CH-34-36 Fueling the Body’s Metabolism – Understanding Biology : Chapter Notes

This Document Contains Chapters 34 to 36 CHAPTER 34: FUELING THE BODY’S METABOLISM WHERE DOES IT ALL FIT IN? Chapter 34 builds on the foundations of Chapter 27 and provides detailed information about animal form and function Students should be encouraged to recall the principles of eukaryotic cell structure and evolution associated with the particular features of animal cells. Multicellularity should also be reviewed. The information in chapter 34 does not stand alone and fits in with all of the chapters on animals. Students should know that animals and other organisms are interrelated and originated from a common ancestor of all living creatures on Earth. SYNOPSIS Animals obtain metabolic energy by eating other organisms. They are not collections of simple molecules, but are composed of macromolecules including proteins, fats, and starches. The degradation of these organic molecules is the process of digestion. Very simple organisms, protists and sponges, exhibit intracellular digestion. All other organisms have extracellular digestion where digestive enzymes are released into an internal body cavity. The most primitive invertebrates have a gastrovascular cavity with one opening that serves as mouth and anus. Higher invertebrates and vertebrates possess a one-way digestive tract with separate mouth and anus. Food is often fragmented before it is digested, some animals store ingested food in specialized organs prior to digestion. Digestion begins in the mouth where teeth aid in the acquisition of food. They are variously shaped for capture, cutting, and grinding. Saliva from three pairs of glands moistens the food and initiates digestion of starches. The process of swallowing begins when food passes into the back of the mouth. It is propelled through the esophagus by peristaltic waves and enters the stomach. A muscular sphincter generally prevents food from reentering the esophagus once it is in the stomach. The inner surface of the stomach is convoluted to accommodate the sporadic ingestion of food, especially by carnivores. The walls of the stomach produce protective mucus in addition to hydrochloric acid and pepsinogen. The production of acid is carefully regulated by gastric hormones to ensure that it can be neutralized sufficiently. Parietal cells produce HCl that provide an acidic ¬environment to keep pepsin active, help denature proteins, and kill ingested bacteria. Passage of chyme into the small intestine is controlled by the pyloric sphincter in response to changes in pH at the beginning of the small intestine. Most digestion occurs within the first part of the small intestine, the duodenum, as a result of the action of intestinal and pancreatic enzymes. The intestine also produces bicarbonate to neutralize the acid from the stomach. The liver produces bile salts to emulsify fats prior to their digestion. Bile is stored in the gallbladder until it is needed. The remaining divisions of the small intestine, the jejunum, and the ileum, are specialized for absorption. The surface area is increased by finger-like projections called villi. The epithelium of each villus is covered with cytoplasmic extensions, the microvilli. Amino acids and sugars cross the intestinal cell membranes into blood capillaries at the brush border. Lipids are broken down into fatty acids and collected in the lymphatic system. The daily volume of food and water that passes through the gut equals nearly 9 liters, almost all is absorbed in the small intestine. A small amount of liquid is reabsorbed in the large intestine, leaving 50 grams of solids and 100 milliliters of liquid to be excreted. The inner surface of the large intestine lacks villi as its main function is to compact the wastes. Some sodium, vitamin K, and other products of bacterial metabolism are also absorbed here. Exit of wastes from the rectum is regulated by two sphincters; the first is involuntary, the second is voluntarily controlled. Ruminants house cellulose-digesting bacteria in the rumen and essentially digest their food twice. Horses have symbiotic bacteria in the caecum, but digestion of cellulose is less efficient because they only digest their food once. The digestive system is under a combination of nervous and hormonal control. Sight and smell of food stimulates salivary and gastric secretions. Food in the stomach stimulates secretion of gastrin, causing production of pepsinogen and HCl. Passage of chyme from the stomach to the intestine inhibits stomach contractions. Cholecystokinin is secreted in response to fat in chyme and secretin is released in response to the acidity of chyme. Nutrients absorbed from the small intestine are directed to the liver, which acts as a metabolic reservoir. Under the influence of pancreatic hormones, it absorbs glucose when there is too much in the blood and releases it when there is too little. Glucose is not stored as is, but is converted to glycogen. Vertebrates obtain several vitamins from the food they eat as they are unable to synthesize them. Humans require 13 vitamins, 8 essential amino acids, essential minerals, and various other trace elements. Simple, small organisms transport nutrients and gases directly across the membrane of each cell. Other organisms are too large and complex for such exchange and need a circulatory system to transport nutrients, gases, and other materials to their cells and remove waste materials from those cells to disposal organs. In open systems there is no distinction between the circulating fluid and the body fluid. In a closed system the circulating fluid is restricted to tubular vessels throughout the animal. In vertebrates, oxygen diffuses into the blood in the gills or lungs, accumulates in the erythrocytes and is carried to all tissues. Waste carbon dioxide is collected at metabolizing tissues and transported back to the gills or lungs for release. Nutrients enter the circulation through the wall of the small intestine and are transported to the liver. The blood transports nutrients to the tissues while metabolic wastes are collected from them and carried to the kidneys for removal. Hormones are also transported through the circulatory system to various target tissues. Heat produced in body tissues is distributed through the bodies of homeothermic birds and mammals. Plasma proteins and platelets are involved in the clotting mechanism that protects against blood loss. White blood cells provide immunity against disease. Heterotrophs obtain energy by oxidizing carbon compounds utilizing oxygen and producing carbon dioxide. Oxygen passively diffuses into the layer of water surrounding the epithelial layers and is driven by the difference in oxygen concentration between the interior of the organism and the environment. This relationship is described by Fick’s law of diffusion. Many animals increase their diffusion constant by circulating fresh water around their bodies. Other animals increase the diffusion surface via special respiratory organs. External gills are the simplest aquatic gas exchange organs. Fish circulate water past their gills and out the opercular openings. Most fish possess moveable gill covers that pump water past their gills, ensuring a constant flow of oxygen to maintain a high diffusion constant. The structure of the gill and its blood supply create a countercurrent flow; maximal diffusion occurs the entire length of the gill. Air-oriented respiratory systems are far less efficient. Insects evolved tubular tracheae; other animals evolved lungs. Amphibians breathe with simple sac lungs augmented by cutaneous respiration. Reptile lungs are more complex as their water-tight skin prevents diffusion. Mammal lungs are highly branched with terminal alveoli. They increase their diffusion surface area to meet the demand for more oxygen with greater metabolic activity. Birds evolved a super-efficient system with unidirectional air flow by utilizing posterior and anterior air sacs. Gas exchange in birds occurs across parabronchi, minute air vessels rather than the blind-ended alveoli of mammals. Avian respiration requires two cycles of inspiration and exhalation to move a single volume of gas through their respiratory system. Their respiration is nearly as efficient as a fish’s due to the 90o cross-current flow between the air and the blood. The mammalian respiratory system is contained within the thoracic cavity. A single trachea connects to two bronchi, each divides into bronchioles that branch into alveoli. Human inhalation is a one-cycle pumping system, there is a small residual volume of air that remains within the lungs. Intrapleural fluid supports the lungs within the pleural cavity and enables the lungs to inflate as a result of pressure changes associated with changes in the size of that cavity. Reptiles, birds, and mammals possess negative pressure breathing (air is sucked into the lungs) while amphibians have positive pressure breathing (air is pushed into the lungs). Breathing in humans is dependent on regular contractions of the thoracic muscles and the diaphragm. The amount of air exchanged in passive inspiration and expiration is the tidal volume: vital capacity is the amount of air expired after a forceful, maximum inspiration equal to three to four times the tidal volume. Breathing is initiated by the respiratory center in the brain. It sends signals to the diaphragm and intercostal muscles to contract. This process is ultimately not under direct conscious control, you cannot asphyxiate yourself by holding your breath. The speed and depth of breathing is dependent on the level of CO2 in the blood. Chemoreceptors sensitive to blood pH are located in the aorta and carotid artery. The central chemoreceptors in the brain sense changes in pH in the cerebrospinal fluid. Blood pH changes occur as CO2 forms carbonic acid and further dissociates into hydrogen and bicarbonate ions. Respiratory gases are transported via the carrier protein hemoglobin. An animal’s oxygen-hemoglobin dissociation curve correlates partial pressure of oxygen and its ability to bind to hemoglobin. Oxygen diffuses into the blood