[Module 8.1] The Digestive System.pdf

MODULE 8.1: THE DIGESTIVE SYSTEM Essential Fatty Acids: It must be obtained from the diet and include certain unsaturated fatty acids. NUTRITION Process: food is taken in, taken apart, and taken up...

MODULE 8.1: THE DIGESTIVE SYSTEM Essential Fatty Acids: It must be obtained from the diet and include certain unsaturated fatty acids. NUTRITION Process: food is taken in, taken apart, and taken up Animals can synthesize most fatty acids needed in the process of animals. (although deficiencies in fatty acids are rare). In general, animals fall into three categories: These synthesize phospholipids, signal molecules, Herbivores: eat plants and algae and fat storage. Carnivores: eat other animals Omnivores: consume animals, plants, or Vitamins: These are organic molecules required in algae the diet in very small amounts. There are 13 vitamins essential for humans. There are also two categories: An animal’s diet must provide: fat-soluble vitamins and water-soluble vitamins. Chemical energy for cellular processes Organic building blocks for macromolecules Essential nutrients ESSENTIAL NUTRIENTS Materials that an animal cannot assemble from simpler organic molecules. It must be obtained from an animal’s diet. It is involved in biosynthesis reactions (conversion of energy from food). Minerals: These are simple inorganic nutrients, There are 4 classes: essential amino acids, essential usually required in small amounts. Ingesting large fatty acids, vitamins, and minerals. amounts of some minerals can upset the homeostatic balance. Essential Amino Acids: Animals require 20 amino DIETARY DEFICIENCIES acids. These must be obtained from food preassembled. Malnutrition: It is a failure to obtain adequate nutrition. It can have negative impacts on health Meat, eggs, and cheese provide all the essential and survival. amino acids and are thus “complete” proteins. Deficiencies in essential nutrients: It can cause Most plant proteins are incomplete in amino acid deformities, disease, and death. content. Individuals who eat only plant proteins need Phosphorus deficiency in cattle, deer, and other to eat specific plant combinations to get all herbivores can be prevented by consuming essential amino acids. concentrated sources of salt or other minerals. 23 Golden Rice is an engineered strain of rice with THE DIGESTIVE PROCESS beta-carotene, which is converted into Vitamin A in the body. Intracellular Digestion: The food particles are engulfed by phagocytosis. Food vacuoles, STAGES OF FOOD PROCESSING containing food, fuse with lysosomes containing hydrolytic enzymes. (Ex: sponges) Extracellular Digestion: It is the breakdown of food particles outside of cells. It occurs in compartments that are continuous with the outside of the animal’s Ingestion: It is the act of eating or feeding. body. (Ex: grasshopper, birds) Digestion: It is the process of breaking food down Gastrovascular Cavity: These are seen in into molecules smaller enough to be absorbed. animals with simple body plans. It functions in both digestion and distribution of nutrients. Absorption: It is the uptake of nutrients by body cells. Alimentary Canal: It is a digestive tube with two openings (mouth and anus). It is seen in more Elimination: It is the passage of undigested material complex animals. It signals a complete digestive out of the digestive system. tract. STRATEGIES FOR EXTRACTING RESOURCES THE MAMMALIAN DIGESTIVE SYSTEM Suspension Feeders: It is seen in many aquatic It consists of an alimentary canal and accessory animals and sifts small food particles in water. glands that secrete digestive juices through ducts. Substrate Feeders: These are animals that live in or The Mammalian accessory glands include: salivary on their food source. glands, pancreas, liver, and gallbladder. Fluid Feeders: These suck nutrient-rich fluid from a Food is pushed along by peristalsis, rhythmic living host. contractions of muscles in the wall of the canal. Bulk Feeders: These eat relatively large pieces of Sphincters: These are valves that regulate the food. movement of material between compartments. 