The Digestive System DIGESTION The breakdown of large

The Digestive System

DIGESTION • The breakdown of large organic molecules into small pieces that can be used by the cells of the body

4 Stages of Digestion 1. Ingestion: taking in nutrients (food/drink) 2. Digestion: break down of complex organic molecules (e. x. , macromolecules) into smaller components 3. Absorption: transport of digested nutrients into body tissues (via the blood stream) 4. Egestion: removal of waste food materials from the body

LOCATIONS 1. 2. 3. 4. Ingestion (mouth) Digestion (mouth, stomach, small intestine) Absorption (small intestine, large intestine) Egestion (colon, rectum, anus)

Food is broken down in 2 ways: • Mechanical Digestion: – The physical breaking down of food • Teeth • Peristalsis in stomach • Chemical Digestion: – The breaking of chemical bonds in large molecules to make smaller molecules that can be used by the body • Done by enzymes

Enzymes • Specialized proteins • Substrate-specific with an active site • Changes shape to either break down compound (digestion) or add something to it

Common Digestive Enzymes Enzyme Which Organ Secretes It? Reactants (what it digests) Products (what is left) Amylase Salivary Glands Pancreas Carbohydrates Maltose Pepsin Stomach Protein Peptides Trypsin Pancreas Large Peptides Small Peptides Peptidase Small Intestine Small Peptides Amino Acids Lipase Pancreas Fatty Acids + Glycerol Maltase Small Intestine Maltose Glucose

What is Digested? MACROMOLECULES ARE DIGESTED: 1. Carbohydrates maltose glucose 2. Fats fatty acids and glycerol 3. Proteins peptides amino acids

Micronutrients Needed in trace amounts (very small amounts) for normal growth and metabolic processes 1) Vitamins § Organic molecules § Vitamin C, K, B, D, B 1, B 2, B 12 etc. 2) Minerals § Non-organic molecules § Elements (e. x. , iron, copper, calcium, phosphorus)

OVERVIEW: Ingest food in mouth • Physical and chemical digestion take place here Food Bolus travels to the stomach • Digestion takes place Digestion and absorption take place in the Duodenum (the first 8 -10 inches of the small intestine) Further absorption occurs in the Large Intestine Egestion begins • Feces is concentrated and stored in the rectum Feces exits the body through the anus

Ingestion & Digestion: MOUTH • Teeth: tear and crush food • Tongue: moves food; forms a food bolus – Taste buds trigger Salivary Glands • Salivary glands secrete saliva: – Saliva = a mixture of water, mucus and AMYLASE – Amylase starts digesting carbohydrates into maltose • Tongue pushes bolus to back of throat to be swallowed

Swallowing • Pharynx: back of throat (food is swallowed) • Epiglottis: covers trachea so food bolus goes down esophagus (NOT down the trachea!) • Esophagus: tube leading to stomach • Peristalsis: rhythmic wavelike muscle contractions that push food along the digestive tract

Digestion - STOMACH • Sphincters: circular muscles that open and close to control what goes in or out 1. Cardiac Sphincter: allows food to enter stomach from the esophagus 2. Pyloric Sphincter: allows food to exit the stomach and enter the duodenum (small intestine) • Rugae: folds of stomach lining ( Surface Area, nutrient absorption)

Stomach Secretions v HCl = (Hydrochloric Acid) • • Kills microbes Makes stomach acidic (optimal p. H for pepsin) v Pepsin – digests/breaks down proteins into peptides v Mucus – protects stomach lining (against the harsh HCl and Pepsin)

Digestion – SMALL INTESTINE • 7 meters long! (longest organ of digestive system) • First 25 cm (8 -10”) is called the DUODENUM – Receives secretions for digestion – Makes its own secretions • CHYME enters from stomach – Partially digested food, water, gastric juice • Key site for digestion and absorption

Secretions into the Duodenum • Ducts from the LIVER and GALL BLADDER take bile to the duodenum • PANCREATIC DUCT takes bicarbonate and enzymes to the duodenum • Inner lining of DUODENUM secretes enzymes into itself

Secretions into the Duodenum Three Sources of Secretions 1. Liver – bile (stored in the Gall Bladder) 2. Pancreas –bicarbonate and enzymes 3. Duodenum - enzymes

Secretions and their Functions LIVER SECRETIONS FUNCTION BILE Emulsifies fat (gives lipase more SA to digest fats) PANCREAS SECRETIONS FUNCTION Bicarbonate Neutralizes HCl from stomach Amylase Breaks down carbohydrates into maltose Trypsin Breaks down large peptides into smaller peptides Lipases Breaks down fats into fatty acids and glycerol S. INTESTINE SECRETIONS FUNCTION Peptidases Break down peptides into amino acids Maltase Break down maltose into glucose

Products of Digestion • The products of digestions are now ready to removed from the digestive tube and transported where needed in the body: – Glucose – Amino acids – Fatty acids – Glycerol

ABSORPTION • Digestion of macromolecules produces nutrients that are small enough to pass through the intestinal wall and into body cells • Most nutrients are absorbed in the small intestine and transported to other body cells by the circulatory system • To increase the rate of absorption, the small intestine has specialized structures to increase surface area

INCREASING SURFACE AREA Absorption (Surface Area) is increased in 3 ways: 1. Villi (singular = villus) – fingerlike projections (folds) in the intestinal wall – Surface Area 2. Microvilli – microscopic, mini-folds along each villus – Surface Area 3. Lacteals – vessels that run through the villi – absorption of fatty acids + glycerol

Inner Surface of Small Intestine

Nutrients The nutrients that get absorbed in the small intestine are the products of digestion Glucose Fatty acids + Glycerol Amino acids These ‘things’ get absorbed into the blood stream and are transported to cells all over the body

Egestion – LARGE INTESTINE Once the nutrients are removed from the small intestine, mostly waste remains and is pushed into the COLON (large intestine) Enters at the Cecum

COLON (aka Large Intestine) 1. 5 m long Twice the diameter of the small intestine

Large Intestine (Colon) 4 Key Functions of the Colon (Large Intestine) 1. Removes water 2. Habitat for E. coli which produce Vitamins B and K 3. Absorption of vitamins and minerals 4. Initiates egestion (waste removal) The remaining fecal matter (feces) is then moved into the rectum by peristalsis