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DIGESTION & ABSORPTION
Chapter 3
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Outline Digestive Tracts The 4 Stages Nutrition Ingestion Digestion
Absorption Egestion Nutrition
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Overview: Digestion and Absorption
Food is taken in, taken apart, and taken up in the process of animal digestion and absorption. In general, animals are heterotrophs which fall into three categories: Holozoic needs to ingest organic or non-organic food and digestion is via alimentary canal Saprophytes digest food extracellularly and absorption is via cell walls Parasites live and obtain food from another living organism Heterotrophs ant. Autotroph Omnivores Variety of specializations Accommodate both vegetation (plants, algal) and meat Herbivores Incisors for clipping Premolars and molars for grinding Plant and algal, mostly autotrophs Carnivores Pointed incisors and enlarged canines Shear off pieces small enough to swallow
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The 4 Main Stages : Ingestion
Ingestion is the act of eating Four types of feeders: Suspension Feeders Substrate Feeders Fluid Feeders Bulk feeders Ingestion, Digestion, Absorption and Egestion Assimilation covered in Liver function
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Humpback whale, a suspension feeder
Fig. 41-6a Baleen Continuous filter feeders Ex: Clams Always have water moving into the mantle cavity via incurrent siphon Particles deposited on gills Do not need food storage area Discontinuous feeders Ex: Squid Uses tentacles to seize prey Allows the beaklike jaws to pull pieces into the mouth with the radula Food storage area needed Figure 41.6 Four main feeding mechanisms of animals sift small food particles from the water Humpback whale, a suspension feeder
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Caterpillar Feces Leaf miner caterpillar, a substrate feeder
Fig. 41-6b Leaf miner caterpillar, a substrate feeder Figure 41.6 Four main feeding mechanisms of animals live in or on their food source Caterpillar Feces
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Mosquito, a fluid feeder
Fig. 41-6c Figure 41.6 Four main feeding mechanisms of animals suck nutrient-rich fluid from a living host Mosquito, a fluid feeder
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Rock python, a bulk feeder
Fig. 41-6d Rock python, a bulk feeder Figure 41.6 Four main feeding mechanisms of animals eat relatively large pieces of food
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Absorption is uptake of nutrients by body cells
Digestion is the process of breaking food down into molecules small enough to absorb In chemical digestion, the process of enzymatic hydrolysis splits bonds in molecules with the addition of water Absorption is uptake of nutrients by body cells Elimination is the passage of undigested material out of the digestive compartment
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Nutrient molecules enter body cells Mechanical digestion
Small molecules Pieces of food Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Mechanical digestion Food Undigested material Figure 41.7 The four stages of food processing 1 Ingestion 2 Digestion 3 Absorption 4 Elimination
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Digestive Compartments
Most animals process food in specialized compartments These compartments reduce the risk of an animal digesting its own cells and tissues In intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles 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
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Gastrovascular cavity
Fig. 41-8 Tentacles Food Gastrovascular cavity Mouth Figure 41.8 Digestion in a hydra Epidermis Gastrodermis
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Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients 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 It can have specialized regions that carry out digestion and absorption in a stepwise fashion
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Digestive Tracts Incomplete versus Complete Tracts
Incomplete tract has a single opening Ex: Planarian Food enters through mouth and muscular pharynx Wastes exit through mouth and muscular pharynx Lacks specialized parts Complete Tract has two openings Ex: Earthworm Food enters through mouth Wastes exit through anus
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Incomplete Digestive Tract of a Planarian
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. mouth digestive tract pharynx Golgi apparatus lysosome gastrovascular cavity a. b.
