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