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Nutrition Digestive system 1 Digestion helps homeostasis A digestive system involves various processes: Ingestion Mechanical digestion Chemical digestion Absorption Elimination 2 Digestion helps homeostasis Chemical digestion involves specific enzymes in the macromolecule breakdown. 3 Animal strategies Heterotrophs are divided into four groups on the basis of their food strategy. Bulk feeders eat food in chunks or whole Filter feeders collect and eat small particles from water 4 Animal strategies Fluid feeders consume fluids as blood or lymph Substrate feeders live on or in the food they eat 5 lase, lase, which which initiates initiates the breakdown breakdown of the of the polysaccharide polysaccharide starch starch ate ebrate tooth tooth shape. shape. lase, which initiates thethe breakdown of the polysaccharide starch tooth shape. into into the the disaccharide disaccharide maltose. maltose. This This digestion digestion is usually is usually minimal minimal he in digestive the digestive process. process. into the disaccharide maltose. This digestion is usually minimal digestive process. in humans, in humans, however, however, because because most most people people don’t don’t chew chew their their food food in humans, however, because most people don’t chew their food very very long. long. very long. different in different kinds kinds of verof verferent kinds of verStimulation Stimulation salivation of salivation irds, e. Birds, which which lack lack teeth, teeth,Stimulation of of salivation ds, which lack teeth, The The secretions secretions of the of the salivary salivary glands glands are controlled controlled by the by the ner-nermachs stomachs (figure (figure 48.5) secretions of the salivary glands areare controlled by the nerchs (figure 48.5) . 48.5) In. In . InThe vous vous system, system, which which humans in humans maintains maintains a constant a constant of of rd, mall small pebbles pebbles ingested ingestedvous system, which in in humans maintains a constant flowflow offlow all pebbles ingested about about half athat milliliter a milliliter per minute minute when when the the mouth mouth is empty is empty the food food by muscular by muscular Herbivores: animals eat plants exclusively; common half a half milliliter perper minute when the mouth is empty of of of examples od by muscular ac-ac- ac-about food. food. This This continuous continuous secretion secretion keeps keeps the the mouth mouth moist. moist. and other other hard hard plant plant ma-ma-food. This continuous secretion keeps the mouth moist. ther hard plant mainclude vertebrates such as cattle, horses and rabbits. The The presence presence of food ofinfood in the in the mouth mouth triggers triggers an increased an increased gested ed more more easily. easily. The presence of food the mouth triggers an increased more easily. rate of secretion. of secretion. Taste Taste buds buds as well asaswell as olfactory as olfactory (smell) (smell) neuneurate ofrate secretion. Taste buds as well olfactory (smell) neurons rons send send impulses impulses to tobrain, the brain, brain, which which responds responds by stimustimudiff toerent diff erent erent rons send impulses toeat thethe which responds by by stimuCarnivores: animals that other animals, such as crabs, squid, iff lating lating the the salivary salivary glands glands (see (see chapter chapter 46). 46). The The most most potent potent thecats. salivary glands (see chapter 46). The most potent many insectslating and stimuli stimuli are acidic acidic solutions; solutions; lemon lemon juice, juice, for example, example, stimuli areare acidic solutions; lemon juice, for for example, cancancan increase increase the rate of salivation of salivation eightfold. eightfold. The The sight, sight, sound, sound, 8.6), used used for chewing, for chewing, thethe rate ofrate salivation eightfold. The sight, sound, sed for chewing, or or orincrease smell or smell food ofthat food can can stimulate stimulate salivation salivation markedly markedly in many in other many mall particles particles and and mix it itor or smell of of food can stimulate salivation markedly in many Omnivores: animals eat both plants and animals. articles and mix itmix Teeth are adapted to different strategies Heterotrophs are divided into three groups on the basis of their food sources. Humans are omnivores, as are pigs and bears. n Herbivore Herbivore Herbivore Carnivore Carnivore Carnivore Omnivore Omnivore Omnivore evolved ved d of ern of s Premolars olars Molars s Horse Lion Horse Horse Horse Human Lion LionLion Human Human Human 6 Digestive system in mammals Vertebrate digestive systems include highly specialized structures molded by diet. The digestive system consists of a tubular gastrointestinal tract and accessory digestive organs. One-way movement through the digestive tract allows different regions of the digestive system to become specialized for different functions. Salamander Stomach Intestine Mouth Anus One-way movement 7 Digestive system in mammals Carnivores have a short digestive tract, as they obtain nutrients from meat more easily. They also have a relatively small caecum 8 Digestive system in mammals Herbivores have a long digestive tract, as it takes a long time to digest cellulose from plants, and a large caecum which houses mutualistic aerobic bacteria which help animals digest the cellulose 9 Digestive system in mammals Some herbivores called ruminants (cows, sheep) have specialized stomaches divided into rumen (1), reticulum (2), omasum (3) and abomasum (4) hosting microbial flora. 