Chapter 42 Animal Digestive Systems.pdf

Chapter 42 Animal Digestive Systems © 2021 Pearson Education Ltd. Lecture Presentations by Nicole Tunbridge and Kathleen Fitzpatrick Figure 42.1a For this herring gull, dinnertime has arrived. Once this meal has been taken in, the tissues of the sea star will be taken apart and its nutrients tak...

Chapter 42 Animal Digestive Systems © 2021 Pearson Education Ltd. Lecture Presentations by Nicole Tunbridge and Kathleen Fitzpatrick Figure 42.1a For this herring gull, dinnertime has arrived. Once this meal has been taken in, the tissues of the sea star will be taken apart and its nutrients taken up. Paradoxically, the classes of nutrients in the sea star—largely proteins, fats, and carbohydrates—also make up the tissues of the gull © 2021 Pearson Education Ltd. Figure 42.1b How can animals extract the nutrients they need from food while not digesting their own tissues? © 2021 Pearson Education Ltd. Concept 42.1: An animal’s diet must supply chemical energy, organic building blocks, and essential nutrients • An adequate diet must satisfy three needs: – Chemical energy for cellular processes – Organic building blocks for macromolecules – Essential nutrients © 2021 Pearson Education Ltd. Essential Nutrients • Required materials that an animal requires but cannot assemble from simple organic molecules are called essential nutrients. • These must be obtained from an animal’s diet. • There are four classes: Figure 42.2 Roles of essential nutrients – Essential amino acids – Essential fatty acids – Vitamins – Minerals © 2021 Pearson Education Ltd. Essential Amino Acids • All organisms require 20 amino acids. • Plants and microorganisms can normally produce all 20. • Animals can synthesize about half from molecules in their diet. • The remaining amino acids, the essential amino acids, must be obtained from food in prefabricated form • Meat, eggs, and cheese provide all the essential amino acids and are thus “complete” proteins. • Most plant proteins are incomplete in amino acid composition. • Vegetarians can easily obtain all essential amino acids by eating a varied diet of plant proteins. © 2021 Pearson Education Ltd. Essential Fatty Acids • Animals can synthesize many of the fatty acids they need. • The essential fatty acids must be obtained from the diet and include certain unsaturated fatty acids (i.e., fatty acids with one or more double bonds). • Animals typically obtain ample amounts of essential fatty acids from seeds, grains, and vegetables their diet. © 2021 Pearson Education Ltd. Vitamins • Vitamins are organic molecules required in the diet in very small amounts. • Thirteen vitamins are essential for humans. • Vitamins are grouped into two categories: fat-soluble and water-soluble. © 2021 Pearson Education Ltd. Table 42.1 Vitamin requirements of humans © 2021 Pearson Education Ltd. Minerals • Minerals are simple inorganic nutrients, usually required in small amounts. • Ingesting large amounts of some minerals can upset homeostatic balance. © 2021 Pearson Education Ltd. Variation in Diet • Animals have diverse diets. • Herbivores dine mainly on plants or algae. • Carnivores mostly eat other animals. • Omnivores regularly consume animals as well as plants or algae. • These terms represent the usual diets of the animals. • Most animals are opportunistic feeders, and broaden their diet when necessary. © 2021 Pearson Education Ltd. Dietary Deficiencies (영양실조) • Malnutrition is a failure to obtain adequate nutrition. • Malnutrition can have negative impacts on health and survival. Deficiencies in Essential Nutrients • Deficiencies in essential nutrients can cause deformities, disease, and death. Figure 42.3 Obtaining essential nutrients from an unusual source • Some grazing animals can obtain missing nutrients by consuming concentrated sources of salt or other minerals. • In children, protein deficiency may arise when their diet shifts from breast milk to foods containing very little protein. © 2021 Pearson Education Ltd. Undernourishment (영양결핍) • Undernourishment results when a diet does not provide enough chemical energy. • An undernourished individual will – Use up stored fat and carbohydrates – Break down its own proteins – Lose muscle mass – Suffer protein deficiency of the brain – Die or suffer irreversible damage © 2021 Pearson Education Ltd. Assessing