Human Transport System - Essay Example

Human transport system Heart Heart of a man is a hallow conical four chambered muscular organ obliquely placed in the thorax above the diaphragm andin between the lungs that circulates blood through out the body. It weighs of about 200 to 425 g and is slightly larger than a human fist. The heart muscles periodically contract and relax forming a cardiac cycle aiding pumping of the blood. In a healthy adult the heart contracts about 72 times pumping approximately 5 liters of blood every minute. Figure 1. Anatomical representation of heart 1 Anatomically heart is divided into two sides-the right side and left side. Right side The right side comprises of two chambers i) Upper right atria which receives blood from the veins and the coronary sinus and pumps blood to ii) lower right ventricle which in turn pumps the blood to lungs through pulmonary artery. The atria and ventricle are separated by auricoventricular septum with a aperture guarded by three flaps called as tricuspid valve which prevents back flow of blood from right ventricle to right atria when right ventricle contracts. The opening of pulmary artery is also guarded by semi lunar valves to prevent the back flow of blood from pulmonary artery to right ventricle when it contracts. Thus right side of the heart receives venous blood from all parts of the body and pumps it to lungs for oxygenation. Left side The left side of the heart also comprises of two chambers iii) upper left thin walled atria which receives oxygenated blood from the lungs through pulmonary veins and pumps to iv) lower left ventricle in turn opens to aorta to distribute to all parts of the body. Here again the atrioventricular septum separates upper and lower left atria and the ventricle with an aperture guarded by two flaps called the 'bicuspid valve' and the opening of aorta is guarded by 'aortic valve'. Circulation of blood in the heart The superior vena cava collecting the deoxygenated blood from upper torso and head and Inferior venacava collecting from the lower torso and legs feeds the right atrium. The right atrium on contraction pours to right ventricle. The right chambers are small compared to left chambers as they carry blood to lungs of about a short distance. From the right ventricle pulmonary artery carries the deoxygenated blood to lungs for reoxygenation. After reoxygenation from lungs the blood is carried through pulmonary vein to left atrium which on contraction pumps to left ventricle. When the left ventricle if full the left atrium contracts pumping the blood in the left ventricle into the aorta which then distributes to entire body by means of small arteries arterioles and capillaries. Types of circulation I) Coronary circulation: Coronary circulation is the circulation of blood through the tissues of the heart for its own nourishment. The two coronary arteries branch from aorta and further branch themselves into smaller arteries capable enough to penetrate the cardiac muscles. II) Pulmonary circulation: The deoxygenated blood in right atrium is pumped to right ventricle and from there to lungs for reoxygenation and back from lungs to left atrium and subsequently to left ventricle is known as pulmonary circulation. III) Systemic circulation: the reoxygenated blood collected from lungs leaves the heart through the main artery-aorta. Aorta supplies the reoxygenated blood to all parts of the body through network of smaller arteries and capillaries. Again after the exchange of oxygen and metabolites it is collected from the capillaries of venous system and directed to the right atrium through two vena cavae. This phase is systemic circulation. During systemic circulation blood passes through kidneys for waste removal known as 'renal circulation' phase and also through small intestine known and 'portal circulation' phase. Structure and functions of the blood vessels Anatomically all blood vessels are made up of three layers i) inner -tunica intima. It is made up of flat endothelial cells resting on a layer of connective tissue with secretion of many vasoactive compounds being the function; ii) middle- tunica media is composed of smooth muscle cells disposed circularly and embedded in a matrix of collagen and elastin fibre. Hence it provides mechanical strength and also contractile power; iii) outer layer-tunica adventitia is composed of connective tissue with tiny blood vessels being nourishing in function. The cardio-vascular system comprises of heart and blood vessels. There are five main types of blood vessels. They are the arteries, the arterioles, the capillaries, the venules and the veins. Artery: They are the main blood vessels