DIGESTION 6.1

The Process Transport The circulatory system delivers the small molecules to cells around your body. Absorption Small molecules are absorbed through the cells in the walls of digestive tissue into blood and lymph (circulatory system). Digestion The series of chemical reactions to break down the food into smaller molecules. Ingestion Eating!

6.1 The problem to solve… Most food molecules (macromolecules) are too large to pass through your cell membrane

Macromolecules Monomers = the smallest building blocks of the molecule Polymer = a large molecule made up of many monomers

Macromolecules Macromolecule: Too big for absorption Monomer: Good size for absorption Carbohydrates  polysaccharides, disaccharides, monosaccharides monosaccharides Lipids  triglycerides glycerol and fatty acids Proteinsamino acids Nucleic Acids  DNA, RNA nucleotides

6.1 Digestion is like… Playing LEGOS Put together (protein in steak) Take Apart (into amino acids) Put back together (into your OWN protein) Take Apart

Enzymes Catalysts: A substance that speeds up the rate of a chemical reaction. How? By lowering the activation energy Enzymes: Proteins that act as biological catalysts.

6.2 Essential Enzymes Remember, enzymes don’t MAKE the reaction happen, they just hold the macromolecule in its active site to help the reaction move more quickly.

Enzymes 1. Substrates bind to enzyme 2. Substrates are converted into products 3. Products are released Enzyme Active Site Enzyme -substrate complex 2

6.1.3 Enzymes SourceSubstrateProductsOptimum pH Amylase ex. Salivary amylase Salivary glands Starch (amylose) Maltose, then glucose 7 (neutral) Protease ex. Pepsin Stomach cells Proteins (polypeptides) Amino acids3 (acidic) Lipase ex. Pancreatic lipase Pancreas cells LipidsGlycerol & fatty acids 7 (neutral)

6.1.4 Digestive Tract Food has two options: 1. Get digested and used by the body 2. Be eliminated as feces

6.1.4 Diagram

Science Museum Proposal You have been asked to create a new exhibit for the Seoul Science Museum. The exhibit should be a walk-through giant digestive tract with interactive features along the way. Your exhibit will be permanently built in the science museum and has a generous budget from an anonymous donor.

6.1.5 Overview of the Functions of Stomach, SI, LI Function Stomach Food is churned with the gastric juices for a period of time. Small Intestine 1. In the duodenum, the food mixes with new secretions from the liver, gall bladder, and pancreas. 2. Digested nutrients (monomers) pass through the villi into the circulatory system. Large Intestine 1. Reabsorb the water from the food, concentrating the undigested (& unabsorbed) food into feces. 2. Home to mutualistic bacteria (eg. E. coli )that keep us healthy and produce Vitamin K.

Stomach Food arrives via esophagus. The stomach keeps its lower sphincter closed to keep the food in for a period of time. The muscles in the wall of the stomach mix the food and gastric juices. Gastric juices: Pepsin – protease enzyme active in acidic pH (3) HCl – Hydrochloric acid creates the acidic pH to break down food & activate pepsin. Mucus – lines the stomach to prevent damage from HCl.

Small Intestines 1. Duodenum: Food mixes with secretions from: Liver  secretes Bile to emulsify (surround and break down) fat Gall Bladder  secretes Bile Pancreas  secretes trypsin (a protease), lipase, amylase and bicarbonate

6.1.7 Villus: The Location of Absorption What we want: LARGE surface area in a small volume for absorption How do we get it? Long Small Intestines Thousands of villi throughout the small intestines.

Villus: Designed for absorption & transport Digested nutrients pass through the 1-cell thick epithelium tissue to get to the circulatory system. Most molecules go to the capillary bed and then are transported through the blood. Fatty acids are absorbed into the lacteal and then are transported through the lymph. Digested Nutrients IN Blood In Blood + Nutrients OUT

Large Intestines 1. Re-absorption of water We want to leave it in the digestive tract to help things flow, up until this point. 2. Home to bacteria Including E. coli (this is what makes feces “dirty”) They get nutrients, water, warmth, safety We get vitamin K, benefits of a healthy gut.

6.1.6 Absorption vs. Assimilation Absorption refers to taking molecules in their monomer form, and absorbing them into the circulatory system (usually through the walls of the villi in the small intestine). Alcohol is actually absorbed into the circulatory system through the stomach. This is why its effects are so “fast acting.” Assimilation is when the absorbed monomer is brought into a body cell and used to build larger molecules.

Food not absorbed… Is eliminated as feces.