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‫فیزیولوژی تکمیلی‬
Advanced Physiology
(part 2, Digestive system)
By: A. Riasi
(PhD in Animal Nutrition & Physiology)
 Introduction
 The primary function of digestive system
 Intracellular and extracellular process in digestive system
 Three specific regions in most animals digestive system:
 Foregut
 Midgut
 Hindgut
 Introduction
 Digestive systems perform four basic digestive process:
 Motility
 Propulsive movements
 Mixing movements
 Secretion
 Digestion
 Absorption
 Digestive system properties
 The digestive system of animals consists of:
 The digestive tract (gastrointestinal tract)
 Accessory digestive organs
 Additional function of the digestive tract:
 Osmoregulation
 Endocrine secretion
 Immune function
 Elemination of toxins
 Digestive system properties
 Regulation of digestive function is complex and synergetic
 The smooth muscle cells of digestive system are single unit type
 The nervous system control digestive system function
 Intrinsic nerve plexuses
 Extrinsic nerves
 Structure of digestive tract
The four layers are the same from esophagus to anal canal
 Structure of digestive tract
 Structure of digestive tract
Adapted from: Anatomy and Physiology of Domestic Animal, Akers and Denbow, 2013
 Intrinsic nervous system
Adapted from: Sherwood et al., Animal Physiology
 Intrinsic nervous system
 Intrinsic nervous system
The enteric nervous system of a rat’s stomach
Adapted from: Sherwood et al., Animal Physiology
 Intrinsic nervous system
 Receptor
activation alters digestive activity through neural
reflexes and hormonal pathways
 Three different types of
sensory receptors:
 Chemoreceptors
 Mechanoreceptors (pressure receptors)
 Osmoreceptors
 Salivary glands
 Acini is a secretary unit of salivary gland
 Each acini secrete fluid into collecting ducts
 Water
 Electrolytes
 Mucus
 Enzymes
 Salivary glands
Three major parts of salivary glands
 Parotid glands
 Submaxillary glands
 Sublingual glands
 Salivary glands
In the histological sections of salivary gland shown above, the cells
stained pink are serous cells, while the white, foamy cells are
mucus-secreting cells.
 Control of salivary secretion
Adapted from: Sherwood et al., Animal Physiology
 Salivary secretion in sheep
Salivary glands
Total salivary Characteristics
volumes (L d)
Site of reflexogenic stimuli
Parotids
3-8
Inferior
molars
0.7-2
Mouth, esophagus,
ruminoreticulum
Mouth, esophagus,
ruminoreticulum
Palatine,
buccal
Pharyngeal,
Submaxillary
2-6
Sublingual,
labial
Total volume
0.1
0.4-0.8
6-16
Serous, isotonic, strongly
buffered
Serous, isotonic, strongly
buffered
Isotonic, strongly buffered Mouth, esophagus,
ruminoreticulum
Mucous, hypotonic,
Mouth during feeding,
weakly buffered
not cudding
Very mucous, hypotonic,
weakly buffered
Mouth
 Swallowing
Eating and swallowing are complex neuromuscular activities
consisting essentially of two stages:
 Oropharyngeal stage
 Esophageal stage
Adapted from: Sherwood et al., Animal Physiology
 Esophagus
 Anatomically
and functionally, the esophagus is the least
complex section of the digestive tube
 It contains the crop in poultry
 Esophagus
 There are two physiologic sphincters:
 Upper and lower esophageal sphincters.
 In ruminants, a nasopharyngeal sphincter is present.
 Esophagus in birds
 Stomach
Adapted from: Sherwood et al., Animal Physiology
Gastric emptying and mixing
Adapted from: Sherwood et al., Animal Physiology
 Factors that influence the rate of gastric emptying
A- Stomach factors
 Amount of chyme in the stomach (more effect)
 Vagus nerve
 Stomach hormone gastrine
 The degree of fluidity of the chyme
B- Duodenum factors
 Fat
(more effect)
 Acid
 Hypertonicity
 Distention
 The
duodenal factors trigger either neural or hormonal
responses

Neural response is mediated through two reflexes:
 Intrinsic nerve plexus (short reflex)
 Autonomic nerves (long reflex) (These reflexes are called the enterogastric reflex)

The hormonal response involves the release duodenal’s several hormones:
 Secretin
 CCK
 Gastric inhibitory peptide or glucose-dependent insulinotrophic peptide
 Avian pancreatic polypeptide (APP)
(These
hormones are known as enterogastrones)
 Stomach
 Two distinct areas for secretion of gastric digestive juice:
 Oxyntic mucosa (contain three type of cells)
 Mucous cells
Chief cells
 Parietal cells or oxyntic cells
 Pyloric gland area (PGA):
 Mucous cells
 Chief cells

