Digestion Topic 6.1

Assessment Statements Explain why digestion of large food molecules is essential Explain why digestion of large food molecules is essential Explain the need for enzymes in digestion Explain the need for enzymes in digestion State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase Draw and label a diagram of the digestive system Draw and label a diagram of the digestive system Outline the function of the stomach, small intestine and large intestine Outline the function of the stomach, small intestine and large intestine Distinguish between absorption and assimilation Distinguish between absorption and assimilation Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.

Series of events 1. Ingestion 2. Digestion 3. Absorption 4. Transport

Why digestion of large molecules is essential Large molecules are too big to pass across any cell membrane Large molecules are too big to pass across any cell membrane Any food we eat must be chemically digested to a suitable size Any food we eat must be chemically digested to a suitable size Molecule typeMolecular form ingested Molecular form after digestion Protein Amino acids LipidsTriglyceridesGlycerol and fatty acids CarbohydratesPolysaccharidesmonosaccharides Nucleic acidsDNA, RNAnucelotides

Digestion allows you to turn molecules into ‘your own’ Example: Example: You eat an egg You eat an egg The egg white (albumin) contains an amino acid called serine The egg white (albumin) contains an amino acid called serine Your stomach/small intestine digests the albumin Your stomach/small intestine digests the albumin Serine diffuses through the cells of the small intestine and then into a capillary Serine diffuses through the cells of the small intestine and then into a capillary Serine is enters a pancreas cell Serine is enters a pancreas cell The cell uses the genetic code of your DNA to build serine into insulin The cell uses the genetic code of your DNA to build serine into insulin Benefits of digestion: Serine is able to leave the albumin and enter the bloodstream Serine helps to synthesize your own protein under the control of your DNA

Need for enzymes To lower activation energy Enzymes are protein molecules which act as catalysts for reactions They lower the activation energy of the reactions that they catalyze Reactions occurring with an enzyme can occur with a lower input of energy than the same reaction without the aid of an enzyme To catalyze hydrolysis reactions Converts large macromolecules to smaller molecules that can be absorbed and then used Amylase puts stress on bonds of glucose held together in a starch molecule Surrounding thermal energy provides molecular motion to break the bonds

Examples of digestive enzymes Salivary amylase Pepsin (a protease) Pancreatic lipase SourceSalivary glandsStomach cellsPancreas cells SubstrateAmylose (starch)ProteinsLipids ProductsMaltose/glucoseAmino acidsGlycerol/fatty acids Optimum pHNeutral (pH 7)Acidic (pH 3)Neutral (pH 7)

Digestive system Any foods you ingest must either be digested and absorbed for use by the body or remain undigested and be eliminated as solid waste (faeces)

Stomach Food brought to stomach by oesophagus Food brought to stomach by oesophagus When you swallow, the food is forced down to your stomach by peristalsis When you swallow, the food is forced down to your stomach by peristalsis Once in the stomach, the food is held for a period of time in order to mix it with a variety of secretions collectively known as gastric juices Once in the stomach, the food is held for a period of time in order to mix it with a variety of secretions collectively known as gastric juices Pepsin – a protease enzyme most active in acidic pH Hydrochloric acid – helps degrade and break down foods and creates the acidic pH necessary for pepsin to be active Mucus – lines the inside of the stomach wall to prevent stomach damage from the hydrochloric acid

The muscular wall of the stomach creates a churning motion in order to mix the food with the gastric juice The muscular wall of the stomach creates a churning motion in order to mix the food with the gastric juice After a period of time, a valve at the lower end of the stomach opens and the food enters the small intestine After a period of time, a valve at the lower end of the stomach opens and the food enters the small intestine

What are you eating in a day? How to read food labels How to read food labels How to read food labels How to read food labels Record the nutrition facts for all of the food that you consume in one meal Record the nutrition facts for all of the food that you consume in one meal

Small intestine 1 st portion is called the duodenum 1 st portion is called the duodenum Secretions are emptied here in order to continue the digestive process: Secretions are emptied here in order to continue the digestive process: Bile from liver and gall bladder Bile from liver and gall bladder Trypsin (a protease), lipase, amylase and bicarbonate from the pancreas Trypsin (a protease), lipase, amylase and bicarbonate from the pancreas

Small intestine villi Molecules are produced that are small enough to be absorbed Molecules are produced that are small enough to be absorbed Inner wall of small intestine is made up of thousands of finger-like extensions called villi which functions to increase surface area for absorption Inner wall of small intestine is made up of thousands of finger-like extensions called villi which functions to increase surface area for absorption Each villus contains a capillary bed and a lacteal (a small vessel of lymphatic system) Each villus contains a capillary bed and a lacteal (a small vessel of lymphatic system)

Absorption Molecules taken into capillary bed and lacteal Taken to a wide variety of body cells Used for energy Assimilation Molecules taken into capillary bed and lacteal Taken to a wide variety of body cells Used for building larger molecules

Large intestine Vast majority of food is absorbed in SI What remains is undigested Much of the water we drink or that is found within food is still present Escherichia coli and other naturally occurring bacteria are mutualists We provide nutrients, water, and a warm environment They synthesize vitamin K and maintain and overall healthy environment Any undigested food is eliminated from the body as solid waste or faeces

Vitamin K Vitamin K is essential in humans and most animals as we cannot synthesize the compound ourselves vitamin K is used by the liver to synthesise prothrombin, which in turn is processed to form the enzyme thrombin; a key enzyme involved in the blood clotting process there is increasing evidence that vitamin K has additional roles in maintaining in bone health There are two forms of vitamin K vitamin K1 – comes from our diet and is found in soybean oil and dark green veggies vitamin K2 - which can come from the bacteria in the gut and indeed E. coli can synthesise menaquinone because it uses it during respiration. As E. coli lives and dies in the gut, the dead cells release vitamin K2, which can then, theoretically, be absorbed and utilised by the body.