1. Gastrointestinal Physiology
Dr. Meg-angela Christi Amores

2. Digestion by Hydrolysis
CARBOHYDRATES
Almost ALL in the diet are: large polysaccharides or disaccharides
Combinations of monosaccharides
H of 1 mono removed, OH of other mono removed = joined
H2O is formed
In DIGESTION: reversal of the process
DIGESTION of CARBS: conversion to monosaccharides

3. Digestion by Hydrolysis
FATS
entire fat portion of diet are triglycerides (neutral fats)
3 fatty acids + glycerol = triglyceride removing 3 H20 m
in DIGESTION: reversal:
fat-digesting enzymes return three molecules of water to the triglyceride molecule and thereby split the fatty acid molecules away from the glycerol

4. Digestion by Hydrolysis
PROTEINS
Formed from amino acids linked in peptide bonds
H from one AA removed, OH from another AA removed
In DIGESTION: reversal or process

5. Digestion Basic chemistry:
in the case of all three major types of food, the same basic process of hydrolysis is involved
Only difference lies in the types of enzymes required to promote the hydrolysis reactions for each type of food

6. CARBOHYDRATE Digestion
FOOD in the diet:
3 major sources of carbs in diet:
Sucrose - ( cane sugar )
Lactose - ( milk )
Starch - (all non-animal food, potatoes, grains)
Other carbs: amylose, glycogen, alcohol, lactic acid, pyruvic acid, pectins, dextrins, cellulose

7. CARBOHYDRATE Digestion
MOUTH: Saliva – ptyalin (a amylase)
STARCH --- maltose (di) and polymers of glucose (mo)
Short stay in the mouth, <5% of starch is hydrolyzed
STOMACH: gastric juice - acidic
Amylase deactivates in stomach, but can digest about % while in the fundus

8. CARBOHYDRATE Digestion
SMALL INTESTINE : DUODENUM
Pancreatic amylase – more powerful
15 to 30 mins of arrival of chyme in duodenum – completely digested
STARCH maltose and glucose polymers
JEJUNUM and ILEUM
four enzymes (lactase, sucrase, maltase, and α-dextrinase)
Lactase – GALACTOSE --- lactose and glucose
Sucrase – SUCROSE ---- fructose and glucose
Maltase – MALTOSE --- glucose and glucose

9. PROTEIN digestion
In the diet: chemically long chains of amino acids bound together by peptide linkages

10. PROTEIN digestion STOMACH PROTEIN ----- Proteoses, polypeptides
Pepsin – most active at pH of 2 to 3 (Needs HCl to be activated)
Only initiates digestion (10 to 20% of total protein)
Special ability to digest COLLAGEN
PROTEIN Proteoses, polypeptides

11. PROTEIN digestion UPPER SMALL INTESTINE
Where most protein digestion occur
Pancreatic enzymes: TRYPSIN, CHYMOTRYPSIN
Proteoses, polypeptides ---- smaller peptides
Pancreatic enzyme: PEPTIDASE (enterocytes)
smaller peptides amino acids

12. FAT Digestion
In the diet: triglycerides, phospholipids, cholesterol, and cholesterol esters
MOUTH, STOMACH
small amount of triglycerides is digested in the stomach by lingual lipase that is secreted by lingual glands in the mouth and swallowed with the saliva (<10%, unimpt)
INTESTINE
Where essentially all fat digestion occurs

13. FAT Digestion Emulsification by BILE first step in fat digestion
break the fat globules into very small sizes
begins by agitation in the stomach to mix the fat
most of the emulsification occurs in the duodenum under the influence of bile
Contain BILE SALTS and LECITHIN
to make the fat globules readily fragmentable by agitation with the water

14. FAT Digestion SMALL INTESTINE Pancreatic LIPASE
triglycerides of the diet are split by pancreatic lipase into free fatty acids and 2-monoglycerides

15. ABSORPTION STOMACH SMALL INTESTINE
poor absorptive area, no villi, with tight junctions
Can absorb alcohol, aspirin
SMALL INTESTINE
Absorbs more than 7 L of fluid per day
many folds called valvulae conniventes (or folds of Kerckring) with villi
intestinal epithelial cell on each villus is characterized by a brush border with microvilli

16. ABSORPTION – small intestine
Daily:
Several hundred grams of carbohydrates
100 or more grams of fat, 50 to 100 grams of amino acids, 50 to 100 grams of ions, and 7 to 8 liters of water
ABSORPTIVE CAPACITY:
several kilograms of carbohydrates per day
500 grams of fat per day
500 to 700 grams of proteins per day
20 or more liters of water per day

17. ABSORPTION Water – diffusion by laws of osmosis
Sodium – active transport

18. ABSORPTION
Chloride – diffusion , thru electronegativity created by sodium
Bicarbonates – combine with Hydrogen to form H2CO3 (carbonic acid), which dissociates to form H2O and CO2 . CO2 readily diffuses, released to lungs

19. ABSORPTION Carbohydrates - absorbed in the form of monosaccharides
most abundant of the absorbed monosaccharides is glucose (80%)
galactose and fructose ( 20%)
by secondary active transport
(Glucose co trasported with SODIUM)

20. ABSORPTION

21. ABSORPTION
Protein
are absorbed through the luminal membranes of the intestinal epithelial cells in the form of dipeptides, tripeptides and amino acids
Energy supplied by active transport of sodium
co-transport (or secondary active transport) of the amino acids and peptides

22. ABSORPTION
Fat
end products first become dissolved in the central lipid portions of bile micelles
monoglycerides and free fatty acids are carried to the surfaces of the microvilli of the intestinal cell brush border and then penetrate into the recesses among the moving, agitating microvilli
diffusion

23. ABSORPTION – large intestine
1500 mL of chyme enter Large Intestine
Most of the water and electrolytes are absorbed
leaving less than 100 milliliters of fluid to be excreted
Most occur the proximal one half of the colon, giving this portion the name absorbing colon
ABSORPTIVE CAPACITY
maximum of 5 to 8 liters of fluid and electrolytes each day

24. DIARRHEA
results from rapid movement of fecal matter through the large intestine
Enteritis: inflammation usually caused either by a virus or by bacteria
mucosa becomes extensively irritated, and its rate of secretion becomes greatly enhanced
Cholera – secretion of 10 to 12 liters per day, lead to death. Max abs capacity of LI: 6 – 8L/d