Transport in Organisms PDF

Transport in organisms is essential in moving and distributing materials, such as fluids and nutrients, to the different parts of the body. Transport in animals differs depending on physical structures. In animals, the nature of the circulatory system varies depending on the size, complexity, and ha...

Transport in organisms is essential in moving and distributing materials, such as fluids and nutrients, to the different parts of the body. Transport in animals differs depending on physical structures. In animals, the nature of the circulatory system varies depending on the size, complexity, and habitat of an organism. In simple animals like sponges and cnidarians, gas exchange happens between the water from the environment and the circulating body fluid. In sponges, water enters through a series of tiny pores in the body to the spongocoel, the large inner central cavity in the sponge. This is where gas exchange happens directly with the cells. In cnidarians such as the hydra, each cell is directly in contact with the external environment since the body wall is only one cell thick. In roundworms, which are pseudocoelomates, body fluid is used for circulation. This is accomplished by the body's movement against the fluids that are directly in contact with the tissues and organs. There are two main types of circulation: open circulation and closed circulation. In the open circulatory system, the hemolymph or the circulating fluid in invertebrates does not pass through enclosed tubes. Instead, it is pumped by the heart to a network of channels and cavities (hemocoels) throughout the body. It is also through this network of channels and cavities where gas exchange takes place. In a closed circulatory system, the blood or circulating fluid passes within blood vessels that transport blood away from and back to the heart. Insects and other arthropods are animals with an open circulatory system. The heart pumps blood into small cavities called hemocoels, where gas exchange between tissues and the hemolymph takes place. Then, blood diffuses back to the central cavity. An earthworm is an invertebrate with a closed circulatory system Here, blood is pumped from the "hearts" to a system of vessels in the different parts of the body and then back to the heart. Vertebrates exhibit a closed circulatory system. These animals have a heart and blood vessels through which the blood circulates. Their circulatory systems may vary from one another in terms of the number of heart chambers. Despite these variations, however, they all function in supplying nutrients and gases to the different parts of the body and in collecting metabolic wastes.. The structures of the circulatory system and their functions are uniquely adapted to keep the complex organism alive. For example, the different blood vessels help transport blood and nutrients to the cells of the body. The circulatory system supplies gases, nutrients, and hormones to the different parts of the body and collects metabolic wastes. A healthy circulatory system regulates normal homeostatic reactions, immunologic reactions, and acid-base balance in the human body. There are four components of the circulatory system: heart, blood, blood vessels, and valves. The human heart is a muscular organ that pumps blood to all parts of the body. It is one of the organs that develop in an embryo about four weeks following fertilization. In the average life span of a person, the heart beats around 2.5 billion times without interruption. A typical adult heart beats approximately 72 times every minute and pumps about 5.5 liters of blood. Your heartbeat can vary depending on your activity. It can be fast as when you run or slow as when you sleep. The heart can beat three times as fast as the normal rate during a strenuous exercise or when you get overexcited reaching about 180 to 195 beats per minute. The heart is composed of cardiac muscle, an involuntary, striated muscle, with associated nervous and connective tissues. An adult heart is about the size of a fist. It has its own pericardial cavity, and is covered by the pericardium. A septum divides the heart into two sides. The right side receives deoxygenated blood collected from the different parts of the body, while the left side receives oxygenated blood from the lungs. Each side of the heart is divided into the upper and lower chambers. The upper chambers are called atria (singular, atrium), while the lower chambers are called ventricles. One-way valves called atrioventricular valves are located between the upper and the lower chambers. The flow of blood to the heart begins with the deoxygenated blood, which comes from the different parts of the body, entering the superior and inferior venae cavae (singular, vena cava) and filling the right atrium. This causes the tricuspid valve, found between the right atrium and right ventricle, to open, bringing blood to the right ventricle. This valve closes when blood reaches the right ventricle to prevent blood backflow (regurgitation). From the right ventricle, blood is pumped into the pulmonary arteries, and then flows to the capillaries of the air sacs in the