IB Biology 6 1 Digestive System Understandings Statement

IB Biology 6. 1 Digestive System

Understandings Statement 6. 1 U. 1 Guidance The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut. 6. 1 U. 2 The pancreas secretes enzymes into the lumen of the small intestine. 6. 1 U. 3 Enzymes digest most macromolecules in food into monomers in the small intestine. 6. 1 U. 4 Villi increase the surface area of epithelium over which absorption is carried out. 6. 1 U. 5 Villi absorb monomers formed by digestion as well as mineral ions and vitamins. 6. 1 U. 6 Different methods of membrane transport are required to absorb different nutrients. Students should know that amylase, lipase and an endopeptidase are secreted by the pancreas. The name trypsin and the method used to activate it are not required. Students should know that starch, glycogen, lipids and nucleic acids are digested into monomers and that cellulose remains undigested.

Applications and Skills Statement 6. 1 A. 1 Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver. 6. 1 A. 2 Use of dialysis tubing to model absorption of digested food in the intestine. 6. 1 S. 1 Production of an annotated diagram of the digestive system. 6. 1 S. 2 Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph. Guidance Tissue layers should include longitudinal and circular muscles, mucosa and epithelium.

6. 1 S. 1 Production of an annotated diagram of the digestive system. Use the animation and video to learn about the digestive system and how to draw it. https: //youtu. be/Nm-p. T 7 fk 6 gs http: //highered. mheducation. com/sites/0072495855/stu dent_view 0/chapter 26/animation__organs_of_digestion. html

6. 1 S. 1 Production of an annotated diagram of the digestive system. Plus add in the accessory organs: the gall bladder, liver and pancreas.

6. 1 S. 1 Production of an annotated diagram of the digestive system.

6. 1 S. 1 Production of an annotated diagram of the digestive system. Now add the annotations to show what happens in digestion.

6. 1 U. 3 Enzymes digest most macromolecules in food into monomers in the small intestine. Digesting large molecule • Most food molecules are large polymers and insoluble. These molecules are broken down so they can be absorbed and assimilated by the body. • They must first be digested to smaller soluble molecules before they can be absorbed into the blood this occurs in 3 ways, mechanical (chewing), chemical (enzymes) and acids (stomach glands).

6. 1 U. 3 Enzymes digest most macromolecules in food into monomers in the small intestine. Enzymes and digestion • Enzymes are biological catalysts that increase the rate of reaction • Digestive enzymes are secreted into the lumen of the gut • Digestive enzyme increase the rate of reaction of the hydrolysis of insoluble food molecules to soluble end products • Digestive enzymes increase the rate of reaction at body temperature

6. 1 U. 3 Enzymes digest most macromolecules in food into monomers in the small intestine.

6. 1 U. 3 Enzymes digest most macromolecules in food into monomers in the small intestine. Human Digestive Enzymes Amylases break down carbohydrates Example: salivary amylase Substrate: starch Product: maltose Source: mouth (salivary glands) Optimum p. H: 7 -7. 8 diagram from: http: //www. teachervision. fen. com/digestive-system/printable/57730. html

6. 1 U. 3 Enzymes digest most macromolecules in food into monomers in the small intestine. Human Digestive Enzymes Proteases break down polypeptides Example: pepsin Substrate: polypeptides Product: amino acids Source: stomach Optimum p. H: 2 diagram from: http: //www. teachervision. fen. com/digestive-system/printable/57730. html

6. 1 U. 3 Enzymes digest most macromolecules in food into monomers in the small intestine. Human Digestive Enzymes The Pancreases produces lipases break down fats and lipids Example: pancreatic lipase Substrate: triglycerides Product: fatty acids & glycerol Source: pancreas, delivered into small intestine Optimum p. H: 7. 2 - 7. 5

The human digestive system

• Digestion begins in the oral cavity (mouth). • Saliva begins the chemical digestion of food. Saliva contains the protein mucin to lubricate the food for swallowing. • Amylase breaks down starch and glycogen. • Food is shaped into a ball (bolus) and is then swallowed. *

6. 1 U. 1 The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut • Peristalsis: is the shortening of muscle by contraction. These muscles provide the force to move food the esophagus to the stomach while mixing food with enzymens. *

• Pharynx (throat): is where the esophagus and the windpipe meet. When food is swallowed, the epiglottis closes the passage to the windpipe. • Esophagus: Conducts food from the pharynx to the stomach. The mouth, pharynx and esophagus are responsible for carbohydrate digestion. • Stomach: produces gastric juice which has a p. H of 2 aiding in digestion. In addition it contains pepsin that breaks down proteins. *After chemical digestion in the stomach, the food has been turned into a nutrient broth called chyme. It takes 2 to 6 hours for the stomach to empty.

