Digestive System

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Functions of the Digestive System Disassemble large organic molecules into smaller component molecules Transfer these to circulatory system for distribution to rest of body Get rid of indigestible material

Steps of digestion 1. Break down food Mechanical Digestion: Grinding large food particles into smaller clumps Reduces the number of molecules per clump Increases total surface area of ingested food Chemical Digestion: Breaking larger molecules into smaller component molecules, by means of a chemical reaction, using enzymes 2. Absorption: Smaller component molecules transported across wall of digestive tract and into blood vessels  3. Elimination : getting rid of undigested food

Organs involved in digestion Two types of organs: Digestive Tract Organs - Food travels through these organs Accessory Organs - Organs that secrete products to help digestion

Digestive Tract Organs Accessory Organs Oral Cavity Pharynx Esophagus Stomach Small Intestine Large Intestine Salivary Glands Liver Gall Bladder Pancreas

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

Why is mechanical processing important? Enzymes must bind to their substrates, but can not access these molecules inside large clumps of food Mechanical processing: increases surface area of food particles Exposes more molecules to enzymes, increases efficiency.

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: Peristalsis is a series of muscle contractions that moves food down the esophagus

Stomach: 1. Stores food and releases small amounts into small intestines 2. Mechanical digestion: churning 3. Chemical digestion: protein digestion begins Stomach wall cells secrete: enzymes hydrochloric acid - Lowers pH to kill pathogens (disease-causing organisms) and activate protein enzymes

Small Intestine: Most chemical digestion occurs lipids, nucleic acids, carbohydrates, and proteins are broken down Absorption of nutrients Helped by secretions of accessory organs

Small Intestine: From Accessory Organs: Liver Bile: produced in liver stored in gall bladder emulsifies lipids so they can be digested Pancreas Pancreatic juices: Enzymes that digest all types of food molecules Chemicals to neutralize pH of chyme

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

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

Pancreas structure increases surface area for absorption: 1. Intestinal wall - folded 2. Villi - Fingerlike projections of intestinal wall; 3. Microvilli - Projections of plasma membrane of intestinal cells

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

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

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

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

Accessory Organs

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

Pancreas 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