plasma within the alveoli and then into the red blood cells. As the oxygen binds with hemoglobin it is removed from the plasma, allowing a greater amount to diffuse. Oxygen is unloaded from capillaries in metabolically active tissues as a result of the Bohr effect. Carbon dioxide is simultaneously absorbed by the blood and is bound to hemoglobin and the red cell cytoplasm. The carbon dioxide is unloaded at the alveoli where hemoglobin preferentially associates with oxygen. Carbon dioxide is carried in the red blood cells through the formation of carbonic acid and bicarbonate. Hemoglobin also transports nitric oxide (NO), a regulatory gas that causes dilation of blood vessels. The blood transports nutrients to the tissues while metabolic wastes are collected from them and carried to the kidneys for removal. Hormones are also transported through the circulatory system to various target tissues. Heat produced in body tissues is distributed through the bodies of homeothermic birds and mammals. Plasma proteins and platelets are involved in the clotting mechanism that protects against blood loss. White blood cells provide immunity against disease. Blood is composed of various metabolites, waste, salts, ions, hormones, nutrients, and proteins in solution in the plasma. Circulating cells include erythrocytes, granular and non-granular leukocytes, and platelets. Arteries carry blood away from the heart; veins carry it back. Capillaries lie between the two and are the location of exchange with individual cells since they have only a single thin layer if endothelial cells. The walls of all other blood vessels are composed of four layers, an innermost endothelium, a layer of elastic fibers, a layer of smooth muscle, and an outer layer of connective tissue. The muscle layer of arteries and arterioles is thicker than that in venules and veins. As a result the resistance and flow of blood in these vessels changes through vasoconstriction or vasodilation. The velocity of the blood in the capillaries is less than in the arteries due to differences in overall vessel area coupled with a constant flow rate. The lymphatic vessels constitute an open system to collect blood fluid lost to the tissues and return it to the closed circulation. The vertebrate heart originated as a simple peristaltic pump in early chordates. Fish evolved the first true heart composed of four consecutive chambers that pumped blood from the heart to the gills to the body and back to the heart. The first separation of systemic and pulmonary circulation is seen in amphibians and reptiles. A complete two-cycle pump evolved independently in birds and mammals. The right side of the heart pumps deoxygenated blood to the lungs while the left side pumps oxygenated blood to the body tissues. The sinoatrial (SA) node, a remnant of the sinus venosus, is the heart’s pacemaker. The wave of depolarization passes through cardiac cell gap junctions. There is a slight delay between atrial and ventricular contractions as the wave of depolarization cannot pass through the connective tissue between the chambers. The wave is conducted via the atrioventricular (AV) node and across both ventricles through the bundle of His and through Purkinje fibers. Cardiac performance is monitored by recording the wave of depolarization in an electrocardiogram. Cardiac output, the volume of blood pumped by each ventricle per minute increases greatly with exercise, the rate at which the heart fills and empties is increased and the ventricles contract more strongly and empty more completely. LEARNING OUTCOMES 34.1 Vertebrate Digestive Systems Are Tubular Tracts 1. List the specialized zones of the vertebrate digestive tract. 34.2 Food Is Processed as It Passes Through the Digestive Tract 1. Identify adaptive variation in vertebrate tooth shape. 2. Describe how food moves through the esophagus. 3. Explain what digestive processes take place in the stomach. 4. Compare and contrast the surfaces of the stomach and small intestines. 5. Name the accessory organs and describe their roles. 6. Name the accessory organs and describe their roles. 7. Explain how absorbed nutrients move into the blood or lymph capillaries. 34.3 The Digestive Tract Is Regulated by the Nervous System and Hormones 1. Explain how the nervous system stimulates the digestive process. 2. Describe the liver’s role in maintaining homeostasis. 34.4 Respiratory Systems Promote Efficient Exchange of Gases 1. Explain how Fick’s Law of Diffusion applies to gas exchange across membranes. 2. Explain how evolutionary adaptations can affect different variables of Fick’s Law. 34.5 Gills Provide for Efficient Gas Exchange In Water 1. Describe how gills take advantage of concurrent flow. 34.6 Lungs Are The Respiratory Organs of Terrestrial Vertebrates 1. Compare the breathing mechanisms of (1) amphibians and reptiles, (2) mammals, and (3) birds. 2. Describe the efficiency of mammalian lungs using Fick’s law of diffusion. 3. Describe how contraction of the diaphragm powers inhalation. 4. Describe how the central nervous system regulates breathing. 34.7 Oxygen and Carbon Dioxide Are Transported by Fundamentally Different Mechanisms 1. Describe the structure of hemoglobin and how it binds oxygen. 2. Describe how hemoglobin’s oxygen affinity changes depending on environmental conditions. 3. Explain how carbon dioxide is transported by the blood. 34.8 Circulating Blood Carries Metabolites and Gases to the Tissues 1. List the principal functions of circulating blood. 2. Describe the solutes present in blood. 3. Distinguish among the types of formed elements present in blood. 4. Describe the origin of formed elements in circulating blood. 34.9 Vertebrate Circulatory Systems Put a Premium on Efficient Circulation 1. Describe the structure of the fish heart. 2. Explain the importance of the evolution of the pulmonary vein. 3. Explain the importance of the complete septum in crocodilian, bird, and mammalian hearts. 34.10 The Four Chambers of the Heart Contract in a Cycle 1. Explain the elements of the cardiac cycle. 2. Describe the role of autorhythmic cells of the SA node. 34.11 The Circulatory Highway Is Composed of Arteries, Capillaries, and Veins 1. Explain how arteries and arterioles withstand pressure. 2. Explain why capillaries cannot withstand high pressures. 3. Compare the structure of veins to arteries. 4. Describe how the lymphatic system operates. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 34 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that all animals have complete digestive systems • Students are unaware of the role of pH in digestion • Students confuse digestion with absorption • Students do not associate the liver and other glands as being digestive system organs • Students view the complete digestive system as being on organ • Students think that all animals evolved at about the same time • Students believe that most animals are vertebrates • Students do not equate humans with being animals • Students believe that all animals have identical organ system structures • Students believe that all land animals use lungs • Students do not know gills are found in aquatic animals • Students believe the circulatory system and respiratory system are not tightly integrated • Students confuse breathing and respiration • Students do not associate diffusion with respiratory system function • Students believe all animals have red blood cells. INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Although no food products are absorbed in the stomach, alcohol and some drugs are absorbed. Alcohol can also be absorbed through the lining of the mouth if it remains there long enough. The presence of small amounts of it in the stomach improves the digestive process by slowing the exit of materials into the small intestine. Discuss the activity of the liver as a detoxifying organ. The liver is frequently the first body organ damaged by toxins, including alcohol. This is readily evidenced by the damage to the liver of alcoholics due to fatty deposits and cirrhosis. Discuss the various feeding strategies of herbivores versus carnivores, endotherms versus ectotherms, and how these strategies affect the anatomy of the skull, jaws, and digestive tract. Discuss the effect of prolonged fasting on muscle. Very active fish (i.e., trout) require large amounts of oxygen and live in cold moving water. Other fish have adapted to water low in oxygen by reducing metabolism (catfish) or by evolving special labyrinth organs (Bettas). Many aquatic turtles significantly increase the time that they can remain submerged by utilizing cloacal respiration. Oxygen in the water diffuses across the cloacal membrane, similar to cutaneous respiration in amphibians and sea snakes. Discuss why birds need the most efficient respiratory systems, especially with regard to their body metabolism and flight altitude. Compare the countercurrent analogy with a heat pump. If very cold air meets very warm air a lot of exchange will occur, but only over a short distance. Most students are relatively familiar with the circulatory system and shouldn’t have much difficulty with this chapter. The most confusing thing is which ventricle pumps blood to the lungs (the right side) and which pumps to the rest of the body (the left side). Since the left ventricle pumps blood through the systemic circulation, it is the largest chamber of the mammalian heart. Stress that circulation is not directional with respect to individual organs, with the exception of circulation to the lungs and from the small intestine to the liver. Blood flows throughout the body reaching every cell in its own good time, like riding a circular subway system. You can’t get from point a to point c without going through point b. Once you’ve passed b, you have to go around the entire circuit again to get back to it. Stress why a two-cycle pump is more effective for terrestrial circulation than a one-cycle pump. