Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Introduction to the Circulatory System Read below about the circulatory system. Answer the questions below attached. The Importance of a Circulatory System Your circulatory system carries nutrients to cells, wastes away from cells, and chemical messages from cells in one part of the body to distant target tissues. It distributes heat throughout the body and, along with the kidneys, maintains acceptable levels of body fluid. No cell is further than two cells away from a blood vessel that carries nutrients. Your circulatory system has 96 000km of blood vessels to sustain your 100 trillion cells. No larger than the size of your fist and with a mass of about 300g, the heart beats about 70 times/min from the beginning of life until death. During an average lifetime, the heart pumps enough blood to fill two large ocean tankers. Every minute, 5 L of blood cycles from the heart to the lungs, picks up oxygen, and returns to the heart. Next, the heart pumps the oxygen-rich blood and nutrients to the tissues of the body. The oxygen aids in breaking down high-energy glucose into low-energy compounds and releases energy within the tissue cells. The cells use the energy to build new materials, repair existing structures, and for a variety of other energy-consuming reactions. Oxygen is necessary for these processes to occur, and the circulatory system plays a central role in providing oxygen. The circulatory system is also vital to human survival because it transports wastes and helps defend against invading organisms. It permits the transport of immune cells throughout the body. The Challenge of Transporting Oxygen and Nutrients Single-celled organisms, such as an amoeba have no need for a circulatory system because oxygen diffuses directly into the cell from the external environment. The products of cellular respiration (carbon dioxide and water) can leave the organism by diffusion as well. Even simple multicellular organisms such as the sponge, have no need for a circulatory system in an acquatic environment. Because the sponge has only two cell layers, all cells remain in contact Sponge – transportation of oxygen and nutrients with water. The flagella pull water into the sponge, bringing oxygen and nutrients into the body. Water and wastes are expelled through the large pore, or osculum, at the top of the body. All things that need to be absorbed or eliminated by the cells can pass directly into or out of each cell. Open and Closed Circulatory System More complex organisms have three cell layers. Relying on diffusion to deliver oxygen and nutrients is too limiting for more complex animals. The middle cell layer, or mesoderm layer, is sandwiched between the ectoderm and endoderm and does not come in direct contact with circulatory fluids or water. Cells of the mesoderm need a circulatory system to bring them into contact with oxygen and nutrients. For this, there are two circulatory systems; the organism physiology and functions play a key role as to which type of circulatory system they have. Open and Closed Circulatory Systems In an open circulatory system, blood carrying oxygen and nutrients is not always contained in blood vessels and is pumped by one or several hearts towards a central cavity where all the cells are bathed in the blood. The blood returns to the heart(s) when the heart(s) relaxes. This type of circulatory system is commonly found in snails, insects and crustaceans. There is no distinction between the blood and the interstitial fluid Snail – has an open circulatory system (refers to fluid between cells) in this system. The contraction of one or more hearts pushes blood from one body cavity to another. Muscular movements by the animal during locomotion can assist blood movement, but diverting blood flow from one area to another is limited. When the heart relaxes, blood is drawn back toward the heart through open-ended pores. In a closed circulatory system, the blood does not come in direct contact with all cells. The blood is separated from other fluids, is transported around the body in blood vessel, and circulates in one direction only. This system is commonly found in earthworms, squids, octopuses, and vertebrates. QUESTIONS 1. Describe the main functions of the circulatory system. 2. Differentiate between an open and closed circulatory system. 3. Identify one advantage and one disadvantage to an open circulatory system. 4. Why do large, multicellular animals require a circulatory system? 5. What purpose is served by the respiratory system? 6. Why is the respiratory surface for terrestrial organisms inside rather than outside the body?