6.1.1 Explain why digestion of large food molecules isessential.6.1.2 Explain the need for enzymes in digestion.(The need for increasing the rate of digestion atbody temperature should be emphasized.)6.1.3 State the source, substrate, products and optimumpH conditions for one amylase, one protease and onelipase.Aim 7: Data logging with pH sensors and lipase, anddata logging with colorimeters and amylase can be used.
6.1.4 Draw and label a diagram of the digestive system.(Show the mouth, esophagus, stomach, small intestine,large intestine, anus, liver, pancreas and gall bladder.The diagram should clearly show the interconnectionsbetween these structures.)6.1.5 Outline the function of the stomach, small intestineand large intestine.6.1.6 Distinguish between absorption and assimilation.6.1.7 Explain how the structure of the villus is related toits role in absorption and transport of the products ofdigestion.
Digestion The mammalian digestive system has 5 basic functions: ingestion –taking food into the digestive system (mouth) peristalsis – the movement of food along the alimentary canal digestion – the breakdown of large, insoluble food molecules into smaller, soluble molecules absorption –the uptake of digested food from the gut into the blood stream egestion – (or defecation) the elimination of undigested food, bacteria and dead cells from the digestive system (large intestine).
Why Digestion? Food is composed of large, insoluble molecules: Carbohydates. Proteins. Lipids. Humans need to break these molecules down into smaller units that: are small enough to be absorbed by the villi in the small intestine. Are in a form that can be used by the cells of the body.
Two Types of Digestion. The alimentary canal is a long muscular tube running from the mouth to the anus. Digestion starts in the mouth. The two types of digestion occurring in the mammalian digestive system are: Physical Digestion (Mechanical Digestion) the action of teeth chewing food, physically breaking the food into smaller pieces Chemical Digestion Involves chemical reactions (Hydrolysis) and the help of catalysts to break food into smaller pieces
Enzymes in Digestion Digestion is a slow process, so special specific catalysts called enzymes are used to speed up digestion at body temperature. The are many different enzymes. Enzymes are: highly specific – one enzyme catalyses one chemical reaction. always proteins sensitive to pH – work best at an certain pH Reusable – not used in the chemical reactions they catalyse Sensitive to heat - broken down (destroyed) by heat - denatured Enzyme names are generally characterised by the ending -ase (however there are exceptions)
Types of Digestive Enzymes Digestive enzymes can be classified into groups depending on their action: Carbohydrases (Amylases) – work on carbohydrates Proteases – work on proteins Lipases – work on lipids
Digestive Enzymes Name of Where it Where it What it What is made Optimum Enzyme is made works works on (products) ph (Source) (Substrate)Amylase Salivary Salivary Mouth Starch Maltose 7 Amylase GlandsProtease Pepsin Wall of Stomach Protein polypeptides 1-2 the stomachLipase Pancreatic Pancreas Small Lipids (fats Fatty Acids and 7 Lipase Intestine and oils) Glycerol
The Digestive System The digestive system can be broken into two parts: The Alimentary canal – a continuous tube running from the mouth to the anus Accessory structures – salivary glands, liver, gall bladder, pancreas. These are outside the alimentary canal and either produce or store secretions which aid in digestion of food. Handout - The Digestive System Handout – Structure and Function
Assimilation Many people confuse the terms: digestion, absorption and assimilation Digestion – the process of breaking down large molecules into smaller ones Absorption – when the small molecules are taken up from the digestive system into the blood stream Assimilation – when these molecules are incorporated into tissues of the body
The Villus The surface of the small intestine is folded to form villi. The surface of the villus is thin, only one layer of epithelial cells. On the surface of epithelial cells are even smaller folds of the plasma membrane called microvilli. This folding greatly increases the surface area for absorption of food molecules. Protein channels in the microvilli membranes allow rapid absorption of food molecules by facilitated diffusion Protein pumps in the microvilli allow absorption of food molecules against a concentration gradient by active transport. Numerous mitochondria in epithelial cells provide ATP for active transport A network of blood capillaries are close to the surface of the villus so the distance for diffusion of food molecules into the bloodstream is small. A lacteal (a branch of the lymphatic system) in the centre of the villus carries away fats after absorption.