Secretions of Large Intestine Ingestion of food GIT Secretions of Large Intestine Dr.Rashid Mahmood

Objectives Secretory functions of Alimentary tract General principals of alimentary secretion Saliva Esophageal Secretion Gastric Secretion Pancreatic Secretion Bile Secretions of small intestine Secretions of large intestine

Basic Mechanisms of Stimulation of the Alimentary Tract Glands Stimuli: Contact of food with Epithelium Tactile stimulation Chemical stimulation Distention Receptors: Epithelium of GIT Afferent and efferent pathways Local Enteric Nervous System Controlled by Hormones Nervous system Effects: Stimulation of glands

Basic Mechanisms of Stimulation of the Alimentary Tract Glands Autonomic Stimulation Parasympathetic ↑ secretion Sympathetic ↓ secretion (↓ blood supply) Initially may be a little ↑ secretion Control by Hormones

Esophageal secretion Mucus Lubrication & Protection Main body Simple mucus glands Initial portion Compound mucus glands Prevent excoriation Gastric end Protection from acidic gastric juices

Characteristics and composition of Gastric secretion (Gastric Juice) 1500-2500 ml/ day pH: 1.0-2.0 HCl Pepsins Gastric Lipase (Digestion of lipids) e.g. Tributyrase: Digests tribytyrin (a butter fat) Gastric Amylase (Digestion of carbohydrates) Mucus Intrinsic factor (for absorption of B-12) Gelatinase (Liquefies Gelatin & Proteoglycans in meat) Electrolytes Na+, K+, Mg++, HPO4--, SO4— Water

3 types of gastric glands Mucus-secreting cells Mucus Oxyntic (Gastric ) glands Digestive enzymes HCl Intrinsic factor Pyloric glands Gastrin

Components of Pancreatic Secretion Exocrine Digestive enzymes Secreted by acinar cells HCO3- - Secreted by duct cells Endocrine Insulin Glucagon

Pancreatic Digestive Enzymes For digestion of Proteins Trypsin Chymotrypsin Carboxypeptidase Elastase For digestion of Carbohydrates Pancreatic Amylase For digestion of Fats Lipase Cholesterol Esterase Phospholipase Colipase (Activated by Trypsin) Bile salt activated Lipase About 1 liter per day

Bile (Objectives) Characteristics Functions Composition Secretion Formation Storage and concentration Emptying of gall bladder Control of bile secretion Roll in fats digestion and absorption Enterohepatic circulation Gallstones

Functions of Liver Ganong (23rd Edition) table 29-1,p.482 Formation and secretion of bile Nutrient and vitamin metabolism Inactivation of various substances Synthesis of plasma proteins Immunity

Bile functions Functions Digestion of fats Absorption of fats Emulsification Large fat particles →small fat particles Absorption of fats Excretion Bilirubin End product of hemoglobin destruction Excess cholesterol

Biliary Secretion by Hepatocytes Bile acids Cholesterol Lecithin Bile pigments Bilirubin Biliverdin Other organic constituents

Gallbladder bile has less and vice versa in case of liver bile; Differences between liver bile and gallbladder bile (table 64-2, Guyton. 11th Edition) Gallbladder bile has less and vice versa in case of liver bile; Na+ Cl- HCO3 Water (89%) Gallbladder bile has more and less in liver bile; Ca++

Secretion of digestive juices Introduction to alimentary glands Saliva Gastric secretions Pancreatic secretions Bile Secretions of small intestine Secretions of large intestine

Secretions of Large Intestine: Mucus secretion Crypts of Lieberkϋhan No villi No enzymes Moderate amount of bicarbonate ions

Regulation of large intestinal secretions Local nervous reflexes Tactile stimuli Parasympathetic stimulation (Pelvic nerves) → ↑ mucus

Functions of Large Intestine Mucus secretion Protection Adherent medium for holding fecal material Protection from bacterial activity (taking place inside feces) Barrier to acids formed in feces (mucus + bicarbonate)

Disorders of large intestine Diarrhea Irritation (e.g. by bacteria) Secretion of large quantities of water & electrolytes Washes away the irritant

Disorders of large intestine Diarrhea Definition: Loss of fluid & Electrolytes via Stools Mechanism: imbalance between secretory and absorptive processes in small & large intestine. ↑ GIT Motility Causes: Irritation (e.g. by bacteria) Secretion of large quantities of water & electrolytes Washes away the irritant

OBJECTIVES (GIT) Physiological anatomy General Principals Circulation of blood through the GIT organs Control of all GIT functions by local, nervous, and hormonal systems Movement of food through alimentary tract Secretion of digestive juices Digestion of food Absorption of water, various electrolytes, and digested products

MCQ: Which of the following statements is not true regarding large intestine A. Crypts of Lieberkuhn do not secrete any digestive enzymes B. Intense irritation caused by bacterial infection results in increased absorption of water and electrolytes C. It does not contain villi D. Mucus contains moderate amounts of bicarbonate ions E. Stimulation of pelvic nerves causes increased mucus secretion B