ASSIGNMENT: Chapter 11,
Clinical Anatomy and Physiology for Veterinary Technicians
Chapter 6, An Illustrated Guide to Veterinary Medical Terminology (might be
different types of digestive systems will be studied in this unit: the monogastric (single
stomach), the ruminant (multiple "stomachs") and the equine
will also be covered briefly.
Monogastric digestion will be studied in depth since many of
the structures and secretions are similar to the other species.
a) Give examples of monogastric and ruminant species
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The oral cavity
The mouth (oral cavity) is the beginning of the
digestive system. Food is grasped and chewed by the teeth. It is broken into smaller more
easily processed pieces. The salivary glands produce salvia which moistens and
lubricates the food for easier swallowing. Some species' (hogs, humans and rats) salvia
contains amylase, an enzyme which begins the chemical breakdown of carbohydrates. There is species
variation in the number of salivary glands and the types of secretions from
The functions of
salivary glands include:
moistening and lubrication of food
secretion of small amounts of
a bacterial static enzymes to help resist infections
cooling the body through panting
protection of oral cavity from drying
enzymatic digestion of carbohydrate by amylase
(certain animals only).
b) Which species cools their body
via the salivary glands?
c) Why do animals salivate before vomiting?
The tongue helps propel food into the esophagus
and is used to "lap up" liquids in dogs and cats.
The esophagus is the muscular "food"
tube which connects the oral cavity to the stomach. It has two muscular layers, one
circular and the other longitudinal. Food is moved "along" in waves
(longitudinal muscle layer) and "squeezed" or segmented by the circular muscle
layer. There is both voluntary and smooth muscle in the esophagus, (the amount varies by
species). The dog, cow and sheep have the most voluntary muscle.
Does the amount of striated
muscle in the esophagus of cattle, sheep and dogs relate to any unique
digestive actions of those species?
The stomach is a muscular and expandable pouch
that regulates the movement of food into the intestines and begins the digestion of
specific nutrients. The stomach contains two functional sphincters for regulation of food
movement. One is at the entrance into the stomach (cardiac sphincter) and the other is at
the exit (pyloric sphincter). These sphincters are composed of bands of smooth muscle
which constrict to partially or fully close.
The stomach contains three muscular layers
right angles to each other. When these muscles contract the gastric contents are churned
and mixed. The inner layer of the stomach is termed the mucosa. It is highly vascular and
contains lots of glands that secrete digestive juices. The mucosa has deep folds called
rugae which can stretch to increase the size of the stomach.
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There are several different gastric secretions
from the various types of gastric glands located in different parts of the stomach.
The secretions include:
gastrin (a hormone)
Hydrochloric acid combines with pepsinogen and is
converted to pepsin, (the "active" chemical form) which begins the breakdown of protein. The enzyme
gastric lipase begins the breakdown of lipids (dietary fats). The hormone gastrin acts as
a messenger, signaling the small intestine to prepare for the arrival of food.
intestine does this by secreting appropriate enzymes. The pH of the stomach is low,
about 2 (which is very acidic). The mucus which is secreted and coats the delicate lining of the
stomach protects it from ulceration.
After gastric digestion is complete the pyloric
sphincter opens allowing food into the intestines. The sphincter relaxes when the
consistency of the food is "soupy" and the pH is very low.
Clear liquids are passed
through the stomach in a short time, usually 30 minutes or less, while solid food may
take hours before leaving the stomach. When food enters the stomach the gastric-colic
"reflex" is stimulated, and the feces moves from the colon (the last part of the
large intestine) to the rectum. This takes about 30 minutes (for evacuation
of feces from the body). This reflex action is caused by enervation
between the stomach and colon.
d) What does this mean in relation to house
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a = esophagus, b =body of stomach, c = pancreas, d= transverse colon,
e=jejunum, f=ileum , g=cecum, h =duodenum
The small intestine
The small intestine is a muscular tube composed of
three parts: the duodenum, jejunum and ileum. There are two smooth muscle layers arranged
in a similar manner to the esophagus, circular and longitudinal. When the longitudinal
muscles contract a wave-like action termed peristalsis,
food moves along the digestive
tract. When the muscles that encircle the intestines contract, there is segmentation of the
The duodenum receives acidic food
from the stomach. It is then mixed with bile from the gall bladder and
digestive enzymes from the pancreas (that enter the duodenum via ducts.) There are also enzymes and chemicals involved in
digestion secreted by the duodenum. These substances act on specific types
of food to digest it before absorption. Most of the chemical
breakdown of food occurs in the duodenum, but there is very little
Much of the absorption of food takes place in the
jejunum. The surface area of the inside of the duodenum and jejunum is increased by
innumerable tiny projections, the villi. The villi are covered with even smaller
microscopic projections on
their surface termed microvilli (brush boarder).
Within the microvilli are extensive capillary networks
and lymphatic vessels. Nutrients are absorbed from the lumen of the intestine into
intestinal cells and then into the capillaries or lymphatic vessels inside
the microvilli and villi.
By this time the large chunks of
food that were ingested have become tiny molecules and can move across cell
membranes. Lipids are absorbed into the lymphatic vessels.
