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Transcript
UNIT 8 NOTES Chapter 40 Sections 1-4 with numerous examples from other chapters as noted These two words are almost always seen together because they go hand in hand: Anatomy – Physiology – Those of you going on to college for anything in the medical field will have to take a course called A&P, Anatomy and Physiology. This is where you learn how you are built and how you work. Depending on where you go to school some of you may use cats in your lab to dissect, and others will have cadavers, real dead people. Once you get over the initial shock, you will be fine. They are dead, feel no pain, and there is no blood. Wait til you see your first operation. There’s blood and that’s gross. Good Luck. Animal form and function are correlated at all levels of organization. This means that all cell organelles like mitochondria and ribosomes, all cells that make up tissues, all tissues etc. etc. all the way up to large parts of organisms like arms and legs are built the way they are, generally, because that is the best shape to get the job done. Here is an example. Polydactyly (extra fingers and toes) is a dominant trait, yet most people only have five on one limb. Why? Wouldn’t more fingers be better? No. If it were, nature would have selected for polydactyly and not against it and we would all need new gloves. Therefore, due to the interaction of an organism with its environment and the genes it possesses, it looks the way it does because that shape will function best in that environment. This also explains convergent evolution like you see in Fig 40.2 pg. 853, Slide 5. Remember, this does not mean that these forms are perfect. It just means that given what there is to work with genetically, this is the best fit so far. Natural selection is a work in progress. An animal’s _____________________ and _________________________ directly affect how it exchanges energy and materials with its surroundings. For single-celled organisms the plasma membrane has enough surface area to accommodate the whole organism’s needs for food and wastes. (Review what we learned about cell size in Unit 2, pg. 99 Fig. 6.8. Cells are small to maximize their surface area to volume ratio (SA/V). This will be on your test.) Even some multicellular organisms like a hydra (Fig. 40.3 pg. 853, slide 7) are small enough and built so that all their body cells are in contact with the environment. This also provides them with enough surface area for exchange of materials. The outer covering of complex multicellular organisms, like you, does not provide enough surface area. Therefore, these organisms must have specific adaptations that allow them to function and survive. More complex organisms have highly folded internal surfaces for exchanging materials (Fig. 40.4 pg. 854, slide 10). Learn some of the examples below! 1 UNIT 8 NOTES What fills the spaces between body cells? How are animals “organized”? Cells are organized into Within multicellular organisms, specialization of organs contributes to the overall functioning of the organism. All of these examples from the human body show adaptations that provide increased surface area internally for diffusion of materials. Why must there be increased surface area? Why must it be internal? The paragraphs below provide you with examples of increased surface area within the human body for exchange of materials with the environment. Later we will discuss the body systems as a whole and learn more about the anatomy and physiology of each system so you will see some of these slides again, but focus on different things. • Digestion of food – CH. 41.3 The human digestive system contains many organs that mechanically break apart food (mouth, stomach), secrete various digestive enzymes to chemically break down food (salivary glands, liver, pancreas), and structures such as villi and microvilli in the small intestines that aid in absorption. Not only do the villi add increased surface area, but the system as a whole does too. Your small intestines are not just a short, straight tube, but very long and convoluted so 20-25 feet of tubing are squashed into a small space. • Circulation of fluids – CH. 42.1 All circulatory systems use a fluid to connect all the cells of an organism’s body to the environment. The fluid is pumped through tubes by a heart. Cells bathed in fluid (ICF) can use diffusion to get nutrients and oxygen, as well as removing wastes. Exchange of these materials also takes place between the ICF and the capillaries, the smallest blood vessels, which branch out to reach almost all cells. • Exchange of gases – CH. 42.5 This involves taking oxygen into the body and removing carbon dioxide. It is not breathing or cellular respiration. This exchange takes place by diffusion at the respiratory surface which can be skin, gills, tracheae, or alveoli inside the lungs. Because the respiratory surface of a lung is not in direct contact with all other parts of the body, the gap must be bridged by the circulatory system. Alveoli in the lungs are surrounded by capillaries. 2 UNIT 8 NOTES • Excretion of wastes – CH. 44.3 All excretory systems involve tubular structures that collect a filtrate. There is then reabsorption of any desirable molecules and secretion of any more toxins or wastes into the tube which then leaves the body. In humans this takes place in the kidneys in a structure called the nephron. Like the alveoli of the lungs, nephrons are surrounded by capillaries. In summary: Villi in Capillaries in small intestines circulatory system Alveoli in lungs Nephron in kidneys nutrients into circulatory system nutrients into cells and wastes out by way of the ICF oxygen in and carbon dioxide out of circulatory system wastes out of circulatory system With all this going on constantly inside your body, how do different parts know what to do and when to do it? Are they just constantly working? Are substances just floating around willy-nilly? No, of course not. Everything is under control, at least most of the time. There are times when things are not under control, when things can go wrong. That is when you are sick. A common way for organisms to keep things under control is feedback. Remember that? It was one way of regulating enzymatic pathways where the final product acted as an inhibitor to a