Digestive Systems Quiz

PDF page 1067: Much information in this chapter is not within the scope of AP . However, the chapter provides us with the opportunity to review concepts we’ve explored previously, including structure and function, macromolecules, energy production, transport of substances across membranes, and enzyme activity. All living organisms require a source of energy and molecules needed to build cells, tissues, and organs. During digestion, food is broken down into smaller molecules for absorption and distribution to all cells of the body. Nutrients are required to carry out cellular processes and maintain homeostasis, and digestion and absorption require the participation of several organs. Different animals have evolved different types of digestive systems specialized to meet their dietary needs. You do not need to memorize details about the different types of animal digestive systems, but you might find it interesting to explore the evolution of the system through a few groups of animals, from intracellular digestion in simple invertebrates to a digestive tract and accessory organs in complex vertebrates. Using a human eating a turkey sandwich as an example, food is ingested through the mouth. The mouth is the location where both mechanical (chewing) and chemical breakdown of food begins via the enzyme amylase, which breaks down carbohydrates into simpler sugars. The food bolus then travels by peristalsis (alternating waves of contraction) down the pharynx and esophagus to the stomach. In the stomach, pepsinogen mixes with hydrochloric acid to form pepsin, which begins digesting proteins, such as turkey, into smaller chains of amino acids. Mucus in the stomach protects its lining from damage by acidity, and the tightening of a sphincter prevents stomach contents from regurgitating into the esophagus. Further digestion of the ingredients of the sandwich occurs in the small intestine aided by a variety of enzymes; for example, bile salts and pancreatic amylase dumped into the small intestine from the gallbladder and pancreas, respectively, help emulsify fats. Once the ingredients of the sandwich have been broken down into smaller nutrient molecules, including amino acids, glucose, and fatty acids, they are absorbed from the small intestine into the circulatory and lymphatic systems. The walls of the small intestine contain small, finger-like projections called villi and microvilli that increase surface area for absorption of nutrients by diffusion. The large intestine or colon does not produce digestive enzymes but functions to absorb water, salts, and some vitamins. Any nutrients from the sandwich are stored in the liver, and wastes are eliminated. Information presented and the examples highlighted in the section support concepts outlined in Big Idea 2 and Big Idea 4

PDF page 1067: Much information in this chapter is not within the scope of AP . However, the chapter provides us with the opportunity to review concepts we’ve explored previously, including structure and function, macromolecules, energy production, transport of substances across membranes, and enzyme activity. All living organisms require a source of energy and molecules needed to build cells, tissues, and organs. During digestion, food is broken down into smaller molecules for absorption and distribution to all cells of the body. Nutrients are required to carry out cellular processes and maintain homeostasis, and digestion and absorption require the participation of several organs. Different animals have evolved different types of digestive systems specialized to meet their dietary needs. You do not need to memorize details about the different types of animal digestive systems, but you might find it interesting to explore the evolution of the system through a few groups of animals, from intracellular digestion in simple invertebrates to a digestive tract and accessory organs in complex vertebrates. Using a human eating a turkey sandwich as an example, food is ingested through the mouth. The mouth is the location where both mechanical (chewing) and chemical breakdown of food begins via the enzyme amylase, which breaks down carbohydrates into simpler sugars. The food bolus then travels by peristalsis (alternating waves of contraction) down the pharynx and esophagus to the stomach. In the stomach, pepsinogen mixes with hydrochloric acid to form pepsin, which begins digesting proteins, such as turkey, into smaller chains of amino acids. Mucus in the stomach protects its lining from damage by acidity, and the tightening of a sphincter prevents stomach contents from regurgitating into the esophagus. Further digestion of the ingredients of the sandwich occurs in the small intestine aided by a variety of enzymes; for example, bile salts and pancreatic amylase dumped into the small intestine from the gallbladder and pancreas, respectively, help emulsify fats. Once the ingredients of the sandwich have been broken down into smaller nutrient molecules, including amino acids, glucose, and fatty acids, they are absorbed from the small intestine into the circulatory and lymphatic systems. The walls of the small intestine contain small, finger-like projections called villi and microvilli that increase surface area for absorption of nutrients by diffusion. The large intestine or colon does not produce digestive enzymes but functions to absorb water, salts, and some vitamins. Any nutrients from the sandwich are stored in the liver, and wastes are eliminated. Information presented and the examples highlighted in the section support concepts outlined in Big Idea 2 and Big Idea 4