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 34. Application • Have students explain why certain animals must sun themselves after eating a large meal. • Have students explain the role of pH in digestion. • Ask students to explain why food can only be absorbed in the digestive system in its simplest molecular form. • Ask students to explain path of oxygen through a gill and a lung. • Have students explain path of an oxygen molecule through an open and closed circulatory system. • Have students explain how the circulatory system responds to different needs of the respiratory system. Analysis • Have students explain why artificial sweeteners taste like but not provide the body with calories. • Have students explain why endotherms have higher caloric needs than exotherms. • Ask students compare the relative effectiveness of incomplete and complete digestive systems. • Have students explain why certain birds can live at very high altitudes at which no other animal can survive. • Have students explain why pollutants that contain iron are harmful to aquatic organisms. • Ask students to compare the adaptations needed for a gill to be used by a land animal. Synthesis • Ask students to design an experiment to test that incomplete digestive system obtain less calories from food than complete digestive systems. • Have students come up with commercial applications for animal digestive enzymes. • Ask the students to come up with an application of the knowledge that food can only be absorbed in its simplest molecular form. • Ask students to come up with the criteria needed for designing an artificial lung. • Have students come up with a commercial application for a chemical that improves the blood’s ability to dissolve oxygen in the fluid component. Evaluation • Ask students to evaluate the effectiveness and safety of dietary drugs that block the digestion of certain foods. • Ask students to evaluate the effectiveness and safety of dietary drugs that block the absorption of certain foods. • Ask students to evaluate the benefits and risks of athletic diets that are composed solely of amino acids and simple sugars. • Ask students to evaluate the effectiveness and safety sports supplements that increase the rate of the circulatory system. VISUAL RESOURCES Obtain photos or scanning electron micrographs showing the various convolutions of the digestive tract. Include the stomach, duodenum, lower small intestine, and the large intestine in the micrographs. Make a super inexpensive model lung using a balloon and an empty 1 or 2 liter plastic bottle. Depress the bottle slightly, place the balloon inside the stem of the bottle (but don’t drop it!). It takes a little dexterity to get the lip of the balloon on the stem of the bottle, but it is possible. When the bottle is released the lung balloon will inflate, when the bottle is depressed it will deflate. This model best exemplifies a garter snake system. They have only a single functional lung in their elongate bodies, the other lung is a mere bubble at the end of the bronchus. Compare the volume of walnuts versus smaller hazelnuts in a jar. Similarly an animal with smaller, more numerous alveoli has a greater lung volume than one with few, large alveoli. Several biological supply companies sell a respiratory model that uses a specially prepared actual cow lung. It is elastic enough that it can be expanded and deflated by breathing into and out of it. Obtain a fresh heart from a butcher or a slaughter house to demonstrate the various anatomical structures. The bigger the better so try for a cow or an ox. As last resort, purchase a preserved heart from a biological supply company. Construct a transparent circulatory system with plastic chambers and tygon tubing. Alternately, purchase and assemble one of the many kits available. Most kits, though, rely on only a single pump to push the “blood” through both systemic and pulmonary circulations IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Digestive System Histology Introduction This demonstration uses digestive system histology images to help students understand the cellular composition of the digestive system. It is a good demonstration for reinforcing histological form and function. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to Boston University histology website at http://www.bu.edu/histology/m/t_diges2.htm Procedure & Inquiry 1. Ask the class what they know about form and function in cell and tissue structure 2. Load up the Boston University histology website and click on digestive system histology images in order of the progress of food through the system. a. Esophagus (H&E) b. Mid/esophagus (Lee's stain) c. Esophageal/stomach junction I (H&E) d. Esophageal/stomach junction II (H&E) e. Colon (H&E) f. Fundic stomach (H&E) g. Pyloric stomach I (H&E) h. Pyloric stomach II (PAS/Pb hematoxylin) i. Pyloro/duodenal junction I (H&E) j. Pyloro/duodenal junction II (H&E) k. Duodenum, cells (H&E) l. Duodenum, glands, and plica (H&E) m. Jejunum I (eosin & toluidine blue) n. Ileum I, villi (H&E) o. Ileum I, Peyer's patches (H&E) p. Jejunum II (PAS/Pb hematoxylin) q. Ileum II, Peyer's patches (H&E) r. Appendix (H&E) s. Colon (H&E) t. Colon, anal canal (H&E) 3. Have students describe the cells and tissue composition. 4. Then see if the students can confirm the function of the organ based on the cellular structure removed. B. Respiratory System Histology Introduction This demonstration uses respiratory system histology images to help students understand the cellular composition of the respiratory system. It is a good demonstration for reinforcing histological form and function. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to Boston University histology website at http://www.bu.edu/histology/m/t_respir.htm Procedure & Inquiry 5. Ask the class what they know about form and function in cell and tissue structure of the respiratory system and associated blood vessels. 6. Load up the Boston University histology website and click on Respiratory system histology images in order of the major respiratory structures and then discuss the finer details: a. Trachea (H&E) b. Extrapulmonary bronchus (PAS/Pb hematoxylin) c. Lung (sheep), intrapulmonary bronchus (H&E) d. Lung (mouse) (PAS/Pb hematoxylin/resorcin-fuchsin) e. Lung (human), intrapulmonary bronchus (PAS/Pb hematoxylin) f. Alveolar sac g. Bronchioles h. Ciliated cell i. Pulmonary artery j. Pulmonary capillary k. Pulmonary vein 7. Have students describe the cells and tissue composition. 8. Then see if the students can confirm the function of the organ based on the cellular structure. LABORATORY IDEAS A. Comparing Digestive Systems This activity has students has students investigate the phylogenetic variation in animal digestive systems. a. Explain to the students that digestive systems vary based on phylogenetics and on feeding styles. b. Then explain that they will be looking for endocrine organs in a fish and frog using a human endocrine system chart as a guide. c. Provide students with the following materials: a. Dissection diagrams b. Slide of flatworm c. Preserved specimen of clamworm d. Preserved specimen of squid e. Preserved specimen of fish f. Dissecting equipment g. Dissecting microscope d. Tell students to note the differences and similarities of the digestive systems between the specimens. e. Then have them record any observations about form and function related to the degree of digestive system specialization in the different organisms. B. Brine Shrimp as a Respiratory System Model This activity has students has students investigate the effects of caffeine and tobacco and respiratory rate using a brine shrimp model. a. Explain to the students that many natural substances affect the respiratory rate of animals. b. Then explain that they will be using brine shrimp to look at effects of various . c. Provide students with the following materials: a. Petri dishes b. Microscopes c. Microscope slides d. pH Indicators ( phenol red or bromothymol blue) e. Large brine shrimp f. Brine shrimp medium g. Test reagents: i. Chewing tobacco ii. Coffee iii. 20% ethanol d. Tell students to design an experiment to investigate the effects of alcohol, coffee, and tobacco water on the respiratory system of the shrimp. Stress that they must do the experiments in a way that they can quantify the results under controlled conditions. e. Then have them prepare an oral report or a poster session of their findings and conclusions that can presented to the class. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students do a lesson do a hands-on program on the animal diets for elementary students. 2. Have students do an education program on the effects of smoking on respiratory system health for elementary school students. 3. Have students tutor high school students studying animal anatomy and physiology. 4. Have students volunteer on environmental restoration projects with a local conservation group. 5. Have students volunteer at a local air quality or lung associate agency. 