Nutritional Needs • Many insights into human nutrition have come from epidemiology (역학), the study of human health and disease in populations. • Neural tube (신경관) defects were found to be the result of a deficiency in folic acid (vitamin B9) in pregnant mothers. • Based on this evidence, the United States in 1998 began to require that folic acid be added to enriched grain products. Figure 42.4 Inquiry: Can diet influence the frequency of birth defects? © 2021 Pearson Education Ltd. Concept 42.2: Food processing involves ingestion, digestion, absorption, and elimination Ingestion (섭취) • Ingestion is the act of eating or feeding. • Four quite different categories describe the feeding mechanisms of most animal species. 1. Filter Feeders • Many aquatic animals are filter feeders, which sift small food particles from the surrounding medium. Figure 42.5 Exploring four main feeding mechanisms of animals © 2021 Pearson Education Ltd. 2. Substrate Feeders • Substrate feeders are animals that live in or on their food source. 3. Fluid Feeders • Fluid feeders suck nutrient-rich fluid from a living host. 4. Bulk Feeders • Bulk feeders eat relatively large pieces of food. • Most animals, including humans, feed this way. Figure 42.5 Exploring four main feeding mechanisms of animals © 2021 Pearson Education Ltd. Digestion (소화) • Digestion is the process of breaking food down into molecules small enough to absorb. • Mechanical digestion, chewing or grinding, increases the surface area of food. • Chemical digestion splits food into small molecules that can pass through membranes; these are used to build larger molecules. • In chemical digestion, the process of enzymatic hydrolysis splits bonds in molecules with the addition of water. Figure 42.UN01 In-text figure, enzymatic hydrolysis of a disaccharide © 2021 Pearson Education Ltd. Absorption (흡수) • Absorption is uptake of small molecules by body cells. Elimination (배설) • Elimination is the passage of undigested material out of the digestive system. © 2021 Pearson Education Ltd. Digestive Compartments (소화 구획) • Most animals process food in specialized compartments. • These compartments reduce the risk of an animal digesting its own cells and tissues. Intracellular Digestion • In intracellular digestion, food particles are engulfed by phagocytosis and liquids by pinocytosis. • Food vacuoles, containing food, fuse with lysosomes containing hydrolytic enzymes. • A few animals, such as sponges, digest all their food in this way. © 2021 Pearson Education Ltd. Extracellular Digestion • In most animal species, hydrolysis occurs by extracellular digestion. • Extracellular digestion is the breakdown of food particles outside of cells. • It occurs in compartments that are continuous with the outside of the animal’s body. • Animals with simple body plans have a gastrovascular cavity (위수강) that functions in both digestion and distribution of nutrients. © 2021 Pearson Education Ltd. Figure 42.6 Digestion in a hydra • More complex animals have a digestive tube with two openings, a mouth and an anus. • This digestive tube is called a complete digestive tract, or an alimentary canal (소화관). • It can have specialized regions that carry out digestion and absorption in a stepwise fashion. © 2021 Pearson Education Ltd. Figure 42.7 Variation in alimentary canals Concept 42.3: Organs specialized for sequential stages of food processing form the mammalian digestive system Figure 42.8 The human digestive system • In mammals, a number of accessory glands secrete digestive juices through ducts into the alimentary canal. • Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder (쓸개, 담낭). © 2021 Pearson Education Ltd. The Oral Cavity, Pharynx, and Esophagus • Food processing begins in the oral cavity. • Teeth with specialized shapes cut, mash, and grind, breaking the food into smaller pieces. • Salivary glands deliver saliva to lubricate food. • Saliva contains mucus, a viscous mixture of water, salts, cells, and glycoproteins. • Saliva also contains amylase, which breaks down starch. © 2021 Pearson Education Ltd. • The tongue movements shape food into a bolus and help with swallowing. • The throat, or pharynx, is the junction that opens to both the esophagus and the trachea. • The esophagus connects to the stomach. • The trachea (windpipe) leads to the lungs. © 2021 Pearson