Agriculture Reference
In-Depth Information
The Abomasum
The abomasum has a capacity of between 2 and 3 liters
and lies on the fl oor of the right side of the abdominal
cavity; sometimes it can be detected also on the left side.
It is pear shaped and is located inside with spiraled folds
of the mucosa. It starts from the communication with the
omasum and ends by the communication with the small
intestine called pylorus. There a powerful sphincter (a cir-
cular muscle) is present, allowing the transit of the ingesta
to pass from the abomasum into the small intestine only
by a refl ex act. In the goat, as in all ruminants, the pyloric
sphincter forms a protuberance called torus pyloricus. The
function of the abomasum is to perform the chemical
digestion (the HCl hydrolysis). Most of the volatile fatty
acids (the short-chain fatty acids) like acetic, butyric, and
propionic acids have been absorbed at this point. The
advantage of the ruminants is that all the bacterial protein
that enters the abomasum provides an adequate protein
source for the host animal. The volatile fatty acids are
energy substrates produced during microbial digestion and
they provide nearly 80% of the ruminant's energy needs.
The goat stomach has a mechanical and a chemical role
in the digestion process, which will be detailed in Chapter
8, Digestive Physiology and Nutrient Metabolism.
intestine is the reabsorption of ingesta water. Also, there
is a microbial fermentation in the cecum and proximal
colon and much less in the distal colon, as the contents
become dehydrated. The cecum is much larger in diameter
than the small intestine. It is almost horizontally posi-
tioned, on the right side of the abdominal cavity. The colon
has three segments called ascending, transverse, and
descending colons. The ascending colon starts from the
cecum as a proximal loop. Then it is coiled making several
infl exions called the spiral loop, and ends as the distal loop.
The transverse colon is very short, in a transverse position
from the right to the left, and continues with the descend-
ing colon. The rectum, followed by the anal canal is the
last segment of the gastrointestinal tract and is located
within the pelvic cavity. The anus is the end and the caudal
opening of the digestive system.
The jejunum, ileum, cecum and ascending colon lie on the
greater omentum, in the space called supraomental recess.
The role of the intestinal mass is to continue the diges-
tion process of the ingesta, and to eliminate the waste
material. The entire physiology of digestion will be
detailed in Chapter 8, Digestive Physiology and Nutrient
Metabolism.
The Annex Glands
The liver is the largest gland of the body, whose complex
role related to digestion will be discussed in Chapter 8,
Digestive Physiology and Nutrient Metabolism.
Situated between the diaphragm and the stomach, the liver
has an oblique position from right to left and from dorsal to
ventral, because of the permanent pressure of the stomach
during the developmental life. The parietal surface lies
against the diaphragm, whereas the visceral surface comes
in contact with the stomach and the intestines (Figure 6.30).
The liver is suspended from the diaphragm by several
ligaments, and is connected to the stomach and the duode-
num by the lesser omentum. The liver is incompletely
divided by lobes. In all ruminants, it is provided by the
fewest lobes: left, quadrate, right, and caudate. The gall-
bladder, where the bile is temporarily stored, is insinuated
between the quadrate and the right lobes. It collects the bile
produced by the liver, leads it through the cystic duct (the
duct of the gallbladder), to empty as the common bile duct
into the duodenum, on the tip of the major duodenal papilla.
The pancreas makes contact with several viscera, such
as the rumen, omasum, spleen, liver, duodenum, right
kidney, and jejunum. It consists of the body, the right lobe,
and the left lobe. The portal vein is surrounded by a pan-
creatic notch. The pancreatic duct opens into the major
duodenal papilla, together with the bile duct.
T HE I NTESTINES
There are small and large intestines in all mammalian
species. The total length of the goat intestines is 20-40
meters, with the small intestine being between 20 and 30
meters. The average size of the large intestine is 7 meters
long. Small and large intestines (with the blood supply)
are shown in Figure 6.29. All intestinal segments have
a lumen and a similar constitution: the external coat is the
peritoneum, the middle coat is represented by smooth
muscles, and the internal coat is a specifi c type of mucosa.
The small intestine consists of three segments: duode-
num, jejunum, and ileum. The lumen of all of the segments
is the same, and is approximately 2 cm in diameter.
Functionally, they facilitate most of the digestion.
The duodenum travels on the right side of the body,
makes several fl exures, and continues with the jejunum. A
small elevation called major duodenal papilla can be seen
inside of it, where the bile duct and the pancreatic duct
open on its tip. The jejunum is the longest segment of the
small intestine. A fold of the peritoneum that is called
mesentery suspends the jejunum. The ileum is the shortest
segment of the small intestine, and it joins the cecum, the
fi rst part of the large intestine.
The large intestine consists of three segments as well:
cecum, colon, and rectum. The main function of the large
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