6. Have students volunteer at the educational center of a zoo or marine park. CHAPTER 35: MAINTAINING HOMEOSTASIS WHERE DOES IT ALL FIT IN? Chapter 35 builds on the foundations of Chapter 27 and provides detailed information about animal form and function Students should be encouraged to recall the principles of eukaryotic cell structure and evolution associated with the particular features of animal cells. Multicellularity should also be reviewed. The information in chapter 35 does not stand alone and fits in with the all of the chapters on animals. Students should know that animals and other organisms are interrelated and originated from a common ancestor of all living creatures on Earth. SYNOPSIS The cell specialization found in complex vertebrates like humans requires extensive integrated control systems. These homeostatic processes are involved with nearly every bodily function and regulate such things as blood glucose levels and body temperature. Homeostasis occurs through various kinds of feedback loops. Negative loops attempt to return a system above or below a certain setpoint to that normal value and include regulation of blood glucose and body temperature. Positive loops accelerate changes and are exemplified by the process of childbirth. Chemical hormones are produced by ductless endocrine glands and are transported to the target organ through the blood. Their actions are broadly based and have long term effects, contrary to the localized, short-term effects of the nervous system. Receptor proteins in the target organs respond to the appropriate chemical messenger and trigger changes in cell activity. Some hormones, like steroid hormones, enter the cell and bind to receptors within the cell’s cytoplasm, altering gene activity. Others, like peptide hormones, do not enter the cell and bind to receptors embedded in the cell membrane. Many hormones require second messengers like cAMP and IP3/Ca++ to effect their molecular message. Multiple second messengers allow for varied control of each hormonal system. For example, the antagonistic actions of epinephrine and insulin on liver cells. Epinephrine uses cAMP as a second messenger, effecting a conversion of glycogen to glucose. Obviously, insulin cannot use the same second messenger on the same cells to illicit the conversion of glucose to glycogen. Many endocrine functions are controlled by the hypothalamus. The posterior lobe of the pituitary is connected to the hypothalamus by neurons. Antidiuretic hormone (ADH or vasopressin) and oxytocin are produced in the hypothalamus and transported to the posterior pituitary through these neurons. The hormones are then released from the posterior pituitary into the general circulation. Oxytocin prepares the female body for childbirth and nursing, while ADH helps regulate water reabsorption by the kidneys. The anterior pituitary is connected to the hypothalamus by short blood vessels through which hypothalamic releasing factors are transported. These releasing hormones stimulate the anterior pituitary to produce specific tropic hormones. The seven hormones are: growth hormone (GH or somatotropin), adrenocorticotropic hormone (ACTH), thyroid stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), and melanocyte-stimulating hormone (MSH). Three of these, GH, PRL, and MSH, are controlled by antagonistic action. Another hormone is produced to inhibit the secretion of the pituitary hormone: somatostatin inhibits GH, PIH inhibits prolactin, and MIH inhibits MSH. TSH, LH, FSH, and ACTH are controlled by negative feedback from the target glands. Each hormone itself inhibits production of its own releasing hormone. The thyroid gland produces thyroxine, which increases oxidative respiration and promotes growth in children. It also produces calcitonin, which stimulates the uptake of Ca++ from the blood to the bones. Parathyroid hormone (PTH) is produced by the four, small parathyroid glands and has a greater involvement with calcium uptake and regulation. Along with aldosterone, it is one of the two hormones that is absolutely essential for survival. PTH is released when the blood Ca++ gets too low as it is necessary for contraction of all muscles as well as proper nerve function. The adrenal gland produces four hormones, two in the medulla and two in the cortex. The medullary hormones, epinephrine and norepinephrine, provide a long ¬lasting alarm response similar to that of the sympathetic nervous system fight or flight response. The cortical hormones, cortisol and aldosterone, stimulate carbohydrate metabolism and regulate blood salt levels, respectively. The pancreas is both endocrine and exocrine in function and regulates blood sugar levels through the balanced secretion of insulin and glucagon. These hormones are produced by the beta and alpha cells, respectively, in the islets of Langerhans. Hormones are produced by several other organs including the ovaries and testes (sex hormones), pineal gland (melatonin), heart (atrial natriuretic hormone), kidneys (erythropoietin), and even the skin. By definition, vitamin D, produced in the skin and carried to the intestine where it stimulates absorption of calcium, is a hormone too. Most marine invertebrates are simple Osmo conformers; they maintain an internal concentration of ions equal to that of their environment. On the other hand, osmoregulators maintain an osmolality independent of their environment. Freshwater vertebrates have a greater internal salt concentration and must constantly exclude water. The internal salt concentration of marine specimens is roughly one-¬third that of the environment. They must retain water to prevent dehydration. Terrestrial animals tend to lose body water to the air through dehydration and must also conserve water. Animals utilize various strategies to regulate water balance. Simple protists and sponges possess contractile vacuoles to exclude water. Flatworms draw fluids from their bodies into flame cells, water and metabolites are reabsorbed, excreted substances are expelled through pores in the body wall. In earthworms, the internal fluid is collected in the nephrostomes and filtered, NaCl is reabsorbed by active transport. The Malpighian tubules of insects secrete potassium ions into the gut which pull body fluids and waste past their filtering apparatus. Vertebrates use the pressure-driven filtration system of the kidney, possible only with their closed circulatory system. Certain small molecules are selectively reabsorbed in the kidneys to help conserve water. Freshwater fish kidneys simply remove excess water that is absorbed. Marine bony fish combat dehydration by drinking enormous quantities of seawater as very little water is reabsorbed in the kidneys. Elasmobranchs reabsorb waste urea to make their blood isotonic with the sea, thus preventing excessive water loss and reducing the need to remove large amounts of ions. Amphibian kidneys operate much the same as those of freshwater fishes. Reptile systems are quite variable as are their habitats. Mammal and bird kidneys are able to produce urine that is more concentrated than their blood plasma, efficiently reabsorbing water from the filtrate. Nitrogenous wastes must be eliminated from the body. Bony fish excrete ammonia, but other vertebrates eliminate the less toxic urea and uric acid. Mammalian kidneys are paired organs with functionally and structurally distinct outer cortex and inner medulla. The mammalian nephron begins in the renal cortex where a mass of glomerular capillaries are surrounded by the Bowman’s capsule. Glomerular filtrate passes from the capsule to the proximal convoluted tubule and into the distal convoluted tubule. One of the key characteristics of the mammalian nephron is the hair-pin-curved loop of Henle. Several nephrons empty into a single collecting duct that empties into the funnel-shaped renal pelvis. Most of the water filtered through the kidney is reabsorbed, a consequence of salt reabsorption. Glucose and amino acids are reabsorbed through active transport carriers. Other foreign molecules and waste products are actively secreted from the nephron. Humans filter vast quantities of liquid through their kidneys. Two-thirds of the water and NaCL is immediately reabsorbed in the proximal tubule, the final third of water is reabsorbed in the collecting duct. The loop of Henle descends deeply into the hypertonic renal medulla. A countercurrent flow results where the filtrate passing through the descending limb loses water to the renal medulla because of the salts transported out of the ascending limb. The collecting tubule contains a very concentrated filtrate especially high in urea. The collecting duct is permeable to urea, which passes into the renal medulla followed by more water. The overall solute concentration of the blood is regulated by altering the hypothalamic output of antidiuretic hormone. ADH causes the collecting ducts to become more permeable to urea. An increase in the osmolality of the blood plasma triggers a sensation of thirst and stimulates ADH secretion. The extracellular fluid in the renal medulla becomes hyperosmotic to the filtrate in the collecting duct. Therefore, even more water leaves the filtrate via osmosis and reenters the bloodstream. This dilutes the blood and returns its osmolarity to normal. Plasma salt balance is regulated by production of aldosterone by the adrenal gland. Aldosterone stimulates reabsorption of sodium in the distal convoluted tubule, decreasing the amount lost in the urine. As a result, whole body sodium increases, as does overall water retention. Atrial natriuretic hormone promotes excretion of salt and water in the urine, opposing the action of aldosterone. All organisms must fight off attack by microbes. The water-tight skin of vertebrates is their first line of defense against invasion by microbes. The oils and sweat produced by glands on the skin’s surface are antimicrobial agents that alter the pH of the skin surface and the latter also contains a bactericidal lysozyme. Macrophages and neutrophils are phagocytic cells that directly ingest bacteria in the second line of defense. Suicidal neutrophils also release bleach bombs that wipe out hordes of bacteria at once. Natural killer cells attack cells already infected by microbes. Proteins also exhibit a nonspecific defense as exemplified by the complement system and interferons. The inflammatory and temperature responses involve substantial bodily responses, altering metabolism and blood flow for example. Fever is the body’s way of stimulating phagocytosis while inhibiting microbial growth. The immune response is the third line of defense. This defense system was utilized by Jenner and Pasteur to combat disease long before there was any knowledge of what triggered the response. The foreign molecules that provoke the specific immune response are antigens. Antibodies are proteins produced by B cell lymphocytes in response to an antigen. The specific immune response protects by active and passive immunity. The vertebrate immune response is not housed in a group of organs. The primary defenders are white blood cells that circulate through the body and are concentrated in the lymph nodes, spleen, liver, thymus, and bone marrow. They comprise three categories: phagocytes that engulf other cells, T cells that mature in the thymus, and B cells that arise from and mature in the bone marrow. Four kinds of T cells exist: inducer, helper, cytotoxic, and suppressor cells. Inducer T cells oversee the development of T cells in the