Education Ltd. • Swallowing causes the epiglottis (후두개) to block entry to the trachea, and the bolus is guided by the larynx, the upper part of the respiratory tract. • Coughing occurs when the swallowing reflex fails and food or liquids reach the windpipe. • Within the esophagus, food is pushed along from the pharynx to the stomach by peristalsis (연동운동), alternating waves of smooth muscle contraction and relaxation. • Valves called sphincters (괄약근) regulate the movement of material between compartments. Figure 42.9 Intersection of the human airway and digestive tract © 2021 Pearson Education Ltd. Digestion in the Stomach • The stomach stores food and processes it into a liquid suspension. • The stomach secretes gastric juice and mixes it with food through a churning action. • The mixture of ingested food and gastric juice is called chyme. © 2021 Pearson Education Ltd. Chemical Digestion in the Stomach • Gastric juice has a low pH of about 2, which kills bacteria and denatures proteins. • Gastric juice is made up of hydrochloric acid (HCl) and pepsin. • Pepsin is a protease, which breaks peptide bonds to cleave proteins into smaller polypeptides. © 2021 Pearson Education Ltd. Figure 42.10 The stomach and its secretions • Parietal cells secrete hydrogen and chloride ions separately into the lumen (cavity) of the stomach. • Chief cells secrete inactive pepsinogen, which is activated to pepsin when mixed with hydrochloric acid in the stomach. • Mucus protects the stomach lining from gastric juice. • Cell division adds a new epithelial layer every three days. © 2021 Pearson Education Ltd. Figure 42.10 The stomach and its secretions Stomach Dynamics • Coordinated contraction and relaxation of stomach muscles churn the stomach’s contents. • Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine. • If the sphincter at the top of the stomach allows movement of chyme back to the lower end of the esophagus, the result is “heartburn”. © 2021 Pearson Education Ltd. Digestion in the Small Intestine • The small intestine is the longest compartment of the alimentary canal. • Most enzymatic hydrolysis of macromolecules from food occurs here. • The first portion of the small intestine is the duodenum. Here, chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself. © 2021 Pearson Education Ltd. Figure 42.11 © 2021 Pearson Education Ltd. • The pancreas produces the proteases trypsin and chymotrypsin, which are activated in the lumen of the duodenum. • Its solution is alkaline and neutralizes the acidic chyme. • Bile salts (담즙산염) facilitate digestion of fats by dispersing big droplets of fats to small droplets and are a major component of bile (담즙, 쓸개즙). • Bile is made in the liver and stored and concentrated in the gallbladder (쓸개, 담낭). • Bile also destroys nonfunctional red blood cells. © 2021 Pearson Education Ltd. Absorption in the Small Intestine • Digestion is largely completed in the duodenum. • In the remaining regions of the small intestine, nutrient absorption occurs. • The small intestine has a huge surface area due to villi and microvilli that are exposed to the intestinal lumen. • The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption. • Transport across the epithelial cells can be passive or active, depending on the nutrient. © 2021 Pearson Education Ltd. Figure 42.12 Nutrient absorption in the small intestine © 2021 Pearson Education Ltd. • The hepatic portal vein (간문맥) carries nutrient-rich blood from the capillaries of the villi to the liver, then to the heart. • The liver regulates nutrient distribution, interconverts many organic molecules, and detoxifies many organic molecules. • Epithelial cells absorb fatty acids and a monoglyceride (glycerol joined to a fatty acid) and recombine them into triglycerides. • These fats (86%) are coated with phospholipids (9%), cholesterol (3%), and proteins (2%) to form water-soluble chylomicrons (유미 지립). • Chylomicrons are transported into a lacteal (유미관), a lymphatic vessel in each villus. • Lymphatic vessels deliver chylomicron-containing lymph to large veins that return blood to the heart. © 2021 Pearson Education Ltd. Figure 42.13 Digestion and absorption of fats © 2021 Pearson Education Ltd. Processing in the Large Intestine • The alimentary canal ends with the large intestine, which is important the absorption of water, vitamin K, and