the gastrointestinal system by jennifer turley and joan thompson © 2013 cengage module 3.1
TRANSCRIPT
The Gastrointestinal System
By Jennifer Turley and Joan ThompsonBy Jennifer Turley and Joan Thompson© © 20132013 Cengage Cengage
Module 3.1
Presentation Overview1. Definitions & Body systems 2. The GI tract3. Enzymes & Hormones4. After digestion:
a. Absorptionb. Transportationc. Utilizationd. 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 tract1. Mouth2. Esophagus 3. Lower esophageal sphincter4. Stomach5. Pyloric sphincter6. Small intestine7. Large intestine/ Colon8. 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 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 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 AbsorptionPassive (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 Nutrients1. Blood vessels: transport water soluble nutrients
Transportation of Nutrients2. 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)
ExamplesAnabolic 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 digestionphysical 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 wasteReferences for this presentation are the same as those for this topic found in module 2 of the textbook