ANIMAL PHYSIOLOGY:
monogastric digestive tract
By: Eko Widodo
ENTER
Pre-test
1. Write an assay of not less
than 300 words on what you
know and understand about
monogastric digestive
physiology (in10 minutes)
 DIGESTIVE SYSTEM
ALIMENTARY
ORGANS
ASSESORY
ORGANS
+
Tonge
Teath
Salivary gland
Liver
pancreas
mouth
pharinx
FEED
Responsibility
Up-take
oesophagus
stomach
Small intestines
Large intestines
cloaca
digestion
absorption
Mouth ~> cloaca
Animals
Capacity (l)
Stomach
Small
intestine
Cecum
Colon
rectum
Dogs
63
23
1
13
Pigs
29
33
6
32
Horse
9
30
16
45
Cattle
71
18
3
8
Sheep &
Goat
67
21
2
10
anatomy
– the physiology of digestion and nutrition,
including:
 anatomical
views and digestive parts
identification
 the process of digestion and absorption
 factors affecting digestibility of feeds
Digestion and Absorption:
 The
process of digestion includes:
– The prehension of food or feed
– The mechanical chewing and grinding
– Mixing with digestive acids and enzymes to
chemically break down the foodstuffs
 The
process of absorption includes:
– Transport of the digested foods across the
intestinal mucosa to the blood or lymph
system
The General Mechanical Process:
 Mastication
- chewing
 Deglutition - swallowing
 Regurgitation - movement of digesta in
reverse order from the stomach to
mouth
 Defecation - voiding the fecal, or waste,
materials from the body
Animal Diet Types:
 Species
may be divided into dietary
preference groups:
– Herbivores consume plant materials,
examples are horses and cattle
– Carnivores consume flesh of other
animals, examples are dogs and cats
– Omnivores consume both plants and
flesh, examples include the primates
Differing Digestive Tracts:
 Farm
animal species have a variety of
digestive systems
– Ruminants have four distinct stomach areas

examples include bovine, ovine and caprine
– Nonruminants (also termed monogastrics)
display considerable variety
 hogs,
dogs, and cats have a single, simple
stomach
 poultry have a two part stomach
 horses have a large, functional cecum
Nonruminant Digestive System:
 Mouth
- prehension and chewing of
food; some carbohydrate enzyme
activity
 Esophagus - route of food from mouth
to stomach
 Stomach - addition of hydrochloric acid
and protein digesting enzymes, mixing
and holding
Nonruminant Digestive System:
 Small
intestine - primary site of
digestion and absorption
 Large intestine - major site of water
absorption and preparation of digesta
for excretion
Nonruminant Variations:
 Poultry
– Mouth: no teeth for chewing
– Esophagus: a “crop” is contained within the
esophagus for food holding and moistening
– Stomach: divided into proventriculus
(glandular area) and ventriculus (crushing
area)
– small intestine: primary site for enzymatic
digestion
– Large intestine: short and exiting into the
cloaca; two large ceca with limited function
Nonruminant Variations:
 Horse
– Large intestine differences:
 cecum
is very large (may contain 50% of
digesta)
 cecum provides some nutrients to the horse via
microbial fermentation
Ruminant Digestive System:
 Many
parts of the tract are similar to
nonruminant monogastric description
 Significant differences include:
– Mouth contains no upper incisors
– Stomach is divided into four major parts
 rumen
 reticulum
 omasum
 abomasum
Ruminant Digestive System:
 Rumen
– Largest digestive area of the compound
stomach
– Majority of fermentation of feedstuffs
occurs here
– Majority of absorption of byproducts of
fermentation - volatile fatty acids or “VFA’s”
Ruminant Digestive System:
 Reticulum
– Receives feed from esophagus
– Initiates mixing, regurgitation, and
eructation
– Environment for fermentation of feedstuffs
Ruminant Digestive System:
 Omasum
– Third area of the stomach receives the
digesta outflow of the rumen/reticulum
– Some water absorption and further
subdivision of feed particles may occur
Ruminant Digestive System:
 Abomasum
– The fourth and final stomach compartment,
but very similar in function to the pig
stomach
– Acid and enzyme stomach
– Final holding and mixing area before the
small intestine
Ruminant Digestive System:
 Selected
terms:
– Regurgitation - controlled reverse
movement of coarse feedstuffs from
reticulum/rumen via esophagus to mouth
for rechewing
– Eructation - expulsion of accumulated
fermentation gases from rumen via
esophagus
– Rumination - refers to the processing of
feedstuffs in the reticulum/rumen, to
include fermentation, regurgitation,
Chemistry of Digestion:
 Digestion
involves enzymes and acids
produced by the host animal or
microbes working in symbiosis with the
host
– Enzymes break specific chemical bonds in
feeds
– Domestic animals produce enzymes to
digest nonfibrous carbohydrates, fats, and
proteins
– Only microbes have enzyme systems to
digest fibrous carbohydrates, such as
Digestion of Carbohydrates:
 General
carbohydrate digesting enzyme
(amylase) in the mouth begins
digestion; little amylase is found in
horses and none in ruminants
 Carbohydrate digesting enzymes
(amylase) from the pancreas, and
intestinal mucosa (sucrase, maltase,
lactase) complete carbohydrate
digestion
Digestion of Proteins:
 Protein
digesting enzyme (pepsin) and
hydrochloric acid in the stomach begin
significant digestion
 Protein digesting enzymes (e.g. trypsin)
from the pancreas and intestinal
mucosa complete digestion in the small
intestine
 Young nursing animals – rennin
coagulates milk allowing more complete
digestion
Digestion of Fat:
 Fat
digesting enzyme (lipase) in the
stomach begins digestion
 Fat digesting enzymes from the
pancreas (lipase) and intestinal mucosa
complete digestion in the small intestine
 To assist in fat digestion, bile from the
liver emulsifies fat into smaller droplets
in the small intestine
Factors Affecting Digestibility:
 Rate
of passage - in general, increased
rate of passage of digesta through the
tract reduces digestibility, factors
increasing rate of passage include:
– Increased level of feeding/intake (ruminants)
– Finer processing (such as grinding) of feed
Note: grinding grain usually increases
digestibility but grinding hay decreases
digestibility
stomach
Divided into cardia (entrance), fundus
(body) and pylorus (termination)
Cardiac gland region
This is not necessarily in the cardia which is
usually non glandular. This mucosa contains
glands which produce mucus.
Fundic gland region
Fundic glands are simple and tubular and
contain 3 types of cells:
1. Mucus neck cells, which produce mucus
2. Parietal cells, which produce HCl
3. Peptic or zymogen cells, which produce
enzymes
Pyloric gland region
These glands are lined entirely with mucussecreting cells like those within the cardiac
glands. The hormone gastrin is produced by
G cells of the pyloric gland.
Gastric juice
Is the total secretory product (fluid) from
the surface epithelial cells and the cardiac,
fundic and pyloric glands of the stomach.
It is colourless and is made up of two
components; a parietal cell acid
component, and an alkaline component
containing pepsin, mucin and electrolytes.
Pepsin
Is synthesised in the peptic cells from
the inactive precursor, pepsinogen. It
begins the digestion of protein in the
stomach if the pH is acid. Proteins are
converted to proteoses and peptones in
the stomach, and digestion of protein
Is completed in the intestine.
Rennin
Is a milk clotting enzyme
secreted as inactive prorennin
which Is activated by the
presence of acid. In adition to
clotting milk rennin also
exhibits proteolytic properties.
It is foundin the gastric juices
of calves, lambs, and young
pigs.
Gastic lipase
Is present in low
concentration in the gastric
juice of carnivores. It can
hydrolyse fats that are
emulsified, such as milk fat
but probably had little effect
on unemulsified fats.