Gastric secretion cells:
 Gastric secretion cells
 Exocrine cells
 Paracrine cells
 Endocrine cells
Adapted from: Sherwood et al., Animal Physiology
 Mechanism of HCl secretion
Adapted from: Sherwood et al., Animal Physiology
Adapted from Animal Physiology, by Sherwood et al., 2005
 Control of gastric secretion
 Cephalic phase (Mediated by vagus nerve and acetylcholin)
 Gastric phase (gastrin has the main effect)
 Intestinal phase (intestinal gastrin has the main effect)
 Bird stomach
 Proventriculus-gizzard processes of digestion in birds
 There are two type of glands into the proventriculus:
 Simple mucosal glands that secrete mucus
 Submucosal glands that secrete HCl and pepsinogen
Interestingly, unlike in mammals, both HCl and pepsinogen are
synthesized with in the same cell (chief or oxynticopeptic cell)
 Bird stomach
 The mucosal lining of the gizzard is covered by koilin
 In birds myoglobin content of the gizzard is approximately
100-fold greater than the breast muscle, and mitochondrial
numbers are also elevated.
 Ruminant stomach
 Rumen development
Rumen microbiology and fermentation
 A large community of microorganisms are
presented in the forestomach.

Bacteria

Protozoa

Fungi
 Ruminant stomach
 Rumen muscles
1
3
4
2
5
Solid lines: internal oblique fiber (ruminal pillars, lips of reticular groove, omasal pillar); broken
lines: longituidal fibers; wave lines: circular fibers. At any given place, there are only two muscle
layers in the stomach wall. 1= cardia; 2= reticulum; 3= rumen 4= omasum; 5= abomasum.
 Ruminant stomach
 Rumen development
Undeveloped Rumen
Developed Rumen
 Ruminant stomach
 Absorptive surface area is enhanced by increasing:
 Papillae length
 Papillae width
 Papillae density
 Ruminant stomach
 The interior surface of the rumen forms numerous papillae
 Ruminant stomach
The 4 layers of the rumen epithelium: stratum corneum (SC), stratum granulosum (SG),
stratum spinosum (SS) and stratum basal (SB).
 Ruminant stomach
 Absorption VFA’s from the ruminal wall
 Ruminant stomach
Relationship between ruminal pH and the associated changes in the ruminal environment and ruminal epithelial
function (reproduced from Penner and Beauchemin, 2010).
 Ruminant stomach
 Rumination
is centrally mediated by the "gastric
centers".
 Tactile stimulation of the reticular and ruminal epithelia is a
powerful stimulus for rumination.
 Ruminant stomach
 The ruminal movements serve to:
 Mix the ingesta
 Aid in eructation of gas
 Propel fluid and fermented foodstuffs into the omasum.
 A cycle of contractions occurs 1 to 3 times per minute.
 Ruminant stomach
 Two types of contractions are identified:

Primary contractions

Secondary contractions
 Small intestine
 Three parts of small intestine
 Duodenum
 Jejunum
 Ileum
 Small intestine
Adapted from http://www.ufrgs.br/imunovet/molecular_immunology/gastrointestinal.html)
 Small intestine
Adapted from http://www.ufrgs.br/imunovet/molecular_immunology/gastrointestinal.html)
 Small intestine
The Meckel’s diverticulum is found in birds small intestine
 Pancreas
Adapted from: Sherwood et al., Animal Physiology
 Pancreas
 Exocrine functions
Enzyme
Substrate
Action
Trypsin, Chymotrypsin, Elastase
Peptides
Endopeptidases; cleave bonds between
amino acids
Carboxypeptidase and
Aminopeptidase
Peptides
Exopeptidases; cleave bonds at the
terminus of a peptide
α - amylase
Polysaccharides: starch and glycogen
Endoglycosidase; cleaves bonds
between carbohydrate monomers to
produce maltose and short carbohydrate
chains.
Pancreatic lipase
Triacylglycerols and 1,2 diacylglycerols
Fatty acids, glycerol and 2 monoacylglycerol
Adapted from wikivet (http://en.wikivet.net)
 Pancreas
 Control of exocrine secretions
 Neural controls
 Endocrine controls
 Cholecystokinin
 Secretin
 Gastrin
 Pancreas
 Liver and gallbladder
 Liver and gallbladder
 Liver blood flow
 75% venous blood from the portal vein
 25% from the hepatic artery
Adapted from: Sherwood et al., Animal Physiology
 Liver and gallbladder
Adapted from: Sherwood et al., Animal Physiology
 Liver and gallbladder
Adapted from http://www.ufrgs.br/imunovet/molecular_immunology/gastrointestinal.html)
 Liver and gallbladder
 Liver and gallbladder
 Lymph formation in liver
 Liver and gallbladder
 Hepatic phagocytic system
 Liver and gallbladder
 Two stage for bile secretion
 Hepatocytes secrete bile into canaliculi
 Bile modification in bile ducts
 Liver and gallbladder
 Pattern and control of bile secretion
 Effect of cholecystokinin
 Effect of secretin