beginning enzyme to shut down the pathway when there was enough product. Well, that same idea is used to regulate your internal environment in a number of different ways. Let’s take a look. There are two types of organisms. Regulators use internal mechanisms to keep their internal environments relatively constant, and conformers allow their internal environments to change with the external environment. Give an example of each: Regulators – Conformers – What do organisms use homeostasis for? Give some examples in humans: Negative feedback is used to keep a variable or condition, like body temperature, for example, at a set point. It works the same way as a thermostat-furnace system (Fig. 40.8 3 UNIT 8 NOTES pg.861, slide 37) does to maintain room temperature. Here are some examples of negative feedback: • Operons in gene regulation – see Unit 6 notes or Ch. 18.1 pg. 351 Remember the trp operon. When bacteria have enough tryptophan it acts as an inhibitor shutting off the operon that codes for the production of the enzymes to make tryptophan. That is negative feedback. • Temperature regulation in animals – see below notes or CH. 40.3 pg. 862 • Plant responses to water limitations – see CH. 36.4 pg. 776 When plants do not have enough water they will close the stomates in the leaves to prevent excess water loss and start to become droopy. • Regulation of blood glucose – see CH. 45.2 pg. 982 This is probably the best and most common example of negative feedback in the human body. You should be familiar with this one and the two hormones insulin and glucagon. These two hormones are antagonistic, which means they work against each other, or do opposite jobs. Here is how this works. You eat something and it gets digested and absorbed into your blood. This increases your blood glucose (sugar) level. This increase triggers your pancreas to release insulin into the blood. Insulin tells your liver to take up the extra glucose and store it as glycogen until it is needed, thus lowering your blood glucose level. Since your cells keep using glucose all the time for energy, eventually your blood glucose will drop below the desired level. This signals your pancreas again, but this time it releases glucagon which tells your liver to convert some of that glycogen to glucose and put it into the blood, thus raising your blood glucose to the desired level. See Fig. 45.12 pg. 983, slides 40-42. Does this always work perfectly? No. If it did there would not be anyone suffering from diabetes. Your endocrine system produces numerous hormones that regulate a multitude of things in your body. I had you look up several and write down what they did in Unit 4. If there is a problem with any one of the glands or hormones that will disrupt control and you will be sick. Below are some examples of diseases or conditions due to lack of control. • Diabetes mellitus in response to decreased insulin – pg. 983. Pancreatic insulin-producing cells are destroyed by the immune system so glucose levels in the blood remain high. The kidneys are not able to reabsorb all the sugar so it stays in the filtrate along with excess water thus producing large amounts of urine. • Dehydration in response to decreased antidiuretic hormone (ADH) pg. 969. ADH is a hormone that tells the kidneys to take up more water to prevent dehydration. It is usually released after you eat salty food or sweat a lot. If ADH is not produced or the receptors are blocked somehow, the aquaporins will not open, urine production will not decrease, and dehydration could result. 4 UNIT 8 NOTES • Graves’ disease (hyperthyroidism) – pg. 990. The thyroid gland does not ‘turn off’ and continuously produces thyroid hormone. • Blood clotting – pg. 913 Positive feedback loops occur in animals, but do not usually contribute to homeostasis. Positive feedback is used to amplify or intensify a change. For example: • Lactation in mammals – When baby animals nurse the mammary glands are stimulated to produce more milk. The more the baby drinks, the more milk is produced. • Onset of labor in childbirth – The pressure of the baby’s head near the opening of the uterus stimulates the uterus to contract. This puts more pressure on the opening causing more contractions which increases the pressure, etc. until the baby is born. • Ripening of fruit – Ethylene (a plant hormone) triggers ripening and ripening triggers more ethylene production. The result is a huge burst in ethylene production which, since it is a gas, spreads from fruit to fruit causing them all to ripen at once. See pg. 834. One of the most important uses for homeostasis in organisms is for thermoregulation. What is thermoregulation? There are basically two ways to do this. Define each and give examples of organisms that use each method: Endothermy: Ectothermy: Endothermy requires more energy than ectothermy, but allows organisms to be active in a wider range of environmental conditions. Both endotherms and ectotherms use behavior to control body temperature, but it is much more pronounced in ectotherms. Think lizards basking in the sun to warm up in the morning. Thermoregulation in many animals is accomplished in part by the circulatory system. See CH. 40 pgs. 864-865, slides 48-51. Constricting or dilating blood vessels near the body 5 UNIT 8 NOTES surface alters the surface area that receives blood and can therefore regulate heat loss. More blood to those vessels, more heat will be lost, and vice versa. Countercurrent exchange is used to minimize heat loss by maximizing the transfer of heat in adjacent fluids that are traveling in opposite directions. As blood leaves the core of the body it transfers heat to blood returning to the core. This is a common method used in marine mammals, water fowl, and some insects. This is why the geese on the pond can still swim in the 40o water without freezing. Other methods of thermoregulation include sweating, panting, and shivering. These are controlled by a region in the brain called the hypothalamus. The hypothalamus is the body’s thermostat and works by negative feedback just like the thermostat in your house. See Fig. 40.16 slide 54, pg. 868. Believe it or not there are even some plants that can regulate their temperature. Skunk cabbage is one example. Very early in spring it begins to grow and melt the snow around it so that it can bloom. It can