Digestive System Topic 6 – Human Anatomy and Physiology Van Roekel – IB Biology 2

Bill What are some enzymes used in the digestive system? Amylase – breaks down starch/carbohydrates Protease – breaks down proteins Lipase – breaks down lipids

6.1.1 Explain why digestion of large food molecules is essential Explain the need for enzymes in digestion. 3 The need for increasing the rate of digestion at body temperature should be emphasized State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase. Any human enzymes can be selected. Details of structure or mechanisms of action are not required Draw and label a diagram of the digestive system. The diagram should show the mouth, esophagus, stomach, small intestine, large intestine, anus, liver, pancreas and gall bladder. The diagram should clearly show the interconnections between these structures Outline the function of the stomach, small intestine and large intestine 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.

Digestion Events Ingestion- eat the food Digestion – series of chemical reactions to break food down into smaller and smaller molecular forms Absorption – small molecules pass through digestive cells and into blood stream/lymphatic vessels Transport – circulatory system delivers molecules to body cells to serve as nutrients

6.1.1 Explain why digestion of large food molecules is essential. Most food molecules are large polymers and insoluble They must first be digested to smaller soluble molecules before they can be absorbed into the blood

Molecule Type Molecular Form Ingested Molecular Form after Digestion Protein Amino acids LipidsTriglycerides Glycerol and fatty acids Carbohydrates Polysaccharides, disaccharides, monosaccharides Monosaccharides Nucleic AcidsDNA, RNANucleotides

Catabolism for Anabolism Molecules are broken down into their smallest components Small components can be used in anabolic reactions to build large molecules, useful to host organism.

Digestion of a Protein Eat egg whites that contain protein albumin Protein contains amino acid serine Inside stomach and small intestine, enzymes break down albumin into monomers, such as serine Serine diffuses through cells, into blood stream, where it is brought to the pancreas Pancreatic cells build serine into hormone insulin.

6.1.2 Explain the need for enzymes in 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

Effect of an Enzyme on Reaction Notice that the normal reaction requires a higher activation energy which would correspond to a high body temperature. This is usually not possible in living organisms. The enzyme-catalysed reaction has a lower activation energy. This lower activation energy would correspond to body temperature but is only possible in the presence of an enzyme

6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase. EXAMPLE FOR Amylase Conditions: Source is the Salivary Gland Substrate is starch (amylose) End product is the disaccharide maltose Optimal pH Action: hydrolysis of 1-4 glycosidic bonds

Example 2 - Pepsin is a protease produced in the stomach Conditions: Source is the stomach Substrate is a polypeptide chains of amino acids End product is amino acids Optimal pH is 2-3 Action is the hydrolysis of peptide bonds within the polypeptide chain (endopeptidase).

Example 3: Pancreatic lipases: Source is the pancreas The substrate is a triglyceride lipid The product is glycerol and fatty acid chains The optimal pH is 7.2 The action of pancreatic lipases also requires the presence of bile salts that emulsify the lipid. This emulsification has two effects: – Increases the surface area of the lipid for the digestion of fat – Exposes the glycerol 'head' structure to the enzyme Action: hydrolysis of ester bonds between the glycerol molecules and the fatty acid chains.

6.1.4 Draw and label a diagram of the digestive system Use your IB Text to get the exact Drawing.

BILL Label the parts of the digestive system on the board to the left. A - Mouth B – Esophagus C – Stomach D – Pancreas E – Large Intestines F – Small Intestines G – Gall Bladder H – Liver I – Rectum

6.1.5 Outline the function of the stomach, small intestine and large intestine. Food brought to stomach by esophagus, using smooth muscle contractions called peristalsis Once in stomach, food is held to mix with gastric juices, consisting of: – Pepsin – protease enzyme – Hydrochloric acid – degrades and breaks down food, creates acidic condition for pepsin – Mucus – lines stomach to prevent damage from HCL Muscular wall churns mixture

Stomach The stomach stores the food from a meal and begins protein digestion (a) Lumen of the stomach which stores the food from a meal (b) Gastric pits from which mucus, enzymes and acid are secreted (c) Mucus secreting cells. Mucus protects the surface of the stomach from auto-digestion (d) Parietal cells that produce HCL which kills microorganism that enter the digestive system (food & tracheal mucus). This also converts inactive pepsinogen to active pepsin (e) Chief cells: produces pepsinogen a protease enzyme

Small Intestine In the small intestine digestion is completed and vast majority of absorption occurs. Uses: – Bile from Liver – Trypsin, lipase, amylase, and bicarbonate from pancreas The products of digestion are absorbed into the blood stream.

Small Intestine (a) Villus which increase the surface area for absorption of the products of digestion (b) Microvilli border of the epithelial cell increases the surface are for absorption. (c) Lacteals are connect to the lymphatic system for the transport of lipids. (d) In the wall of the small intestine are the capillary beds/blood vessels to transport absorbed products to the general circulation, There are also the muscle to maintain peristalsis

Large Intestine (Colon) The colon is responsible for the reabsorption of water from the gut. Contains large number of E. Coli – synthesize Vitamin K and maintain Healthy environment Any undigested food is eliminated as feces (a) The lumen of the colon (b) The mucus producing goblet cells (b) Muscular walls to maintain peristalsis

BILL Complete the DBQ you received at the door.

6.1.7Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion. Villi increases surface area of digestive system Each villus contains a capillary bed and lacteal – Capillary bed is a small vessel for circulatory system – absorbs most nutrients except fatty acids – Lacteal is a small vessel of the lymphatic system – absorbs fatty acids

6.1.7Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion. (a) folds increase SA:VOL ration by X 3 (b) Villi project into the lumen of the gut increasing the surface area by X 10 (c) Microvilli are outward folds of the plasma membrane increasing the surface area another X10

Absorption vs. Assimilation Absorption: digested nutrients are absorbed through digestive cells, into the blood stream or lymphatic system Assimilation: Movement of nutrients into body cell to be used for energy (glucose) or to build larger molecules (amino acids)

Absorption vs. Assimilation - Good Resource