vertebrae.

The apex of the heart points downwards and forwards to the

left and corresponds to the interspace between the fifth and

sixth ribs, two inches below the left nipple. Its atrial

border corresponds to a line drawn across the sternum on a

level with the upper border of the third costal cartilage.

Its lower border (apex) corresponds to a line drawn across

the lower end of the same bone, near the xiphoid process.

Its upper surface is rounded and convex, directed upwards

and forwards, and formed mainly by the right ventricle and

part of the left ventricle. The posterior surface of the

heart is flattened and rests upon the diaphragm muscle. Of

its two borders, the right is the longest and thinnest, the

left is shorter but thicker and round.

Size:

In an adult, the heart measures about five inches in

length, three and a half inches in the broadest part of its

transverse diameter, and two and a half inches in its

antero-posterior. The average weight in the male varies

from ten to twelve ounces. In the female, the average

weight is eight to ten ounces. The heart will continue to

grow in size up to an advanced period of life. This growth

is more obvious in men than in women.3

Circulation of Blood in an Adult:

The heart is subdivided by a longitudinal muscular

septum into two lateral halves which are named right and left

according to their position. A transverse muscle divides

each half into two cavities. The upper cavity on each side

is called the atria/auricle, and the lower side is called

the ventricle. The right atrium and ventricle form the

venous side of the heart. Dark venous blood is pumped into

the right atrium from the entire body by the superior (SVC)

and inferior vena cava (SVC), and the coronary sinus. From

the right atrium, the blood passes into the right ventricle

and from the right ventricle, through the pulmonary artery

into the lungs.3 Once the blood becomes

oxygenated/arterialized by its passage through the lungs, it

is returned to the left side of the heart by the pulmonary

veins which open into the left atrium. From the left

atrium, the blood passes into the left ventricle where it is

distributed by the aorta and its subdivisions through the

entire body.

Morphology of Each Heart Chamber:

The right atrium is a little longer than the left. Its

walls are also somewhat thinner than the left. The right

atrium is capable of containing about two ounces of fluid.

It consists of two parts, a principle cavity/sinus, and an

appendix auriculae. The sinus is a large

quadrilateral-shaped cavity located between the IVC and the

SVC. Its walls are extremely thin and are connected on the

lower surface with the right ventricle and internally with

the left atrium. The rest of the right atrium is free and

unattached. The appendix auricle is a small conical

muscular pouch. It projects from the sinus forwards and to

the left side, where it overlaps the root of the pulmonary

artery.6

There are four main openings into the right atrium;

the SVC, IVC, coronary sinus, and the atriculo-ventricular

opening. The larger IVC returns blood from the lower half

of the body and opens into the lowest part of the right

atrium, near the septum. The smaller SVC returns blood from

the upper half of the body and opens into the upper and

front part of the right atrium. The coronary sinus opens

into the right atrium between the IVC and

auriculo-ventricular opening. It returns blood from the

cardiac muscle of the heart and is protected by a

semicircular fold of the lining membrane of the atrium,

called the coronary valve. The auriculo-ventricular opening

is the large oval aperture of communication between the

right atrium and ventricle. There are two main valves

located within the right atrium; the Eustachian valve and

the coronary valve.3 The Eustachian valve is located

between the anterior margin of the IVC and the

auricule-ventricular orifice. It is semilunar in form. The

coronary valve is a semicircular fold of the lining membrane

of the right atrium, protecting the orifice of the coronary

sinus.

The right ventricle is triangular-shaped and extends

from the right atrium to near the apex. Its anterior surface

is rounded and convex and forms the larger part of the front

of the heart. Its posterior surface is flattened, rests on

the diaphragm muscle, and forms only a small part of this

surface. Its inner wall is formed by the partition between

the two ventricles, the septum, and bulges into the cavity

of the right ventricle. Superiorly, the ventricle forms a

conical structure called the infundibulum from which the

pulmonary artery arises. The walls of the right ventricle

are thinner than those of the left ventricle. The thickest

part of the wall is at the base and it gradually becomes

thinner towards the apex. The cavity can contain up to two

ounces of fluid.

There are two openings in the right ventricle; the

auriculo-ventricular opening and the opening of the

pulmonary artery. The auriculo-ventricular opening is the

large oval opening between the right atrium and the right

ventricle. The opening is about an inch in diameter. It is

surrounded by a fibrous ring, covered by the lining membrane

of the heart (endocardium), and is larger than the opening

between the left atrium and the left ventricle. It is

protected by the tricuspid valve. The opening of the

pulmonary artery is round and is situated at the top of the

conus arteriosus, close to the septum. It is on the left

side and is in front of the auriculo-ventricular opening.

