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

2. 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

3. 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

4. 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

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

6. Characteristics and composition of Gastric secretion (Gastric Juice)
ml/ day
pH:
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

7. 3 types of gastric glands
Mucus-secreting cells
Mucus
Oxyntic (Gastric ) glands
Digestive enzymes
HCl
Intrinsic factor
Pyloric glands
Gastrin

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

9. 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

10. 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

11. 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

12. 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

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

14. 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++

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

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

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

19. 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)

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

21. 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

22. 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

23. 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