Johnson Essentials of the Living World 7e Chapter 25 PDF

Because learning changes everything. ® Chapter 25 The Path of Food Through the Animal Body Lecture Outline Essentials of the Living World Seventh Edition George Johnson, Joel Bergh © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent...

Because learning changes everything. ® Chapter 25 The Path of Food Through the Animal Body Lecture Outline Essentials of the Living World Seventh Edition George Johnson, Joel Bergh © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.  25.1 Food for Energy and Growth 1 The food animals eat provides both a source of energy and essential molecules that the animal body is not able to manufacture for itself. An optimal diet contains more carbohydrates than fats and also a significant amount of protein. © McGraw Hill, LLC 2  Figure 25.1: The nutrition plate Source: US Department of Agriculture. MyPlate. © McGraw Hill, LLC 3  25.1 Food for Energy and Growth 2 Carbohydrates are obtained primarily from grains, fruits, and vegetables. Carbohydrates contain about 4.1 calories per gram. Dietary fats are found in oils, margarine, and butter and are abundant in fried foods, meats, and processed snack foods. Fats contain 9.3 calories per gram. Proteins can be obtained from many foods, including dairy, poultry, meat, and grains. Proteins have 4.1 calories per gram. © McGraw Hill, LLC 4  25.1 Food for Energy and Growth 3 In wealthy countries, being significantly overweight is common. This is due to habitual overeating and high-fat diets, in which fats constitute over 35% of the total caloric intake. The standard measure of appropriate body weight is the body mass index (BMI), estimated as your body weight in kg, divided by your height in meters squared. © McGraw Hill, LLC 5  Figure 25.2: Are you overweight? 66% of American adults are overweight with a BMI of 25 or more. Access the text alternative for slide images. © McGraw Hill, LLC 6  25.1 Food for Energy and Growth 4 Over the course of evolution, many animals have lost their ability to manufacture certain substances they need. Many vertebrates are unable to manufacture one or more of the 20 amino acids used to make proteins. Humans are unable to synthesize 8 amino acids, which must be obtained from proteins in food. These are called essential amino acids. © McGraw Hill, LLC 7  25.1 Food for Energy and Growth 5 In addition to supplying energy, food must also supply essential minerals. Some minerals are required in very small amounts and are called trace elements. Essential organic substances that are used in trace amounts are called vitamins. © McGraw Hill, LLC 8  25.2 Types of Digestive Systems 1 Heterotrophs are divided into three groups on the basis of their food sources. Herbivores eat plants exclusively. Carnivores are meat eaters. Omnivores eat both plants and animals. Sponges digest their food intracellularly. All other animals digest their food extracellularly, within a digestive cavity. © McGraw Hill, LLC 9  25.2 Types of Digestive Systems 2 A gastrovascular cavity is found in cnidarians and flatworms. This cavity has only a single opening that serves as both a mouth and an anus. There is no specialization within this type of digestive system because every cell is exposed to all stages of digestion. © McGraw Hill, LLC 10  Figure 25.3: The gastrovascular cavity of Hydra Access the text alternative for slide images. © McGraw Hill, LLC 11  25.2 Types of Digestive Systems 3 A digestive tract with a separate mouth and anus is called an alimentary canal. This permits specialization and the transport of food is in one direction. Physical forces, such as chewing and grinding, first break the ingested food into smaller fragments. Chemical digestion occurs primarily in the intestine and involves hydrolysis reactions that liberate food subunits. Products of digestion are absorbed into the blood. Any molecules in the food that are not absorbed by the animal are excreted through the anus. © McGraw Hill, LLC 12  Figure 25.4: One-way digestive tracts Access the text alternative for slide images. © McGraw Hill, LLC 13  25.3 The Human Digestive System 1 In humans and other vertebrates, the digestive system consists of a gastrointestinal tract and accessory organs. The tubular gastrointestinal tract has a layered structure. Mucosa: innermost layer comprised of epithelium. Submucosa: second layer comprised of