thymus. Helper T cells initiate the immune response. Cytotoxic T cells lyse cells infected with the invading microbe. The immune response is terminated by suppressor T cells. B cell progeny differentiate into plasma and memory cells. Plasma cells produce antibodies. MHC-I proteins are cell surface proteins present on all nucleated cells. MHC-II proteins are found on macrophages, B cells, and CD4+ T cells. These proteins provide a self/nonself identification that is critical for the function of T cells. CD8 and CD4 are coreceptors associated with cytotoxic and helper T cell receptors, respectively. The cell-mediated immune response is a complex reaction associated with T cells, antigens, and interleukins. B cell receptors secrete antibodies, the basis of the humoral immune response. Antibodies are Y-shaped immunoglobin proteins composed of light and heavy chains. The terminal portions of the light chains of the Y arms are highly variable and confer specificity to the antibody. T receptors are similar in structure. The immune system is capable of generating millions of different receptors via somatic rearrangement. Receptor genes are not single nucleotide sequences, but are assemblages of three or four randomly selected DNA segments. B receptors can produce 16,000 different heavy chains. Light chains produce another 200 million different combinations. Antibodies are important in medical diagnosis, most commonly through the ABO and Rh blood typing systems and the production of monoclonal antibodies. Clonal selection produces a memory of the agent causing an infection so that a more efficient response is mounted the next time that invader is encountered. There are two primary mechanisms to defeat a vertebrate’s immune system. The first mechanism is that which is employed by the AIDS virus. It destroys the CD4+ T cells upon which the entire immune response depends. Without helper T cells, the immune response is never successfully initiated. As a result, an AIDS patient succumbs to diseases that a healthy individual readily fights off. The second mechanism, antigen shifting, relies on the nature of the surface antigens of the invaders. The antigens are altered frequently enough that the immune system cannot properly mount a defense. Autoimmune diseases result when a body fails to recognize its own self antigens. Allergies occur due to an abnormal immune response to allergens. Immediate hypersensitivity results from an abnormal B cell response; delayed hypersensitivity is an abnormal T cell response. LEARNING OUTCOMES 35.1 Homeostasis Maintains a Constant Internal Environment 1. Explain how negative feedback loops lead to homeostasis. 2. Classify organisms based on temperature regulation. 3. Describe mechanisms for temperature homeostasis in endotherms. 35.2 Hormones Are Chemical Messages That Direct Body Processes 1. Describe the role of hormones in regulating body processes. 2. Differentiate between lipophilic and hydrophilic hormones. 3. Explain how steroid hormone receptors activate transcription. 4. Explain how the signal carried by peptide hormones crosses the plasma membrane. 35.3 The Pituitary and Hypothalamus Are the Body’s Control Centers 1. Explain why the pituitary is considered a compound gland. 2. Describe the connections between the hypothalamus, posterior pituitary, and anterior pituitary. 35.4 Peripheral Endocrine Glands Play Major Roles in Homeostasis 1. Describe the actions of thyroid hormones. 2. Describe the components of Ca2+ homeostasis. 3. Compare the actions of the hormones of the adrenal medulla and the adrenal cortex. 4. Contrast the effects of insulin and glucagon on levels of blood glucose. 5. Describe how melatonin establishes a 24-hour circadian rhythm in vertebrates. 35.5 Animals Are Osmoconformers or Osmoregulators 1. Differentiate between osmoconformers and osmoregulators. 35.6 The Kidney Maintains Osmotic Homeostasis in Mammals 1. Name and describe the primary components of a kidney. 2. Describe the fate of major classes of molecules passing through the kidney. 3. Relate the structure of a nephron to its function. 35.7 Hormones Control Osmoregulation 1. Describe how ADH maintains osmotic homeostasis. 2. Describe the relationship between control of blood osmolarity and blood pressure. 35.8 The Immune System Defends the Body 1. Describe the function of pattern recognition receptors. 2. Describe the inflammatory response. 3. Define the characteristics of adaptive immunity. 35.9 Cell-Mediated Immunity Involves Helper and Killer T Cells 1. Describe the function of cytotoxic T cells. 2. Explain the role of helper T cells. 35.10 In Humoral Immunity, B Cells Produce Protective Antibodies 1. Describe the structure of an antibody molecule. 2. Explain how antibody diversity is generated. 3. Explain how vaccination prevents disease. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 34 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. This is a difficult topic for beginning students to understand. • Students believe that all hormones are steroids • Students confuse the mechanisms of lipophilic and hydrophilic hormone action • Students think that all animals evolved at about the same time • Students believe that animals can sense emotions and danger • Students believe that only humans have a well-developed endocrine system • Students are unaware of the genetic conservation of animal hormones • Students believe that most animals are vertebrates • Students do not equate humans with being animals • Students believe that all animals have identical organ system structures INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Stress that the neuroendocrine system is still under the control of the central nervous system and is dependent on signals from sensory neurons. The action of the neuroendocrine system differs from that of the sympathetic neurons in terms of duration and spectrum. Tiny amounts of chemicals in the blood are circulated to multitudes of target cells and are active until degraded. This requires a relatively small expenditure of raw materials and energy. To sustain continued sympathetic action would require great amounts of energy with continual nervous activity. Each hormone has an apparent profound effect on a few body organs and less noticeable effects on many organs. Such subtle effects of the major hormones continue to be discovered as biochemical and molecular techniques improve. Indeed, if the connection between the brain and a target organ were simple and singular, the control would likely be relegated to the nervous system. A great many interactions exist for which science is not yet aware. To remember which hormone controls which aspect of blood glucose, glucagon is made when blood “glucose is gone.” Discuss the care with which exogenous hormones and mimics (steroids, oral contraceptives, insulin) must be used to prevent upset of natural body hormones. Those controlled by feedback loops are frequently most affected. Oxytocin is often used to treat esophageal impactions (choke) in horses. The usual treatment is surgery, quite dangerous and not always successful. Although oxytocin causes smooth muscle, present in the lower third of the esophagus, to contract, the upper two-thirds of the esophagus in horses is striated, voluntary muscle. Oxytocin causes this muscle to relax, the blockage clears on its own or is readily manipulated by the veterinarian. (Equus, March 1998) Explain why insulin may not be taken by pill form versus why the hormones for contraception can be taken by pill form. Describe the gross anatomy of a mammalian kidney including the osmotic differences between the cortex and the medulla. Then indicate the location of the various parts of the nephron: capsule, proximal and distal convoluted tubules, descending and ascending limbs of the loop of Henle, collecting duct, and associated blood vessels. Finally put everything together by following a drop of blood and its filtrate through the capsule, into the nephron and out the collecting duct. Most students have experienced the effects of caffeine and ethanol on their urine output and will be interested in the physiology that regulates urine output. Compare the operation of a dialysis machine to that of a normal kidney. Discuss why artificial dialysis is necessary relative to increased levels of blood urea nitrogen (BUN) and creatinine. The kidneys excrete many metabolic toxins and drugs, penicillin and tetracycline for example. Excess vitamin C is also dumped here (and turns the urine bright orange). Many of these compounds can cause damage to the renal tubule when used for too long. Explain the absence of blood in the urine of a healthy individual. Explain the need for providing a urine specimen to your doctor. Emphasize the importance of vaccinations and list the immunizations that are required prior to attending school. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 46. Application • Have students explain why heating lamps are needed to for raising reptiles in captivity. • Have students explain why an organism controls body temperature to prevent its temperature from raising or lowering 5oC. • Have students describe the similarities of endocrine system and nervous system cellular communication. • Have students explain why hormones can flow to every cell in the body and yet only affect particular cells. • Ask students to explain why certain chemicals can cause the same effects as hormones. • Have students explain how the immune system would work if helper T-cells are not able to function. • Have students explain the chemical properties of a molecule that an organism’s immune system would recognize as a foreign antigen. • Ask students to describe why viruses that alter cell membrane proteins could induce an autoimmune response in an organism. Analysis • Have students explain how an osmoregulator would adapt to being placed in a saltwater environment. • Have compare and contrast the energy needs of ectotherms and endotherms. • Ask students to describe how the diet of an organism affects urinary system function. • Have students explain the differences and similarities between lipophlic and hydrophilic hormone action. • Have students explain the consequences of damage to the pancreas that reduces hormone production. • Ask students analyze the pros and cons using insulin injections to replace the role of insulin in people with diabetes mellitus. • Ask students to describe how mutations that affect antibody genes would impact the immune system. Synthesis • Ask students to design an experiment to test relationship between environmental temperature and efficiency of digestive system function in ectotherms. • Ask students to design an experiment to test the effects of giving growth hormone injections to slow down the aging process in mammals. • Have students design an experiment to test if certain pollutants compete with estrogen for the estrogen receptor. • Ask the students come up with a commercial use of molting hormone in insects. • Have students come up with a medical application for a technique that produces B-cells that can make antibodies against particular antigens. • Ask the students come up with a simple method of determining if peanuts could cause severe allergies in a person. Evaluation • Ask students evaluate the value of letting people monitor their health by measuring urea content of their urine. • Ask students and value and safety of drugs called thermogens that elevate the body’s temperature. • Ask students evaluate the accuracy of studying amphibians as a model for human metabolism. Ask students evaluate the claims that plant hormones can be used to supplement deficiencies in human hormones. • Ask students evaluate the effectiveness of using pig insulin to treat people with diabetes mellitus. • Ask students evaluate the accuracy of using fish to study endocrine regulation in humans. • Ask students evaluate the benefits and risks of developing a vaccine against HIV. • Have students debate the decision to vaccinate all young girls against the sexually transmitted disease called human papilloma virus. VISUAL RESOURCES Obtain a brain model and point out the location, size, and relationship of the pituitary gland to the hypothalamus. Use diagrams and models different animals to show the similarities and differences in endocrine system organs. Obtain various samples of vertebrate kidneys from the butcher or slaughter house. Few kidneys resemble the “kidney bean” structures possessed by those animals a student typically dissects. Set up a simple dialysis experiment to proceed as you lecture. Construct models of the T and B receptors, 3-D for a small class, 2-D for use on an overhead in a large class. You can show the variety of possible receptors if you make several different interchangeable H, V, and J pieces. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Hormone Feedback Review Introduction This demonstration uses animations to help students review feedback related two antagonistic hormones. It was developed by the British Broadcasting Corporation for K-12; however, many of the animations are appropriate for reviewing general biology concepts. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to BBC Animations website at http://www.bbc.co.uk/schools/gcsebitesize/teachers/biology/activities.shtml Procedure & Inquiry 1. Ask the class what they know about endocrine system feedback of blood sugar. 2. Load up the BBC website and click on the following links in the sequence below. a. Insulin synthesis b. Osmoregulation c. Glucoregulation 3. Have students review the concepts after each sequence. 4. Ask the students to briefly explain what other endocrine system feedback systems use antagonistic hormones. B. Animated Immune System Introduction This demonstration uses animated images of immune system function to help students understand immune system function. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to University of Maryland Medical School website at http://www.umm.edu/aniplayer/index.html Procedure & Inquiry 6. Tell the class they will be viewing animations about immune system function 7. Load up the University of Maryland Medical School website and click on the Immune System bar 8. Select Immune Response 9. Go through the animations 10. Have students describe the activities they viewed 11. Select Phagocytosis 12. Have students describe the activities they viewed A. Digestive System Histology Introduction This demonstration uses urinary system histology images to help students understand the cellular composition of urinary system. It is a good demonstration for reinforcing histological form and function. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to Boston University histology website at http://www.biology.ualberta.ca/facilities/multimedia/index.php?Page=252 Procedure & Inquiry 13. Ask the class what they know about ion and water balance in fish. 14. Load up the University of Alberta website and click on the Fish Gill Models. 15. Select Fresh Water 16. Go through the animations of the two models. 17. Have students describe the activities of the models. 18. Select the Salt Water 19. Have students explain the strategies of ion balance in fresh water and salt water fish LABORATORY IDEAS A. Comparative Endocrinology This activity has students has students use a human endocrine system diagram to look at the similarities and differences of endocrine system organization in other vertebrates. a. Explain to the students that all vertebrates evolved from fish-like ancestors and carry out similar endocrine functions. However, do explain that there may be some evolutionary differences. b. Then explain that they will be looking for endocrine organs in a fish and frog using a human endocrine system chart as a guide. c. Provide students with the following materials: a. Detailed diagram of human endocrine system b. Preserved specimen of fish c. Preserved specimen of frog d. Dissecting equipment e. Dissecting microscope d. Instruct students to use the human endocrine system chart to try to identify the endocrine system components of a fish and a frog. e. Have them record the ease of using the human diagram to do this for each specimen. Use their observations as a discussion point for the degree of difference and similarity in vertebrate endocrine systems. B. Virtual Immunology This on-line activity has students investigating the use of an enzyme-linked immunosorbent assay (ELISA) to understand immune system testing. It also demonstrates the clinical used antibodies. a. Explain that they will be conducting a virtual laboratory using antibodies to test for the presence of antigens. b. Provide students with the following materials: a. Computers with Internet Access b. Web browser bookmarked to Howard Hughes Medical Institute Website at: http://www.hhmi.org/biointeractive/vlabs/ c. Ask students to go to the Immunology Lab link. d. Have them “Enter the Lab” and carry out the procedures. e. Tell the students to answer the questions and record any observations in a laboratory book. f. Have the class look up the different uses of ELISA in medicine and other applications. C. Urine as an Indicator of Kidney Function This activity has students has students investigate the chemistry of urine as an indicator of urinary system function and health. a. Explain that they will be looking for endocrine organs in a fish and frog using a human endocrine system chart as a guide. b. Provide students with the following materials: a. Urine test strips (Multistix or equivalent) sliced lengthwise in half b. Test tubes c. Test tube rack d. “Artificial Urine” Samples i. Sample 1 1. Dissolve 3g sodium chloride, 5g urea, 1g glucose powder and 1g albumin powder in 100ml water. Add 1 drop of 2M hydrochloric acid. ii. Sample 2 1. Dissolve 3g sodium chloride, 5g urea and 1g glucose powder in 100ml water. Add 3 drops of 2M hydrochloric acid. iii. Sample 3 1. Dissolve 3g sodium chloride and 1g glucose powder in 100ml water. Add 3cm3 of 1M ammonia solution. iv. Sample 4 1. Dissolve 3g sodium chloride, 5g urea and 1g albumin powder in 100ml water. v. Sample 5 1. Dissolve 3g sodium chloride, 1g glucose powder and 1g albumin powder in 100ml water. e. Charts of normal urine results c. Tell students to test the different urine and investigate the reasons why they are testing the selected urine components. d. Ask them to note the differences and similarities of the urine samples. e. Then have them compare the samples to the measurements of normal urine and have them look up the probable causes of any variation from the normal. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students do a lesson do a hands-on program exercise and the cardiovascular system for elementary school students. 2. Have students do a lesson do a hands-on program on the animal homeostasis for elementary students. 3. Have students tutor high school students studying animal anatomy and physiology. 4. Have students volunteer on environmental restoration projects with a local conservation group. 5. Have students volunteer at the educational center of a zoo or marine park. 6. Have students do a lesson do a program on how the body fights disease for elementary school students. 7. Have students tutor high school students studying immune system function. 