salt. • It includes the colon (결장), cecum (맹장), and rectum (직장). • The colon leads to the rectum and anus. • The cecum aids in the fermentation of plant material and connects where the small and large intestines meet. • The human cecum has an extension called the appendix (충수), which plays a minor role in immunity. © 2021 Pearson Education Ltd. Figure 42.14 Junction of the small and large intestines • The colon completes the recovery of water that began in the small intestine. • Feces, the wastes of the digestive system, become more solid as they move through the colon. • The community of bacteria living on unabsorbed organic material in the colon contributes about one-third of the dry weight of feces. • Feces are stored in the rectum until they can be eliminated through the anus. • Two sphincters between the rectum and anus control bowel movements. © 2021 Pearson Education Ltd. Concept 42.4: Evolutionary adaptations of vertebrate digestive systems correlate with diet • Digestive systems of vertebrates are varied, with many adaptations linked to an animal’s diet. Dental Adaptations • Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet. • The success of mammals is due in part to their dentition, which is specialized for different diets. • Nonmammalian vertebrates have less specialized teeth, though exceptions exist. – For example, the teeth of poisonous snakes are modified as fangs for injecting venom. © 2021 Pearson Education Ltd. Figure 42.15 © 2021 Pearson Education Ltd. Stomach and Intestinal Adaptations • Many carnivores have large, expandable stomachs. • Herbivores and omnivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation. © 2021 Pearson Education Ltd. Figure 42.16 The alimentary canals of a carnivore (coyote) and herbivore (koala) Mutualistic Adaptations • The coexistence of humans and many bacteria involves mutualistic symbiosis. • Some intestinal bacteria produce vitamins. • They also regulate the development of the intestinal epithelium and the function of the innate immune system. • The microbiome is the collection of the microorganisms living in and on the body. • Scientists use a DNA sequencing approach based on the polymerase chain reaction to study the microbiome. • More than 400 bacterial species have been found in the human digestive system using this method. • There are differences in the microbiome associated with diet, disease, and age. © 2021 Pearson Education Ltd. Figure 42.17 Variation in human gut microbiome at different life stages © 2021 Pearson Education Ltd. • Helicobacter pylori is an acid-tolerant bacterium that has been found to cause stomach ulcers (위궤양). • H. pylori can disrupt stomach health by eliminating other bacterial species from the stomach. © 2021 Pearson Education Ltd. Figure 42.18 The stomach microbiome and stomach health • Studies on the microbiome have led to therapies for intestinal infections; one is fecal microbial transplantation. • The microbiome of a healthy individual is introduced into the patient’s intestine. • This approach has been used to treat diarrhea (CDI) caused by the bacterium Clostridium difficile. Figure 42.19 Clostridium difficile • Another treatment against antibiotic-resistant (항생제 내성) pathogens makes use of bacteriophages, viruses that infect bacteria but not human cells. © 2021 Pearson Education Ltd. Mutualistic Adaptations in Herbivores • Many organisms whose diet consists largely of cellulose have fermentation chambers. • Here, mutualistic microorganisms digest cellulose. • Rabbits and rodents pass food through their alimentary canal twice to recover important nutrients. • The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants (반추동물). © 2021 Pearson Education Ltd. Figure 42.20 Ruminant digestion 벌집위 중판위 주름위 반추위 • Giant tubeworms have no digestive system and instead obtain nutrients from mutualistic bacteria within their bodies. Figure 42.21 Giant tubeworm, an animal without a digestive system. © 2021 Pearson Education Ltd. Concept 42.5: Feedback circuits regulate digestion, energy storage, and appetite • The processes that enable an animal to obtain nutrients are matched to the organism’s circumstances and need for energy. © 2021 Pearson Education Ltd. Regulation of Digestion • The digestive system is activated step-wise as needed. • The steps are regulated by the enteric nervous system (장신경계), a network