1. Ingestion of food
GIT
Digestion
Dr.Rashid Mahmood

2. Digestion Definition of Digestion
Digestion is the process of dismantling food into their constituent parts It requires hydrolysis, enzyme cleavage and fat emulsification

3. Hydrolysis Hydrolysis of Carbohydrates→ Monosaccharides
Hydrolysis of Fats → Fatty Acids
Hydrolysis of Proteins → Amino Acids

4. Digestion of food molecules

5. Digestion of Carbohydrates
Carbohydrates in diet
Sucrose
Cane sugar
Lactose
Milk
Starches
Non-animal Carbohydrates
Other Carbohydrates
Amylose, Glycogen, alcohol, lactic acid, pyruvic acid, pectins, dextrins etc.
Cellulose: not digestible
Contd………

6. Digestion of Carbohydrates
Contd………
Action of Ptylin (Amylase):
5% digestion in mouth
15-35% in stomach (before it is inactivated by HCl)
More Powerful
Cellulose: Not digested
Absorbed

7. Lactose intolerance Low levels of Lactase Intolerance to Milk
Yogurt is better tolerated

8. Digestion of Proteins Collagen (Meat)
Gelatinase: liquefies some proteoglycans in meat

9. Digestion of Fats Which is the main enzyme for digestion of fats?
Lingual Lipase: < 10% digestion (Not important)
Enteric Lipase: < 10% digestion (Not important)
Cholesterol Esterase digests Cholesterol Esters
Phospolipase A2 digests Phospolipids

10. Transport of lipids across the intestinal epithelium

12. Absorption

13. Objectives (Absorption )
Stomach
Poor absorptive area
No villi
Tight junctions
Alcohol, some drugs (e.g. Aspirin)
Small intestine
Folds
Villi
Microvilli
→↑ surface area
Large intestine

14. Absorption
Definition of Absorption
Absorption is the process of moving nutrients and other materials from the external environment of the Gastrointestinal tract into the internal environment

15. Absorption in Small intestine

16. Objectives (Absorption in Small intestine)
Physiological anatomy
Absorption of water
Absorption of carbohydrates
Absorption of proteins
Absorption of fats
Absorption of ions
Absorption of vitamins
Disorders

17. Folds (Valvulae conniventis or Folds of Kerckring))
Surface area × 3

18. Small intestine absorptive surface
1 cm
1 mm
1μm
× 1000 =
250m2 =
Tennis court

19. Longitudinal section of Villus

20. Cross section of Villus

21. Brush border of GIT Epithelial cell

22. Absorption of water
Diffusion
Osmosis

23. Motion Sickness (Contd……)
Rapidly changing direction or rhythm of movement →
stimulation of receptors in vestibular labyrinth of inner ear →
stimulation of vestibular nuclei in cerebellum →
stimulation of Chemoreceptor trigger zone →
stimulation of Vomiting Center

24. Nausea Often a prodrome of Vomiting
Anorexia: Often a prodrome of Nausea
Conscious recognition of subconscious excitation in an area of the medulla closely associated with or part the vomiting center
Ill-defined and unpleasant subjective sensation
Contd………

25. Nausea Contd……… Causes Irritative impulses from GIT Motion sickness
Impulses from cerebral cortex
Vomiting may occur occasionally without nausea

26. GIT obstruction 1 2
Sites of Obstruction 3 4

27. Last slide: Flatus

28. Gases in GIT “Flatus” Sources Swallowed air Formed in gut
Bacterial action
Diffusion from blood into GIT

29. Gases in GIT “Flatus” Stomach Small intestine Oxygen & Nitrogen
Swallowed air
Expelled by belching
Small intestine
Little amounts
Passed from stomach

30. Gases in GIT “Flatus” Large intestine Foods Bacterial action
Carbon dioxide, Methane, Hydrogen
Sometimes Oxygen → Explosive Mixture → care during cautery
Foods
Beans
Cabbage
Onion
Cauliflower
Corn

31. Gases formed Per day = 7 to 10 liters
Gases in GIT “Flatus”
Gases formed Per day = 7 to 10 liters
Gases expelled per day = 0.6 liters
Rest: absorbed by blood
Expelled by lungs