2. • Food is continuously subjected to
movement that break it up and
ensure that its effective mixture with
the digestive juices from the time of
its entrance into the mouth until the
undigested residue leave the body.
• The first part of this process,
prehension, mastication, swallowing
of food constitute an ordered
sequence of event that result in
bolus of food mixed with saliva
entering the stomach.
INTRODUCTION
3. PREHENSION
•Conveying the food into mouth
is called prehension. method
are vary in different animals,
but in all domestic animal the
,lips , teeth, and tongue are the
principal organ of this function
4. • Sensitive mobile lips its main prehension
organ
• During grazing lips are drawn back to
allow the incisor teeth to serve the grass
at its base
HORSE
• Tongue is the main prenesile organ
• It is long, rough, mobile and can readily
curved around herbage which is then
drawn between the incisor teeth and
dental pad and served by movement of
head
COW
5. SHEEP
• Sheep have a cleft upper lip, which permit very
close grazing. the incisor teeth and the tongue are
its principal organ
PIG
• Pig dig up the ground with the snout rooting, and
food is carried to the mouth largely by the action of
the pointed lower lip
DOGS AND CATS
• Dogs and cats convey food through the mouth by
means of the tongue
6. MASTICATION
• Mechanical breakdown of food in the mouth
• Main purpose of mastication is to break down the food to
provide a greater surface area for digestive juices and
chewing is to mix food thoroughly with saliva such mixing
ensures adequate lubrication of the food bolus for its
uninterrupted passage down the esophagus
• In the domestic animal the incisors teeth are used to
procure food by a tearing and scraping action and molar
teeth are used for grinding food
• In carnivores and omnivores the movement of jaw are in a
vertical plane and produce a shearing action
• In case of herbivores the movement are in a lateral due to
tough, coarse plant food
7. DEGLUTITION
• Passage of food from the mouth, through
the pharynx and esophagus to the stomach
• It commences as a voluntary act but become
reflex during its execution, and it is relatively
rapid event that involve many structure
• After mastication and salivation, the mouth
and tongue bring the food bolus into a
position that it on the midline between the
tongue and hard palate and suitable for
swallowing
8. • At this stage the food is in contact with receptors of
the posterior part of the mouth and posterior wall of
pharynx
• Impulses from the receptors pass along the
Glossopharyngeal nerve, superior laryngeal branch of
vagus nerve, maxillary division of the trigeminal nerve
to the salivary center in medulla
• Afferent impulses in the swallowing center also arise
from the lower part of the pharynx and the upper part
of the epiglottis
• Swallowing center also form by collection of nerves
cells located in the floor of fourth ventricle of the brain
• Different afferent pattern may stimulate the center, but
once it is stimulated, complete sequence of events
associated with swallowing is evoked by discharge of
impulses through motor nuclei of cranial nerve 5, 9, 10,
11, 12
9. The pattern of movement brought about by the rapid
sequential discharge of impulses along the motor nerve in
response to stimulation of afferent receptors by the food
It begins with a series of events that have their objective
closing of the nasopharynx and trachea from the mouth
cavity to prevent of food material into these areas
Respiration is inhibited at this stage
End result of all these events is that the mouth and the
pharynx form a completely closed chamber
10. ESOPHAGUS
•Once the bolus of food has entered the
esophagus the bolus takes a path through
a long tube that varies in width and
functions which essentially consists of at
least two muscle layers that will act to
propel the bolus down the tract
•Contraction of these muscles is controlled
by a novel and unique collection of
neurons that form the enteric nervous
system, the so‐called “brain of the gut.”
11. ENS
• functions from esophagus to anus. It consists of two layers of
nerve cell bodies named on the basis of their location
• The cell bodies of the submucosal plexus (Meissner’s plexus)
lie within the submucosa below the tunica mucosa.
• The cell bodies of the myenteric plexus (Auerbach’s plexus) lie
between the inner circular smooth muscle layer that stretches
around the circumference of the intestine and the outer
longitudinal smooth muscle cells that runs parallel the length
of the intestine.