Hydrochloric acid
Is produced by the parietal cells of
the fundic glands of the stomach of
all vetebrates. HCl activates pepsin
and rennin and aids pepsin in
protein digestion by lowering the
pH of the stomach contents.
Phases of gastric juice secretion
Cephalic phase
Presence of food in the mouth may result
in the secretion of gastric juice in the
stomach.
Gastric phase
When food reaches the stomach, gastric
juice secretion Increases for a period up
to several hours.
Intestinal phase
When products of gastric
digestion reach the duodenum,
intestinal gastrin is produced.
Pancreas and pancreatic secretion
The pancreas consists of exocrine and
endocrine portions. The exocrine part
consists of acini responsible for the
production of pancreatic juice and ducts
which convey the juice to the duodenum.
The endocrine portion is made up of the
Islets of langerhans which secrete insulin
into the bloodstream.
Pancreatic juice is secreted under the
influence of two hormones produced In
the mucosa of the duodenum.
Secretin increases the rate of flow
and hydrocarbonate concentration of
the pancreatic juice.
Pancreozymin increases the amount
of enzymes In the pancreatic juice. An
additional factor which results in a
pancreatic juice rich in enzymes Is
neurogenic stimulation by the vagus
nerve.
Pancreatic juice contains sodium
carbonate, which neutralises acid from
the stomach and Increases alkalinity of
intestinal fluid, and a number of enzymes
for the hydrolisis of proteins, fats and
carbohydrates.
There are 3 major group of enzymes In
pancreatic juice.
1. Pancreatic proteases or proteolitic
enzymes in the pancreas are trypsin,
chymotrypsin A, chymotrypsin B, and
the carboxypeptidases.
2. Pancreatic amylase is an αamylase,
probably structurally identical to
salivary amylase secreted in an active
state. Amylase attacks starch grains and
produces dextrins and maltose. Maltase
is also present in pancreatic juice and it
hydrolyses maltose to glucose.
Pancreatic lipase is secreted in an
active form and it hydrolyses fats into
carboxylic (fatty) acids and glycerol.
Pancreatic lipase is most effective
after the fats have been emulsified by
bile.
Bile is a greenish yellow liquid
consisting largely of water, bile salts,
bile pigments and cholesterol with
smaller amount of fats and inorganic
salts.
Intestinal secretion
Intestinal juice, called succus entericus, is
produced by the intestinal glands scattered
throughout the entire small intestine, and
submucosal duodenal glands. Secretion of
these glands is stimulated by the presence of
food in the intestine. The release of
intestinal juice Is also brought about by
hormone called enterocrinin.
In addition to water, salts and mucus, a number of
enzymes have been described In the intestinal
juice. These include enterokinase (which activates
trypsinogen), and the following inverting
enzymes:
Maltase - hydrolyses maltose to glucose
Sucrase - sucrose to glucose and levulose
Lactase - lactose to glucose and galactose
Peptidase - peptides to amino acids
Polynucleotidase - splits nucleic acids into
mononucleotides
Nucleotidase - nucleotide into nucleosides and
phosphoric acid
prehension
The manner in which food is grasped. Picked up,
carried to the mouth, mixed with saliva and
manipulated before swallowing
deglutition
The process in which food particles are
swallowed whole and pass to the crop
Passage of ingesta through the tract
Rate
The rate of feed passage through the
alimentary canal is influenced by the
consistency, hardness and water content
of the feed and by the amount consumed.
Factors Affecting Digestibility:
 Rate
of passage - in general, increased
rate of passage of digesta through the
tract reduces digestibility, factors
increasing rate of passage include:
– Increased level of feeding/intake (ruminants)
– Finer processing (such as grinding) of feed
Note: grinding grain usually increases
digestibility but grinding hay decreases
digestibility
Motility
1. Crop and esophagus
2. Proventriculus
3. Gizzard
4. Small intestine
5. Large intestine