that carry oxygeneated blood from the heart. Arteries are thick walled and elastic in nature. The cell walls of arteries are made up of three layers i) An outer connective tissue layer ii) middle -elastic and muscular tissue layer iii) inner-endothelial layer. Pulmonary artery is the only artery which carries impure blood and all other arteries carry only oxygenated blood. Arterioles: The arteries branches into arterioles supplied with nerves and are thin walled. Capillaries: Further arterioles sub divide into capillaries which are thin walled and the lumen of capillaries varies from 7 to 10 microns. This is site of exchange for substances between blood and tissues. The arteries and their subdivisions which carry oxygenated blood from heart constitute the "Arterial System". Figure 2 Network of capillaries Venules: The capillaries further begin to thicken and merge to form venules. Veins: The smaller venules unite to form veins. They carry blood towards the heart. The network of veins forms the venous system of circulatory system. Functions of the circulatory system The main and basic function of circulatory system is transportation of blood. Apart from this function it performs various other important functions as it carries blood which is responsible for: Transportation of substances: Transportation of nutrients from digestive system, exchange of gases, of metabolic wastes from different parts of the body to excretory organs, hormones from the endocrine glands to target organs. Thermoregulation is maintained by vasodilatation and vasoconstriction in skin. Immunity: Due to the phagocytic nature and immune boosting mechanism of blood components and also the blood clotting in case of injury. Components of blood and their function Blood is a very vital fluid connective tissue. The total volume of blood in the system is about 5 to 6 liters. Blood is composed of two major components-liquid component and solid components consisting of blood cells and platelets. Plasma Plasma is straw colored liquid component of blood in which the cell components of blood are suspended. 90% of plasma is made up of water in which 8-10% of solids are dissolved. The solids include 1) proteins such a) serum albumin responsible for osmotic pressure of plasma b) serum globulin are immunogenic in nature c) serum fibrinogen assisting in blood clotting. 2) Inorganic constituents such as sodium, calcium, potassium, etc., necessary for almost all physiological functions like maintaining blood pressure, exerting osmotic pressure, etc., 3) Organic constituents other than proteins such as urea, uric acid, xanthine, creatine, ammonia, amino acids, phosphor, lipids, cholesterol, glucose etc., 4) internal secrections such as antibodies, hormones and various enzymes. Blood cells I) Erythrocytes: Erythrocytes are also known as Red blood cells. In human RBC is biconcave disc shaped without nucleus and with an average life span of about 110 days. RBCs are manufactured in the red marrow of the bone and stored in the spleen. The RBC contains respiratory pigment called hemoglobin which gives the blood red color. In a normal man the count of RBC is about 50,00,000/cubic/mm of blood. Function: Due to the presence of the respiratory pigment RBC they are the transporters of gases from lungs to all parts of the body and vice versa. II) Leukocytes: Leukocytes also known as White Blood Cells (WBC) are nucleate cells. Based on the presence of granules in their cytoplasm they are further grouped as i) granulocytes and ii) agranulocytes. 1. Granulocytes: They are WBC with cytoplasm granules with varying shapes of nucleus which is usually shrunken. Granulocytes are further classified as: a) Eosinophilis: they posses two lobed nucleus, spherical in shape and their cytoplasmic granules stain with acid dyes such as eosin. Function: detoxification of foreign particles, involved in allergic responses boosting body immunity. b) Basophils: The nucleus is 'S' shaped with two or more constrictions. The granules take up basic stains such as methylene blue. Function: These cells are known to contain anticoagulants, heparin, histamine which is a vasodialator and serotonin which is a vasoconstrictor. They are known to control the viscosity of the connective tissue ground substance. c) Neutrophils or heterophils: The nucleus is polymorphic where it could be elongated, bent, twisted and has several angular lobes. The granules stain with neutral dyes. They are phagocytic in nature assisting in wound healing. 