Chapter 3 Cellular Form and Function PDF

Because learning changes everything. ® Chapter 3 Cellular Form and Function ANATOMY & PHYSIOLOGY The Unity of Form and Function NINTH EDITION KENNETH S. SALADIN © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use...

Because learning changes everything. ® Chapter 3 Cellular Form and Function ANATOMY & PHYSIOLOGY The Unity of Form and Function NINTH EDITION KENNETH S. SALADIN © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill.  Introduction to a Cell The cell is the basic, living, structural, and functional unit of the body. Cytology is the study of cell structure. Cell physiology is the study of cell function. © McGraw Hill 2  Cells: many different types Introduction to a Cell Neurons Red blood cells Oocytes Simple Squamous Epithelium Muscle cells Sperm cell http://faculty.washington.edu/chudler/ca1pyr.html http://www.worldofstock.com/closeups/PHE1014.php © McGraw Hill http://www.cytochemistry.net/microanatomy/blood/blood_cells.htm 3  Cell Shapes Note: A cell’s shape can appear different if viewed Figure 3.1 in a different type of section (longitudinal versus cross section) © McGraw Hill 4  The Relationship Between Cell Surface Area and Volume Human cell size Most cells about 10 to 15 μm in diameter Egg cells (very large) 100 μm diameter Some nerve cells over 1 m long Limit on cell size: an overly large cell cannot support itself, may rupture For a given increase in diameter, volume increases more than surface area Volume proportional to cube of diameter Surface area proportional to square of diameter Why does this matter? Figure 3.2 Access the text alternative for slide images. © McGraw Hill 5 The cell can be divided into three principal parts: 1. Plasma membrane (cell membrane) - flexible barrier. 2. Cytoplasm a. Cytosol - fluid portion. b. Organelles - internal cellular structures other than the nucleus. 3. Nucleus - contains DNA or genetic material.. © McGraw Hill 6 7 Along with cells, another important component of the body are the body fluids, mostly watery solutions. 1. The fluid within body cells is the intracellular fluid (ICF). 2. The fluid outside of body cells is the extracellular fluid (ECF) (also called intercellular fluid) found as: a. Extracellular fluid (ECF) filling the narrow spaces between cells of tissues is called interstitial fluid. b. Extracellular fluid (ECF) in blood vessels is called plasma. c. Other types of ECF's include lymph in lymphatic vessels and cerebrospinal fluid (CSF) in the meninges of the nervous system). © McGraw Hill 7  The Plasma Membrane Plasma membrane—border of the cell - a flexible yet sturdy barrier that surrounds the cytoplasm of the cell. The fluid mosaic model describes its structure. The membrane consists of a "sea of lipids", with proteins afloat or anchored, Has intracellular and extracellular faces - Intracellular side of membrane faces cytoplasm and extracellular face faces outwards. Figure 3.4 Access the text alternative for slide images. © McGraw Hill a: © Don Fawcett/Science Source 8  The Plasma Membrane 3 The functions of the plasma membrane include: Physical barrier. Regulation of exchange of molecules and ions with the environment. Sensitivity to the environment. Structural support. Figure 3.5b Access the text alternative for slide images. © McGraw Hill 9 10 Lipid Bilayer 98% on membrane molecules are lipids The phospholipid bilayer forms the basic framework of the cell membrane. The membrane consists of two phospholipid layers. Within these layers are also two other types of lipid molecules, cholesterol (lipid with a ring structure) and glycolipids (lipid with attached carbohydrate groups). © McGraw Hill 10 11 The phospholipid bilayer forms because of the amphipathic nature of the phospholipid molecules. The phospholipids orient themselves within the bilayer by positioning themselves with the hydrophilic "heads" directed outwards and the hydrophobic "tails" directed inwards. About 75% of the lipids making up the lipid potion of the membrane are phospholipid molecules. The hydrophilic, polar heads face the polar watery fluid on two sides: 1) intracellular fluid (ICF, cytosol) on the inside 2) extracellular fluid (ECF) on the outside. The hydrophobic, nonpolar fatty acid tails are directed towards the inside of the plasma membrane, forming the nonpolar, hydrophobic region in the phospholipid membrane's interior. Cholesterol molecules make up about 20% of lipid potion of membrane. Cholesterol molecules are interspersed among phospholipids and provide some rigidity to the membrane. Higher concentrations of cholesterol molecules can increase membrane fluidity by preventing the phospholipid molecules from packing too closely together. Glycolipids appear only on the side of the membrane that faces the extracellular fluid. They make up the remaining 5% of membrane lipids. They contribute to the glycocalyx. © McGraw Hill 11  Membrane Proteins Make up about 2% on