be found around here in damp places such as the Utica marsh. Obviously this plant is not regulating its temperature all the time since it does not grow all winter long. It begins to increase its temperature when it gets cues from the environment that spring has arrived. Other organisms also respond to changes in their external environment and may show patterns or cyclic changes like the skunk cabbage. What is this process called? Thermoregulation is just one example of responding to changes in external environments. The following several examples illustrate this concept and are pulled from many different chapters in your text as noted. Some of these we will discuss in class. You must be familiar with some of these as general examples of this concept, but you do not need to know them all. • Photoperiodism and phototropism in plants – plants bloom in response to day/night length; plants grow toward the light. pgs. 839 and 825, respectively. • Taxis and kinesis in animals – animals move toward or away from something in their environment (taxis); or a change in activity in response to a stimulus (kinesis). See CH. 51. These are both behavioral responses. • Chemotaxis in bacteria, sexual reproduction in fungi – bacteria change their movement in response to chemicals. See pg. 559. Fungi change to a mode of sexual reproduction in response to a chemical stimulus released by neighboring fungi. See pg. 639. • Nocturnal and diurnal activity: circadian rhythms pgs. 1072 and 1122. This concept will be discussed more in Unit 9. 6 UNIT 8 NOTES The following example is in the PowerPoint, slides 56-58, pg. 872. • Hibernation and migration in animals – animals enter a physiological state of low activity and lower metabolism (torpor) or change location in response to external cues of decreasing temperature and food scarcity. This allows the animal to conserve energy and survive on less through times of stress. Migration is a behavioral mechanism whereas hibernation is an actual physiological change within the organism. Estivation is similar to hibernation but occurs during periods of high temperature such as July. Homeostatic mechanisms reflect both common ancestry and divergence due to adaptation in different environments. We will now take a look at some different ways organisms have developed to gain nutrients, remove wastes, and exchange gases. Keep evolution in mind as we discuss these and try to see the similarities and differences. Several different organisms may have the same mechanisms for maintaining homeostasis such as countercurrent exchange or a closed circulatory system. This indicates a common ancestor at some point. However, these mechanisms can still have differences because these organisms have adapted to different environments and beneficial changes were selected for by natural selection to best suit those particular environments. Again, there are numerous examples listed here with accompanying page numbers where they can be found in your text. I encourage you to read those sections ONLY. Don’t read all of these chapters- there is way too much information. Concentrate on one or two examples (dot bullets) under each bolded heading so that you can use them as examples on a test in a short answer question. Organisms have various mechanisms for obtaining nutrients and eliminating wastes. Digestive Compartments Why do animals process food in specialized compartments? • Digestive mechanisms in animals such as food vacuoles, gastrovascular cavities, one-way digestive systems. See pgs. 882-884, slides 59-65. Protists have food vacuoles, organelles that contain enzymes to break down food. This is intracellular digestion. Hydra have a gastrovascular cavity. It is a digestive compartment that has one opening and also functions to distribute nutrients. This is extracellular digestion. Undigested material is eliminated through the same opening. Earthworms, grasshoppers, birds, and humans all have one-way tube systems with specialized compartments. Systems like these are called complete digestive tracts or alimentary canals. Food enters one end of the tube and is digested along the way. Whatever the body needs is absorbed and what is left over is eliminated from the other end of the tube. This waste was NEVER IN THE BODY!! 7 UNIT 8 NOTES Gas exchange occurs across specialized respiratory surfaces which must be moist. What is gas exchange? The respiratory surface is where gas exchange takes place. By what process? • Respiratory systems of aquatic and terrestrial animals. See pgs. 916-919, slides 66-76. In very simple animals such as sponges and flatworms, every cell of the body is close enough to the external environment for gases to diffuse quickly between all cells. These animals stay wet or moist for this to occur. Larger aquatic organisms have gills. Gills are outfoldings of the body surface that are suspended in the water. This provides a great increase in surface area. Water must constantly move over the surface for gas exchange to occur. Blood flows in the opposite direction that the water flows (countercurrent exchange) allowing for more efficiency. Terrestrial animals have branching tube systems. Insects have tracheal systems that have fine branches that take air close to the surface of every cell in the body. Larger animals have lungs that provide a large surface for gas exchange but must also use the circulatory system to transport the gases to and from all body cells. • Gas exchange in aquatic and terrestrial plants – Terrestrial plants have stomates in their leaves that are regulated by guard cells. When open the stomates allow gas exchange and water vapor to leave (transpiration). The majority of these stomates are on the underside of the leaves so that when the sun is shining it is not pulling too much water out of the plants. Aquatic plants have stomates on the upper leaf surface because the lower surface is in the water. Having holes in the lower leaf surface here would fill the leaf full of water. I have no idea what completely submerged plants like kelp do. My guess is simple diffusion, but I may be wrong? Osmoregulation balances the uptake and loss of water and solutes. What is osmoregulation? Osmoregulation is discussed in CH. 44 pgs. 954-957. • Osmoregulation in bacteria, fish and protists Any of these organisms living in freshwater will tend