Digestion AP Biology Unit 6
General Steps • Ingestion = food is taken in (eating ) • Digestion = Food is broken down into smaller pieces /molecules • Absorption = Nutrient molecules are absorbed into body cells • Elimination = undigested material exits the body
Types of Digestion • There are two kinds of digestion – mechanical and chemical • Mechanical = Food is broken down into smaller pieces (chemical structure not changed) • Chemical = Food is broken down into smaller molecules (chemical structure changed)
Intracellular Digestion • In the animal kingdom, only sponges (Phyla Porifera) do this exclusively. • Steps: • Cells engulf food via phagocytosis or pinocytosis, forming food vacuole. • Lysosomes fuse with food vacuoles; hydrolytic enzymes break down food.
Extracellular Digestion • All animals (except sponges) perform this mode of digestion • Digestion begins in a compartment continuous with the outside of the animal’s body (gut). • What is the advantage of extracellular digestion? • animal can take in a lot of food at once and slowly digest it
Extracellular Digestion • Enzymes are secreted to break food into smaller molecules. • After the food has been broken down, many animals continue digestion intracellularly. • Animals that perform extracellular digestion can have a variety of different digestive systems.
Gastrovascular Cavity • Gastrovascular cavity = digestive sac with a single opening • Animals that have a gastrovascular cavity = Hydra • Phyla Cnidarian (includes jellyfish, anemones, corals)
Digestion in Gastrovascular Cavities • Tentacles sting prey and stuff it into opening • Digestive enzymes are secreted to allow for extracellular digestion • Nutritive muscular cells then engulf food particles and complete digestion intracellularly • Undigestible material leaves through mouth (no anus)
Complete Digestive Tracts • Complete digestive tract = digestive tube running throughout body • Organisms with a complete digestive tract have both a mouth and an anus
Question… • Why would having a separate entry and exit point be beneficial? • digestion can be broken down into steps • there can be specialization of digestive tissues for these steps
Human Digestion • Where do the four steps in food processing occur?
Human Digestion • Ingestion = mouth • Digestion = mouth, Stomach, Small Intestines • Absorption = Small Intestines, Large Intestines • Elimination = End of large intestines
Oral Cavity, Pharynx, Esophagus • Participate in ingestion and digestion • Mechanical Digestion • By teeth and tongue (chewing) • Chemical Digestion • Salivary amylase begins digestion of carbohydrates (starch glucose)
Oral Cavity, Pharynx, Esophagus • Epiglottis = flap that covers the trachea during swallowing, so food travels down “right pipe” (the esophagus) • Peristalsis (muscle contractions) will involuntarily continue movement of the mass of food (bolus)
Stomach • Important in storage & digestion • What advantage do folds in the stomach tissue provide? • Allows the stomach to expand to hold more food • Tissue is also very elastic so that it can stretch
Stomach • Gastric juice continues digestion: • HCl converts pepsinogen into pepsin (active enzyme) • Pepsin hydrolyzes (breaks down) protein. • Gastric juice is churned with bolus to break down food and kill bacteria
Stomach: Pepsin • What kinds of bonds are broken by pepsin? • Peptide bonds • What kind of reaction is this? • Hydrolysis
Protection of the stomach • Stomach protects itself from self-digestion by • keeping pepsinogen stored away from HCl until pepsin is needed • lining stomach with mucus
Small Intestine • Participates in digestion and absorption • Peristalsis allows for movement of chyme and digestive juices down the small intestine.
Digestion in the Small Intestine • Digestion is usually completed in theduodenum (first section) with the help of digestive juices
Digestive Juices • Digestive juices come from 4 sources, entering the duodenum: • Pancreas • produces digestive enzymes • produce basic bicarbonate solution (buffer against stomach acid)
Digestive Juices also come from • Lining of duodenum • produces digestive enzymes • Liver • Produces bile • Gallbladder • Stores bile
Bile • contains bile salts • breaks up fat droplets into very small pieces (emulsification) • Increases surface area for lipase to digest into micelles • micelles are then absorbed
Question… • Does bile perform mechanical or chemical digestion? • Mechanical– breaking it up into smaller pieces
Protection of Small Intestine • Small intestine and adjacent organs are protected from digestive enzymes by producing inactive forms that are only activated in the duodenum.
Absorption of Nutrients • Occurs in the jejunum (mid-small intestine) and ileum (end-small intestine) • Nutrients are absorbed into the blood vessels and lymph vessel (lacteals). • Water is also absorbed here.
Absorption of Nutrients • Villi and microvilli • Projections of the lining of the small intestine • Benefit? • Increases the surface area in these regions increases amount of nutrient absorption
Large Intestine • responsible for water recovery from digested material • Feces = Waste of digestive tract • Bacteria live here (including E. coli) that live on feces and produce vitamins B and K () and stinky gases • End of colon = rectum • End of rectum = anus
Food in the stomach Stomach cells release GASTRIN • Increased secretion of: • HCl • Pepsin • Increased movement in stomach Faster delivery of chyme to small intestine small intestine cells release CHOLECYSTOKININ (CCK) small intestine cells release SECRETIN pancreas releases sodium bicarbonate to neutralize acid pancreas releases digestive enzymes gallbladder releases bile Digestion of food Control of Digestive System Lower pH inhibits gastrin release CCK slows movements of stomach down
Nervous System Control of Digestion • The Autonomic Nervous System controls the internal environment by controlling muscles in various organ systems • Sympathetic division (“fight or flight”): inhibits digestion, promotes release of glucose from liver • Parasympathetic division (“rest and digest”): stimulates digestion • Enteric division: neurons that control the secretions of the digestive organs.
Diabetes • Blood sugar levels are controlled by hormones
Diabetes (continued) • Diabetes mellitus is a condition in which insulin is not produced or cells are insulin resistant • Type 1 – • can’t produce insulin • Type 2 • cells no longer respond to insulin • End result: glucose cannot be used by cells blood sugar is too high (homeostasis not maintained)