PDF page 1077: The stomach is the major site for protein digestion in animals other than ruminants. Protein digestion is mediated by an enzyme called pepsin in the stomach chamber. Pepsin is secreted by the chief cells in the stomach in an inactive form called pepsinogen. Pepsin breaks peptide bonds and cleaves proteins into smaller polypeptides; it also helps activate more pepsinogen, starting a positive feedback mechanism that generates more pepsin. Another cell type—parietal cells—secretes hydrogen and chloride ions, which combine in the lumen to form hydrochloric acid, the primary acidic component of the stomach juices. Hydrochloric acid helps to convert the inactive pepsinogen to pepsin. The highly acidic environment also kills many microorganisms in the food and, combined with the action of the enzyme pepsin, results in the hydrolysis of protein in the food. Chemical digestion is facilitated by the churning action of the stomach. Contraction and relaxation of smooth muscles mixes the stomach contents about every 20 minutes. The partially digested food and gastric juice mixture is called chyme. Chyme passes from the stomach to the small intestine. Further protein digestion takes place in the small intestine. Gastric emptying occurs within two to six hours after a meal. Only a small amount of chyme is released into the small intestine at a time. The movement of chyme from the stomach into the small intestine is regulated by the pyloric sphincter. When digesting protein and some fats, the stomach lining must be protected from getting digested by pepsin. There are two points to consider when describing how the stomach lining is protected. First, as previously mentioned, the enzyme pepsin is synthesized in the inactive form. This protects the chief cells, because pepsinogen does not have the same enzyme functionality of pepsin. Second, the stomach has a thick mucus lining that protects the underlying tissue from the action of the digestive juices. When this mucus lining is ruptured, ulcers can form in the stomach. Ulcers are open wounds in or on

PDF page 1067: Much information in this chapter is not within the scope of AP . However, the chapter provides us with the opportunity to review concepts we’ve explored previously, including structure and function, macromolecules, energy production, transport of substances across membranes, and enzyme activity. All living organisms require a source of energy and molecules needed to build cells, tissues, and organs. During digestion, food is broken down into smaller molecules for absorption and distribution to all cells of the body. Nutrients are required to carry out cellular processes and maintain homeostasis, and digestion and absorption require the participation of several organs. Different animals have evolved different types of digestive systems specialized to meet their dietary needs. You do not need to memorize details about the different types of animal digestive systems, but you might find it interesting to explore the evolution of the system through a few groups of animals, from intracellular digestion in simple invertebrates to a digestive tract and accessory organs in complex vertebrates. Using a human eating a turkey sandwich as an example, food is ingested through the mouth. The mouth is the location where both mechanical (chewing) and chemical breakdown of food begins via the enzyme amylase, which breaks down carbohydrates into simpler sugars. The food bolus then travels by peristalsis (alternating waves of contraction) down the pharynx and esophagus to the stomach. In the stomach, pepsinogen mixes with hydrochloric acid to form pepsin, which begins digesting proteins, such as turkey, into smaller chains of amino acids. Mucus in the stomach protects its lining from damage by acidity, and the tightening of a sphincter prevents stomach contents from regurgitating into the esophagus. Further digestion of the ingredients of the sandwich occurs in the small intestine aided by a variety of enzymes; for example, bile salts and pancreatic amylase dumped into the small intestine from the gallbladder and pancreas, respectively, help emulsify fats. Once the ingredients of the sandwich have been broken down into smaller nutrient molecules, including amino acids, glucose, and fatty acids, they are absorbed from the small intestine into the circulatory and lymphatic systems. The walls of the small intestine contain small, finger-like projections called villi and microvilli that increase surface area for absorption of nutrients by diffusion. The large intestine or colon does not produce digestive enzymes but functions to absorb water, salts, and some vitamins. Any nutrients from the sandwich are stored in the liver, and wastes are eliminated. Information presented and the examples highlighted in the section support concepts outlined in Big Idea 2 and Big Idea 4