to take in water due to osmosis and lose salts by diffusion. Too much water will cause cells to bloat and possibly burst, so there 8 UNIT 8 NOTES must be a mechanism for removing excess water. Bacteria have cell walls that function to keep some water out and allow the cell to maintain its shape. Freshwater fish do not drink much and excrete large amounts of dilute urine. Marine fish do the opposite- drink a lot and excrete salts and very little urine. Protists have a contractile vacuole that acts as a pump to remove excess water. Salts must be replaced in the diet or by active transport. • Osmoregulation in aquatic and terrestrial plants Terrestrial plants must have ways of preventing water loss. Leaves have a waxy cuticle covering them and it is usually thinker in plants that live in dry areas. Some plants (cacti) have modified their leaves and stems so much they do not resemble other types of land plants. Stomates also function in water balance in plants. The guard cells will close the stomates when water becomes low. Again, I have no idea what aquatic plants do. They may be isoosmotic and therefore neither gain nor lose water. An animal’s nitrogenous wastes reflect its phylogeny and habitat. • Nitrogenous waste production and elimination in aquatic and terrestrial animals. See pgs. 959-964 slides 79-96. Nitrogenous wastes are produced from the breakdown of proteins and nucleic acids. Excretion is the process of removing these and other metabolic wastes. The particular waste that an animal produces generally depends on its habitat and access to water. Fig. 44.9 pg. 959, slide 80, shows the different nitrogenous wastes. Ammonia is highly toxic and requires a lot of water to dilute so it is mainly excreted only by small aquatic animals and fish mostly by diffusion. Mammals and larger marine fishes and sharks produce urea from ammonia. The liver produces the urea and it then removed from the blood by the kidneys and excreted in urine. Urea requires less water to dilute to safe levels than ammonia, but does require more energy to make. Insects, reptiles, and birds excrete uric acid. It requires much more energy to produce, but is relatively nontoxic and does not dissolve in water. It is excreted as a paste so access to water is not an issue. Key functions of most excretory systems: – Filtration: pressure-filtering of body fluids – Reabsorption: reclaiming valuable solutes – Secretion: adding toxins and other solutes from the body fluids to the filtrate – Excretion: removing the filtrate from the system • Excretory systems in flatworms, earthworms and vertebrates See pgs. 961-963, slides 8996. Flatworms have protonephridia – a system of dead-end tubules capped by flame bulbs that filter ICF and release filtrate into the tubules. The filtrate then 9 UNIT 8 NOTES is released to the external environment. These function mainly in osmoregulation. Earthworms have metanephridia – a system of tubules that have an internal opening. These function in both excretion and osmoregulation. Each segment of the worm has a pair. Fluid enters through the opening and moves through the tubule to a bladder that opens to the outside. The tubule is surrounded by capillaries and most solutes are reabsorbed. Wastes stay in the tubule and are excreted to the outside. Vertebrates have kidneys – specialized organs that function in both excretion and osmoregulation. The functional unit of the kidney is the nephron which is a collection of tubules that receives filtrate from the blood. As the filtrate passes through the tubules water and salts are reabsorbed and wastes remain in the tubule to be excreted. More or less water is reabsorbed depending on internal conditions. Circulatory systems link exchange surfaces with cells throughout the body. What are the two types of circulatory systems? What are the three basic components? An example of an organism with an open system is Vertebrates such as you have closed systems with three types of vessels. List all three and state where each carries blood from and to: 10 UNIT 8 NOTES • Circulatory systems in fish, amphibians and mammals. See pgs. 900-903, slides 104-107. Pay closes attention to Fig. 42.5 pg. 902, slide 107. The construction of the heart in each of these different types of animals gets more complex as you move from left to right in the diagram. This also shows you the pattern of evolution since mammals and birds came later. Fish have a closed circulatory system with single circulation and a two chambered heart. Blood leaves the heart, goes to the gills for gas exchange, and then travels to the rest of the body before returning to the heart. Amphibians have a closed circulatory system with double circulation and a three chambered heart with two atria and one ventricle. Most of the oxygen poor blood leaves the ventricle and goes to the lungs, but there is some mixing. Blood returning from the pulmonary circuit enters the other side of the heart and most of it is sent out to the body. Reptiles also have a closed circulatory system with double circulation and a three chambered heart with two atria and one ventricle. Here the ventricle is partially divided by a septum, except in alligators. Mammals have a closed circulatory system with double circulation and a four chambered heart. Blood coming back from the body enters one side of the heart and then goes to the lungs for gas exchange. Blood returning from the lungs enters the other side of the heart and then goes out to the body. There is no mixing of oxygen rich and oxygen poor blood. This is very important for endotherms due to their higher energy demand. This type of circulation can deliver more oxygen more efficiently. Before we talk about energy allocation and use, let’s put together everything we just learned about. The only way to really learn about the human body, or any organism, is to look at all the parts, learn their names and functions, and where each one is located. Done. Now to really understand you have to put it all together and see how each part works with other parts and how the organism functions as a whole. Two sections from the course outline I was given from the College Board are: Interactions and coordination between organs provide essential biological activities. • Stomach and small intestines • Kidney and bladder • Root, stem and leaf Interactions and coordination between systems provide essential biological activities. • Respiratory and circulatory • Nervous and muscular • Plant vascular and leaf (These are just some examples. Every part works with many other parts.) 