24  flows back to the esophagus. This is caused by weak sphincter muscles at the esophagus or relaxation at the wrong time. CHEMICAL DIGESTION IN THE STOMACH Oral Cavity: This is where the first stage of digestion takes place. Salivary Glands: These deliver saliva to lubricate food. Teeth: These chew food into smaller particles. Tongue: This shapes food into a bolus and helps with swallowing. Gastric Juice: It has a low pH of about 2, which kills Throat/Pharynx: This is the junction that opens to bacteria and denatures proteins. It is made up of both the esophagus and the trachea. hydrochloric acid (HCI) and pepsin. Esophagus: This conducts food from the pharynx Pepsin: It cleaves proteins into smaller peptides. down to the stomach by peristalsis. Parietal Cells: These cells secrete hydrogen and Trachea: This leads to the lungs. chloride ions separately into the cavity of the stomach. Swallowing: It causes the epiglottis to block entry to the trachea. Chief Cells: These cells secrete inactive pepsinogen, which is activated to pepsin when Coughing: This occurs when the swallowing mixed with HCI in the stomach. reflex fails and food or liquids reach the trachea. Mucus: This lubricates and protects the stomach lining from gastric juice. Digestion in the Stomach Chemical Digestion in the Stomach: Positive It stores food and begins digestion of proteins. The Feedback stomach secretes gastric juice, which converts a meal to chyme. Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine. Gastroesophageal Reflux Disease (GERD): This happens when gastric juices from the stomach 25  THE SMALL INTESTINE In Digestion Evolutionary adaptations of vertebrate digestive Small Intestine: It is the longest compartment of the systems correlate with diet alimentary canal. Most enzymatic hydrolysis of macromolecules from food occurs in this. The digestive systems of vertebrates are variations on a common plan. However, there are intriguing Duodenum: This is the first portion of the small adaptations, often related to diet. intestine. It is where chyme from the stomach mixes with digestive juices from the pancreas, liver, Dental Adaptations gallbladder, and the small intestine. Dentition: It is an animal’s assortment of teeth. The Pancreas: It produces proteases trypsin and success of mammals is due in part to their dentition, chymotrypsin that are activated in the lumen of the which is specialized for different diets. duodenum to neutralize the acidic chyme. Nonmammalian vertebrates have less specialized Gallbladder: This stores bile that is made in the liver. teeth, although exceptions exist. (Ex: Snakes) The bile aids in digestion and absorption of fats. Stomach & Intestinal Adaptations In Absorption Many carnivores have large, expandable stomachs. Herbivores and omnivores generally Villi & Microvilli: It increases the small intestine’s have longer alimentary canal than carnivores, surface area. It creates a brush border that greatly reflecting the longer time needed to digest increases the rate of nutrient absorption. vegetation. Transport across the epithelial cells can be passive or active depending on the nutrient. Mutualistic Adaptations THE LARGE INTESTINE The coexistence of humans and many bacteria In Processing involves mutualistic symbiosis. The Cecum: It aids in the fermentation of plant Some intestinal bacteria produce vitamins and can material. It connects where the small intestine and also regulate the development of the intestinal large intestine meet. epithelium and the function of the innate immune system. The human cecum has an extension called the appendix, which plays a minor role in immunity. Many herbivores have fermentation chambers, where mutualistic microorganisms digest cellulose. The Colon: This completes the reabsorption of water Ruminants: Animals that have the most that began in the small intestine. elaborate adaptations for an herbivorous diet. Feces: This includes undigested material and bacteria, it becomes more solid as they move through the colon. It is stored in the rectum until REGULATION OF DIGESTION elimination through the anus. Each step in the digestive system is activated as Two sphincters between the rectum and anus needed. control bowel movements 26 The enteric division of the nervous system helps to Insulin & PYY: These are hormones secreted by regulate the digestive process. the small intestine after meals, both suppress appetite. The endocrine system also regulates digestion through the release and transport of hormones. Leptin: This is produced by adipose (fat) tissue. It suppresses appetite and plays a role in regulating body fat levels. Summary: Mammalian Digestive Organs GLUCOSE HOMEOSTASIS Glucose: It is a major fuel for cellular respiration. It is a key source of carbon skeletons for biosynthesis. Insulin & Glucagon: These are hormones that regulate the breakdown of glycogen into glucose. Liver: It is the site for glucose homeostasis. REGULATION OF APPETITE AND CONSUMPTION Hormones: It regulates long-term and short-term appetite by affecting a “safety center” in the brain. Ghrelin: It is a hormone secreted by the stomach wall, triggers feelings of hunger before meals. 27