lungs. Here, the blood gives off carbon dioxide and some water and takes in oxygen. Once oxygenated, the blood flows to the pulmonary veins, into the left atrium. With pressure buildup, the mitral valve, located between the left atrium and left ventricle, opens, and oxygenated blood is pumped into the left ventricle. Again, blood fills up this chamber creating an increase in pressure which initiates the opening of the aortic valve. The "lub dub" sound that you hear using a stethoscope is the sound produced by the heart during contraction and relaxation. The "lub" sound is caused by the closing of the atrioventricular (AV) valves during ventricular contraction. The "dub" sound is caused by the closing of the valves that lead out of the heart. Systemic circulation begins when oxygenated blood is delivered from the aorta to the different parts of the body. lub-contraction dub-relaxation. Blood is the internal circulating medium of the human body. The primary function of blood is to carry nutrients and oxygen to the cells of the body and carry away carbon dioxide and nitrogenous waste from body cells. It consists of 55% plasma, the liquid part, and 45% blood cells or formed elements. The formed elements are red blood cells (erythrocytes), white blood cells (leukocytes), and blood platelets (thrombocytes). Erythrocytes transport oxygen and carbon dioxide. They have a lifespan of approximately four months. Leukocytes help in the body's defense against infection and immunity, while thrombocytes are essential in blood clotting. Plasma is composed of water, proteins, electrolytes, and other substances. Proteins such as hormones, fibrinogen, globulins, and albumin are found in blood plasma along with nutrients, waste products, and some dissolved gases. Cells receive nourishment from nutrients carried in the plasma. These substances include minerals, vitamins, amino acids, and glucose absorbed during the process of digestion and transported to the cells. It also transports waste materials to the excretory system for excretion. Blood vessels serve as "highways" through which blood is circulated in the body. There are three types of blood vessels: arteries, veins, and capillaries. Arteries are thick-walled vessels that carry oxygenated blood from the blood to different body organs and tissues. Their thick walls help to counteract the pressure exerted on them by the contraction of the heart muscles. The largest artery in the body is the aorta, the only artery that leads out of the left ventricle. Veins, which are thin-walled vessels compared to arteries, carry deoxygenated blood toward the heart. There are two large veins in the body, smooth muscle the superior and inferior venae cavae. The abundant microscopic blood vessels that carry blood throughout the tissues and organs, connecting the small veins and arteries, are called capillaries. Capillaries are the thinnest blood vessels made of only one layer of cells. They serve as sites through which materials between the blood and cells are exchanged. Because they are very thin, diffusion of materials across their walls readily takes place. Capillaries, which link an artery to a vein, also supply the brain with oxygen, keeping a person conscious. This is a continuous cyclic process for as long as the person lives. Valves are flaps of tissues that prevent the backward flow or regurgitation of blood (Figure 1.6). These are located between the atrium and the ventricle, and at the base of arteries that are attached to the ventricles of the heart. The closure of the valves creates the heart sounds heard during auscultation, a medical term for the act of listening to internal sound of the body that usually uses a stethoscope. Valves can also be found in large veins along the lower extremities to prevent the backward flow of blood. The heart valves are the bicuspid (mitral), tricuspid, aortic, and pulmonary valves. William Harvey was the first to show that the heart and blood vessels form a continuous, closed circulatory system (Figure 1.7). Generally, blood circulation in the body can be divided into pulmonary circulation and systemic circulation. Pulmonary circulation is the movement of blood from the heart to the lungs, and back to the heart. Systemic circulation follows pulmonary circulation. Once blood is in the aorta of the heart, it moves out of the heart to be circulated to all parts of the body and other subsystems. Coronary circulation is a subsystem that supplies blood to the heart itself. As an organ, the heart needs to be supplied with blood, too. There are two coronary arteries that branch off from the aorta and transport blood to the arterioles that penetrate the tissues of the heart. From here, blood returns to the right atrium through the coronary sinus, a large vessel. If a vessel from the heart is blocked, it prevents blood to flow to the heart muscle and could lead to heart attack, or myocardial infarction. Renal circulation is another subsystem that moves blood through the kidneys and back to the heart. There are two renal arteries that branch out to the kidneys and supply them with blood. In turn, the kidneys filter the blood of nitrogenous waste materials.