membrane molecules, but are much larger and constitute about 50% of the weight of the membrane. Proteins float in the “sea of lipid” (i.e., phospholipid bilayer); some are anchored by cytoskeleton and some are able to move freely (like ice cubes floating in water). They are divided into two categories: 1. Integral proteins – these proteins are embedded in the plasma membrane, and may be exposed on both of the ECF (ICF) sides, or only one side of the plasma membrane. Because integral proteins are amphipathic, they also may interact with both the hydrophilic extracellular region, and the hydrophobic interior of the phospholipid membrane. Some integral proteins are transmembrane proteins, which means the pass completely through the phospholipid bilayer. 2. Peripheral proteins – These proteins are loosely attached to either the inside or outside of the plasma membrane. The peripheral proteins on the intracellular side are usually attached to a transmembrane protein as well as the cytoskeleton inside the cell. © McGraw Hill 12 13 Many membrane proteins are glycoproteins. These are integral or peripheral proteins that have chains of sugar molecules attached to them and are located on the outside surface of the plasma membrane. Collectively, glycoproteins and glycolipids form a carbohydrate-enriched coat, called the glycocalyx, around the outside of a cell. The glycocalyx has several functions: 1. Act as signature sequences that allow cells to recognize one another, and is important in immune function. 2. Adherence. 3. Protection from digestion. 4. Attracts water molecules. © McGraw Hill 13  Functions of Membrane Proteins Figure 3.7 Access the text alternative for slide images. © McGraw Hill 14  Membrane Transport Transport of material across the cell membrane is essential as some substances are needed in the cell for metabolism and other substances must be moved out as waste or for export. The plasma membrane is selectively permeable – it allows some things to move across easily and not other things. It is generally permeable to small solutes that are soluble in lipids, nonpolar or hydrophobic (e.g., O2, CO2, lipid-based hormones). It is impermeable to water-soluble, polar or hydrophilic substances (e.g., ions, glucose). These substances can only cross the membrane through carrier or channel proteins. Substances move across the cell membrane by three types of transport processes: 1. Diffusion – random movement of a substance down its concentration gradient. It does not require energy (passive). 2. Carrier-mediated transport – movement of a substance that requires the presence of specialized integral proteins. It may or may not require energy (passive or active). 3. Vesicular transport – movement of large amounts of material across a membrane. In this process, the material becomes enclosed and is transported within a tiny membrane-surrounded sac called a vesicle. It does require energy. 16 1. Diffusion – concentration gradients Because the membrane is selectively permeable, some substances occur in higher concentration inside, while others occur in higher concentration outside (e.g., [Na+] and [O2] are higher outside, [K+] and [CO2] are higher inside). This results in a concentration gradient across the cell membrane called a chemical gradient. Also, more anions end up inside the cell, and more cations outside the cell. This results in a charge difference across the cell membrane called a charge gradient. The inner surface of the membrane is more negatively charged and the outer surface is more positively charged. Together these two gradients form the electrochemical gradient, which helps move substances across the membrane. This is very important to a cell's function, especially an excitable cell like a neuron or muscle cell. © McGraw Hill 16  Diffusion across Cell Membranes Diffusion is the movement of molecules by random motion (Brownian motion) from areas of high concentration to areas of low concentration. E.g., a sugar cube in a cup of coffee: sugar molecules move away from the cube, and eventually equilibrium is reached. The diffusion rate across plasma membranes is influenced by several factors: 1. Diffusion distance 2. Size or mass of the diffusing substance 3. Temperature 4. Steepness of the concentration gradient 5. Electrical forces 6. Surface area © McGraw Hill 17 Two Types of Diffusion 1.Simple diffusion – small nonpolar and hydrophobic molecules (e.g., O2, CO2, steroids, short-chain fatty acids, fat-soluble vitamins) can diffuse through the lipid bilayer. Large nonpolar molecules can get stuck in the membrane. 2. Channel-mediated diffusion – mostly for small, inorganic ions and water. Each ion channel is specific for a particular ion. © McGraw Hill 18  Osmosis: A Special Case of Diffusion Osmosis is the movement (diffusion) of water through a selectively permeable barrier from an area of higher concentration of water to an area of lower concentration of water across the membrane. Alternately, water moves from an area of lower solute concentration (hypotonic) to an area of higher solute concentration (hypertonic). Figure 3.14 Access the text alternative for slide images. © McGraw Hill 19 20 Water moves through cells in two ways: 1. Through special channel proteins called aquaporins. 