connective tissue. Muscularis: third layer of two layers of muscle tissue. Serosa: outer layer comprised of connective tissue. © McGraw Hill, LLC 14  Figure 25.5: The human digestive system Access the text alternative for slide images. © McGraw Hill, LLC 15  Figure 25.6: The layers of the gastrointestinal tract Access the text alternative for slide images. © McGraw Hill, LLC 16  25.4 The Mouth and Teeth 1 Different vertebrates have different specializations of the digestive system that reflect the way they live. Many vertebrates have teeth, and chewing (mastication) breaks up food into small particles and mixes it with fluid secretions. Birds, which lack teeth, break up their food in the gizzard. © McGraw Hill, LLC 17  25.4 The Mouth and Teeth 2 Reptiles and fish have homodont dentition, teeth that are all the same. Most mammals have heterodont dentition, teeth of different specialized types. Incisors: chisel-shaped nipping teeth. Canines: sharp, pointed teeth for tearing. Premolars and molars: flat teeth for grinding. © McGraw Hill, LLC 18  25.4 The Mouth and Teeth 3 The general pattern of heterodont dentition is modified in different mammals depending on their diet. Carnivorous mammals: the canines are prominent, and the premolars and molars are more blade-like. Herbivorous mammals: the incisors are well developed, the canines are often absent, and the premolars and molars are large, flat teeth with ridges. © McGraw Hill, LLC 19  Figure 25.8: Diagram of heterodont dentition Access the text alternative for slide images. © McGraw Hill, LLC 20  25.4 The Mouth and Teeth 4 Humans are omnivores and human teeth are specialized for eating both plant and animal material. Humans have carnivorous type teeth in the front of the mouth and herbivorous teeth in the back. Children have only 20 teeth but these are lost during childhood and replaced by 32 adult teeth. The tooth is a living organ. © McGraw Hill, LLC 21  Figure 25.9: Human teeth Access the text alternative for slide images. © McGraw Hill, LLC 22  25.4 The Mouth and Teeth 5 Inside the mouth, the tongue mixes food with a mucous solution called saliva. Saliva moistens and lubricates food so that it is easier to swallow. Saliva also contains a hydrolytic enzyme called salivary amylase. This enzyme initiates the breakdown of starch into the disaccharide maltose. © McGraw Hill, LLC 23  25.4 The Mouth and Teeth 6 When food is ready to be swallowed, a sequence of events occur that causes food to go into the esophagus. Food is prevented from going into the respiratory tract by the epiglottis. © McGraw Hill, LLC 24  Figure 25.10: The human pharynx, palate, and larynx Access the text alternative for slide images. © McGraw Hill, LLC 25  25.5 The Esophagus and Stomach 1 The esophagus is a muscular tube that connects the pharynx to the stomach. The upper third is enveloped in skeletal muscle for voluntary control of swallowing. The lower two-thirds is surrounded by involuntary smooth muscle. Rhythmic waves of contractions, called peristalsis, propel food towards the stomach. © McGraw Hill, LLC 26  Figure 25.11: The esophagus and peristalsis Access the text alternative for slide images. © McGraw Hill, LLC 27  25.5 The Esophagus and Stomach 2 The movement of food from the esophagus into the stomach is controlled by a ring of circular smooth muscle, called a sphincter. Contraction of the sphincter prevents food in the stomach from moving back into the esophagus. In humans, stomach contents can be brought back out during vomiting. The relaxing of the sphincter may lead to acid reflux, which is when stomach acid moves into the esophagus. This produces a burning sensation known as heartburn. © McGraw Hill, LLC 28  25.5 The Esophagus and Stomach 3 The stomach is a saclike portion of the digestive tract. The stomach contains an extra layer of smooth muscle for churning food. Gastric juice is released by cells of the gastric glands in the lining of the stomach. Parietal cells secrete hydrochloric acid (HCL). Chief cells secrete pepsinogen. Pepsinogen requires a low pH to be activated into pepsin, a protease that begins the digestion of proteins. © McGraw Hill, LLC 29  Figure 25.12: The stomach and gastric glands Access the text alternative for slide images. © McGraw Hill, LLC 30  25.5 The Esophagus and Stomach 4 Gastric juice has a pH of 2, much more acidic than the 7.4 pH of blood. The low pH helps to denature