PDF page 1078: an organ caused by bacteria (Helicobacter pylori) when the mucus lining is ruptured and fails to reform. Small Intestine Chyme moves from the stomach to the small intestine. The small intestine is the organ where the digestion of protein, fats, and carbohydrates is completed. The small intestine is a long tube-like organ with a highly folded surface containing fingerlike projections called the villi. The apical surface of each villus has many microscopic projections called microvilli. These structures, illustrated in Figure 25.12, are lined with epithelial cells on the luminal side and allow for the nutrients to be absorbed from the digested food and absorbed into the blood stream on the other side. The villi and microvilli, with their many folds, increase the surface area of the intestine and increase absorption efficiency of the nutrients. Absorbed nutrients in the blood are carried into the hepatic portal vein, which leads to the liver. There, the liver regulates the distribution of nutrients to the rest of the body and removes toxic substances, including drugs, alcohol, and some pathogens.

PDF page 1070: Omnivores are animals that eat both plant- and animal-derived food. In Latin, omnivore means to eat everything. Humans, bears (shown in Figure 25.4a), and chickens are example of vertebrate omnivores; invertebrate omnivores include cockroaches and crayfish (shown in Figure 25.4b).

PDF page 1067: Much information in this chapter is not within the scope of AP . However, the chapter provides us with the opportunity to review concepts we’ve explored previously, including structure and function, macromolecules, energy production, transport of substances across membranes, and enzyme activity. All living organisms require a source of energy and molecules needed to build cells, tissues, and organs. During digestion, food is broken down into smaller molecules for absorption and distribution to all cells of the body. Nutrients are required to carry out cellular processes and maintain homeostasis, and digestion and absorption require the participation of several organs. Different animals have evolved different types of digestive systems specialized to meet their dietary needs. You do not need to memorize details about the different types of animal digestive systems, but you might find it interesting to explore the evolution of the system through a few groups of animals, from intracellular digestion in simple invertebrates to a digestive tract and accessory organs in complex vertebrates. Using a human eating a turkey sandwich as an example, food is ingested through the mouth. The mouth is the location where both mechanical (chewing) and chemical breakdown of food begins via the enzyme amylase, which breaks down carbohydrates into simpler sugars. The food bolus then travels by peristalsis (alternating waves of contraction) down the pharynx and esophagus to the stomach. In the stomach, pepsinogen mixes with hydrochloric acid to form pepsin, which begins digesting proteins, such as turkey, into smaller chains of amino acids. Mucus in the stomach protects its lining from damage by acidity, and the tightening of a sphincter prevents stomach contents from regurgitating into the esophagus. Further digestion of the ingredients of the sandwich occurs in the small intestine aided by a variety of enzymes; for example, bile salts and pancreatic amylase dumped into the small intestine from the gallbladder and pancreas, respectively, help emulsify fats. Once the ingredients of the sandwich have been broken down into smaller nutrient molecules, including amino acids, glucose, and fatty acids, they are absorbed from the small intestine into the circulatory and lymphatic systems. The walls of the small intestine contain small, finger-like projections called villi and microvilli that increase surface area for absorption of nutrients by diffusion. The large intestine or colon does not produce digestive enzymes but functions to absorb water, salts, and some vitamins. Any nutrients from the sandwich are stored in the liver, and wastes are eliminated. Information presented and the examples highlighted in the section support concepts outlined in Big Idea 2 and Big Idea 4

PDF page 1076: secreted from the (b) salivary glands. Enzymes in the saliva begin to digest starches and fats. With the help of the tongue, the resulting bolus is moved into the esophagus by swallowing. (credit: modification of work by the National Cancer Institute) Esophagus The esophagus is a tubular organ that connects the mouth to the stomach. The chewed and softened food passes through the esophagus after being swallowed. The smooth muscles of the esophagus undergo a series of wave like movements called peristalsis that push the food toward the stomach, as illustrated in Figure 25.10. The peristalsis wave is unidirectional—it moves food from the mouth to the stomach, and reverse movement is not possible. The peristaltic movement of the esophagus is an involuntary reflex; it takes place in response to the act of swallowing.