2. By slipping through temporary spaces between membrane lipids caused by their movement. https://healthjade.com/wp-content/uploads/2019/04/aquaporins.jpg © McGraw Hill 20 © 2018 Pearson Education, Inc. a Isotonic solution b Hypotonic solution c Hypertonic solution In an isotonic saline solution, no In a hypotonic solution, the water In a hypertonic solution, water osmotic flow occurs, and the red flows into the cell. The swelling moves out of the cell. The red blood cells appear normal in size may continue until the plasma blood cells crenate (shrivel). and shape. membrane ruptures, or lyses. Water molecules Solute molecules SEM of a normal RBC SEM of swollen RBC in SEM of crenated RBCs in an isotonic solution a hypotonic solution in a hypertonic solution © McGraw Hill 21 22 Tonicity of a solution relates to how the solution influences the shape of body cells Tonicity is important in intravenous (IV) solutions. A solution can be: Isotonic – the concentrations of solutes are the same on both sides of the membrane and water molecules enter and exit at the same rate. A red blood cell immersed in an isotonic solution maintains its normal shape. o Isotonic IV solutions – isotonic saline solution (0.9% NaCl). Hypotonic – the concentration of solutes is higher inside the cell and water moves into the cell, where it occurs in low concentration. A red blood cell immersed in a hypotonic solution undergoes hemolysis (i.e., it bursts). Hypertonic – the concentration of solutes is lower inside the cell and water moves out of the cell, where it occurs in higher concentration. A red blood cell immersed in a hypertonic solution undergoes crenation (i.e., it shrinks). © McGraw Hill 22  Effects of Tonicity on RBCs Figure 3.15a Figure 3.15b Figure 3.15c Hypotonic, isotonic, and hypertonic solutions affect the fluid volume of a red blood cell. Notice the crenated and swollen cells. Access the text alternative for slide images. © McGraw Hill (a-c): © David M. Philips/Science Source 23 24 2. Carrier-Mediated Transport In carrier-mediated transport, integral proteins bind specific ions or organic substances and carry them across the plasma membrane. All forms of carrier- mediated transport have the following characteristics: 1. Specificity – each carrier protein binds and transport only certain substances. For example, a glucose transporter only carries glucose. 2. Saturation limits – the rate of substance transport is limited by the availability of carrier proteins. 3. Regulation – the cell can control (regulate) the activity of carrier proteins, especially through the action of hormones. There are two types of carrier-mediated transport: facilitated diffusion and active transport. © McGraw Hill 24  Facilitated Diffusion Many nutrients (e.g., amino acids, glucose) are highly charged or too large to diffuse through channels. These substances can be passively transported across the plasma membrane by carrier proteins in a process called facilitated diffusion. In facilitated diffusion, substances move down their concentration gradient, so that no energy is required (passive). The molecule to be transported binds to a specific receptor site on the carrier protein. The binding alters the shape of the protein, which then releases the molecule on the other side of the plasma membrane. Figure 3.17 © McGraw Hill 25 26 Active transport Active transport is an energy-requiring process in which carrier proteins move solutes regardless of concentration gradient. There is two types of active transport depending on the source of energy used to drive the process: 1. Primary active transport – energy from the hydrolysis of ATP changes the shape of a transport protein. The most common primary active transport mechanism in the body is called the sodium-potassium exchange pump (also called the Na+/K+ ATPase). Up to 40% of our body's energy is spent just making this pump run. Each cell of our body has thousands of these pumps in its membrane, working all the time. © McGraw Hill 26  The Na+/K+ pump The sodium-potassium exchange pump maintains the concentration gradients of Na+ (high outside) and K+ (high inside) across the cell membrane. It works like this: 1. Three Na+ in the cytosol bind to the pump. 2. This causes ATP to be hydrolyzed to ADP, and the phosphate group removed from ATP is attached to the pump protein. The pump protein changes shape, causing it to release the Na+ into the ECF. 3. In its new shape, two spots are available for K+ ions to bind to the pump. When they bind, they make the pump release the phosphate group, and the pump springs back to its original shape. 