Pharmacology for health students it is about gastrointestinal drugs, mechanism of there actions and there adverse effects.

1. Physiology of the Digestive System

2. Contents
• Organs of GIT
• Function of the GIT
• Functional structures of GIT:
• Regulation of GIT
• Movement of GIT
• Secretions of GIT

3. Digestive System (GIT)
• The digestive system: processes
food, extracts nutrients and
eliminates wastes.
• It provide
• Nutrients
• Water and
• Electrolytes
- Four processes of GIT:
- Digestion: mechanical or
chemical
- Secretion: enzymes,
electrolytes (HCl,
NaHCO3), mucous, and
hormones
- Absorption: nutrients, water
& electrolytes
- Motility: propulsive or
mixing
Digestive organs

4. GIT and its natural defense
• GIT is hollow at both ends (mouth- to - Anus).
• Harbor microorganisms in its luminal surfaces.
• GI-system can protect itself by:
– Mouth: Saliva contains lysozymes, IgA etc.
– Stomach: HCl, Pepsin etc. have bactericidal effect
– SI (e.g., Payer's patches): Immuno-competent lymph tissues
– Macrophages: located in intestinal walls act to defend from
bacterial invasion etc.

5. GIT-organs and its accessories
1. Mouth
2. Pharynx
3. Esophagus
4. Stomach
5. SI
6. LI
7. Rectum
(Anus)
Main GI-Organs
Accessory Organs
1. Salivary
glands
2. Pancreas
3. Liver &
4. Gallbladder
Structure of the gut
The alimentary canal
that used to digests and
absorbs food

6. Layers of the GIT
1. Mucosa: protection, secretion
& absorption.
2. Submucosa: blood vessels,
glands, lymph, nerve plexuses
are found.
 motility + secretion
3. Muscularis externa: Circular &
Longitudinal smooth muscle.
– mix and propel the chyme.
–
4. Serosa: outer most protective.

7. Regulation of GIT
Neural & Hormonal Regulation
A. Neural regulation of GI-activities: includes that of
a. Extrinsic (Autonomic N fibers)
b. Intrinsic (Enteric fibers)
Myenteric (Auerbach’s) plexus: (motility of the GIT)
Submucosa (Meissner’s) plexus: (secretions)
c. Somatic NS: voluntary
B. Hormonal regulation: Includes secretion of different hormones
like Gastrin, CCK, Secretin, GIP etc.
C. Paracrine Regulation:
-E.g.- Histamine (stimulates parietal cells to secrete HCl
-Somatostatin (inhibit secretion of gastrin by G-cells)

8. Receptors of the GI Tract
• Receptors initiate GI-reflexes that:
– Activate or inhibit GIT
• Mechanoreceptors:
~ respond to distension, spastic contraction
• Chemoreceptors:
~ respond to osmolarity, irritation, pH, presence of fat
and protein food and end products of digested food
• Thermoreceptors: respond to warm food/drinks
• Pain receptors: respond to tissue injury in the GIT.

9. Movements of the GIT
• Two basic types of movements
occur in the GIT:
1. Propulsive movements:
• cause food to move forward at an
appropriate rate for digestion and
absorption.
• Peristalsis: is propulsive
movement in the form of
contractile rings around the gut
and propels to the anal ward
direction.
Peristalsis and Segmentation

10. 2. Mixing movements :
• which keep the intestinal contents thoroughly mixed at all
times.
• Mixing contractions are beneficial to mix the food contents
with gastric juice (chyme).

11. Function of Saliva
a. Digestion: CHO-digestion begins in saliva .
• The enzyme ptyline breaks starch- to-maltose.
• Lingual lipase begins fat digestion in the mouth.
b. Protection: has anti-microbial actions (contains Lysozyme &
thiocyanate) that kills microbes.
c. Lubrication: Mucin found in saliva facilitates moistening
and swallowing of food, involved in speech.
d. Endocrine function: Sex steroids are found in saliva to
plasma levels.

12. Stomach
• Rugae ( a fold) increases SA.
• Function:
 Storage up to 1.5L of food.
 Mixing of food to form chyme.
 Slow emptying the food into the SI at
a rate suitable for digestion and
absorption.
 Secretary function: HCl, mucous,
pepsin, gastrin, IF
• Sterilization,
• Digestion: breakdown of proteins
begins.
• Absorption
• Facilitates defecation

13. Secretary function of GIT
* Primary secretary products of GIT are:
~ Digestive enzymes ~ GI-hormones
~ Mucous ~ Electrolytes (HCl, NaHCO3)
Factors stimulating GIT secretions
* Local mechanical factors: distension, irritation, pH
* Nervous stimulation: ANS, ENS (submucosal plexus)
 Sympathetic stimulation inhibits GIT-secretions
 Parasympathetic stimulation increases GIT-secretions
* Hormonal mechanisms:
 Gastrin increase HCl secretion
 Secretin increases NaHCO3 secretion from pancreas