PDF page 1069: Carnivores are animals that eat other animals. The word carnivore is derived from Latin and literally means “meat eater.” Wild cats such as lions, shown in Figure 25.3a and tigers are examples of vertebrate carnivores, as are snakes and sharks, while invertebrate carnivores include sea stars, spiders, and ladybugs, shown in Figure 25.3b. Obligate carnivores are those that rely entirely on animal flesh to obtain their nutrients; examples of obligate carnivores are members of the cat family, such as lions and cheetahs. Facultative carnivores are those that also eat non-animal food in addition to animal food. Note that there is no clear line that differentiates facultative carnivores from omnivores; dogs would be considered facultative carnivores.

PDF page 1070: Animals have evolved different types of digestive systems to aid in the digestion of the various foods they consume. The simplest example is that of a gastrovascular cavity and is found in organisms with only one opening for digestion. Platyhelminthes (flatworms), Ctenophora (comb jellies), and Cnidaria (coral, jelly fish, and sea anemones) use this type of digestion. Gastrovascular cavities, as shown in Figure 25.5a, are typically a blind tube or cavity with only one opening, the “mouth”, which also serves as an “anus”. Ingested material enters the mouth and passes through a hollow, tubular cavity. Cells within the cavity secrete digestive enzymes that break down the food. The food particles are engulfed by the cells lining the gastrovascular cavity. The alimentary canal, shown in Figure 25.5b, is a more advanced system: it consists of one tube with a mouth at one end and an anus at the other. Earthworms are an example of an animal with an alimentary canal. Once the food is ingested through the mouth, it passes through the esophagus and is stored in an organ called the crop; then it passes into the gizzard where it is churned and digested. From the gizzard, the food passes through the intestine, the nutrients are absorbed, and the waste is eliminated as feces, called castings, through the anus.

PDF page 1074: Ruminants Ruminants are mainly herbivores like cows, sheep, and goats, whose entire diet consists of eating large amounts of roughage or fiber. They have evolved digestive systems that help them digest vast amounts of cellulose. An interesting feature of the ruminants’ mouth is that they do not have upper incisor teeth. They use their lower teeth, tongue and lips to tear and chew their food. From the mouth, the food travels to the esophagus and on to the stomach. To help digest the large amount of plant material, the stomach of the ruminants is a multi-chambered organ, as illustrated in Figure 25.8. The four compartments of the stomach are called the rumen, reticulum, omasum, and abomasum. These chambers contain many microbes that break down cellulose and ferment ingested food. The abomasum is the “true” stomach and is the equivalent of the monogastric stomach chamber where gastric juices are secreted. The four-compartment gastric chamber provides larger space and the microbial support necessary to digest plant material in ruminants. The fermentation process produces large amounts of gas in the stomach chamber, which must be eliminated. As in other animals, the small intestine plays an important role in nutrient absorption, and the large intestine helps in the elimination of waste.

PDF page 1074: Ruminants Ruminants are mainly herbivores like cows, sheep, and goats, whose entire diet consists of eating large amounts of roughage or fiber. They have evolved digestive systems that help them digest vast amounts of cellulose. An interesting feature of the ruminants’ mouth is that they do not have upper incisor teeth. They use their lower teeth, tongue and lips to tear and chew their food. From the mouth, the food travels to the esophagus and on to the stomach. To help digest the large amount of plant material, the stomach of the ruminants is a multi-chambered organ, as illustrated in Figure 25.8. The four compartments of the stomach are called the rumen, reticulum, omasum, and abomasum. These chambers contain many microbes that break down cellulose and ferment ingested food. The abomasum is the “true” stomach and is the equivalent of the monogastric stomach chamber where gastric juices are secreted. The four-compartment gastric chamber provides larger space and the microbial support necessary to digest plant material in ruminants. The fermentation process produces large amounts of gas in the stomach chamber, which must be eliminated. As in other animals, the small intestine plays an important role in nutrient absorption, and the large intestine helps in the elimination of waste.