It is protected by the semilunar valves.3

There are two main valves associated with the right

ventricle; the tricuspid valve and the semilunar valves.

The tricuspid valve consists of three segments of a

triangular shape, formed by the lining membrane of the heart

(endocardium). They are strengthened by a layer of fibrous

tissue and muscular fibers.1 These segments are connected

by their bases to the auriculo-ventricular orifice, and by

their sides with one another, so as to form a continuous

membrane which is attached around the margin of the

auriculo-ventricular opening. Their free margin and

ventricular surfaces are attached to many delicate tendinous

cords called chordae tendinae. The central part of each

valve segment is thick and strong while the lateral margins

are thin and indented. The chordae tendinae are connected

with the adjacent margins of the main segment of the valves.

The semilunar valves guard the opening of the pulmonary

artery. They consist of three semicircular folds formed by

the endothelial lining of the heart and are strengthened by

fibrous tissue. They are attached by their convex margins

to the wall of the artery at its junction with the

ventricle. The straight borders of the valve are unattached

and are directed upwards in the course of the vessel,

against the sides of which they are pressed during the

passage of blood along its canal. The free margin of each

valve is somewhat thicker than the rest of the valve and is

strengthened by a bundle of tendinous fibers. During the

passage of blood along the pulmonary artery, these valves

are pressed against the sides of its cylinder. During

ventricular diastole (rest), when the current of blood along

the pulmonary artery is checked and partly thrown back by

its elastic walls, these valves become immediately expanded

and close the entrance of the tube. 3

The left atrium is smaller but thicker than the right

atrium. It consists of two parts; a principle cavity/sinus

and an appendix auriculae. The sinus is cuboidal in form

and is covered in the front by the pulmonary artery and the

aorta. Internally, it is separated from the right atrium by

the septum auricularum. Behind the sinus on each side, it

receives the pulmonary veins. The appendix auriculae in the

left atrium is narrower and more curved than the same

structure in the right atrium. Its margins are more deeply

indented, presenting a kind of foliated appearance. Its

direction is forwards towards the right side, overlapping

the root of the pulmonary artery.

There are two main openings in the left atrium; the

openings of the four pulmonary veins and the

atrial-ventricular opening. Two of the four pulmonary veins

open into the right side of the atrium and two open into the

left side. The two veins on the left exit into the atrium

through a common opening. None of the pulmonary veins have

valves. The atrial-ventricular opening is the large oval

opening of blood flow between the atrium and the ventricle.

It is smaller than the same opening between the right atrium

and ventricle.3

The left ventricle is longer and more conical shaped

than the right ventricle. It forms a small part of the left

side of the anterior surface of the heart and a large portion

of the posterior surface. It also forms the apex of the heart

because it extends beyond the right ventricle. Its walls

are nearly twice as thick as those of the right ventricle.

They are thickest in the broadest part of the ventricle,

becoming gradually thinner towards the base and also towards

the apex, which is the thinnest part of the left ventricle.

There are two main openings in the left...

You should cite this paper as follows:

MLA Style
. EssayMania.com. Retrieved on 25 May, 2012 from
    <http://essaymania.com/94250/the-human-heart-and-functions>

More College Papers

The Impossibility Of Evolution essay
Creation vs. Evolution While the theory of evolution is very commonly accepted amongst most scholars and intellectuals, when the scientific facts used to 'support' it are closely examined, it becomes apparent that it is merely that: a theory. Inaccurate information, misguided philosophers, and in s

Future Of Internet essay
The Future of Internet 04/24/2000 Forum Paper Table of Contents 1. Audience Page 2 2. Introduction Page 3 3. Body of Forum Paper 3.1 Influences in Businesses Page 4 3.2 Influences in Education Page 6 3.3 Influences in Communication Page 7 4. Survey Page 8 5. Reflection Page 9 6. Conclu

The Gaia Hypothesis essay
The Gaia Hypothesis The Gaia Hypothesis is a hypothesis that was developed by James Lovelock and Lynn Margulis in the late 1970's. James Lovelock is a British scientist, an atmospheric chemist, and also an inventor with an education in human physiology. Lynn Margulis was a microbiologist during the