Digestive System

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Cells require nutrients obtained from food and oxygen The Digestive System will: Disassemble large organic molecules into smaller component molecules Transfer these to circulatory system for distribution to rest of body Get rid of indigestible material Functions of the Digestive System

Mechanical Digestion: Grinding large food particles into smaller clumps (reducing # molecules per clump) Chemical Digestion: Breaking larger molecules into smaller component molecules, by means of a chemical reaction, using enzymes Absorption: Smaller component molecules transported across wall of digestive tract and into blood vessels Elimination : getting rid of undigested food Different steps of digestion

Organs involved in digestion Two types of organs: Digestive Tract Organs Accessory Organs

Stomach Oral cavity Small intestine Esophagus Large intestine Pancreas Liver Gall Bladder Salivary glands Digestive tract (Muscular tube w/ specialized segments) Accessory glands (secrete substances that aid with digestion) Pharynx Components of the digestive system

Oral Cavity: Mechanical processing- chewing Chemical Digestion- saliva secretion: carbohydrate digestion Epiglottis: “Lid” that closes over opening to trachea - Prevents food entering airway

Enzyme must bind to substrate, so enzyme must have access to these larger molecules. Mechanical processing: increases surface area of food particles Exposes more molecules to enzymes, increases efficiency. Why is mechanical processing important?

Swallowing:

Pharynx and Esophagus: No mechanical processing, digestion, or absorption, Merely conducts food to stomach. If you stand on your head, will the food still move to your stomach? YES: food moves down by muscle contractions of the esophagus (= peristalsis)

Stomach: Storage for food Mechanical processing: churning Chemical digestion: protein digestion - enzymes secreted from stomach wall hydrochloric acid also secreted - Lowers pH to kill pathogens (disease-causing organisms) and activate protein enzymes

Small Intestine: Function: Most chemical digestion occurs in the small intestines (lipids, nucleic acids, carbohydrates, proteins) Absorption of nutrients

Small Intestine: From Accessory Organs: Bile produced in liver stored in gall bladder Pancreatic juices (enzymes)

Digestion Mechanical - Lipids not water soluble, but enzymes are - Bile will break up large groups of lipid molecules into smaller droplets so enzymes can act on them (Emulsification) Bile enters the small intestine through the bile duct Chemical - Carbohydrate, protein, & lipid digestion enzymes secreted from pancreas enzymes located in the intestinal wall Small Intestine:

Absorption - Component molecules diffuse across intestinal wall into circulatory system Villi (fingerlike projections)

Increased surface area for absorption: Intestinal wall - folded Villi - Fingerlike projections of intestinal wall; Microvilli - Projections of plasma membrane of intestinal cells

Amino acids, glucose, other water soluble nutrients absorbed into the capillaries

What are lacteals? Inside the villi are vessels of the lymphatic system that absorb the fatty acids and glycerol.

Large Intestine (colon): - Absorbs water; - Contains lots of bacteria (mostly E. coli), bacteria digest some remaining food, bacteria produce vitamins; - Responsible for elimination of undigested food = feces)

Blood leaving intestines is transported to the liver via the hepatic portal vein for processing [molecules modified, toxins removed]

The liver Removes unwanted or harmful chemicals (detoxification) including chemicals produced in the body, unwanted chemicals taken into the body (e.g. carcinogens), and medications. Hepatocytes - Liver cells - the liver's main functional units.

Pancreas

Main enzyme producing organ of digestive system Pancreatic duct enters the small intestine to deliver fluid (pancreatic juice) through a small hole in the wall of the second part of the duodenum Pancreatic juice contains enzymes capable of digesting all food types - protein, fat and carbohydrates