PDF page 1071: Through evolution, vertebrate digestive systems have adapted to different diets. Some animals have a single stomach, while others have multi-chambered stomachs. Birds have developed a digestive system adapted to eating unmasticated food. Monogastric: Single-chambered Stomach As the word monogastric suggests, this type of digestive system consists of one (“mono”) stomach chamber (“gastric”). Humans and many animals have a monogastric digestive system as illustrated in Figure 25.6ab. The process of digestion begins with the mouth and the intake of food. The teeth play an important role in masticating (chewing) or physically breaking down food into smaller particles. The enzymes present in saliva also begin to chemically break down food. The esophagus is a long tube that connects the mouth to the stomach. Using peristalsis, or wave-like smooth muscle contractions, the muscles of the esophagus push the food towards the stomach. In order to speed up the actions of enzymes in the stomach, the stomach is an extremely acidic environment, with a pH between 1.5 and 2.5. The gastric juices, which include enzymes in the stomach, act on the food particles and continue the process of digestion. Further breakdown of food takes place in the small intestine where enzymes produced by the liver, the small intestine, and the pancreas continue the process of digestion. The nutrients are absorbed into the blood stream across the epithelial cells lining the walls of the small intestines. The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces; it is stored until it is excreted through the rectum.

PDF page 1077: Stomach A large part of digestion occurs in the stomach, shown in Figure 25.11. The stomach is a saclike organ that secretes gastric digestive juices. The pH in the stomach is between 1.5 and 2.5. This highly acidic environment is required for the chemical breakdown of food and the extraction of nutrients. When empty, the stomach is a rather small organ; however, it can expand to up to 20 times its resting size when filled with food. This characteristic is particularly useful for animals that need to eat when food is available.

PDF page 1071: Through evolution, vertebrate digestive systems have adapted to different diets. Some animals have a single stomach, while others have multi-chambered stomachs. Birds have developed a digestive system adapted to eating unmasticated food. Monogastric: Single-chambered Stomach As the word monogastric suggests, this type of digestive system consists of one (“mono”) stomach chamber (“gastric”). Humans and many animals have a monogastric digestive system as illustrated in Figure 25.6ab. The process of digestion begins with the mouth and the intake of food. The teeth play an important role in masticating (chewing) or physically breaking down food into smaller particles. The enzymes present in saliva also begin to chemically break down food. The esophagus is a long tube that connects the mouth to the stomach. Using peristalsis, or wave-like smooth muscle contractions, the muscles of the esophagus push the food towards the stomach. In order to speed up the actions of enzymes in the stomach, the stomach is an extremely acidic environment, with a pH between 1.5 and 2.5. The gastric juices, which include enzymes in the stomach, act on the food particles and continue the process of digestion. Further breakdown of food takes place in the small intestine where enzymes produced by the liver, the small intestine, and the pancreas continue the process of digestion. The nutrients are absorbed into the blood stream across the epithelial cells lining the walls of the small intestines. The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces; it is stored until it is excreted through the rectum.

PDF page 1073: the first of two stomachs, called the proventriculus, which contains digestive juices that break down food. From the proventriculus, the food enters the second stomach, called the gizzard, which grinds food. Some birds swallow stones or grit, which are stored in the gizzard, to aid the grinding process. Birds do not have separate openings to excrete urine and feces. Instead, uric acid from the kidneys is secreted into the large intestine and combined with waste from the digestive process. This waste is excreted through an opening called the cloaca.

PDF page 1074: Birds have a highly efficient, simplified digestive system. Recent fossil evidence has shown that the evolutionary divergence of birds from other land animals was characterized by streamlining and simplifying the digestive system. Unlike many other animals, birds do not have teeth to chew their food. In place of lips, they have sharp pointy beaks. The horny beak, lack of jaws, and the smaller tongue of the birds can be traced back to their dinosaur ancestors. The emergence of these changes seems to coincide with the inclusion of seeds in the bird diet. Seed-eating birds have beaks that are shaped for grabbing seeds and the two-compartment stomach allows for delegation of tasks. Since birds need to remain light in order to fly, their metabolic rates are very high, which means they digest their food very quickly and need to eat often. Contrast this with the ruminants, where the digestion of plant matter takes a very long time. Although both birds and humans are vertebrates, birds have a relatively higher metabolic rate than humans.

PDF page 1074: c. a. Birds have smaller surfaces to lose heat than humans, so their metabolic rate must be higher.