Ingestion of food GIT Digestion Dr.Rashid Mahmood

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

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

Digestion of food molecules

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………

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

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

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

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

Transport of lipids across the intestinal epithelium

Absorption

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

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

Absorption in Small intestine

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

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

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

Longitudinal section of Villus

Cross section of Villus

Brush border of GIT Epithelial cell

Absorption of water Diffusion Osmosis

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

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………

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

GIT obstruction 1 2 Sites of Obstruction 3 4

Last slide: Flatus

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

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

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

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