DIGESTION & ABSORPTION Chapter 3

Outline Digestive Tracts The 4 Stages Nutrition Ingestion Digestion Absorption Egestion Nutrition

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

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

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

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

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

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

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

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

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

Gastrovascular cavity Fig. 41-8 Tentacles Food Gastrovascular cavity Mouth Figure 41.8 Digestion in a hydra Epidermis Gastrodermis

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

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

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.

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

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

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

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

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

Duodenum of small intestine Fig. 41-10a 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 41.10 The human digestive system Large intestine Rectum Anus Appendix Cecum

A schematic diagram of the human digestive system Fig. 41-10b Salivary glands Mouth Esophagus Gall- bladder Stomach Small intestine Liver Pancreas Large intestine Figure 41.10 The human digestive system Rectum Anus A schematic diagram of the human digestive system

Fig. 41-10 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 41.10 The human digestive system Rectum Rectum Anus Anus Appendix A schematic diagram of the human digestive system Cecum

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

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

Esophageal sphincter contracted Glottis Larynx Trachea Esophagus Fig. 41-11-1 Food Epiglottis up Tongue Pharynx Esophageal sphincter contracted Glottis Larynx Trachea Esophagus To lungs To stomach Figure 41.11 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

Esophageal sphincter contracted Epiglottis down Glottis Larynx Trachea Fig. 41-11-2 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 41.11 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

Esophageal sphincter contracted Epiglottis down Glottis Fig. 41-11-3 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 41.11 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

Peristalsis in the Digestive Tract Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. esophagus bolus

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

Folds of epithelial tissue Fig. 41-12a Esophagus Sphincter Stomach Sphincter 5 µm Small intestine Folds of epithelial tissue Interior surface of stomach Figure 41.12 The stomach and its secretions

Gastric juice is made up of hydrochloric acid and the enzyme pepsin Fig. 41-12b 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 41.12 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

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 41.12 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

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

Duodenum of small intestine Liver Bile Gallbladder Stomach Pancreas Figure 41.14 Hormonal control of digestion Duodenum of small intestine

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

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

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

Carbohydrate digestion Fig. 41-13a 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 41.13 Enzymatic hydrolysis in the human digestive system Disaccharidases Epithelium of small intestine (brush border) Monosaccharides

Protein digestion Proteins Pepsin Stomach Small polypeptides Fig. 41-13b 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 41.13 Enzymatic hydrolysis in the human digestive system Epithelium of small intestine (brush border) Dipeptidases, carboxypeptidase, and aminopeptidase Monosaccharides Amino acids

Nucleic acid digestion Fig. 41-13c Nucleic acid digestion DNA, RNA Lumen of small intestine Pancreatic nucleases Nucleotides Nucleotidases Nucleosides Epithelium of small intestine (brush border) Nucleosidases and phosphatases Figure 41.13 Enzymatic hydrolysis in the human digestive system Nitrogenous bases, sugars, phosphates

Fat digestion Fat globules Bile salts Lumen of small intestine Fig. 41-13d Fat digestion Fat globules Bile salts Lumen of small intestine Fat droplets Pancreatic lipase Glycerol, fatty acids, monoglycerides Figure 41.13 Enzymatic hydrolysis in the human digestive system

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 41.13 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

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

Vein carrying blood to hepatic portal vein Fig. 41-15 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 41.15 The structure of the small intestine Lymph vessel Nutrient absorption Villi Intestinal wall

Vein carrying blood to hepatic portal vein Fig. 41-15a Vein carrying blood to hepatic portal vein Muscle layers Large circular folds Villi Figure 41.15 The structure of the small intestine Key Nutrient absorption Intestinal wall

Microvilli (brush border) at apical (lumenal) surface Fig. 41-15b Microvilli (brush border) at apical (lumenal) surface Lumen Blood capillaries Epithelial cells Basal surface Epithelial cells Lacteal Figure 41.15 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

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)

Lumen of small intestine Triglycerides Fatty acids Monoglycerides Fig. 41-16 Lumen of small intestine Triglycerides Fatty acids Monoglycerides Epithelial cell Triglycerides Phospholipids, cholesterol, and proteins Figure 41.16 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

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

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

Fig. 41-17 Figure 41.17 Digital image of a human colon

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