The Gastrointestinal System Module 3.1 The Gastrointestinal System By Jennifer Turley and Joan Thompson © 2013 Cengage

Presentation Overview Definitions & Body systems The GI tract Enzymes & Hormones After digestion: Absorption Transportation Utilization Excretion

Digestion The breaking down of food by both mechanical & chemical means Mechanical- physical churning & contraction of stomach Involves muscles and nerves Chemical- enzymes, bile & acidic environment break down food Involves acid, enzymes, and hormones

Enzymes Proteins that catalyze (aka speed up) metabolic reactions are necessary for most biochemical reactions to occur Without enzymes, metabolism would be extremely slow! Enzymes are not changed by reactions they speed up Digestive enzymes specifically break down food substances Examples include: amylase for carbohydrates, protease for proteins, and lipase for lipids/fat

Hormones Chemicals produced & secreted by cells (typically in an endocrine gland) Travel through bloodstream and affect the behavior of cells at distal sites in the body Examples of hormones in digestion include: cholecystokinin and secretin

GI tract

GI tract Mouth Esophagus Lower esophageal sphincter Stomach Pyloric sphincter Small intestine Large intestine/ Colon Rectum/ Anus

1. Mouth Mechanical digestion in mouth= chewing (i.e. mastication) Chemical digestion in mouth= saliva, which contains amylase (for lubrication and to start digestion) Goal: food becomes bolus

2. Esophagus 3. Lower esophageal sphincter Connects mouth to stomach Peristalsis begins Peristalsis- a muscular “wave” action that occurs throughout the intestinal tract. It is controlled by the central nervous system and facilitates excretion by propelling food stuff through the body. 3. Lower esophageal sphincter Prevents food from coming out of stomach

4. Stomach 5. Pyloric sphincter Muscular organ & storage reservoir Mechanically digests food by mixing & churning Chemically digests food with bile acid & enzymes (pepsin) Goal: bolus food becomes chyme 5. Pyloric sphincter Regulates movement of food out of stomach and into small intestine

Accessory Organs Liver, gall bladder & pancreas Liver- makes bile Gallbladder- stores bile Pancreas- makes specific enzymes for the digestion of carbs, proteins & fats - also secretes insulin

Function of Bile Emulsifier  increases digestive efficiency

6. Small Intestine Primary site of absorption Made of villi and microvilli  increase surface area

3 Mechanisms of Absorption Passive (Simple) Diffusion: Nutrients pass freely across membranes via a concentration gradient Facilitated Diffusion: Nutrients diffuse across membranes using a specific transport protein/ receptor Active Transport: Nutrients move across membranes against a concentration gradient using a specific/selective transport protein & energy/ATP

3 Mechanisms of Absorption

7. Large Intestine/ Colon Minimal absorption of nutrients Mostly absorbs water Formation/ storage of feces

8. Rectum/ Anus Last section of colon where excretion occurs End of GI tract

Transportation of Nutrients 1. Blood vessels: transport water soluble nutrients

Transportation of Nutrients 2. Lymphatic vessels: transport fat soluble nutrients

Cellular storage Short term, intermediate & long term storage Dependent on type of nutrient, cell-type, tissue/ organ

Metabolic Usage Catabolic reaction- Breaking down; are degrading or destroying nutrients, proteins, etc Anabolic reaction- Building up; are synthesizing or constructing nutrients, proteins, etc Homeostasis- The balance of catabolic and anabolic reactions in your body to achieve equilibrium (a relatively stable internal environment)

Examples Anabolic or Catabolic? Q1: Inside your mouth, what action does amylase have on the food you eat? Q2: What action is occurring when triglycerides are formed?

Excretion The Kidney- water & water soluble waste The Skin- water & water soluble waste The Lung- carbon dioxide & water The Colon/ Large Intestine- Water is removed & waste (bacteria, fiber, sloughed cells, & undigested food) is compacted

Summary Body uses both mechanical & chemical means for digestion physical churning + mix of enzymes & hormones The GI tract & order of organs Accessory organs  liver, gall bladder & pancreas Nutrient absorption & transportation Assimilation of nutrients, storage, & metabolic usage Excretion of waste References for this presentation are the same as those for this topic found in module 2 of the textbook