4. The two K+ are released into the cytosol. The pump is now back to its original state, ready to Figure 3.19 bind more Na+ and go again. Each cycle uses one ATP molecule. © McGraw Hill 27  Secondary Active Transport 2. Secondary active transport – energy comes from an ionic concentration gradient that was established by primary active transport. The energy stored in a Na+ gradient is used to drive other substances across the membrane (i.e., the other substances gets a "free ride"). As Na+ leaks into the cell, another substance can be simultaneously transported in the same direction by cotransport/symport (e.g., glucose and amino acids enter the cell with Na+) or in the opposite direction by countertransport/antiport (e.g., H+ and Ca2+ exit the cell while Na+ enters the cell). Such transporters are especially important in the kidneys. Figure 3.18 © McGraw Hill 28 29 3. Vesicular Transport Molecules that are too large to be moved by passive or active transport cross the membrane in vesicles. A vesicle is a small membrane-bound sac, formed when a bit of cell membrane pinches off. All types of transport using vesicles (also called bulk transport) require energy supplied by ATP. Vesicles can move in two directions: Exocytosis is movement of substances out of a cell. o Exocytosis is used by cells that produce secretions (e.g., secretory cells, nerve cells). Products meant to go outside of the cell are packaged in carrier vesicles and brought to the plasma membrane. The membrane of the vesicle fuses with the plasma membrane and the cargo is delivered to the extracellular fluid. © McGraw Hill 29  Phagocytosis Endocytosis is movement of substances into a cell. There are three types of endocytosis: 1. Phagocytosis or "cell eating" – uptake of large particles (e.g., worn-out cells, bacteria, viruses) (Figure 3-22). When taken into the cell, the particles are enclosed in a phagosome, which then fuses with a lysosome (a type of organelle). Lysosomes contain acids and enzymes that can digest large particles. Figure 3.20 Access the text alternative for slide images. © McGraw Hill 30  2. Pinocytosis or "cell drinking" – non-selective uptake of fluid surrounding the cell, which allows the cell to sample its surroundings. Whatever is taken up in pinocytic vesicles is digested by lysosomes and delivered into the cell (e.g., amino acids, fatty acids). What is not useful to the cell is collected in a residual body and dumped outside the cell. 3. Receptor-mediated endocytosis – highly specific type of endocytosis by which cells take up specific ligands For example, the HIV virus attach to the CD4 receptor on helper T cells (a type of white blood cells) and are transported in by receptor-mediated endocytosis. Figure 3.21 © McGraw Hill (1-3): Courtesy of the Company of Biologists, Ltd. 31  Transcytosis Transcytosis is a method by which substances can cross the cell. Substances enter the cell by endocytosis, and cross the cell within a vesicle to exit the opposite side of the cell by exocytosis. Figure 3.22 Access the text alternative for slide images. © McGraw Hill © Don Fawcett/Science Source 32 33 Cytoplasm The cytoplasm has two components: (1) the cytosol and (2) a variety of organelles that perform different functions in the cell. The cytosol is the intracellular fluid portion of the cytoplasm that surrounds organelles (Figure 3-1). It is composed mostly of water, but is thick and jelly-like due to dissolved proteins, carbohydrates, lipids and inorganic substances. Functionally, the cytosol is the medium in which many metabolic reactions occur. Organelles are specialized structures that have characteristic shapes and that perform specific functions in cellular metabolism. © McGraw Hill 33  Structure of a Representative Cell Figure 3.4 Access the text alternative for slide images. © McGraw Hill 34  The Cytoskeleton Cytoskeleton—network of protein filaments and cylinders Determines cell shape, supports structure, organizes cell contents, directs movement of materials within cell, contributes to movements of the cell as a whole Composed of: microfilaments, intermediate fibers, microtubules Figure 3.24 Access the text alternative for slide images. © McGraw Hill b: © Dr. Torsten Wittmann/Science Source 35 36 Ribosomes Ribosomes—small granules of protein and RNA Found in nucleoli, in cytosol, and on outer surfaces of rough ER, and nuclear envelope They “read” coded genetic messages (messenger RNA) and assemble amino acids into proteins specified by the code © McGraw Hill 36 37 Endoplasmic Reticulum Endoplasmic reticulum—system of channels (cisterns) enclosed by membrane Rough endoplasmic reticulum—parallel, flattened sacs covered with ribosomes Continuous with outer membrane of nuclear envelope, often largest organelle Produces phospholipids and proteins of nearly all cell membranes Synthesizes proteins that are packaged in other organelles or secreted from cell © McGraw Hill 37 38 Smooth endoplasmic