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

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

3. 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

4. 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

5. 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

8. GI tract

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

10. 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

11. 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

12. 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

13. 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

14. Function of Bile
Emulsifier  increases digestive efficiency

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

16. 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

17. 3 Mechanisms of Absorption

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

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

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

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

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

23. 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)

24. 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?

25. 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

26. 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