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Complete Digestive Tract of an Earthworm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. typhlosole anus mouth pharynx intestine esophagus crop gizzard
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Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Typhlosole
Fig. 41-9a Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Typhlosole Figure 41.9a Variation in alimentary canals Lumen of intestine (a) Earthworm
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Foregut Midgut Hindgut Esophagus Rectum Anus Crop Mouth Gastric cecae
Fig. 41-9b Foregut Midgut Hindgut Esophagus Rectum Anus Crop Figure 41.9b Variation in alimentary canals Mouth Gastric cecae (b) Grasshopper
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Stomach Gizzard Intestine Mouth Esophagus Crop Anus (c) Bird
Fig. 41-9c Stomach Gizzard Intestine Mouth Esophagus Crop Anus Figure 41.9c Variation in alimentary canals (c) Bird
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The Mammalian Digestive System: Organs Specialization
The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal Valves called sphincters regulate the movement of material between compartments Humans digestive tract is complete and extracellular Part of a tube-within-a-tube body plan Begins with a mouth and ends in an anus Extracellular:- Digestive enzymes are secreted by The wall of the digestive tract, or By nearby glands
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Duodenum of small intestine
Fig a Tongue Sphincter Oral cavity Salivary glands Pharynx Esophagus Sphincter Liver Stomach Ascending portion of large intestine Gall- bladder Duodenum of small intestine Pancreas Small intestine Small intestine Figure The human digestive system Large intestine Rectum Anus Appendix Cecum
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A schematic diagram of the human digestive system
Fig b Salivary glands Mouth Esophagus Gall- bladder Stomach Small intestine Liver Pancreas Large intestine Figure The human digestive system Rectum Anus A schematic diagram of the human digestive system
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Fig Tongue Sphincter Salivary glands Oral cavity Salivary glands Pharynx Mouth Esophagus Esophagus Liver Sphincter Stomach Gall- bladder Ascending portion of large intestine Stomach Gall- bladder Duodenum of small intestine Pancreas Small intestine Liver Small intestine Small intestine Pancreas Large intestine Large intestine Figure The human digestive system Rectum Rectum Anus Anus Appendix A schematic diagram of the human digestive system Cecum
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The Oral Cavity, Pharynx, and Esophagus
The first stage of digestion (ingestion) is mechanical and takes place in the oral cavity Mouth Three major pairs of salivary glands Saliva contains salivary amylase (Digestion) Salivary amylase initiates starch digestion Tongue is composed of striated muscle Mixes chewed food with saliva Forms mixture into bolus
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Pharynx and Esophagus Pharynx Esophagus
Where digestive and respiratory passages come together Soft palate closes off nasopharynx Epiglottis Covers opening into trachea Keeps food from air passages (most of the time) Esophagus Takes food to stomach by peristalsis Peristalsis - Rhythmical contraction to move contents in tubular organs
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Esophageal sphincter contracted Glottis Larynx Trachea Esophagus
Fig Food Epiglottis up Tongue Pharynx Esophageal sphincter contracted Glottis Larynx Trachea Esophagus To lungs To stomach Figure From mouth to stomach: the swallowing r Salivary glands deliver saliva to lubricate food Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers eflex and esophageal peristalsis
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Esophageal sphincter contracted Epiglottis down Glottis Larynx Trachea
Fig Food Epiglottis up Tongue Pharynx Esophageal sphincter contracted Epiglottis down Glottis Larynx Trachea Esophagus Esophageal sphincter relaxed Glottis up and closed To lungs To stomach Figure From mouth to stomach: the swallowing reflex and eso The tongue shapes food into a bolus and provides help with swallowing The region we call our throat is the pharynx, a junction that opens to both the esophagus and the trachea (windpipe) The trachea leads to the lungs phageal peristalsis
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Esophageal sphincter contracted Epiglottis down Glottis
Fig Food Epiglottis up Tongue Epiglottis up Pharynx Esophageal sphincter contracted Epiglottis down Glottis Glottis down and open Esophageal sphincter contracted Larynx Trachea Esophagus Esophageal sphincter relaxed Glottis up and closed Relaxed muscles To lungs To stomach Contracted muscles Relaxed muscles Sphincter relaxed Figure From mouth to stomach: the swallowing reflex and esophageal peristalsis The esophagus conducts food from the pharynx down to the stomach by peristalsis Swallowing causes the epiglottis 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 Stomach
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Peristalsis in the Digestive Tract
