Lolo Essay Research Paper Forwards and backwards (стр. 1 из 3)

Lolo Essay, Research Paper

Forwards and backwards to the right and are at the same level of the fifth to eight dorsal vertebrae. The apex of the heart points downwards and forwards to the left and corresponds to the space between the fifth and sixth ribs. However, in thin people, the hearts apex may be pointing more downwards than to the left. Its atrial border corresponds to a line drawn across the sternum on a level with the upper border of the third costal cartilage. Its apex corresponds to a line drawn across the lower end of the same bone. Its upper surface is rounded and convex, directed upwards and forwards, which is formed mainly by the right ventricle and a part of the left ventricle. The back surface of the heart is flattened and rests upon the diaphragm. Of its two borders, the right is the longest and thinnest, the left is shorter but thicker and round. The muscles that make up the heart are known as cardiac muscles. Cardiac muscle only exists in the heart, not like skeletel muscle which is found in many parts of the body. Cardiac muscle fibers possess striations that are typical of skeletel muscle. However, they only respond to the autonomic nervous system and electrical commands that are generated from the heart. Skeletel muscle may have many nuclei, but cardiac muscle only has one nucleus. As well, cardiac muscle is very small compared to the larger skeletel muscle. As fitting with its duty, cardiac muscle has many mitochondria to convert food into energy faster than other muscles. Cardiac muscles communicate between junctions that are laid down between the muscles. They are called intercalated disks. Along certain points of the disks, cell membranes fuse together. The electrical current required to cause the muscles to contract pass through the cells easily and the adjoining cells will respond as well due to the intercalated disks. The cardiac muscle is really a large number of cells working together that function to act as a single cell.

There are many proteins that give cardiac, as well as other muscles, to contract. Thin bundles of protein called myofibrils run the length of each fiber. Within the myofibrils are filaments (tiny threads of protein) that are arranged in a repeating pattern called a sarcomere. The filaments in each sacromere are made up of the proteins actin and myosin. Two clusters of actin are set in each end of the sacromere stretch towards the centre but do not touch. There are continuos threads of myosin located at the end of the sarcomere. The contraction can occur because of the region where the actin and myosin over lap each other. Small hooks on the myosin binds to the actin filaments and pull towards the centre of the sarcomere. This happens through the rapid ratchet-like actions of the myosin and actin pulling together. When the sarcomere pulls together, the fiber contracts and so does the muscle. In order for this to occur again, the sarcomere must be stretched out, which is caused by the blood re-entering the heart, expanding it.

In an adult, the heart measures about five inches in length, three and a half inches in the broadest part of its horizontal diameter, and two and a half inches in its posterior. The average weight in the males is 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 old age. This growth is more obvious in men than in women.

The heart is subdivided by a muscle called the septum into two halves, which are named right and left according to their position. A muscle divides each half into two cavities. The upper cavity on each side is called the atria or 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 vena cava(SVC) and inferior vena cava (IVC), 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 lܥe # ⠠Р ” ߝ , l , l

G ( 캠 T  Q X

G Times New Roman


Arial Times New Roman Navraj Grewal The Circulatory System February 1997

In all organisms, circulation involves all of the fluids of the body and the continual movement of them between the various tissues in the body. It is a process of taking in material that is required for metabolism and delivering it to the cells of the body. The by-products then to be delivered out of the body into the environment. Invertebrate animals have many different liquids, cells and methods of circulation. There are two kinds of circulation paths: open circulatory system and closed circulatory system. All vertebrates use the closed system. This means that the fluid is carried through the body in a network of vessels. In contrast, the open system does not use this method, rather the fluid passes freely throughout the tissues. In the closed system, the two fluids are blood and lymph. They are each in their own intricate network. Blood uses the cardiovascular system and lymph uses the lymphatic system. The highest amount of complexity is reached in the human body.

All organisms take molecules from their environment and use them in metabolism to produce their energy. The by-products are then removed into the environment. An organism creates a difference between the internal environment of the animal in relation to the external environment. With cells, either as single organisms, (ie, ameba) or as parts of a multicellular animal (ie, human beings), there is a requirement of taking molecules in by direct diffusion through a cell wall or by vacuoles. The process of cyclosis, streaming of fluid cytoplasm) distributes the metabolic product. The molecules are conveyed between cells and throughout the body of multicellular organisms in the circulatory fluid called the blood. It travels through the body in blood vessels which is pumped through by the heart. There is a major role in homeostasis (the constancy of the internal environment) played by the lymph and blood. This occurs, because the fluids distribute substances to parts of the body when and where required by taking it away from other areas where there may be a surplus which may be harmful.

