The Digestive System You are what you eat!
Try to label the diagram (PENCIL!!)
What is Digestion? Digestion: the breakdown of large macromolecules (proteins, fats, carbohydrates) into smaller molecules so that they can be absorbed by the circulatory system and used by cells Proteins Fats amino acids triglycerides Carbohydrates sugars (glucose, sucrose, lactose etc.)
The Digestive System Consists of Alimentary canal/gastrointestinal tract: 6-9 meters long! Extends from mouth all the way to the anus. Includes the mouth, esophagus, stomach, small intestine, large intestine, rectum and anus Pathway food takes
The Digestive System Consists of Associated Organs: connected to the gastrointestinal system via a series of ducts. Include the salivary glands, liver, gall bladder, pancreas
Four Steps of Digestion 1) Ingestion: the taking IN of nutrients (eating) 2) Digestion: the mechanical and chemical breakdown of food into molecules 3) Absorption: the passing of the broken down molecules into the bloodstream (mostly done in small intestine) 4) Elimination/Egestion: the removal of solid waste (undigested food) from the body
2 Processes of Digestion 1) Mechanical/Physical Digestion: Involves chewing, mashing, chopping, breaking food into smaller pieces and physical movement of food 2) Chemical Digestion: Involves enzymes to break food down into macromolecules and nutrients needed at the cellular level (via hydrolysis)
1) Mouth (ingestion, digestion mech+chem) Mechanical digestion begins: o Chewing breaks food down into smaller particles so that chemical digestion can occur faster Chemical digestion begins: o 3 pairs of salivary glands Parotid glands Sublingual glands Submandibular (Submaxillary) glands
1) Mouth (ingestion, digestion mech+chem) Chemical digestion begins: o o o 3 pairs of salivary glands Parotid glands Sublingual glands Submandibular (Submaxillary) glands Secrete saliva which contains: Mucus keeps food moist, gets rolled into a bolus by the tongue Salivary amylase begins to breakdown starch Maltase converts maltose glucose Secretion is stimulated by the presence of FOOD Tongue is a muscle that pushes food to back of mouth where it is swallowed)
2) Esophagus Swallowing reflex takes over to move the bolus down the esophagus o The esophagus is lined by a film of slippery mucous to aid the bolus in moving down Bolus is moved to the stomach by peristalsis o Rhythmic muscle contractions
3) Stomach (digestion mech+chem) Cardiac sphincter controls movement of bolus into the stomach and prevents stomach acid from re-entering the esophagus Salivary amylase swallowed from the mouth continues to digest starch until the ph gets too low! (amylase does NOT function at low ph levels!)
3) Stomach (digestion mech+chem) Glands in the stomach lining secrete gastric juice containing: i. Hydrochloric acid (HCl) Keeps stomach contents at ph 1-3, aids in digestion Low ph also kills most pathogens Stomach lining is protected by a regenerating coating of mucus Stomach ulcers Heliobacter pylori
3) Stomach (digestion mech+chem) Glands in the stomach lining secrete gastric juice containing: ii. Pepsin (HCl + pepsinogen) Digests proteins (proteins polypeptides) ~2L of acid/gastric secretions produced per day Senses can increase the production/secretion of these gastric juices Carbohydrates (CHO) and fats (LIP) are NOT broken down in the stomach; too acidic, enzymes are inhibited! Partially digested liquid food in acid is now called chyme
4) Small Intestine (digestion chem, absorption) Approx. 7 meters long Pyloric sphincter regulates movement of chyme into the small intestine in small spurts Divided into 3 sections: i. Duodenum ii. Digestion of proteins and carbohydrates finishes Digestion of fats begins Jejunum iii. Ileum
4) Small Intestine (digestion chem, absorption) Associated organs: i. LIVER: ii. Produces bile salts/bile to emulsify (dissolve) fats GALL BLADDER: Stores bile until needed Common bile duct connects the liver and gall bladder to the duodenum to release bile into the small intestine **if the common bile duct becomes blocked, bile salts can accumulate in the skin or blood and produces a yellow colour in a condition called jaundice**
4) Small Intestine (digestion chem, absorption) Associated organs: iii. PANCREAS: Produces pancreatic juice which is released into the duodenum via the pancreatic duct Sodium bicarbonate neutralizes chyme, leaving small intestine basic (ph ~ 9) 28 digestive enzymes, some of which are: a) Trypsin (polypeptides peptides) b) Peptidase (peptides animo acids) c) Lipase (fats fatty acids and glycerol) d) Maltase/Sucrase/Lactase (Disaccharides Monosaccharides) **Some people do NOT produce lactase = Lactose Intolerant)
Pancreas also produces insulin, Type 1 diabetes (immune system destroys insulin-producing cells of pancreas) THEREFORE: Insulin isn t produced and glucose builds up in blood
4) Small Intestine (digestion chem, absorption) Inner walls of intestine are covered small projections called villi and these are covered with even tinier projections called microvilli ( brush border ) surface area
4) Small Intestine (digestion chem, absorption) Each villus has a blood supply of capillaries where the nutrients resulting from digestion are absorbed into the blood by diffusing through the cells of the intestinal lining
5) Large Intestine (absorption; egestion) Ileocaecal valve prevents waste products from re-entering the small intestine Water and minerals are absorbed from undigested food Bacteria helps to further breakdown the undigested food i. Cecum ii. Ascending Colon iii. Transverse Colon iv. Descending Colon v. Sigmoid Colon
6) Rectum and Anus (egestion) Rectum stores waste which is then expelled
Try to label the rest of the Digestive System Diagram before we take it up!