11 UNIT 8 NOTES In other words, all of your body’s organs and organ systems need to work together for you to function and remain healthy. Try to think of the many ways your different parts interact. What happens to a PBJ when you eat it? How are you able to walk to your next class? Being able to trace that PBJ from your mouth to becoming energy to creating waste to the toilet is what this whole section is about. All of your parts work together to function as a whole and none of your parts can function without the rest. Together they all maintain homeostasis and keep you functioning. What happens if there is a disruption in homeostasis? Yup. You get sick because something is not working the way it should. This can be caused by injury, disease, or even an environmental cause. Here are just a couple examples. We will discuss your immune system in much more detail in CH 43 next. Biological systems are affected by disruptions to their dynamic homeostasis. Disruptions at the molecular and cellular levels affect the health of the organism. • Physiological responses to toxic substances – toxins often interfere with cell communication thus preventing cells from doing something they have been told to do or doing something they haven’t been told to do. Some toxins can alter the permeability of membranes thus changing osmolarity and causing osmotic imbalances for the organism. • Dehydration – lack of water can prevent wastes from being removed or other cellular processes from taking place. • Immunological responses to pathogens, toxins and allergens – See CH. 43 below. Energy Allocation and Use All living systems require constant input of free energy. Organisms use free energy to maintain organization, grow and reproduce. Review: What is the process that releases this energy from food and puts it into the usable form of ATP? What is metabolic rate? There is a relationship between metabolic rate per unit body mass and the size of multicellular organisms — generally, the smaller the organism, the higher the metabolic rate. Scientists are not sure why just yet. It may be due to the larger surface area to volume ratio for smaller animals which causes them to lose more heat/volume. 12 UNIT 8 NOTES Reproduction and rearing of offspring require free energy beyond that used for maintenance and growth. Different organisms use various reproductive strategies in response to energy availability. • Seasonal reproduction in animals and plants – organisms reproduce only at times when there is plenty of food and water available for young, or when seed dispersal methods can be best used. • Life-history strategy (biennial plants, reproductive diapause) Biennial plants require two years to complete their life cycle. They flower and produce fruit only in the second year. Radishes and carrots are common examples, but we eat them after the first year. Another is Equisetum, or horsetail, a plant commonly found on the side of the road. One year it grows in its gametophyte form and the other its sporophyte form, one of which looks like a horse’s tail. Reproductive diapause occurs often in insects and plants. It is a period when growth or activity is greatly diminished or stopped. This occurs in eggs, insect pupae, seeds, or any time the life cycle can be suspended for a while, usually to wait for better living conditions. Excess acquired free energy versus required free energy expenditure results in energy storage or growth. Energy (food) taken in beyond what is needed to maintain a BMR is extra and can be used by the organism to increase in size or weight, or biosynthesis. Storing the extra for later is often referred to as weight gain in humans. Insufficient acquired free energy versus required free energy expenditure results in loss of mass and, ultimately, the death of an organism. Chapter 43 Sections 1-4 Plants and animals have a variety of chemical defenses against infections that affect dynamic homeostasis. Pathogens are infectious agents such as bacteria and viruses that cause disease. An immune system enables organisms to defend themselves against pathogens. There are two types of defense systems: nonspecific, or innate immunity, and specific, or acquired immunity. When does an organism get innate, nonspecific immunity and what does it consist of? 13 UNIT 8 NOTES When does an organism get acquired, specific immunity and what does it consist of? Refer to Fig. 43.2 pg. 931, slide 118 for a brief description of both. To keep these two straight, try this. Innate means something you are born with. It has the same root as natal (birth), prenatal (before birth), and neonatal (new birth). Here the innate response is the defense mechanisms you are born with to fight off disease, which really isn’t a lot, so it works in a very general way, like skin keeping pathogens out of the body. Acquired immunity is going to be immunity that your body develops towards specific pathogens that you encounter during your life. This kind of immunity you are not born with, but get, or acquire, as you live. Plants, invertebrates and vertebrates have multiple, nonspecific immune responses. Yes, even plants and lowly insects have some form of defense from pathogens. They DO NOT, however, have specific immune systems that produce antibodies. If a virus invades a plant leaf the plant can just drop the leaf and be done with it. That takes far less energy than maintaining a specific immune response. Sometimes these organisms have genetic mutations that make them resistant to certain things such as viruses or pesticides. RESISTANCE IS NOT IMMUNITY!! Resistance is genetic and immunity involves antibody production. If you do not have the capability of producing antibodies you can not become immune. Innate or nonspecific immune responses include barriers such as an exoskeleton or skin, mucous membranes, and other secretions to keep pathogens out of the body. If this doesn’t work and a pathogen gets inside, there are other internal defenses that kick in. These would be phagocytic cells that attack and eat the invaders, antimicrobial peptides that attach to and destroy pathogens, an inflammatory response, or