The Digestive System Part II Structures, Functions & Enzymes

The Digestive System The digestive system is responsible for the breakdown of large, complex organic materials into smaller components that are used by the tissues of the body

The 4 Stages of Digestion The 4 stages of digestion 1.Ingestion – taking nutrients into the body 2.Digestion – the breakdown of complex compounds into smaller components by enzymes 3.Absorption – the transport of digested nutrients to the tissues of the body 4.Egestion – the removal of food wastes from the body

The Mouth Digestion begins in the mouth. Teeth helps by mechanically breaking down food into smaller pieces. Salivary glands produce saliva which contains salivary amylase – an enzyme that breaks starch down into simpler sugars.

The Epiglottis To swallow food, the soft palate raises up to block off the passageway to the nasal passageway and The epiglottis flips down to block the entrance to the trachea.

The Esophagus Once food leaves the mouth it is called a bolus. It travels from the mouth to the stomach along the food tube known as the esophagus. Peristalsis are wave-like contractions that push the bolus along the entire digestive tract.

The Stomach The stomach is the site of food storage and first protein digestion The rugae (ridges) in the stomach allow it to expand from about 50 ml to 1.5 L. The stomach has numerous areas: the cardiac area, the fundus, the body and the pyloric area.

The Stomach The cells in the lining of the stomach secrete gastric juices. Gastric fluids include: 1.Mucus 2.Hydrochloric acid 3.Pepsinogen

The Stomach Mucus – protects the lining of the stomach from the gastric juices; Hydrochloric acid – kills harmful bacteria and other harmful substances in food. It also converts pepsinogen into its active form – pepsin, a protein digesting enzyme. Pepsinogen – converts to pepsin to digest protein.

The Stomach Pepsin - breaks down long amino acid chains in proteins into shorter chains called polypeptides. Activation Pepsiogen + HCl Active Enzyme Pepsin Protein Breakdown Protein Breakdown into Polypeptides

Sphincters Constrictor muscles the occur along the digestive tract. Sphincters control the movement of the food and waste from one area of the digestive system to the next.

The Small Intestine & Pancreas Most digestion and nutrient absorption takes place in the small intestine. It can be divided into 3 zones: 1.Duodenum 2.Jejunum 3.ileum

The Small Intestine & Pancreas The chyme that enters the duodenum from the stomach is very acidic. It must be neutralized. When acids enter the small intestine, a chemical called prosecretin is converted into the hormone secretin. Secretin travels through the bloodstream to the pancreas causing it to release bicarbonate ions.

The Small Intestine & Pancreas Now that the chyme is alkaline, the pepsin becomes inactive. The pancreas also secretes other enzymes such as trypsinogen. Once it reaches the duodenum the enzyme enterokinase converts the inactive trypsinogen into the active form – trypsin. Trypsin further breaks down proteins into shorter chain peptides..

The Small Intestine & Pancreas The pancreas also secretes: 1.erepsins which complete the digestion of proteins from short-chain peptides into individual amino acids. 2.Pancreatic amylase – further the digestion of carbohydrates into disaccharides. These are finally broken into monosaccharides by the enzyme disaccharidases.

The Small Intestine & Pancreas The pancreas also secretes: 3.Lipases from the pancreas break down lipids. Pancreatic lipase breaks fats into fatty acids and glycerol. Phospholipase breaks down phosphlipids.

The Liver and Gall Bladder The liver produces bile salts that speed up the digestion of fats. When fats enter the duodenum, a hormone cholecystokinin (CCK) is released and carried to the gall bladder. This triggers the gall bladder to relase the bile. Bile emulsify and breaks down large fat globules.

The Large Intestine Reabsorbs water Absorbs some vitamins Contains the bacteria, E.Coli that uses waste materials to make vitamins B and K. Fibre helps to hold some water in the waste and adds “bulk” making it easier to remove from the body.