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Amy Young Three Definitions – Erythrocyte INTRODUCTION In this assignment we are to choose a somewhat complex term used in our discipline or profession and define it in three ways, including: a parenthetical definition, a sentence definition, and an expanded definition. We do this in order to study and practice the writing techniques associated with defining terms and with peer review. This will help us understand how important definitions are to technical writing and what role they play, as well as how the situation and audience determine whether a definition is needed and in what level of detail it should be given. THE SITUATION An introductory biology laboratory or class at a college or university teaching students about the human circulatory system. The audience is made up of mainly first year students, with little to no background in biology. They have likely been educated, earlier in this course, about the general structure of a cell and the basic organic molecules: carbohydrates, proteins and fats. Parenthetical Definition An erythrocyte (red blood cell) carries oxygen in the blood. Sentence Definition An erythrocyte is a common type of blood cell that contains the protein hemoglobin, carries oxygen from the lungs to other tissues in the body, and gives blood its red colour. Expanded Definition Erythrocytes (e-RITH-rō-sīts) are a type of blood cell, commonly called Red Blood Cells (RBCs). Their name originates from the Greek words erythro, meaning red, and cyte, which means cell (Chabner 504). Why are erythrocytes red? Erythrocytes contain multiple copies of an oxygen-carrying protein called hemoglobin. When oxygen and hemoglobin combine they produce the bright red colour of blood. Figure 1. normal red blood cells flowing freely in a blood vessel. The inset image shows a cross-section of a red blood cell with hemoglobin. (Red Blood Cells – PubMed Health) What do erythrocytes look like? Erythrocytes are generally 8 µm in diameter and have a biconcave shape (Figure 1). Biconcave means concave on both sides. Their shape gives them a larger surface area, which is ideal for gas exchange. Figure 2. Components of blood, shows the breakdown of blood into liquid plasma and solid formed elements, and is then further broken down into their component parts. (Components of Blood - Mosby) How are erythrocytes different from other cells? Erythrocytes are made up of a selectively permeable membrane, cytosol, and hemoglobin. Mature red blood cells lack a nucleus and other organelles, features other cells in the body commonly have. The lack of a nucleus, which houses a cell’s DNA and ribosomes, means erythrocytes are unable to reproduce. Instead, all internal space is available to store and transport oxygen and carbon dioxide (Tortora et al. 360). What is the lifespan of an erythrocyte? Erythrocytes live around 120 days in the bloodstream because of the wear and tear their membranes faces as they squeeze through capillaries (tiny blood vessels in the lungs). Worn out red blood cells are destroyed by macrophages (scavenger cells) in the spleen, liver, and bone marrow. When red blood cells are broken down, the iron from the hemoglobin protein is recycled to be used in making hemoglobin for new erythrocytes (Chabner 506). How many erythrocytes are there in a drop of blood? A healthy adult has 5–5.5 million red blood cells per microliter (µL) of blood. To put this in perspective, one drop of blood is about 50 µL. Every second, 2-10 million worn out erythrocytes are destroyed (Tortora et al. 359). The production of red blood cells must keep up with this rate in order to maintain an adequate amount of erythrocytes in the blood. What are the components of blood? Blood is made up of cells suspended in plasma, a clear, light yellow liquid. Cells make up 45% of the volume of blood and include erythrocytes, leukocytes (White Blood Cells), and platelets (Clotting factors). The other 55% of the volume of blood is plasma, a solution of water, proteins, sugar, salts, hormones, and vitamins (Figure 2). Where do erythrocytes come from? All blood cells come from the same source (type of stem cell), but they develop in different ways (Figure 3). Erythrocytes are made in the bone marrow. When the Blood stem cell is exposed to the hormone erythropoietin (EPO) it is stimulated to produce new red blood cells (Chabner 506). How do erythrocytes reach their mature form? Near the end of erythrocyte formation, the red blood cell Figure 3. Blood cell development. A blood stem cell goes through precursor ejects its nucleus. The several steps to become a red blood cell, platelet, or white blood cell. loss of the nucleus causes the (White Blood Cells - PubMed Health) center of the cell to indent, producing the erythrocyte’s characteristic shape. At the time red blood cells are released into the bloodstream they still contain a few organelles, but after 1-2 days they reach their mature adult state (Tortora et al. 361-62). WORKS CITED Chabner, Davi-Ellen. The Language of Medicine, 9th ed. Saint Louis: Saunders, 2011: 504-506. Print. “Components of Blood.” PetalSchools. 2001. Web. 27 May 2016. <http://www.petalschools.net/users/jbullard/Illustrations/Ch%2012-13/components.jpg> “Red Blood Cells (Erythrocytes).” PubMed Health. September 2015. Web. 27 May 2016. <http://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0022014/> Tortora, Gerard J., and Bryan Derrickson. Introduction to the Human Body: the essentials of anatomy and physiology, 8th ed. New York: John Wiley & Sons, 2010: 358-362. Print. “White Blood Cells (Leukocytes).” PubMed Health. September 2015. Web. 27 May 2016. <http://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0022046/>