Transcript Chapter 41
Chapter 41 Digestion and Absorption Essential Idea: The structure of the wall of the small intestine allows it to move, digest, and absorb food. travismulthaupt.com 1 Food Processing Can be broken into 4 main stages: 1. Ingestion-taking in food-polymers. 2. Digestion-breaking down polymers. 3. Absorption-taking up small molecules from digestive compartment. 4. Elimination-excretion of undigested material from digestive compartment. travismulthaupt.com 2 Food Processing Animals prevent digestion of themselves by performing these functions in specialized compartments. There are two general types: – 1. Intracellular digestion – 2. Extracellular digestion travismulthaupt.com 3 Digestion Digestion is important because it allows organisms to extract energy from a substance. The process of digestion takes advantage of surface area on a number of different levels. Digestion involves enzymes. 4 1. Intracellular Digestion Food particles get engulfed by phagocytosis and pinocytosis. Food vacuoles contain hydrolytic enzymes. These break down food particles without digesting the cell.travismulthaupt.com 5 Mammalian Digestion Food enters the oral cavity. Gets chewed, rolled into a bolus and pushed into the esophagus. Peristalsis is the contraction of circular and longitudinal muscles that moves food through the travismulthaupt.com digestive system. Epithelium Mucosa Mucosa Mucosa Circular Muscles 6 Longitudinal Muscles https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/the-digestive-system-23/absorption-225/absorption-in-the-small-intestine-1105-808 Mammalian Digestion In the stomach, food gets mixed with gastric juice (low pH and enzymes) which breaks down the proteins. In the small intestine, the pancreas releases more enzymes that aid in digestion. – Lipase – Protease (endopeptidase) – Amylase 7 Mammalian Digestion Within the small intestine, most macromolecules in food are digested into monomers. Cellulose is a macromolecule that remains undigested. 8 A Lipase Reaction 9 Protease Reaction 10 Amylase Reaction 11 2. Extracellular Digestion Extracellular digestion occurs within a compartment which is continuous with the outside of an animal’s body. These cavities allow an animal to eat large amounts of food. travismulthaupt.com 12 2. Extracellular Digestion Food moves in one direction and digestive functions can be broken into different parts. travismulthaupt.com 13 Stomach The stomach is a muscular organ. It is an important organ involved in the second phase of digestion. It is involved in protein digestion using proteases and strong acids. Food becomes chyme. 14 Pepsinogen-Pepsin Reaction When food enters the stomach, it is stimulated to secrete pepsinogen and HCl. travismulthaupt.com 15 Pepsinogen-Pepsin Reaction The HCl converts pepsinogen into pepsin. The pepsin breaks down the proteins of the food. travismulthaupt.com 16 Pepsinogen-Pepsin Reaction As the food leaves the stomach, the parietal cells stop secreting HCl and the chief cells stop secreting pepsinogen. Also, autodigestion of the stomach is prevented by the mucous lining. travismulthaupt.com 17 Digestion Enzymatic churning turns the ingested food into chyme. The small intestine is very long and is where much of the nutrients are absorbed. It is very specialized for its function. Copyright ©2005 Pearson Education, Inc. Publishing as Pearson Benjamin Cummings. All rights reserved travismulthaupt.com 18 Digestion The first part of the small intestine is called the duodenum. More enzymatic digestion occurs here when enzymes from the liver, pancreas, gall bladder, and glands from the intestine mix. travismulthaupt.com 19 Digestion The jejunum and ilieum are specialized in food absorption. travismulthaupt.com 20 The Small Intestine The surface area is about the size of a tennis court. The villi and microvilli are the adaptations that increase the absorption of monomers, mineral ions, and vitamins. travismulthaupt.com 21 The Small Intestine Each villus is penetrated by blood vessels and a lymph vessel (lacteal). Nutrients are transported to the blood from here. travismulthaupt.com 22 The Small Intestine Both active and passive transport occur within the cells of the small intestine. Active transport allows a higher proportion of nutrients to be absorbed than would passive transport. travismulthaupt.com 23 The Ileum In the ileum, active transport by the villi is responsible for the absorption of: – Simple sugars – Amino acids – Vitamins – Minerals 24 Absorption of Nutrients Substances absorbed via diffusion include: – End products of fat digestion--glycerol, monoglycerides, and fatty acids – Water soluble vitamins – Water 25 Fatty Acid and Glycerol Digestion Glycerol and fatty acids get absorbed by the epithelium and recombined into fats within cells. travismulthaupt.com 26 Fatty Acid and Glycerol Digestion They are mixed with cholesterol, coated with protein and form small globules called chylomicrons (emulsified fat). They are transported to the lacteals, converge into larger vessels of the lymph system and ultimately into the veins and heart. travismulthaupt.com 27 A Lipase Reaction 28 Nutrient Digestion Other nutrients absorbed by the epithelium converge in the hepatic portal vein that leads to the liver. travismulthaupt.com 29 Nutrient Digestion Further processing of the nutrients occurs here. Nutrient processing ensures that the blood contains the proper mix of nutrient molecules for the body. travismulthaupt.com 30 The Large Intestine Its main function is to absorb water that enters the canal as digestive juice. 90% of the water that enters the alimentary canal is absorbed by the small and large intestine. The resulting waste is called feces. travismulthaupt.com 31 The Large Intestine The large intestine is rich in flora--most commonly the harmless form of E. coli. The cecum is where the small and large intestine meet. The rectum is where the large intestine ends. http://medicalpicturesinfo.com/cecum-picture/ travismulthaupt.com 32