1. Digestive Physiology
The primary function of the digestive system is move nutrients from the external environment into the body

2. Outline Digestion & Absorption of nutrients
Secretion of digestive chemicals
Regulation of Digestion
Regulation of Metabolism

3. Digestion & Absorption of Protiens
Proteins digested in stomach & small intestine
Proteins are broken into smaller peptides & amino acids by:
1) Pepsin: Stomach
2) Trypsin & chymotrypsin: SI
3) Exopeptidases: SI
3) Peptides/Amino Acids are absorbed in SI by:
1) Cotransport then Antiport with H+
2) Cotransport then Antiport with Na+
3) Transcytosis via vesicles

4. Digestion & Absorption of Fats
Emulsified fats are digested by Lipase & Colipase
End products move into SI wall
1) Monoglycerides & fatty acids: simple diffusion
2) Cholesterol: NPC1L1 transporter
5) End products are re-comined in absoptive cells to form Chylomicrons
6) Chylomicrons travels through lymph to body

5. Digestion & Absorption of Carbohydrates
Carbs digested in mouth & SI
Complex Carbs are digested into Disaccharides by amalyase & alpha-amylase
Maltose, Sucrose, Lactose
3) Disaccharides are digested into Monosacch. By:
1) Maltose by Maltase to glucose
2) Sucrose by Sucrase to glucose + fructose
3) Lactose to Lactase to glucose + galactose
4) Monosaccharides can FINALLY! be absorbed
1) Glucose & Galactose via Na+-glucose Symporter
2) Fructose via Glut5 & Glut2 transporter
Na+-Glucose Symporter
Glut5
Glut2

6. Absorption of Vitamins, Ions, Minerals, Water
Vitamins: Fat-Soluble (A, D, E, K) – transported with fats
Water-Soluble (C, B) – mediated transport
Minerals: Ca2+ (hormonally controlled ion channels/Active transport) – used everywhere
Iron (???)- needed for RBC
Ions: Na+ - active transport, symport, antiport
Water: Follows Na+ & other absorbed solutes by Osmosis

7. Secretion: Salivary Glands
Parotid, Sublingual, & Submandibular glands secrete Saliva
Saliva contains Alpha-amylase (carbs), lingual lipase (fats)

8. Secretion: Stomach * * Acid Secretion
1) Protein in food activates
enteric nervous system
2) Gastric enzymes activate a
variety of pathways
3) Secretion of H+ &
Pepsinogen
Pepsinogen converted to
Pepsin by H+
Surface Mucosa
Gastric Glands
Vasculature *
Muscle *
Drugs for heartburn & ulcers (Zantac, Pepcid) block Histamine receptors in stomach!

9. Secretion: Pancreas Pancreas secretes Trypsin & Trypsinogen
Pancreatic Duct
Small Intestine
Pancreas
Pancreas secretes
Trypsin & Trypsinogen
Exopeptidases
Amylase
Lipase
Bicarbonate Ions (raise pH)
Pancreatic Enzymes work best at higher pH
Acini Cells
Islet Cells

10. Secretion: Small Intestine
Villi
Crypts with glands
Vasculature
Small Intestine
Muscle
Glands with crypts secrete:
Amylase, Maltase, Lactase, Sucrase
Peptidase
Enterokinase (activates trypsin!)

11. Secretion: Bile Bile is secreted by the LIVER Stored in Gall Bladder
Without Bile….fat digestion is very slow

12. Why doesn’t the digestive system digest itself?
Digestive tract is made of cells that can be digested by enzymes!
Mucus forms a protective barrier between intestinal walls & acids/bases, enzymes
Mucous Cells in Stomach
Goblet Cells in Small Intestine
Goblet Cell

13. Outline Digestion & Absorption of nutrients
Secretion of digestive chemicals
Regulation of Digestion
Regulation of Metabolism

14. Regulation of Digestion: Thinking with your stomach
Long Reflexes – CNS
Parasympathetic- Increase Digestion
Sympathetic – Slow Digestion
2) Short Reflexes – Enteric Nervous System
Ingested food and pH trigger self-regulating changes in digestive system
Neurons located in walls of digestive system
3) Digestive Peptide (Hormones)
Digestive system release several hormones to regulate itself and communicate with brain
Autonomics work with the Enteric System to coordinate Digestive Function
Digestive Peptides:
CCK, Gastrin, Secretin, GIP, Motilin, GLP-1

15. The Liver Bile Production: Fat Emulsification
Processes & Detoxifies Absorbed Products
Hepatic Portal System
carries products to and from liver
3) Storage: Liver is a major storage site of glucose & some vitamins

17. Cholesterol Metabolism
VLDL = Very Low Density Lipoprotien
LDL = Low ‘’
IDL = Intermediate ‘’
HDL = High ‘’
LPL = Lipoprotien Lipase (Endothelial Enzyme)
CE = Cholesteryl Esters

18. Cholesterol Synthesis
‘Statins’ = Inhibit HMG CoA reductase
Reduce Total Cholesterol *

19. Bile Acid Sequestrants
Bile Acids with Fats REMAIN in Digestive Tract
Acids + Cholesterol + Triglycerides
are
Excreted via Feces!

20. Amino Acid Metabolism -Some AA are used by body
-Excess is metabolized by the liver
-End product is NH3 or NH4 = TOXIC
-NH3 and NH4 repackaged for
transport and excretion
1) Urea Cycle
2) Glutamate-Glutamine Transport
Kidney excretes urea and NH4 via urine

21. Amino Acid Metabolism
Urea, Glutamate and Glutamine carry Ammonia(ium) (NH3, NH4+) to kidney for excretion
Glutamine