14. Small Intestine
• Runs from pyloric sphincter
to the ileocecal valve
• Is site for completion of
digestion and absorption.
• Has three subdivisions:
• Duodenum, Jejunum,
Ileum
• The bile and pancreatic duct
join duodenum.
Digestive enzymes
Peptidase: splits peptides into AAs
2. Disaccharidase: sucrase, maltase
and lactase.
3. Intestinal lipase: splits neutral fats
into glycerol & FAs.
Regulation of SI secretion
• Local factors: tactile, distension,
irritation, PH.
• Hormonal: Secretin, CCK, VIP,
Glucagon, GIP
• Nervous: vagal and sympathetic
stimulation
• Enteric reflexes: stimulation of
submucosal plexus

15. Digestion in the Small Intestine
Carbohydrates
• Mouth: salivary amylase
• Oesophagus & stomach:
nothing happens
• Duodenum: pancreatic
amylase
• Brush border enzymes
(maltase, sucrase & lactase)
Digestion of Proteins
Stomach
• HCl denatures or unfolds
proteins
• Pepsinogen pepsin
• Pepsin proteins to
peptides
Pancreas
• split peptide to AA
SI
• Brush border enzymes
carboxypeptidases
aminopeptidases
dipeptidase

16. Dietary source of fat
• Triglycerides, Cholesterol, cholesterol esters and PL
Fat Emulsified fat FFA + Glycerides
-Lingual lipase
-Gastric lipase
-Pancreas lipase
Cholesterol Bile salt FFA + Glycerides
Cholesterol esters Cholesterol Esterase
Phospholipids-A2 Phospholipase FFA + Phospholipids
Digestion of Lipids
Bile salt

17. Absorption in the SI

18. Large Intestine
 Is subdivided into cecum, colon,
rectum, and anal canal
• The cecum: contains appendix
 Colon has distinct regions:
ascending colon, transverse
colon, descending colon, and
sigmoid colon
• The sigmoid colon joins the
rectum
• The anal canal

19. Valves and Sphincters of the Rectum and Anus
 Valves of the rectum stop feces from being passed with gas
• The anus has two sphincters:
– Internal anal sphincter composed of smooth muscle
– External anal sphincter composed of skeletal muscle
• Ileocecal valve (sphincter) : connects ileum -to- cecum. It is
mostly in a contracted state b/s:
a. Prevents bacterial penetration back to the SI.
b. It permits slow flow of chyme to the LI

20. Large intestine
• LI does not have villi, but has
goblet cells that secrete mucus.
Function of the large intestine
1. Absorption of drugs & water
2. Electrolyte (like NaCl) absorption
3. Mucous & HCO3
- secretion
4. Storage, transport, and evacuation
of feces
5. Bacterial fermentation in the
colon stimulates synthesis of
vitamins K.
• Movement in the LI
• Two types of movements
1. Mixing movements
(Haustration)
2. Propulsive movements
(mass movements)
• Mass movement :is initiated by
local distension, gastro-colic
reflex
* Poor motility: causes greater
absorption and constipation
* Excess motility: causes less
absorption and diarrhoea.

21. Defecation reflex

22. 22
Pancreas
• Pancreas contains two types of
secretary glands:
1. Endocrine cells (islets of
Langerhans)
* secrete hormones
2. Exocrine cells (acinar cells)
* secrete digestive enzymes called
pancreatic juice.
a. Digestive enzymes: necessary to
digest CHO, fat, and protein.
b. Bicarbonates : to neutralize the
gastric juice
c. Water and electrolytes (Na+, K+
etc.)

23. Hormonal regulation of pancreatic secretion
Secretin: causes NaHco3
bicarbonate release.
GIP: increased insulin
release
CCK: increased digestive
enzyme release
• Parasympathetic
impulse
Stimulate secretion of
pancreatic enzyme

24. Liver and gallbladder
Liver
• Is the heaviest gland.
• Weighs 1.36kg.
• Located below diaphragm in
the abdomen
• The liver is divisible into left
and right lobes, separated by
the falciform ligament.
•
• Right lobe larger
• Gallbladder on right lobe

25. Functions of the liver
1. Metabolism:
CHO
 glycogenesis, gluconeogenesis
and glycogenolysis
Lipid
 β-oxidation, formation of PL, LP,
synthesis of cholesterol
Protein
• Deamination of AAs
• Converts ammonia (NH3) into
urea.
• Synthesizes plasma proteins
fibrinogen and gamma globulin.
2. Inactivation of drugs & hormones
3. Removes the waste product bilirubin
4. Releases bile salts
5. Stores: fat soluble vitamins, iron,
copper and blood reservoir
6. Filtration of blood:
• Old blood cells & bacteria.
• Removes blood clots and toxins
7. Activates vitamin D
8. Synthesis of clotting factors (F-I, II,
VII, IX, X)