proteins and keep pepsin active. Active pepsin hydrolyzes food proteins into short chains of polypeptides that are not fully digested until the mixture enters the small intestine. Chyme is the name for the mixture of partially digested food and gastric juice. © McGraw Hill, LLC 31  25.5 The Esophagus and Stomach 5 Overproduction of gastric acid can occasionally eat a hole through the wall of the stomach, called a gastric ulcer. Normally the stomach epithelial cells are protected by alkaline mucus. Susceptibility to ulcers is increased by an infection of the bacterium Helicobacter pylori. © McGraw Hill, LLC 32  25.6 The Small and Large Intestines 1 The intestine is the primary digestive organ of the body. Only relatively small portions of chyme are introduced into the small intestine at one time. This allows time for acid to be neutralized and enzymes to act. In the small intestine, carbohydrates, protein, and lipids are broken down and absorbed into the bloodstream. © McGraw Hill, LLC 33  25.6 The Small and Large Intestines 2 While some enzymes necessary for digestion are secreted by the cells of the intestinal wall, most are made in the pancreas. The pancreas is a large gland located near the stomach. The pancreas sends its secretions via a duct that empties into the first part of the small intestine, the duodenum. © McGraw Hill, LLC 34  25.6 The Small and Large Intestines 3 Much of the food energy the vertebrate body harvests is obtained from fats. Fat digestion involves bile salts that are secreted into the duodenum by the liver. The bile salts act like detergents and make drops of fat into microscopic droplets. This process is known as emulsification. This increases the surface area for the enzyme lipase to work on in order to break down the fat. © McGraw Hill, LLC 35  25.6 The Small and Large Intestines 4 After the duodenum, the small intestine consists of Jejunum where digestion continues. Ileum where water and digested products are absorbed. The lining of the small intestine is folded into ridges, which are covered with fine projections called villi (singular, villus). Each of the cells covering the villus is covered by a field of microprojections called microvilli. © McGraw Hill, LLC 36  Figure 25.13: The small intestine Access the text alternative for slide images. © McGraw Hill, LLC 37  Figure 25.14: Microvilli in the small intestine Steve Gschmeissner/SPL/Science Source © McGraw Hill, LLC 38  25.6 The Small and Large Intestines 5 The large intestine is shorter but has a wider diameter than the small intestine. No digestion takes place here. Only about 6% to 7% of fluid absorption occurs here. Some water, sodium, and vitamin K. The main function of the large intestine is to compact and store undigested material as feces. © McGraw Hill, LLC 39  25.7 Accessory Digestive Organs 1 The pancreas secretes fluid through the pancreatic duct into the duodenum. The fluid contains a host of enzymes. Trypsin and chymotrypsin digest proteins. Pancreatic amylase digests polysaccharides. Lipase digests fats. The pancreas secretes bicarbonate, which neutralizes the HCL from the stomach. © McGraw Hill, LLC 40  25.7 Accessory Digestive Organs 2 In addition to being an exocrine gland, the pancreas is also an endocrine gland. It produces hormones in the Islets of Langerhans. The two most important pancreatic hormones are insulin and glucagon. © McGraw Hill, LLC 41  25.7 Accessory Digestive Organs 3 The liver is the largest internal organ of the body. The liver produces bile and stores it in the gallbladder where it is concentrated. Bile consists of bile pigments and bile salts. Bile salts aid in fat digestion. The arrival of fatty food in the duodenum stimulates the gallbladder to contract, causing bile to be released. © McGraw Hill, LLC 42  Figure 25.15: The pancreatic and bile ducts empty into the duodenum Access the text alternative for slide images. © McGraw Hill, LLC 43  25.7 Accessory Digestive Organs 4 Veins carry blood from the stomach and intestine to the liver. The liver processes substances from the blood. Alcohol and other drugs are taken into liver cells and metabolized. The liver also removes toxins, pesticides, carcinogens and other poisons by converting them into less toxic forms. © McGraw Hill, LLC 44  Figure 25.16: The organs of the digestive system and their functions Access the text alternative for slide images. © McGraw Hill, LLC 45