natural killer cells. • Plant defenses against pathogens include molecular recognition systems with systemic responses; infection triggers chemical responses that destroy infected and adjacent cells, thus localizing the effects. Plants that get an infection or virus in a leaf can destroy surrounding tissue and actually cause the leaf to fall off without infecting the rest of the plant. • Invertebrate immune systems have nonspecific response mechanisms, but they lack pathogen-specific defense responses. This means invertebrates, like insects, do not produce antibodies against pathogens. They only rely on barrier defenses, phagocytic cells, and antimicrobial peptides to defend against 14 UNIT 8 NOTES pathogens. Invertebrates produce many types of antimicrobial peptides that target classes of microbes such as fungi or bacteria rather than a specific fungus or specific bacterium. • Vertebrate immune systems have nonspecific and nonheritable defense mechanisms against pathogens. Vertebrates use their skin and mucus as the first line of defense. Enzymes found in mucus help to destroy many microbes as does stomach acid. There are also phagocytic white blood cells (neutrophils and macrophages) that circulate throughout the body and congregate in the spleen and lymph nodes to attack any pathogens that have gotten in. Antimicrobial peptides and proteins also attack microbes or stop them from reproducing. Vertebrates also have a second line of defense that invertebrates do not have. This includes the inflammatory response and natural killer (NK) cells. Describe the inflammatory response: Local swelling at the site of injury, redness, fever, and pus are all part of the inflammatory response and are considered normal. Septic shock, however, is a systemic (whole body) response to a pathogen that can be life threatening. Basically, your body tries so hard to kill off the pathogen that it damages itself. Natural killer cells attack any cells in the body (except RBCs) that no longer exhibit the “self” antigen (a class 1 MHC protein) on their surface. Many cells that have become infected by a virus or become cancerous no longer have this antigen so they are no longer recognized by the NK cells and are destroyed. How can some pathogens avoid destruction? Mammals use specific immune responses triggered by natural or artificial agents that disrupt dynamic homeostasis. Specific immune responses are slower to occur than nonspecific responses, but once activated usually last throughout the life of the organism. Specific responses are triggered by actual exposure to an infecting agent. This can be from infection by a pathogen (actually getting sick) or by vaccination. 15 UNIT 8 NOTES In acquired immunity, lymphocyte receptors provide pathogen-specific recognition. The mammalian immune system includes two types of specific responses: cell mediated and humoral. See Fig. 43.16 pg. 942, slide 142, and below. Your immune system is very complicated and can be difficult to understand. You may need to read this several times and be sure to ask questions if you don’t get it. Remember, you aren’t the only one. Also, this is a general overview. There are gory details that have been left out to, hopefully, make it easier for you to understand. If you want to be an immunologist or toxicologist then read the book and good luck. Both of these responses use white blood cells called lymphocytes. What do lymphocytes do? What are the two types and where do they mature? Each individual lymphocyte is ____________________________________to recognize a specific type of molecule. For this reason you have hundreds of different lymphocytes to recognize hundreds of different molecules. Lymphocytes have thousands of receptors to recognize its specific molecule and each one is the same. What is an antigen? So if an antigen is the foreign molecule the lymphocyte responds to, then all those receptors on one lymphocyte are recognizing the same antigen. Something like what you see in Fig. 43.9 pg. 937, slide 133. Let’s start with the humoral response. Here is where the B cells come in. B cells produce plasma cells that make antibodies or immunoglobulins. Each antibody is specific to the particular antigen that the original B cell could recognize and is basically a copy of the B cell receptors. These antibodies are proteins that are secreted by the plasma cell. They have a Y shape. The antibody recognizes the antigen by shape. Since each antigen has a unique shape every antigen will be recognized only by the antibody with the corresponding shape, and different antigens will have to have different corresponding antibodies. This is why you need multiple vaccinations- the chicken pox antibodies will not recognize the flu antigens, and vice versa. 16 UNIT 8 NOTES Now let’s take a look at the cell-mediated response. This involves T cells. Fig. 43.12 pg. 939, slide 133 shows the basics. When antigens are displayed by Class I MHC molecules (antigen presentation) they are recognized by cytotoxic T cells that kill those infected cells. Cells that display Class I MHC molecules are usually body cells that have been infected. Cells that display Class II MHC molecules are macrophages and B cells that have found foreign material circulating in the body. Helper T cells, as well as cytotoxic T cells, can bind to these molecules and activate both cytotoxic T cells and B cells to produce antibodies and mount a full scale attack. What does MHC stand for? A second exposure to an antigen results in a more rapid and enhanced immune response. This is because once your body has been exposed to a particular antigen you make memory B and T cells that recognize that antigen. Upon exposure again, you can immediately produce plasma B cells, antibodies, and cytotoxic T cells to reduce or eliminate infection. Fig. 43.16 pg. 942, slide 142 sums everything up nicely for you. Humoral immune response involves activation and clonal selection of B cells, resulting in production of secreted antibodies. Cell-mediated immune response involves activation and clonal selection of cytotoxic T cells. Fig. 43-16 Humoral (antibody-mediated) immune response Cell-mediated immune response Key Antigen (1st exposure) + Engulfed by Antigenpresenting cell + Stimulates Gives rise to + + B cell Helper T cell + Cytotoxic T cell + Memory Helper T cells + + + Antigen (2nd exposure) Plasma cells Memory B cells + Memory Cytotoxic T cells Active Cytotoxic T cells Secreted antibodies Defend against extracellular pathogens by binding to antigens, thereby neutralizing pathogens or making them better targets for phagocytes and complement proteins. Defend against intracellular pathogens and cancer by binding to and lysing the infected cells or cancer cells. What cells aid in both responses? 