reticulum Lack ribosomes Cisterns more tubular and branching Cisterns thought to be continuous with rough ER Synthesizes steroids and other lipids Detoxifies alcohol and other drugs Calcium storage Rough and smooth ER are functionally different parts of the same network © McGraw Hill 38 Golgi complex—a system of cisterns that synthesizes carbohydrates and puts finishing touches on protein synthesis Receives newly synthesized proteins from rough ER Sorts proteins, splices some, adds carbohydrate moieties to some, and packages them into membrane-bound Golgi vesicles Figure 3.29 Access the text alternative for slide images. © McGraw Hill © David M. Phillips/Science Source 39  Lysosomes—package of enzymes bound by a membrane Generally round, but variable in shape Functions Intracellular hydrolytic digestion of proteins, nucleic acids, complex carbohydrates, phospholipids, and other substances Autophagy—digestion of cell’s surplus organelles Autolysis—“cell suicide”: digestion of a Figure 3.30a surplus cell by itself Access the text alternative for slide images. © McGraw Hill (a-b): © Don Fawcett/Science Source 40 41 Peroxisomes—resemble lysosomes but contain different enzymes and are produced by endoplasmic reticulum Function is to use molecular oxygen to oxidize organic molecules Reactions produce hydrogen peroxide (H2O2) Catalase breaks down excess peroxide to H2O and O2 Neutralize free radicals, detoxify alcohol, other drugs, and a variety of blood-borne toxins Break down fatty acids into acetyl groups for mitochondrial use in ATP synthesis In all cells, but abundant in liver and kidney Figure 3.30b © McGraw Hill 41  Mitochondria Mitochondria—organelles specialized for synthesizing ATP Surrounded by a double membrane Inner membrane has folds called cristae Spaces between cristae called matrix Matrix contains ribosomes, enzymes used for ATP synthesis, small circular DNA molecule Multiple molecules of mitochondrial DNA (mtDNA) “Powerhouses” of the cell Energy is extracted from organic molecules and transferred to ATP Figure 3.32 Access the text alternative for slide images. © McGraw Hill © Keith R. Porter/Science Source 42 43 Cilia and Flagella Cilia function to move fluid an material along the cell’s surface (e.g. airways). Flagella generate forward motion (sperm cells only). https://rep.bioscientifica.com/view/journals/rep/159/2/images/REP-19-0096fig1.jpeg https://upload.wikimedia.org/wikipedia/commons /3/33/Blausen_0750_PseudostratifiedCiliatedCol umnar.png © McGraw Hill 43  Nucleus The nucleus is usually the most prominent feature of a cell when you look under a microscope (Figure 3-10). Most body cells have a single nucleus; some (red blood cells) have none, whereas others (skeletal muscle fibers) have several. The parts of the nucleus include: Nuclear envelope – membrane similar to the plasma membrane. Genes – the cell’s hereditary units consisting of the genetic material (DNA). o Each gene represents a set of directions (i.e., blueprint) to make a specific polypeptide or protein. o Genes are arranged in single file along chromosomes. Each chromosome is a long molecule of DNA that is coiled together with several proteins (Figure 3-11). ▪ Human somatic cells (body cells, not reproductive cells) have 46 chromosomes arranged in 23 pairs (2 copies of each) and are diploid. ▪ Human reproductive cells have 23 chromosomes (single copy) and are haploid. © McGraw Hill 44  Structure of the Nucleus Figure 3.27 Access the text alternative for slide images. © McGraw Hill 45  The Nucleus as Seen by Electron Microscope Figure 3.26a Figure 3.26b © McGraw Hill a: © Richard Chao; b: © E.G. Pollock 46 47 Control of Cell Destiny A cell in our body has three possible destinies: 1. Maintain itself without dividing – many nerve and muscle cells have long lifespan without dividing. 2. Grow and divide – cell division is necessary to replace worn-out cells or to grow. Generally, the longer the life expectancy of a cell, the slower its mitotic rate. Stem cells continuously divide and give rise to more daughter cells. o 3. Die – cell death is also necessary during embryonic development (some cells are only needed at some stages of development), and to eliminate body cells, such as cancer cells or virally-infected cells. o Apoptosis – genetically controlled cell death where "suicide" enzymes kill the cell. Apoptosis is a normal type of cell death, whereas necrosis is a pathological type of cell death due to tissue injury. © McGraw Hill 47  Because learning changes everything. ® Chapter 4 Genes and Cellular Function ANATOMY & PHYSIOLOGY The Unity of Form and Function NINTH EDITION KENNETH S. SALADIN © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill.  