8. Have students set up a vaccination information booth at a local health fair CHAPTER 36: REPRODUCTION AND DEVELOPMENT WHERE DOES IT ALL FIT IN? Chapter 36 builds on the foundations of Chapter 27 and provides detailed information about animal form and function Students should be encouraged to recall the principles of eukaryotic cell structure and evolution associated with the particular features of animal cells. Meiosis, mitosis, and multicellularity should also be reviewed. The information in chapter 36 does not stand alone and fits in with the all of the chapters on animals. Students should know that animals and other organisms are interrelated and originated from a common ancestor of all living creatures on Earth SYNOPSIS Asexual reproduction produces genetically identical cells by the process of fission, budding, or parthenogenesis. Sexual reproduction increases genetic diversity even though such change is not always favored by natural selection. It has greatly contributed to the versatility of vertebrates. External fertilization is common in aquatic animals; eggs are laid in great quantities though few survive to adulthood. Three different strategies of development are associated with internal fertilization: oviparity, ovoviviparity, and viviparity. Most bony fish exhibit external fertilization, though some fertilize internally, and even fewer give birth to live young. Conversely, most cartilaginous fishes have internal fertilization and viviparous development. Amphibian fertilization is external with oviparous development divided into three stages. The young undergo lengthy development consisting of time spent in the egg and as a larva before becoming a terrestrial adult. Reptiles and birds are wholly terrestrial animals and exhibit internal fertilization. All birds are oviparous as are most reptiles, though some are either ovoviparous or viviparous. Fertilization in mammals is also internal and, excluding the monotremes, all are viviparous. This predominantly male hormone causes the indifferent embryonic gonads to develop into male external genitalia. Without testosterone, these same structures become female external genitalia. The male penis and female clitoris develop from the same structure, as do the male scrotal sacs and female labia majora. The male reproductive system continually produces sperm within the seminiferous tubules of the testes. Leydig cells located between the tubules secrete testosterone. Resurgence of testosterone production at puberty initiates sperm production and development of male secondary sexual characteristics. Upon completion of development, the sperm travel to the epididymis where they become fully motile. Sperm are then delivered to the vas deferens and exit through the urethra. The male penis is composed of erectile tissue, blood vessels, and the urethra. The penis becomes turgid when the erectile tissue is engorged with blood. Stimulation moves sperm into the urethra along with other seminal fluids produced by the seminal vesicles and prostate gland. Several hundred million sperm must be released to ensure fertilization. The production of sperm and testosterone are under the control of FSH and LH secretion from the anterior pituitary. Females do not produce eggs continually throughout life. At birth, each ovary possesses all of its primary oocytes arrested in prophase I of meiosis. The maturation of an egg within a Graafian follicle is initiated by follicle¬ stimulating hormone (FSH), which also causes a slow increase in estradiol (estrogen) production. The pituitary responds to these changes by producing luteinizing hormone (LH) and causes the release of the egg. It is swept into the fallopian tubes and is carried along by beating cilia moving it toward the uterus. The corpus luteum secretes progesterone, which induces the proliferation of the uterine lining. When fertilization does not occur, progesterone and estradiol production ceases and the thickened, highly vascularized uterine lining is expelled. Females of most mammal species have a sexual reproductive cycle called estrus that corresponds to the series of ovulation events in humans. Humans do not exhibit estrus cycles and are sexually receptive at all times. The human menstrual cycle lasts, on average, 28 days and incorporates successive hormone release to stimulate egg release (the follicular phase) and to prepare the uterus for possible pregnancy (the luteal phase). Several forms of contraception exist to prevent unwanted birth. In general they include methods that kill or block sperm, inhibit egg maturation, or deter implantation of the embryo. The most effective birth control is abstinence, followed by permanent surgical intervention in either the male or the female. The process of fertilization, the uniting of male and female gametes, is divided into three phases: penetration, activation, and fusion. In mammals, once the first event has occurred, no additional sperm are able to fertilize the egg. Eggs of some animals can be activated by physical stimulation and thus be induced to develop parthenogenetically. After fertilization, the zygote undergoes several mitotic divisions (cleavage) producing a greater number of smaller cells. The patterns of cell cleavage in vertebrates are influenced by the amount and location of yolk in the developing egg. Primitive aquatic vertebrates exhibit a symmetrical blastula with evenly sized cells. Advanced fish and amphibians develop an asymmetrical blastula with small cells at one pole and large cells at the other. The blastula of reptiles and birds is a small disk located on top of the yolk. Mammal embryos develop internally, the blastula resembles that of a reptile although there is little yolk present. The structure of the blastula determines future developmental events as cells in different positions contain different portions of the original egg cytoplasm, signal substances that affect development. Each cell is also in contact with different sets of neighbor cells, influencing development through positional information. At this stage, each cell has already been given its own unique developmental fate. The formation of primary ectoderm, endoderm, and mesoderm is a result of an event called gastrulation. The patterns of gastrulation vary among the different kinds of vertebrates. The gastrula forms by simple invagination (primitive chordates), movement of layers of cells over the yolk (aquatic vertebrates), or by cell differentiation without movement (reptiles, birds, and mammals). In mammals, the mesoderm arises from the cells of the upper layer, the ectoderm. The ectoderm eventually becomes the epidermis and neural tissue. The mesoderm forms connective, muscular, and vascular tissue. The endoderm becomes the lining of the gut and its derivative organs. Neurulation occurs only in chordates and results in the formation of the notochord and the hollow dorsal nerve cord. The formation of the neural crest occurs only in vertebrates, resulting in the development of the gill chambers, the nervous system, the skull, and various sensory organs. In determination, the developmental fate of a cell can be predicted and occurs very early in development. A “committed” cell’s developmental fate cannot be altered and occurs later. The evolution of neural crest was critical to the development of vertebrate predatory characteristics. These include greater physical activity, improved sensory detection of prey, improved spatial orientation, and quicker sensory responses. Patterns of development are built upon other patterns that occurred in earlier forms. For example, mammal development elaborates on reptile development which elaborates on amphibian development. This evolution of development gave rise to the phrase “ontogeny recapitulates phylogeny,” true with the consideration that embryonic stages reflect their embryonic rather than adult ancestry. Terrestrial vertebrates, including humans, evolved membranes derived from embryonic tissue, but not contained within the embryo—the extraembryonic membranes that include the amnion, chorion, yolk sac, and allantois. The amnion surrounds the embryo bathed in sea waterlike amniotic fluid. In birds and reptiles, the chorion lies immediately inside the egg shell. In mammals, the part of the chorion that is in contact with the endometrium becomes the fetal placenta. Development in humans requires a nine-month commitment by the mother. Pregnancy is frequently undetected in the first month even though organogenesis in the embryo is complete at this time. Morphogenesis occurs in the second month, and by the end of the third month the limbs of the fetus are fully formed and show movement. Significant growth occurs during the second and third trimesters; the weight of the fetus doubles several times. In some mammals, birth is initiated by changes in fetal hormone levels. In humans, an increasing amount of placental estradiol causes the uterus to release prostaglandins. Sensory feedback stimulates the release of oxytocin, also associated with uterine contractions. Lactation and the milk-ejection reflex require different hormones. Rapid growth in the baby continues after birth, especially in terms of neural and sensory development. LEARNING OUTCOMES 36.1 Mammals Are Viviparous 1. Compare and contrast viviparity, oviparity, and ovoviviparity. 36.2 The Human Male Reproductive System Is Typical of Mammals 1. Describe the sequence of events in spermatogenesis. 2. Describe semen and explain how it is released during mating. 3. Explain how hormones regulate male reproductive function. 36.3 The Human Female Reproductive System Undergoes Cyclic Gamete Development 1. Describe the sequence of events in production of an oocyte. 2. Compare the female reproductive tracts of mammals. 3. Compare the different types of birth control. 36.4 The First Step in Development Is Fertilization 1. Describe the events necessary for fertilization to occur. 2. List different ways that polyspermy is blocked. 36.5 Cells of the Early Embryo Are Totipotent 1. Differentiate between different types of stem cells. 2. Differentiate between therapeutic and reproductive cloning. 3. Differentiate between therapeutic and reproductive cloning. 4. Describe how nuclear reprogramming can be used to accomplish therapeutic cloning. 36.6 Cleavage leads to the Blastula Stage 1. Define the terms cleavage and blastula. 2. Describe the different patterns of cleavage seen in animals. 3. Explain what regulative development is. 36.7 Gastrulation Forms the Basic Body Plan of the Embryo 1. Explain how gastrulation reorganizes the developing embryo. 2. Name the extraembryonic membranes in amniotes. 36.8 The Body’s Organs Form in Organogenesis 1. Describe examples of organogenesis. 2. Describe the events of neurulation and somitogenesis. 3. Explain the migration of neural crest cells and their role in organ development. 36.9 Human Development Takes Nine Months 1. Describe the major developmental events in the first trimester. 2. Describe the major developmental events in the second and third trimesters. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 36 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that animals exclusively reproduce sexually • Students are unaware that placental animals produce eggs • Students believe that all animals have internal fertilization • Students are confused by the distinction between placental and ovoviviparity • Students have a misunderstanding of the anatomical features of hermaphrodites • Students believe that all hermaphrodites can fertilize themselves • Students believe that estrogen is only hormone involved in the menstrual cycle • Students think that all animals evolved at about the same time • Students believe that most animals are vertebrates • Students do not equate humans with being animals • Students believe that all animals have identical organ system structures • Students are unaware of the similarity of embryological development of animals • Students are unaware of the role of hormones and cell signals in embryological development • Students believe that the environment plays little role in embryological development INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Know your own ability to discuss this subject and the maturity of your audience to determine how detailed your lecture will be. Most biologists should be able to get through the physical description of the reproductive system without difficulty. The physiology of human intercourse may be assigned as a reading material topic. Explain contraception carefully. Be informative without preaching. Again, know your audience. Stress that only chordates undergo neurulation and only vertebrates form the neural crest. This shows evolution at work, improving a basic pattern by the addition of successive small steps. Discuss the need for brain growth after birth, especially in hominids. The size of the head must be small to pass through the birth canal. External stimuli are also required to form nerve tracts and neuronal associations. The latter is not as necessary in the lower vertebrates and more primitive mammals as most early activity is innate. Present additional information on the evolutionary aspects of the entire reproductive system. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 36. Application • Have students explain why parthenogenesis is a favorable form of reproduction under consistent environmental conditions. • Have students explain why dolphins, which are aquatic mammals, reproduce using copulation methods typical of terrestrial animals. • Have students explain why terrestrial organisms evolved internal fertilization. • Have students explain how diploidy is ensured during sexual reproduction each generation. • Have students explain the value of extraembryonic membranes in the survival of land animals. • Ask students how variations in yolk content in an egg affect gastrulation. Analysis • Have students explain why women on fertility drugs have multiple births with at least 4 twins at during one pregnancy. • Have students explain why dolphins, which are aquatic mammals, reproduce using copulation methods typical of terrestrial animals. • Ask students to explain why egg laying mammals are scarce and have a low diversity compared to placental mammals. • Have students explain any value to the evolution of extraembryonic membranes in aquatic animals. • Have student describe how mutations to genes associated with neuralization would affect an organism’s development. • Ask students to explain the relations between hox genes and somitogenesis. Synthesis • Ask students to design an experiment to investigate if human testosterone is identical in function to male hormones in other vertebrates. • Have students come up with a medical application for the knowledge that all animal female hormones are very similar in chemical structure and function. • Ask the students evaluate the possible effects of changes in global rainfall patterns on amphibian reproduction. • Ask students to design an experiment to test relationship between environmental temperature and egg development in amphibians. • Have students come up with an application of the knowledge that human blastomeres are not committed to a particular path. • Ask the students come up with strategy to test when mammalian embryonic cells become committed to forming one lineage of cell types. Evaluation • Ask students to evaluate the pros and cons of using monotremes to understand embryonic development of placental mammals. • Ask students to evaluate the effectiveness and safety of birth control treatments that prevent ovulation. • Ask students to evaluate the effectiveness and safety of birth control treatments that prevent sperm formation. VISUAL RESOURCES Obtain different kinds of eggs, showing variation in size and yolk content. Try to obtain more than just avian eggs. Fish eggs are readily available in bait stores (caviar is a bit too expensive for most teachers), amphibian eggs can be collected in the early spring. A pet store that specializes in reptiles may have some infertile snake or lizard eggs, or at least the remains of already hatched eggs. Models are extremely helpful to illustrate the movement of cells during gastrulation and neurulation. In a large class, color-coded transparencies will suffice. This may be a good time to show a short film that shows the progression of development. Bring in embryology models or use overhead diagrams. Animations and movies about development in different organism are useful for showing concepts that cannot demonstrated in easily during lecture. Obtain some different methods of birth control. Many students have never seen a female condom or a diaphram. Point out the side effects of each method. Contact the campus health service to find out which birth control methods are available to students and the cost of each. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Demonstrating Life Cycle Strategies Introduction This demonstration uses animations of three difference animals to show students representative reproductive strategies in animals. It is a good demonstration for building a general foundation for animal reproduction Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to University of Alberta website at http://www.biology.ualberta.ca/facilities/multimedia/index.php?Page=252 Procedure & Inquiry 1. Ask the class to think about the term life cycle 2. Load up the University of Maryland Medical School website. 3. Click on the life cycle websites: a. Adult Form and Life Cycle of a Jellyfish b. Life Cycle of Obelia (phylum Cnidaria; class Hydrozoa) c. Schistosoma Infection in Humans and Snails 4. Have students explain the differences and similarities of the life cycles 5. Ask the students to explain the human life cycle B. Fetal Development Timelines Introduction This demonstration uses instructor-controlled animations to help students understand the stages of human embryology. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to Boston University histology website at http://www.umm.edu/aniplayer/index.html Procedure & Inquiry 6. Tell the class they will be viewing animations about embryological development. 7. Load up the University of Maryland Medical School website and click on the Reproductive System bar 8. Select Fetal Development Interactive Tool 9. Go through the two animations 10. Have students describe the stages of development that they viewed 11. Then go through the formation twins movie 12. Have students describe the events they viewed LABORATORY IDEAS A. Reproductive System Histology This activity has students investigate the histology of the reproductive tract as a way of determining form and function. a. Explain that they will be investigating histological properties and differences in the female and male reproductive systems. b. Provide students with the following materials: a. Microscopes b. Diagrams of reproductive system histology c. Prepared slides: i. Female 1. Ovary 2. Fallopian tube 3. Uterus, normal 4. Uterus, proliferative phase ii. Male 1. Testicle 2. Epididymis 3. Prostate gland 4. Spermatic cord c. Tell students to investigate and write down the properties of the male and female reproductive structures. They should be able to explain how the tissues are characteristic of the function of the particular structure. d. Ask them to note the differences and similarities of the female and male systems. B. Embryo Issues Virtual Lab This activity has students investigate the effects of teratogens on human development. a. Explain that they will be using a virtual human embryology website to answer questions about toxicological effects of pollutants on human development. b. Provide the students with the following: a. Computers with Internet Access b. Web browser bookmarked to Visembryo Website at: i. http://www.visembryo.com/baby/index.html c. Tell students to explore the Visembryo website and familiarize themselves with the stages of embryological development. d. Tell hand out a sheet with the following inquiry questions to investigate: a. Suppose an industrial accident occurred and released a teratogenic chemical into the air. Women in a nearby community were breathing the air and some of the women were pregnant. The teratogen absorbs into the lungs and will pass along through the placenta. This teratogen is broken down and exits the body within one week. b. Evaluate any possible damage to the embryo for women who were at the following stages of pregnancy: i. 1 week ii. 20 days iii. 30 days iv. 4 months v. 6 months vi. 8 months e. Ask the student to be specific about the possible organ systems affected at that particular time of development. f. Ask the students if the results would be different if the chemical was stored in body fat reserves for long periods of time. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students volunteer at a reproductive services clinic. 2. Have students tutor high school students studying animal anatomy and physiology. 3. Have students volunteer for a local STD education clinic. 4. Have students develop sex education materials in cooperation with nurses and health education teachers at a local high school. 5. Have student develop a PowerPoint presentation on comparative embryology for local high school teachers. Instructor Manual for Understanding Biology Kenneth Mason, George Johnson, Jonathan Losos, Susan Singer 9780073532295, 9781259592416