17 UNIT 8 NOTES There are several slides here that explain the roles of helper T cells, cytotoxic T cells and B cells. These are here to show you how these parts work together. For example, activated helper T cells secrete cytokines which stimulate other lymphocytes. The parts of your immune system work together for the good of the whole just like the rest of your organs and organ systems work together. What is the difference between active immunity and passive immunity? What is in a vaccine? What molecules cause organ rejection? People, and animals, generally remain healthy as long as the immune system functions properly. Unfortunately, sometimes it doesn’t. Like any other system of the body there can be malfunctions. What is an allergy? What is released by the mast cells that causes all the typical allergy symptoms? And what type of drugs do you take for an allergy? Now you know why they are called that. What causes an autoimmune disease? What is antigenic variation? Give an example. 18 UNIT 8 NOTES What is latency? (Hint: the lysogenic life cycle of viruses) Inborn immunodeficiency is caused by a defect in the immune system. It may have a genetic or developmental cause that prevents it from functioning properly. Acquired immunodeficiency syndrome (AIDS) has a different cause. What causes AIDS? Why is it such a devastating disease? What about this virus makes it so hard to defend against or produce a vaccine? Chapter 48 Sections 1-4 The neuron is the basic structure of the nervous system that reflects function. Neurons are nerve cells that transfer information within the body. Neurons use two types of signals: 1. 2. Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. Processing of information takes place in simple clusters of neurons called ganglia or a more complex organization of neurons called a brain. Nervous systems process information in three stages: 1. 2. 3. Neuron Structure and Function A typical neuron has a cell body, axon and dendrites. The structure of the neuron allows for the detection, generation, transmission and integration of signal information. Many 19 UNIT 8 NOTES axons have a myelin sheath that acts as an electrical insulator. State what each part does and draw and label a picture of a typical neuron below. Use Fig. 48.4 pg. 1049, slide 167. Cell body – Dendrites – Axon – A synapse is a junction between an axon and another cell. In your drawing above indicate where the synapse would be and draw the cell body and dendrites of another cell making sure to show that the two cells DO NOT TOUCH each other. How does information get across the synapse? As you can see, neurons are funky looking, very specialized cells. Some are fairly short and others are extremely long. Clusters of long neurons make up your spinal cord. Once you reach adulthood and stop growing your neurons have also reached adulthood and have entered the G0 state of the cell cycle. This is why spinal cord and brain injuries are so devastating. Neurons in the G0 state can not regenerate or repair themselves so they can no longer function for communication. There is a tremendous amount of research going on in this field, but no one has as yet been able to figure out how to induce a neuron to grow or repair itself. There has been some success in rerouting other neurons, say from one arm to a leg to get some mobility, but that is about it. Sometimes one part of the brain may take over functions once performed by a damaged part, but that takes much time and does not always happen. Why? Don’t know. Sometimes when you have surgery and nerves are cut you may lose some feeling. Again, sometimes it comes back and sometimes it doesn’t. Why? Don’t know. As complicated as your immune system is, your nervous system is much more and still holds many secrets we are unable, as yet, to figure out. At the beginning of this chapter we said that neurons use two types of signals, electrical and chemical. The neurotransmitter that crosses the synapse is the chemical signal. More on that later. Its fairly simple. The electrical signaling is, of course, more complicated. Remember when we learned about respiration and photosynthesis and how ATP was made? There was a proton pump at work in chemiosmosis that pumped protons to the outside of a membrane as electrons traveled through the ETC. This set up a membrane 20 UNIT 8 NOTES potential with a positive charge on one side and negative on the other. The charge difference, as well as the concentration gradient, helped the protons to flow back through the ATP synthase and make ATP. Neurons also use a pump and have a membrane potential or voltage across their plasma membranes. This voltage is measurable with many of today’s diagnostic tools. A message travels down the axon of a neuron as a change in membrane potential. What is the resting potential? Formation of the Resting Potential Membranes of neurons are polarized by the establishment of electrical potentials across the membranes. • In a mammalian neuron at resting potential, the concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell • Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane • These concentration gradients represent chemical potential energy • The opening of ion channels in the plasma membrane converts chemical potential to electrical potential • A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell Fig. 48-6 • Anions trapped inside the cell contribute to the negative charge within the neuron • See Fig. 48.6 pg. 1050, slide 172 Key Na+ K+ OUTSIDE CELL OUTSIDE [K+] CELL 5 mM INSIDE [K+] CELL 140 mM [Na+] [Cl–] 150 mM 120 mM [Na+] 15 mM [Cl–] 10 mM [A–] 100 mM INSIDE CELL (a) (b) 21 Sodiumpotassium pump Potassium channel Sodium channel UNIT 8 NOTES When a neuron is at rest, just hangin’ out, the inside of the membrane is negatively charged and the outside is positively charged. This charge difference is maintained by the action of the sodium-potassium