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Advanced PhysiologyAdvanced Physiology(part 1, Digestive system)(part 1, Digestive system)
By: A. Riasi (PhD in Animal Nutrition & Physiology)
فیزیولوژی تکمیلی
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
Introduction
Introduction
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
Introduction
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
Introduction
The four layers are the same from esophagus to anal canal
Introduction
Introduction
Introduction
The enteric nervous system of a rat’s stomach
Introduction
Receptor activation alters digestive activity through neural
reflexes and hormonal pathways
Three different types of sensory receptors:
Chemoreceptors
Mechanoreceptors (pressure receptors)
Osmoreceptors
Different parts of digestive tract and the functions
Mouth
Obtaining and receiving food
Mouth
Taste buds are composed of groups of about 40 columnar
epithelial cells bundled together along their long axes.
Salivary glands
Acini is a secretary unit of salivary gland
Each acini secrete a fluid into collecting ducts
Water
Electrolytes
Mucus
Enzymes
Three major parts of salivary glands
Parotid glands
Submaxillary glands
Sublingual glands
Salivary 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.
Salivary glands
Control of salivary secretion
Simple reflex
Other input
Conditioned reflex
+Cerebral cortex
Salivary center in medulla
Pressure receptors and chemoreceptors in mouth
+
+
Autonomic nerves
Salivary galnds
Salivary secretion
+
+
+
Salivary glandsTotal salivary volumes (L d)
Characteristics Site of reflexogenic stimuli
Parotids
Inferior molars
Palatine, buccal, pharyngealSubmaxillary
Sublingual, labial
3-8
0.7-2
2-6
0.4-0.8
0.1
Serous, isotonic, strongly bufferedSerous, isotonic, strongly buffered
Isotonic, strongly buffered
Mucous, hypotonic, weakly buffered
Very mucous, hypotonic, weakly buffered
Mouth, esophagus, ruminoreticulumMouth, esophagus, ruminoreticulum
Mouth, esophagus, ruminoreticulumMouth during feeding, not cudding
Mouth
Total volume6-16
Salivary secretion in sheep
Eating and swallowing are complex neuromuscular activities
consisting essentially of two stages:
Oropharyngeal stage
Esophageal stage
Swallowing
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
Esophagus in birds
In monogastric mammals, the stomach is divided into three section:
Stomach
Stomach
Microscopic anatomy of the stomach
Muscularis: has an additional oblique layer
Epithelial lining composed of goblet cells
Gastric pits contain gastric glands
Stomach
A remarkable ability for significant changes in volume
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
Stomach
Gastric secretion cells:
Gastric secretion cells
Exocrine cells
Paracrine cells
Endocrine cellsType of secretary cell
Product secretedStimuli for secretion
Function (s)
Exocrine cells
Mucous cellsAlkaline mucusMechanical stimulation by contents
Protects mucous against mechanical, pepsin, and acid injury
Chief cellsPepsinogenAch, gastrinWhen activated, begins protein digestion
Parietal cellsHClAch, gastrin, histamine
Activates pepsinogen, breaks down connective tissue, denatures proteins, kills micro-organisms
Endocrine/ paracrine cells
Enterochromaffin-like cells
HistamineAch, gastrinStimulates parietal cells
G cellsGastrinProtein products, ACh
Stimulates parietal , chief, and ECL cells
D cellsSomatostatinAcidInhibits parietal, G, and ECL cells
Mechanism of HCl secretion
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)
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)
The duodenal factors trigger either neural or hormonal
responses
Gastric emptying and mixing
A- Stomach factors Amount of chyme in the stomach (more effect)
Vagus nerve
Stomach hormone gastrine
B- Duodenum factors
The degree of fluidity of the chyme
Fat (more effect)
Acid
Hypertonicity
Distention
Factors that influence the rate of gastric emptying
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
Bird stomach
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
Undeveloped Rumen Developed Rumen
Ruminant stomach
Rumen development
Ruminant stomach
Pre-ruminant period
Ruminant stomach
Pre-ruminant period
Absorptive surface area is enhanced by increasing:
Papillae length
Papillae width
Papillae density
Ruminant stomach
Ruminant stomach
Milk only Milk and grain Milk and hay
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
Light micrographs of rumen papillae biopsied during the high forage and hogh grain diets (Adapted from Steele et al. 2009)
Rumen properties Largest compartment
On left side of animal
Contains micro-organisms
Ferments cellulose
Absorbs VFA’s
Divided into chambers
Continually contracting
Contains papillae
Produces CO2 and CH4
pH close to neutral (6 - 7)
Ruminant stomach
Rumination
Rumination occurs in resting.
The highest incidences of rumination occur during
afternoon and in the middle of the night.
Ruminant stomach
Ruminant stomach
The time spent ruminating by a given animal depends:
The texture of the food
The amount of food ingested
Cattle may ruminate from 35 to 80 minutes per
kilogram of roughage consumed
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 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
Ruminant stomach
Ruminant stomach
Ruminant stomach
Rumen investigation and sampling
Ruminant stomach