There are many invertebrate animals that live in the water and the supplying of fluid is not extremely important. For land dwelling creatures however, the fluid that reaches the tissues is supplied by drinking water. It is absorbed in the alimentary canal and passed into the bloodstream. Fluid can leave the blood with food or other organic compounds that are dissolved in the stream. From the blood they all pass into the tissue needing the material. This material is then returned in the form of lymph. Lymph passes through in lymphatic channels, which provides the lymphatic circulation.

However, in many invertebrates, circulating fluid is not restricted to blood or lymphatic vessels. Both of the functions of the circulating and tissue fluid are combined as a single fluid. This is known as hemolymph. The internal circulatory system transports important gases and nutrients around the body of an organism. It removes unwanted products of metabolism from the tissues and carries it to the excretory organs.

For the blood and fluid to be moved or pumped throughout the body, an organism

requires an organ to pump the fluid. The heart is “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. The blood is then passed to the left ventricle, which forces it through 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 delivered much of its oxygen and organic molecules. The blood then passes through the right ventricle into the lungs where it gets oxygenated. In the heart, there are four major valves, 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.

The heart is placed below the alimentary canal in front of the centre of the chest. It is located in it’s own body cavity. The two atria are pointed upwungs. Once the blood becomes oxygenated by its passage through the lungs, it returns 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.

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 and an appendix auriculae. The sinus is a large quadrilateral-shaped cavity located between the IVC and the SVC. Its walls are very thin and are connected on the lower surface with the right ventricle and with the left atrium. The rest of the right atrium is 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.

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 of the atrium called the coronary valve. The auriculo-ventricular opening is the large oval opening 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. 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. There are two main valves associated with the right ventricle; the tricuspid valve and the semilunar 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. 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. As seen in the diagram to the right. 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. When blood flow is in the direction of the opening of the valve it causes the valve to open. This occurs when the heart pumps the blood (systole). During rest of the heart (diastole), the current of blood along the pulmonary artery is thrown back by its elastic walls, these valves become immediately expanded and close the entrance of the tube. The valves are attached by their border to the wall of the artery at its connection with the ventricle. The free flap of each valve is thicker than the rest of the valve and is strengthened by a bundle of tendinous fibers.

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 cubed in shape and is covered in the front by the pulmonary artery and the aorta. In the heart , 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 auriculae in the right atrium. Its borders are more deeply pressed in, causing a folded 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. This is because there is less pressure on the veins than in the arteries. 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.

The left ventricle is longer and more cone shaped than the right ventricle. It forms a small part of the left side of the front surface of the heart and a large par of the back surface. It also forms the apex of the heart because it extends beyond the right ventricle. Its walls are almost 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. This is the thinnest part of the left ventricle.

There are two main openings in the left ventricle, the atrial-ventricular opening and the aortic opening. The atrial-ventricular opening is located behind and to the left side of the aortic opening. The opening is a slightly smaller than the same opening between the right atrium and right ventricle. Its position is the center of the sternum. It is surrounded by a very dense fibrous ring and is covered by the lining membrane of the heart and is protected by the mitral valve. The circular aortic opening is located in front of and to the right side of the atrial-ventricular opening. It is separated by one of the segments of the mitral valve. The opening is protected by the semilunar valves. The semilunar valves have no chordae tendonae, therefore they are simpler in structure than the atrial-ventricular valves.

There are two valves located within the left ventricle; the mitral valve and the semilunar valve. The mitral valve is attached to the circumference of the atrial-ventricular opening in the same way that the tricuspid valve is attached on the opposite side of the heart. The valve contains a few muscular fibers and is strengthened by fibrous tissue. It is formed by the lining of the heart, the endocardium. It is larger, thicker, and stronger than the tricuspid and consists of two segments of differing size. The mitral valves are connected to many chordae tendonae. Their attachment is the same as on the right side except they are thicker, stronger and there are not as many. The semilunar valves surround the aortic opening. They are similar in structure and attachment to those of the pulmonary artery. However, they are larger, thicker, and stronger than those of the right side. Between each valve and the cylinder of the aorta is a deep depression called the sinuses of Valsalva. The depressions are larger than those at the root of the pulmonary artery.

The heart and its vessels are surrounded by a membranous sac called the pericardium. The pericardial sac is composed of two layers. The parietal pericardium and the visceral pericardium with the space in-between the two called the pericardial cavity. The parietal pericardium is made up of mostly compact fibrocollagenous tissue along with elastic tissue. It is a membrane of loose irregular connective tissue that is lined internally by a mesothelium which is simple squamous epithelium. The visceral pericardium forms the internal lining of the pericardium and comes over the outer surface of the heart. This reflection forms the outer layer of the epicardium. The visceral epicardium is also composed of fibrocollagenous tissue with elastic tissue, but is smooth mesothelium. The pericardial cavity is located between the parietal and visceral pericardium and contains small amounts of serous fluid.

Copyright © 2015-2018. All rigths reserved.