Digestion

Learning Objectives Identify and locate the sources of the major digestive enzymes Summarise the breakdown of carbohydrates, proteins and lipids by enzymes Explain the necessary conditions for enzymes to work in the human alimentary canal

Insoluble to soluble

Four Steps of Digestion 1. Ingestion- food entering digestive system 2. Digestion- Break down of food from insoluble lumps to soluble molecules (smallest units) Mechanical- physical break down of food Chemical- break down of food catalysed by enzymes 3. Absorption- movement of digested food from the alimentary canal into the blood stream 4. Egestion- removal of undigested food and waste products.

Enzymes http://www.biotopics.co.uk/other/anenz.html

The Mouth Mouth: begins digestion Teeth (mechanical digestion) Tongue (mechanical digestion) Saliva (chemical digestion) Source: three pairs of salivary glands Composition: mucous, enzyme, water (carbohydrase) salivary amylase

Mouth: begins digestion Teeth (mechanical digestion) Tongue (mechanical digestion) Saliva (chemical digestion) Source: three pairs of salivary glands Composition: mucous, enzyme (carbohydrase) salivary amylase

Carbohydrate Digestion Takes place in the: mouth, duodenum and jejunum Chemically digested by the enzymes: salivary amylase, amylase, moltase, sucrase lactase. Source of enzyme Salivary glands – salivary amylase Pancreas – amylase Jejunum wall – moltase, sucrase and lactase

Types of Carbohydrate Starch a very large molecule digested to maltose and then glucose Lactose a sugar milk digested to galactose and glucose Sucrose a table sugar digested to fructose and glucose

Create a table for Carbohydrases Digestive enzyme Source of enzyme Place of work Role

Do we eat glycogen? If so where from?

Protein digestion Takes place in the stomach, duodenum, and jejunum. Chemically digested by the enzymes pepsin, trypsin chymotrypsin carboxypeptidase peptidase Gastric glands secretes pepsinogen ( converted to pepsin by hydrochloric acid) Pancreas secretes trypsin chymotrypsin carboxypeptidase Jejunum wall secretes peptidase

Endopeptidases Exopeptidases Break bonds between molecules within the peptide chain. This increases the number of end amino acids e.g. trypsin and chymotripsin Exopeptidases Break bonds between end amino acids in the chain. This frees individual amino acids e.g. carboxypeptidase and peptidase

Protein Protein is a large molecule made of many sub units called amino acids Many amino acids joined together make a polypeptide Several amino acids joined together make a peptide

Create a table for peptidases Digestive enzyme Source of enzyme Place of work Role

Fat digestion Takes place in the mouth stomach but mainly duodenum Chemical digestion by lipase Bile Pancreas secrets lipase Liver makes bile which is stored in the gall bladder and released into the duodenum

Fat Fat forms globules and must be reduced in size to make digestion faster Bile disperses the large globules into very small ones by emulsification Lipase is able to work on very small droplets turning them to fatty acids and glycerol

Structure of the Stomach Wall

Stomach Function Mechanical and chemical digestion Functions: food storage, digestion, regulation of delivery Gastric juice: specific cells secrete Parietal cells- Hydrochloric acid: produces a pH of about 1.0, kills bacteria. Chief cells- Pepsinogen is converted to active enzyme pepsin by the acid to begin protein digestion Goblet cells- Mucus: protects stomach lining from acid

Gastric pits Goblet cell secret mucus Oxyntic cells secret hydrochloric acid Chief cells secret pepsinogen a precursor of pepsin

Stomach Contraction mechanical digestion Stomach contractions: blend food and propel forward Direction: from cardiac sphincter to pyloric sphincter Chyme: result of mixing, affects hormone secretions regulating peristalsis and emptying of stomach

Gastric ulcer Helicobacter pylori is one of the most common causes of peptic ulcer. Ulcers can also be caused or worsened by drugs such as aspirin and ibuprofen

Pancreas and gall bladder Pancrease secretes: the enzymes trypsin, lipase and amylase Bicarbonate ions to increase the pH in the duodenum Gall Bladder releases: Bile to emulsify fat Bicarbonate ions to increase the pH of the duodenum Why does the pH need changing?

Duodenum This is where: The acidic chyme from the stomach is converted to an alkaline solution so that pancreatic enzymes can work polypeptides are digested to peptides by trypsin Starch is digested to maltose by amylase Fat is emulsified by bile and digested by lipase to fatty acids and glycerol

Jejunum Functions Secrets the enzymes: Structure Peptidase to digest peptides to amino acids Maltase to digest maltose to glucose Sucrase to digest sucrose to glucose and fructose Lactase to digest lactose to glucose and galactose Structure Mucosa adaptations: villi containing blood and lymphatic capillaries

Optimum temperature What is the optimum temperature for enzymes in the digestive system? 40 OC Explain why it is 40 OC and not 37 OC

Ileum Main Function: To absorb the soluble molecules, vitamins, minerals and water (8.5 litres) from the lumen of the ileum into the blood

Colon Absorption of: Water (0.4 litres) Vitamins Salts Soluble fibre is digested by bacteria which results in gas e.g. nitrogen, carbon dioxide, methane, hydrogen sulphide and hydrogen

Colon content Stools containing fibre are larger than those without Large stools will distend the gut Distension of gut stimulates the peristalsis Peristalsis is about twice an hour in the colon

Try the activity Enzymes linked to food types Food type – enzyme – product – place

Have a go at the massive gap fill

Learning Objectives List the 4 main functions of the digestive system Define an enzyme Outline the difference between chemical and mechanical digestion Describe the role of peristalsis in the movement of the contents of the gastrointestinal tract Describe the role of the stomach in mechanical and chemical digestion including the composition of gastric juice Describe the role of bile and pancreatic juice in digestion in the duodenum Describe the role of the jejunum Described the role of the colon