Advanced Physiology (part 1, Digestive system) By: A. Riasi (PhD in Animal Nutrition &...

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