6. 1 U. 4 Villi increase the surface area of epithelium over which absorption is carried out. Structure: Small Intestine digestion is completed in the SI. The products of digestion are absorbed into the blood stream. *

Structure: Small Intestine (A)Blood Capillaries move digested food molecules into the blood from the lumen of the ileum. B) Lacteals are connect to the lymphatic system for the transport of lipids. (C) Mitochondria Providing ATP for active transport of the products of digestion (D) Microvilli border of the epithelial cell increases the surface are for absorption.

6. 1 S. 2 Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph The small intestine contains four distinct tissue layers from the lumen 1. Mucosa – inner lining, includes villi 2. Submucosa – connective tissue (between the mucosa and muscle) Submucosa layer Muscular layer Serosa layer 3. Muscular layer – inner circular and outer longitudinal muscle perform peristalsis 4. Serosa – protective outer layer

6. 1 U. 2 The pancreas secretes enzymes into the lumen of the small intestine. • Pancreas: produces the enzymes amylase to digest carbohydrates, lipases to digest lipids, and proteases to digest polypeptides. In addition it produces an alkaline solution made of bicarbonate. The bicarbonate acts as a buffer to help neutralize the acidic chyme.

6. 1 A. 1 Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver. Liver: produces bile which contains no digestive enzymes, but helps in the absorption of fats. Emulsification

6. 1 A. 1 Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver. Liver: In addition, working with the pancreas the liver removes excess monosaccharides from the blood after they have been broken down from disaccharides and polysaccharides in the small intestines. Excess sugars are converted back into a polysaccharide (Glycogen) Two Steps 1. Glycogenesis Excess glucose in the blood is convert into glycogen. 2. Glycogenolysis conversion of glycogen into glucose and then released into the blood

6. 1 A. 1 Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver. The digested glucose is absorbed and then transported to various body tissues 1. Glucose is co-transported* with sodium ions into the epithelial cells (of the villus). 2. Glucose moves by facilitated diffusion into the lumen of the villus. 3. Glucose then diffuses a short distance into the adjacent capillaries where it dissolves into the blood plasma. 4. Blood in the capillaries moves to to venules then to the hepatic portal vein which transports the glucose to the liver. 5. The liver absorbs excess glucose which it converts to glycogen for storage.

6. 1 U. 6 Different methods of membrane transport are required to absorb different nutrients. How is membrane transport involved in absorption of nutrients from the small intestine? Method of transport Nutrients Outline Simple diffusion Lipids are non-polar and therefore can pass freely through hydrophobic core of the plasma membrane into the epithelial cells (down the concentration gradient ) Facilitated Diffusion Fructose, vitamins Water-soluble (hydrophilic) molecules use channel proteins to pass phospholipid bilayer and enter the epithelial cells (down the concentration gradient) Active Transport Glucose, amino Protein pumps use ATP to move molecules acids and mineral against the concentration gradient into the ions epithelial cells Endocytosis (Pinocytosis) Antibodies from breast milk The plasma membrane folds inward to form vesicles to absorb larger molecules without digesting them

Large Intestine (LI): * • Is also called the colon. • The primary job of the LI is to reabsorb water. • Together, the SI and the LI reabsorb ~ 90% of the water that was used for digestion. • Wastes become more solid as they move through the LI through peristalsis and results in feces.

6. 1 U. 5 Villi absorb monomers formed by digestion as well as mineral ions and vitamins. Absorption and assimilation: insoluble food molecules are digested to soluble products in the lumen of the gut. Absorption: 1. The soluble products are first taken up by various mechanisms into the epithelial cells that line the gut. 2. These epithelial cells then load the various absorbed molecules into the blood stream. Assimilation: 1. The soluble products of digestion are then transported to the various tissues by the circulatory system. 2. The cells of the tissues then absorb the molecules for use within this tissues

Absorption and assimilation

6. 1 A. 2 Use of dialysis tubing to model absorption of digested food in the intestine. Dialysis tubing can be used to model absorption The tubing is semi-permeable and contains pores typically ranging 1 – 10 nm. in diameter. Predict what will happen to the glucose and starch after 15 minutes

Bibliography / Acknowledgments