10 Human digestive system Our digestive system is adapted to an omnivorous diet. The breakdown of the nutrients requires the coordination of several digestive enzymes secreted from specialized cells. The major organs or structures that coordinate digestion within the human body include: • mouth • esophagus • stomach • small and large intestine • liver 11 The mouth Both first mechanical (biting and chewing) and chemical digestion occur in the mouth. Humans have four kinds of 32 teeth: incisors (for biting); canines (for tearing); premolars and molars (for crushing food). Three pairs of salivary glands secrete saliva that contains an enzyme called amylase, which digests starch molecules into smaller disaccharides. During chewing, the tongue moves food about and manipulates it into a mass called a bolus. The bolus is pushed down into the pharynx (throat). Molars (3) Premolars (2) Canines (1) Incisors (2) 12 The esophagus The esophagus is a muscular tube that passes from the pharynx to the stomach. During swallowing, the air passage is blocked by soft palate (1) and epiglottis (2), so the food bolus enters the esophagus (3). Palate Epiglottis Esophagus 13 The esophagus After swallowing, peristaltic movements (a rhythmic series of muscular contractions) push the food bolus in the esophagus to the stomach. 14 The stomach The stomach is a saclike organ. Its inner surface is highly convoluted, enabling it to fold up when empty and open out like an expanding balloon as it fills with food. The human stomach has a volume of only about 50 mL when empty, but, it may expand to contain 2 to 4 L of food when full. Carnivores that engage in sporadic gorging as an important survival strategy possess stomachs that are able to distend even more. 15 The stomach Layers of stomach muscle contract and attack the bolus of food with gastric juices to form a soupy liquid called chyme. Where the esophagus joins the stomach, a valvelike muscle, the cardiac sphincter, relaxes as the bolus passes through and then quickly closes. A second sphincter, the pylorus, connects to the beginning of the intestines. 16 The stomach The stomach 1. stores food 2. prepares food for second chemical digestion. 3. plays a role in protein digestion. Gastric glands secrete an hormone that is converted to the enzyme pepsin which digests large proteins into smaller proteins (peptides) The food is mixed with gastric acid juices containing pepsin. To protect the stomach wall from the acid, a third type of cell secretes mucus that lines the stomach cavity. 17 Gastric acids and the ulcer The human stomach produces about 2 L of HCl every day, creating a very acidic solution (pH=2). The low pH in the stomach helps denature food proteins, making them easier to digest. In adult humans, only proteins are partially digested in the stomach; no significant digestion of carbohydrates or fats occurs there. The acidic solution within the stomach also kills most of the bacteria that are ingested with the food. Overproduction of gastric acids can occasionally eat a hole through the wall of the stomach, causing a peptic ulcer. Different reasons cause peptic ulcers such as the infection of the bacterium Heliobacter pylori and the consumption of some types of foods. 18 The intestine: Breakdown, Absorption, and Elimination 19 The small intestine The chyme spurts from the stomach through a sphincter into the 5 to 9 meters long small intestine. Here absorption of nutrients takes place. Small nutrient molecules are absorbed by the villi on the intestinal wall. villi 20 Accessory organs secrete enzymes into the small intestine The main organs that aid digestion are the pancreas, liver, and gallbladder. They empty their secretions (pancreatic juice and bile), primarily composed of enzymes, through ducts directly into the small intestine Liver 21 Pancreas, Liver and Gallbladder The pancreas, secretes pancreatic fluid into the duodenum through the pancreatic duct. This fluid contains a group of enzymes, including trypsin, which digest proteins; amylase, which digests starch; and lipase, which digests fat. The liver is the largest internal organ of the body. The main secretion is bile, a fluid mixture consisting of: 1.The bile pigments: do not participate in digestion; they are waste products resulting from the liver’s destruction of old red blood cells and are ultimately eliminated with the feces 2.The bile salts play a very important role in preparing fats for subsequent enzymatic digestion After bile is produced in the liver, it is stored and concentrated in the gallbladder. The arrival of fatty food in the duodenum stimulates the gallbladder to contract, causing bile to be transported through the common bile duct and injected into the duodenum 22 The chemical digestion •The enzymes digesting carbohydrate include amylase (for starch), maltase (for maltose), sucrase (for sucrose) and lactase (for lactose). •For fats, the principal enzyme is lipase. Before this enzyme can act, the large globules of fat must be broken into smaller droplets by bile. •Protein digestion is accomplished by several enzymes, including trypsin. Peptides are broken into smaller peptides, and peptidase reduces the peptides to amino acids. •Nuclease digests nucleic acids into nucleotides. 23 The large intestine The large intestine absorbs water, minerals and vitamins and prepare waste for elimination. Is divided into cecum, colon and rectum. The cecum controls the flux of material through the intestine and the appendix protects from infections. 24 The large intestine The colon is the last portion of the digestive tract and extracts the last water and minerals from waste before final elimination. Bacteria-aided fermentation occurs. Transverse colon Ascending colon Descending colon The rectum is the final part of the large intestine and terminates in the anus. Here feces are formed and expelled. Rectum Anus 25 Nutrition disorders Obesity is defined as weighing 30% more than ideal body weight. Obesity is often associated with Type 2 Diabetes and cardiovascular diseases. Other common nutrition disorders are anorexia nervosa (distorted body image that leads to hypo-nutrition) and bulimia nervosa (binge-eating and purging). 26 Liver diseases Liver malfunctioning has effects on the whole organism. Liver disorders include: • • • Hepatitis: inflammation of the liver caused by viruses Cirrhosis: damage of tissues leading to loss of liver functions Liver cancer 27