• These nerve cell bodies extend sensory fibers to the
secretory, absorptive, and enteroendocrine cells lining the
lumen of the gut, as well as sensory fibers within the lamina
propria, submucosa, and muscle layers. These sensory
neurons can detect a variety of changes within the gut,
12. • including distension (stretch receptors), pH of the
luminal contents, osmolarity, and even the
presence of certain toxins.
• These sensory neurons can then relay that
information to other neurons within the
submucosal or myenteric plexus which may in turn
activate efferent neurons within the submucosal
and myentericnerve plexuses to respond to the
detected change.
• The efferent neurons of the ENS can secrete a wide
variety of neurotransmitters to interact with
receptors on their target cells. These include
acetylcholine, norepinephrine
13. INNERVATION
• Main motor nerve supply to the esophagus is from
the vagus nerve
• Variation among different species, cervical region
receive fiber from recurrent larnygeal nerves ,
reminder of the esophagus receive fiber from the
throcic vagal trunk
• Wall of the esophagus are made up of smooth
muscle, a myenteric plexus is present, this
myenteric plexus does not exist in species in which
esophagus made up entirely of striated muscle
14. MOVEMENT OF ESOPHAGUS
• Movement of esophagus associated with swallowing
is perisataltic wave that trevel from the upper
esophagus to lower esophagus sphincters
Primary peristalsis - elicited only by a swallowing
movement
Secondary peristalsis – introduction of bolus or
foreign body will elicite a peristaltic movement
• The significance of secondary peristalsis appear to
that if primary wave initiate by a swallow succeeds
only in passing the bolus into the upper portion of
the esophagus, then the bolus itself cause a series of
reflex that will derive the bolus onward
15. Movement of bolus down to
oesophagus
• The lower oesophageal sphincter is normally kept
tightly shut to prevent stomach contents and acid from
entering the oesophagus.
• As with most sphincters of the gastrointestinal tract,
the lower oesophageal sphincter consists of a greatly
enlarged inner circular smooth muscle. Gastrin, a
hormone synthesized by enteroendocrine
• cells in the pyloric stomach when the stomach is
distended, and vagal parasympathetic stimulation act
together to keep the sphincter muscle tightly shut.
Relaxation of the lower oesophageal sphincter is
mediated by VIP, a neurotransmitter produced by
16. • local ENS neurons in response to the presence of a
bolus of food distending the area of the sphincter
muscle.
• In most species, opening of the lower esophageal
sphincter is accompanied by a peristaltic wave
within the esophagus, which pushes the bolus into
the stomach, and relaxation of the musculature of
the stomach, reducing pressure within the stomach
so that as the lower esophageal sphincter relaxes
material is not ejected into the esophagus.
• Distensibility of the stomach can be a factor
limiting the size of meals
17. Gastro-intestinal smooth muscle
In the smooth muscle, as in other excitable tissues, there is normally an electric
potential of about -50mV
Slow waves are, spontaneous, slow, transient depolarization of the membrane
potential apparenetly conducted for varying distance along the tract
Spikes are faster transient depolarization that can occur in burst at the period of
maximal depolarization of a slow wave these rapid transient precede and appear
to intiate contraction
Parasympathetic stimulation increase the rate at which these potentials depolarize
the membrane, thus increasing the Rate of spike discharge.
Sympathetic stimulation prolongs the rate at which the generator potential
depolarize the membrane and thus slow the rate of spike discharge
18. MOTOR FUNCTION OF STOMACH
FUNCTION
• Storage of food and the controlled release of its contents into
the duodenum
• Antrum is the gastric pump and regulates the propulsion of
food pass into the pyloric sphincter and into the duodenum
RATE OF GASTRIC EMPTYING
• Liquid leaves the food at faster rate than does particulates
thus the stomach is given time for necessary solubilzation and
partial digestion of its particulate contents
• Rate at which fluid content are delivered to the duodenal
receptors responding to the chemical composition of the meal
• Rate of gastric emptying is a function of the square root of the
volume
19. VOMITING (EMESIS)
Vomiting is the spasmodic and forceful ejection of the stomach
contents to mouth through dilated oesophagus.
o Vomiting is very rare in horse
o In carnivores and omnivore vomiting is common
o Herbivores and rodent never vomit
o The vomiting centre is located in the medulla
o The cranial nerves 5, 7, 9, 10 and 12 to the upper gastro-intestinal
tract
o spinal nerves to the diaphragm and abdominal muscles are the
efferent nerves involved in the reflex act of vomiting.