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. esophagus bolus
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Stage 2: Digestion (Stomach)
The stomach stores food and secretes gastric juice Stomach Stomach wall has deep folds Folds disappear as the stomach fills to an approximate volume of one liter Epithelial lining of the stomach has millions of gastric pits, which drain gastric glands Pepsin is a hydrolytic enzyme that acts on protein to produce peptides Food mixing with gastric juices becomes acid chyme Chemical Digestion
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Folds of epithelial tissue
Fig a Esophagus Sphincter Stomach Sphincter 5 µm Small intestine Folds of epithelial tissue Interior surface of stomach Figure The stomach and its secretions
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Gastric juice is made up of hydrochloric acid and the enzyme pepsin
Fig b Interior surface of stomach Epithelium 3 1 Pepsinogen Pepsin Pepsinogen and HCl are secreted. 2 HCl Gastric gland 2 HCl converts pepsinogen to pepsin. 1 3 Pepsin activates more pepsinogen. Mucus cells H+ Cl– Chief cells Chief cell Figure The stomach and its secretions Gastric juice is made up of hydrochloric acid and the enzyme pepsin Parietal cells secrete hydrogen and chloride ions separately 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 Parietal cells Parietal cell
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Figure 41.12 The stomach and its secretions
Esophagus Sphincter Stomach Sphincter 5 µm Small intestine Folds of epithelial tissue Interior surface of stomach Epithelium 3 1 Pepsinogen and HCl are secreted. Pepsinogen Pepsin 2 Gastric gland HCl 2 HCl converts pepsinogen to pepsin. 1 3 Pepsin activates more pepsinogen. Mucus cells H+ Figure The stomach and its secretions Coordinated contraction and relaxation of stomach muscle churn the stomach’s contents Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine Junction between stomach and small intestine controlled by a sphincter When the sphincter relaxes, a small quantity of chyme passes into the small intestine Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Helicobacter pylori Cl– Chief cells Chief cell Parietal cells Parietal cell
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STAGE 2: Digestion (Small Intestine)
The small intestine is the longest section of the alimentary canal It is the major organ of digestion and absorption The first portion of the small intestine is the duodenum, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself Chemical Digestion
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Duodenum of small intestine
Liver Bile Gallbladder Stomach Pancreas Figure Hormonal control of digestion Duodenum of small intestine
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Duodenum: The Pancreas
The pancreas produces proteases trypsin and chymotrypsin, protein-digesting enzymes that are activated after entering the duodenum Its solution is alkaline and neutralizes the acidic chyme Pancreatic amylase digests starch to maltose Trypsin digests protein to peptides Lipase digests fat droplets to glycerol and fatty acids
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Duodenum: The Liver In the small intestine, bile aids in digestion and absorption of fats Bile is made in the liver and stored in the gallbladder Bile contains bile salts which break up fat into fat droplets via emulsification Helps maintain glucose concentration in blood by converting excess into glycogen
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Small Intestine The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine Most digestion occurs in the duodenum; the jejunum and ileum function mainly in absorption of nutrients and water These complete digestion of peptides and sugars
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Carbohydrate digestion
Fig a Carbohydrate digestion Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Oral cavity, pharynx, esophagus Salivary amylase Smaller polysaccharides, maltose Stomach Polysaccharides Lumen of small intestine Pancreatic amylases Maltose and other disaccharides Figure Enzymatic hydrolysis in the human digestive system Disaccharidases Epithelium of small intestine (brush border) Monosaccharides
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Protein digestion Proteins Pepsin Stomach Small polypeptides
Fig b Protein digestion Proteins Pepsin Stomach Small polypeptides Polypeptides Pancreatic trypsin and chymotrypsin Lumen of small intestine Smaller polypeptides Pancreatic carboxypeptidase Amino acids Small peptides Figure Enzymatic hydrolysis in the human digestive system Epithelium of small intestine (brush border) Dipeptidases, carboxypeptidase, and aminopeptidase Monosaccharides Amino acids
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Nucleic acid digestion
Fig c Nucleic acid digestion DNA, RNA Lumen of small intestine Pancreatic nucleases Nucleotides Nucleotidases Nucleosides Epithelium of small intestine (brush border) Nucleosidases and phosphatases Figure Enzymatic hydrolysis in the human digestive system Nitrogenous bases, sugars, phosphates