pump that keeps pumping K+ in and Na+ out. There are numerous other ion channels found within the membrane, some open, some closed. When a stimulus is received by a dendrite changes take place in the plasma membrane which could cause the cell to temporarily open some ion channels that were closed and change the membrane potential. If more K+ channels open and more K+ diffuse out, then the inside becomes MORE negative and the magnitude of the membrane potential increases. This is called hyperpolarization and does not create a signal that is sent to other cells. Other stimuli the cell receives may cause different channels to open causing a depolarization or reduction in the magnitude of the membrane potential. If the stimulus is strong enough and enough voltage-gated Na+ channels open then a massive depolarization may take place causing an action potential. As ion channels in the membrane open and close along the axon, the electrical signal (action potential) is transmitted from one end of the cell to the other. Think of it as doing the wave at a ball game. You stand up then sit back down and the next person stands up and sits back down, etc. In a neuron ion channels open then close then the channels next to those open then close, etc. Every stimulus does not generate an action potential. When does an action potential occur? An action potential is an all-or-nothing response. If the stimulus is not strong enough to cause depolarization to reach that threshold, there will be no action potential. Action potentials are the nerve impulses, or signals, that carry information along axons. One neuron can produce hundreds of action potentials a second, and frequency can be an indication of the strength of a stimulus. Even as rapid fire as this may seem, a second action potential can not be initiated for a short period right after an action potential. What is this called? What causes this? Action potentials can only travel in one direction. Toward what? Why? 22 UNIT 8 NOTES Schwann cells, which form the myelin sheath, are separated by gaps (nodes) of unsheathed axon over which the impulse travels (jumps) as the signal propagates along the neuron. This insulating layer causes what to happen to the action potential, or impulse? OK. We have now received a stimulus, created an action potential, and transmitted that impulse down an axon and have reached the axon terminal at a synapse. Now what does it do? We still have no response so it can’t just quit. When an impulse reaches the end of the axon it triggers the release of a chemical called a neurotransmitter. The impulse causes this neurotransmitter to be released by the presynaptic neuron. The neurotransmitter is then received by the postsynaptic neuron which transmits the signal and generates a response. The response can be stimulatory or inhibitory. See Fig. 48.15 pg. 1057, slide 194. Notice that the postsynaptic neuron has ligand-gated ion channels that open when they receive the neurotransmitter and allow Na+ and K+ to start diffusing and change the membrane potential. Once the neurotransmitter has done its job, it needs to leave the synaptic cleft so that another signal can be sent at another time without interference. It can be taken up by other cells, diffuse away, or be degraded by enzymes. The same neurotransmitter can produce different effects in different types of cells. Some common neurotransmitters are: • Acetylcholine – most common • Epinephrine • Norepinephrine • Dopamine • Serotonin • GABA Drugs are often made to physically resemble neurotransmitters so that some neural pathways can be turned on or off artificially. Sometimes this is good, as is the case with opiates that are used as pain killers for people with chronic pain. Sometimes this is bad when people without pain use them just to feel good and become addicted. Chapter 49 Sections 1-3 So now you know how a neuron works. If you put a bunch of them together throughout an organism, you have a nervous system. This system is capable of receiving signals from the internal or external environment and affecting homeostasis. Together with the endocrine system in your body it regulates pretty much everything that goes on inside you, as well as how you think and move. For the most part we will concentrate on your nervous system, but, just so you know, there are other types. The simplest one is a nerve net found in cnidarians (hydra, jellyfish). These are just a bunch of interconnected nerve cells, 23 UNIT 8 NOTES but a system nonetheless. You are a higher order animal and therefore, have a more complicated system with nerves. What are nerves? Your entire nervous system has two parts- the central nervous system (CNS) and the peripheral nervous system (PNS). What two parts make up your CNS? Your PNS is all the rest of your nerves. They receive signals from your spinal cord. Your spinal cord also controls all of your reflexes without bothering your brain. That’s a good thing because if you took time to think about responding to some stimuli you might be injured or dead before you came to a conclusion. What is the function of cerebrospinal fluid? Label the main parts of the brain as you go through slides 206-213: Different regions of the vertebrate brain have different functions. List some of the functions for each part: • Midbrain (brainstem) 24 UNIT 8 NOTES • Hindbrain (cerebellum) • Forebrain (cerebrum) contains right and left cerebral hemispheres in humans The two hemispheres of the cerebrum are connected by the corpus callosum which allows them to communicate. Your right hemisphere controls the left side of your body and the left hemisphere controls the right side of your body. The cerebral cortex, the outer part, or gray matter, is where you do all your thinking. Each half of your brain is divided into four lobes that have different functions. There are areas that are for emotions, motor skills and movement, hearing, vision, smell, taste and math. The left hemisphere is better at math and language- the “book smart” people, and the right side is better at pattern recognition and emotions- the “artsy” people. This is called lateralization, the differences between the two sides. This is a generalization too. It does not mean that if you can draw well you can’t do math. Most learning depends on how much effort you are willing to put in to learn. 25