20. Contin…
• After a deep involuntary inspiration, the glottis and the nasopharynx
are closed by elevation of soft palate.
• Relaxation of oesophagus, gastro-oesophageal junction and the body
of the stomach followed by strong pyloric contraction.
• The intra-thoracic pressure is increased by the contraction of
diaphragm and abdominal muscles.
• Additional pressure exerted by the contraction of abdominal muscles
and the diaphragm, force the stomach contents into mouth through
the relaxed oesophagus.
21. INTESTINAL MOTILITY
The functions of the intestinal movements are :
• To mix the ingesta with digestive secretions
• To bring the digested products in contact with
intestinal mucous membrane for absorption
• To move the food masses from place to place in the
intestine
• To expel the residue from the rectum through anus
• To assist in flow of blood and lymph through vessels
of intestinal wall
22. Motility in small intestine
• Motility of the small intestine occurs in two phases:
– one during digestive period following food intake and
– the second phase during interdigestive period, when less
food is present in gut
Digestive phase
Two patterns of motility occurs:
propulsive/peristalsis
nonpropulsive/segmentation.
23. Segmentation
• Contraction of circular muscles.
• During segmentation, a mass of food lying in a length of intestine (3-
4cm long) is divided into smaller ovoid pieces by constrictions caused
by circular muscles.
• Within few seconds, the constricted portions relax and new areas get
constricted.
• Segmentation may be taking place in many different areas of small
intestine at the same time.
• The amplitude of segmentation varies and is strong after feeding.
• The effect of segmentation is to mix the food material with digestive
secretions
• Myogenic in origin
• Increased by vagal stimulation and inhibited by epinephrine.
• Segmentation occurs in dogs 17-18 times a minute in the upper
jejunum and 12-14 times a minute in the ileum.
25. Peristalsis
• This is the main mechanism for the onward movements of
semisolid intestinal contents.
• Achieved by creation of a rings of contraction
• A Stimulus at any point in the intestine can cause
contraction above and distension below.
• The wave of contraction and relaxation moves along the
intestine as a peristaltic wave
• Movement is neurogenic and is carried out by intrinsic
nerves
26. Movements of caecun and colon
• Ingesta first enter the caecum of the horse …colon
• In sheep first colon - caecum
• In ruminants , rodents – caecum (microbial digestion) and retrograde
movement of the contents from proximal colon to the caecum(delay
transit)
• In horse no retrograde movement
• Large colon and caecum …microbial digestion …horse
• In general two types of contractile movements..colon
• First – stationary haustral contractions …mixing
• Second - oral and aboral peristaltic movements
27. Control of large intestine motility
• Slow wave activity in colon
• Direction and force of contraction differ from SI
• Pacemaker in midcolon – electrical slow waves …both directions
• Pacemaker in proximal colon – slow waves…aborally(low freq.)
• Aboral transit is delayed
• Colon pacemaker – second type signal – migrating spike burst
- Mass movement of the ingesta
• Neural and endocrine control – not well understood
• Cholinergic drugs – increases contractions
• Adrenergic drugs – inhibitory to spike activity (at high doses)
• Gastrin and CCk stimulate contractions …colon smooth muscle
• Secretin inhibit contractions
28. Defecation
• Defecation is a reflex act in which faeces are
discharged from the terminal colon and rectum
• Efferent pathway – defecation reflex … cholinergic
• Frightened animals frequently defecate