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Fat digestion Fat globules Bile salts Lumen of small intestine
Fig d Fat digestion Fat globules Bile salts Lumen of small intestine Fat droplets Pancreatic lipase Glycerol, fatty acids, monoglycerides Figure Enzymatic hydrolysis in the human digestive system
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Figure 41.13 Enzymatic hydrolysis in the human digestive system
Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Oral cavity, pharynx, esophagus Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Salivary amylase Smaller polysaccharides, maltose Stomach Proteins Pepsin Small polypeptides Lumen of small intes- tine Polysaccharides Polypeptides DNA, RNA Fat globules Pancreatic amylases Pancreatic trypsin and chymotrypsin Pancreatic nucleases Bile salts Maltose and other disaccharides Fat droplets Nucleotides Smaller polypeptides Pancreatic lipase Pancreatic carboxypeptidase Glycerol, fatty acids, monoglycerides Amino acids Figure Enzymatic hydrolysis in the human digestive system Epithelium of small intestine (brush border) Small peptides Nucleotidases Nucleosides Disaccharidases Dipeptidases, carboxypeptidase, and aminopeptidase Nucleosidases and phosphatases Monosaccharides Amino acids Nitrogenous bases, sugars, phosphates
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STAGE 3: Absorption (Small Intestines)
The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen The enormous microvillar surface greatly increases the rate of nutrient absorption
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Vein carrying blood to hepatic portal vein
Fig Vein carrying blood to hepatic portal vein Microvilli (brush border) at apical (lumenal) surface Lumen Blood capillaries Epithelial cells Basal surface Muscle layers Large circular folds Epithelial cells Villi Lacteal Key Figure The structure of the small intestine Lymph vessel Nutrient absorption Villi Intestinal wall
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Vein carrying blood to hepatic portal vein
Fig a Vein carrying blood to hepatic portal vein Muscle layers Large circular folds Villi Figure The structure of the small intestine Key Nutrient absorption Intestinal wall
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Microvilli (brush border) at apical (lumenal) surface
Fig b Microvilli (brush border) at apical (lumenal) surface Lumen Blood capillaries Epithelial cells Basal surface Epithelial cells Lacteal Figure The structure of the small intestine Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream Capillaries and veins from the lacteals converge in the hepatic portal vein and deliver blood to the liver and then on to the heart Lymph vessel Villi Key Nutrient absorption
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Has ridges and furrows that give it a corrugated surface
Villi are ridges on the surface, which contain even smaller ridges, microvilli Greatly increase absorptive area Each villus contains blood capillaries and a lymphatic capillary (lacteal)
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Lumen of small intestine Triglycerides Fatty acids Monoglycerides
Fig Lumen of small intestine Triglycerides Fatty acids Monoglycerides Epithelial cell Triglycerides Phospholipids, cholesterol, and proteins Figure Absorption of fats Each villus contains a network of blood vessels and a small lymphatic vessel called a lacteal After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells These fats are mixed with cholesterol and coated with protein, forming molecules called chylomicrons, which are transported into lacteals Capillaries and veins from the lacteals converge in the hepatic portal vein and deliver blood to the liver and then on to the heart Chylomicron Lacteal
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STAGE 3: Absorption (Large Intestines)
The colon of the large intestine is connected to the small intestine 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, which plays a very minor role in immunity Larger in diameter, but shorter in length than small intestine Absorbs water, salts, and some vitamins Cecum has small projection - appendix Colon subdivided into ascending, transverse, descending, and sigmoid colon Opening to anal canal - Anus
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Junction of the Small Intestine and the Large Intestine
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. large intestine small intestine cecum vermiform appendix
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Fig Figure Digital image of a human colon
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STAGE 4: Egestion (Large Intestines)
A major function of the colon is to recover water that has entered the alimentary canal Wastes of the digestive tract, the feces, become more solid as they move through the colon Feces are stored in the rectum until they can be eliminated Two sphincters between the rectum and anus control bowel movements Feces pass through the rectum and exit via the anal canal where the opening is call the anus. The colon houses strains of the enterobacteria Escherichia coli, some of which produce vitamins
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