2. Agranulocytes: These WBC do not contain granules in their cytoplasm. They are of two types: Lymphocytes: The nucleus is round or indented produced by lymphoid tissue. They are of two types-T lymphocytes, B lymphocytes. Function: Phagocytic in nature, stimulates antibody production and also detect and kill cancer cells. Monocytes: They are the largest among the WBC formed in lymphoid tissue. The nucleus is kidney or horse shaped. Function; Phagocytic and produce globulins to combat chemicals released during disease or injury. III) Thrombocytes: Also known as blood platelets are without nucleus, lesser in number than RBC and WBC. Function: Blood clotting/coagulation of blood. Diseases associated with heart Two major diseases associated with myocardial infarction are Atheroma and Thrombosis. Thrombosis Thrombosis is an abnormality due to the formation of internal clot in the blood vessels obstructing the blood flow. An injury causing damage to the endothelial lining of blood vessels induces coagulation process resulting in the formation of thrombin from the cleavage of prothrombin (Grum and Bhatt, 2005). Thrombin being potent vasoconstrictor and platelet aggregant inducing more platelets at the site of injury. According to Virchow's triad (Dickson, 2004) thrombosis may occur due to: Hyper coagulation of blood as in case of genetic disorders or autoimmune disease, Endothelial cell injury due to trauma, infection, or turbulent flow at bifurcations, Hemostasis (variations in blood flow may be due to stagnation of blood flow or sloe movement of blood flow past the point of injury). Thrombus may isolate from the site of injury and enter the blood circulation as embolus blocking a blood vessel. In case of a bacterial infection the thrombus may differentiate spreading the infection through out the circulatory system and also forming metastatic abscesses at places of rest. Atheroma Atheroma is an unhealthy condition of the blood vessel where there is accumulation and swelling of artery walls with the deposits of lipids and formation of fibrous tissue. The accumulations of WBC macrophages that have taken by oxidized low- density lipoprotein (LDL) usually occur between the endothelium lining and the smooth muscle wall of the arterial tube. They accumulate cytoplasmic membranes associated with high cholesterol content forming foam cells. These foam cells degenerate releasing their contents to be invaded by macrophages creating an extra lipid core on the inner central surface of atheroma plaque. The outer plaque calcifies, becomes metabolically less active and rigid resulting in total occlusion. Atheroma affects only arteries supplying heart, brain and abdominal viscera. Diseases associated with blood Two major diseases associated with blood are: Anemia and Leukemia (Blood disease,2008) Anemia Anemia derived from Greek means 'without blood'. Anemia is a pathogenic condition of blood arising mainly due to qualitative or quantitative deficiency of hemoglobin resulting in hypoxia in organs. Anemia occurs due to i) the simultaneous production of red blood cells and hemoglobin does not occur with the normal rate of their destruction ii) excessive destruction exceeds production iii) excessive haemorrhage. RBC production failure may be due to deficiency of folic acid, iron or Vitamin B12, due to other diseases, due to leukemia or tumor etc., Severity and tolerance differs from person to person. The most noticeable symptoms of anemia are pallor of the skin, mucous membranes, and nail beds. There are various kinds of Anemia the details of which are beyond the scope of this article. Leukemia Leukemia is a potentially fatal disease of the blood arising due to the presence of large number of WBC where the counts may range from as 500,000 per cubic millimetre and even 1,000,000 per cubic millimeter. There two types of leukemia; myelogenous and lymphocytic which are further subdivided into acute and chronic categories based on the duration of the untreated disease. The exact reason for leukemia is not known, but ionizing radiations, mutations have been recognized certain risk factors. Symptoms of leukemia is general weakness and fatigue due to anemia, hemorrhages in skin, nosebleeds or gum bleeding due to a decrease in the platelet count. Further details regarding types and treatment are beyond the scope of this article. References Dickson, B.C.2004, 'Virchow's triad' The Southern Medical Journal vol.97, pp.915-916. Blood disease. 2008. In Encyclopdia Britannica. Retrieved April 24, 2008, from Encyclopdia Britannica Online: http://www.britannica.com/eb/article-33526 Grum, H.S and Bhatt, D.L. 2005. Thrombin, an ideal target for pharmacological inhibition; A review of direct thrombin inhibitors. American Heart Journal (in press) 1url:http://www.rbch.nhs.uk/images/dorset_health_centre/heart_diagram.jpg Read More