of neurons dedicated to the digestive organs. • The endocrine system also regulates digestion through the release and transport of hormones. Figure 42.22 Hormonal control of digestion Cholecystokinin (CCK) © 2021 Pearson Education Ltd. Regulation of Energy Storage • The body stores energy-rich molecules that are not needed for metabolism right away. • In humans, energy is stored first in the liver and muscle cells in the form of glycogen. • Excess energy is stored in fat in adipose cells. • When fewer calories are taken in than expended, the human body expends liver glycogen first, then muscle glycogen and fat. © 2021 Pearson Education Ltd. Glucose Homeostasis • Glucose homeostasis relies predominantly on the opposing effects of two hormones, insulin and glucagon. • These regulate the breakdown of glycogen into glucose. • The liver is the site for glucose homeostasis. – A carbohydrate-rich meal raises insulin levels, which triggers the synthesis of glycogen. – Low blood sugar causes glucagon to stimulate the breakdown of glycogen and release glucose. © 2021 Pearson Education Ltd. • Insulin acts on nearly all body cells to stimulate glucose uptake from blood. • Brain cells are an exception; they can take up glucose whether or not insulin is present. • Glucagon and insulin are both produced in the islets of the pancreas. • α cells make glucagon, and β cells make insulin. © 2021 Pearson Education Ltd. Figure 42.23 Homeostatic regulation of cellular fuel © 2021 Pearson Education Ltd. Insulin function Hormonal regulation of glucose metabolism by insulin. Insulin is synthesized in pancreatic β cells in response to hyperglycemia. It binds to insulin receptors in target cells (red arrows) such as skeletal muscle cells, hepatocytes and adipocytes and induces signaling pathways that promote glucose uptake, catabolism or storage. This reduces plasma glucose levels. © 2021 Pearson Education Ltd. Diabetes Mellitus • The disease diabetes mellitus is caused by a deficiency of insulin or a decreased response to insulin in target tissues. • Cells are unable to take up enough glucose to meet metabolic needs. • The level of glucose in the blood may exceed the capacity of kidneys to reabsorb it. • Sugar in the urine is one test for diabetes. © 2021 Pearson Education Ltd. Type 1 Diabetes: insulin-dependent • 10% of Diabetes patients. • Type 1 diabetes is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas. • It usually appears during childhood. • Treatment consists of insulin injections, typically several times per day. • Currently, genetically engineered bacteria produce human insulin at a reasonable cost. © 2021 Pearson Education Ltd. Type 2 Diabetes: insulin-independent • 90% of Diabetes patients. • Normally release insulin, but cells does not make glucose transports in the plasma membrane and can’t use glucose from your blood for energy. Both blood insulin and glucose levels go up (Insulin-Resistance). • Insulin-resistance syndrome includes a group of problems like obesity, high blood pressure, high cholesterol, and type 2 diabetes. It could affect as many as 1 in 3 Americans. It induces metabolic syndrome. • Hyperplasia, Hypertrophy  High insulin, amylin  Hypoplasia, Hypotrophy  low insulin, hyperglycemia. • Hyperosmolar hyperglycemic state. © 2021 Pearson Education Ltd. Regulation of Appetite and Consumption • Over-nourishment can lead to obesity, the excess accumulation of fat. • Obesity contributes to type 2 diabetes, cancer of the colon and breasts, and cardiovascular disease. • Researchers have discovered several of the mechanisms that help regulate body weight. © 2021 Pearson Education Ltd. • Hormones regulate long-term and short-term appetite by affecting a “satiety center (만복중추)” in the brain. Figure 42.24 A few of the appetiteregulating hormones • Ghrelin, a hormone secreted by the stomach wall, triggers feelings of hunger before meals. • Insulin and PYY, a hormone secreted by the small intestine after meals, both suppress appetite. • Leptin, produced by adipose (fat) tissue, also suppresses appetite and plays a role in regulating body fat levels – ob, db © 2021 Pearson Education Ltd. *The gut hormone peptide YY (PYY) is a 36-amino acid peptide that is synthesized and released from specialized enteroendocrine cells called L-cells. 생쥐 (ob/ob or db/db vs normal) © 2021 Pearson Education Ltd.