Cell Division Cell division is the process by which cells reproduce themselves. It consists of nuclear division (mitosis or meiosis) and cytoplasmic division (cytokinesis). Copyright © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 49  Mitosis Cell division that results in an increase in the number of body cells (two new cells per dividing cell) is called somatic cell division, and it involves mitosis and cytokinesis. Produces two daughter cells that are identical to the parent cell (and each other) and have the same number of chromosomes (diploid daughter cells). This type of division occurs in billions of our body cells each day. The DNA of the cell is duplicated, and one copy goes to each cell. Sometimes, in this process, errors or mutations Figure 4.15 parts 3 & 4 occur. © McGraw Hill (both): © Ed Reschke 50 51 Meiosis Cell division that results in the production of sperm and eggs is called reproductive cell division (occurs only in testes and ovaries), and it consists of a meiosis and cytokinesis. In reproductive cell division, a cell undergoes two divisions which result in four reproductive or germ cells that have half of the normal number of chromosomes (haploid daughter cells) © McGraw Hill 51  Cancer Cancer is a group of diseases characterized by uncontrolled cell proliferation. We are constantly subject to mutations in genes. Sometimes these mutations are caused by exposure to carcinogens, which are substances or agents that have been shown to cause cancer Also, as we age, DNA replication becomes less error-proof, and we gradually accumulate mutations in our cells. Mutagens cause mutations in cells Mutations do not always have serious consequences © McGraw Hill 52 53 A large proportion of our DNA serves as "filler" or "repeat", and does not contain essential genes. A mutation in these regions is unlikely to have significant consequences. Many genes code for proteins involved in either suppressing cell division when it should not occur, or making cell death happen when it should. If these genes are mutated, a tumor may grow. These modified genes are called an oncogenes. © McGraw Hill 53 54 Tumors are masses of cells that are dividing uncontrollably. A tumor can be benign or malignant. The study of tumours is called oncology. Benign tumors are relatively harmless, except that their size may interfere with normal body function (e.g., a tumor in the brain) or they may be disfiguring. Benign tumors are not cancerous. Malignant tumors are cancerous. They are made up of cells that have not only lost track of their growth, but have also lost track of their place in the body and the normal controls that keep cells in the organs where they belong. The movement of cancerous cells throughout the body is called metastasis. © McGraw Hill 54  Cancer Carcinogens Mutagens oncogene Tumor (cell mass) Tumors (oncology) Melanoma Benign (non-cancerous) Malignant tumors metastasis http://www.meddean.luc.edu/lumen/MedED/medicine/dermatology/melton/melan1.htm © McGraw Hill http://www.medscape.com/viewarticle/461106_3 http://www.aans.org/education/journal/neurosurgical/may03/14-5-nsf-toc.asp 55 56 Cancers are named for the tissue that they develop in: Carcinomas (the most common cancer type) arise from epithelial cells. o E.g., lung cancer (various types), breast and prostate cancer (adenocarcinomas - cancerous glandular cells), skin cancer (melanoma - cancerous skin cells that produce the pigment melanin). Sarcomas arise from connective tissue – e.g., osteosarcoma is cancer of bone tissue. Leukemias arise from blood-forming organs – e.g., lymphocytic leukemia affect blood-forming stem cells in the bone marrow. Lymphomas originate in the lymphatic system – e.g., Hodgkin and non-Hodgkin lymphoma results in uncontrolled growth of lymphocytes (a type of white blood cells). Cancer cells divide rapidly and continuously, and trigger angiogenesis, the growth of new networks of blood vessels, to provide nourishment for themselves. © McGraw Hill 56 57 Treatment of Cancer Treating cancer is a subject of a lot of medical research, and we lack really effective ways of specifically killing only cancer cells. Cancer cells differ from normal body cells only in that they are not controlling their growth and their location. This makes it difficult to kill them, as there is nothing dramatically different about them that makes them easy to target with drugs and other treatments. Various treatments include: Surgery removes a tumor, but does not always remove metastasized cells, so follow-up therapy with chemicals or radiation may be necessary to kill those. Chemotherapy and radiation therapy – both target cells that are in the process of dividing. Unfortunately, these methods also kill other dividing cells in the body, particularly developing blood cells, and cause illness and discomfort in patients (e.g., nausea, hair loss). Immunotherapy uses substances made by the body or in a laboratory to boost the immune system and help the body find and destroy cancer cells. Further information on cancer (description, risk factors, diagnosis, treatment, support, research, etc.) can be obtained from the Canadian Cancer Society website. © McGraw Hill 57