The last portion of the small intestine is the
ileum. The ileum is the major area for absorption of water and water soluble vitamins from
the small intestine. It joins with the large intestine, a small
"pouch" also diverges off the intestine here termed the cecum.
e) What is the cecum called in humans?
The length of the small intestine varies
among species, herbivores have the longest (relative to their size). A cow can have as much as
50 yards of small intestines, the average sized dog has about 4 1/2 yards of small
intestine. But the dog has such an extensive network of villi and microvilli that the
actual surface area for absorption is estimated at 100 square meters!
The large intestine
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Descending colon cross section
The colon is divided into three parts based
location in the abdomen. The first part, the ascending colon, is directed cranially. The
transverse colon crosses from the right to the left side of the abdomen and the last part
the descending colon is directed caudally.
The rectum is the last portion of the large
intestines and the storage area for feces. The exit of the digestive system to the
environment is the anus.
The large intestine has no villi, but in horses
and hogs contains outpouchings or saccules. There is bacteria in the large intestines of
all species, which ferment and assist in the breakdown of plant fiber. There are also
mucus secreting glands which lubricate the feces.
The absorption here is similar to that of the
ileum, primary water, electrolytes and vitamins (but NOT the fat soluble A, D, E &
K) are absorbed.
Movement of food through the intestinal tract.
Food is propelled through the digestive tract by
the contraction of smooth muscles. The longitudinal muscles of the intestines cause
peristalsis, the slow, wave like rhythmic contractions that moves food through the system.
The contraction of the muscles encircling the intestines causes segmentation and the
mixing of food with digestive juices.
These contractions are influenced by three factors:
1) the autonomic nervous system (primarily the vagus nerve of the parasympathetic
2) hormones released from one part of the digestive system acting on another
3) the intrinsic system of the intestinal tract
The intrinsic system is a specialized nervous
system located within the digestive tract which acts somewhat similar to, but separate
from, the regular nervous system. Throughout the digestive system pacemaker tissue
(similar to the pacemaker tissue in the heart) is located. This tissue triggers activity
in the smooth muscles which causes regular peristalsis and segmentation.
The last part of the digestive process is
evacuation of the rectum (defecation). It involves the defecation reflex. When the rectum
is distended with food it causes contraction of smooth muscle and the relaxation of the
anal sphincter muscles, which are voluntary striated muscles. In very young animals the
sphincter muscle is not well developed and between the gastric-colic reflex and the
defecation reflex there is little control over bowel movements. There is considerable
species variation in numbers of bowel movements per day, cows may defecate 20 times daily
while carnivores generally defecate 2-3 times daily.
Accessory Organs of digestion
The pancreas is a
long, thin delicate organ that sits behind the stomach and next to duodenum. It is a
pinkish gray color and appears glandular. The pancreas produces the following substances
which are essential in the digestive process:
1) amylase, an enzyme, involved in carbohydrate digestion
2) lipase, an enzyme, involved in lipid digestion
3) trypsinogen which is
activated to trypsin, also an enzyme, and is involved in protein
bicarbonate which acts to neutralize acid is also secreted.
A duct leaves the pancreas
carrying these substances and empties into the duodenum. In some species the pancreatic
duct joins with the bile duct (forming the common bile duct) and other species have a
secondary pancreatic duct.
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The liver is the largest organ in
the body (discounting the skin) and it is very complex. It performs many
life sustaining functions. It is located behind the diaphragm and is divided into
lobes which are visible with the naked eye. Lobes are composed of microscopic lobules.
To understand the functioning of the liver, it is
important to appreciate the complicated microscopic anatomy of the liver,
remember - form follows function. Lobules are
microscopic six sided hexagon like structures, formed by tall columns (or slabs) of cells
radiating outward from a central vein. These columns are arranged somewhat like the spokes
of a wheel, with a central vein in the center. There is a small space between
the columns of cells, the sinusoids. The sinusoids are where the liver cells, hepatocytes,
are exposed to blood.
a=central vein, b=hepatocytes (liver cells in "slabs"), c= sinusoid,
d=arteriole(from hepatic artery), e=lymphatic vessel, f= venule from portal vein
Hepatic blood supply:
The blood supply to the liver is
unique. Three main vessels run to and from the liver.
1) The hepatic artery, which supplies oxygen and
nutrients for liver metabolism.
2) The hepatic vein, which drains unoxygenated blood from the liver to the
3) The portal vein, part of the portal hepatic system. A portal system
connects a capillary bed to another capillary bed. The portal vein
connects capillary beds between the gastrointestinal system and the liver.
Although the portal vein brings blood to the
liver, this blood has very little oxygen so the liver has another source of oxygenated
blood, the hepatic artery. The hepatic artery branches off the aorta, about 30% of the
total cardiac output flows to the liver. The hepatic vein leaves the liver carrying
nutrients for the body (made by the liver) and waste products. It empties into the vena cava.
The large prominent portal vein brings blood to the liver, remember
arteries usually bring blood "to" organs. The
portal vein receives
blood from the gastrointestinal tract capillaries (stomach, pancreas, spleen and
intestines). The intestinal capillary bed attaches to another
capillary bed, inside the liver. The blood coming from the intestinal capillaries contains
nutrients (molecules) from digested and absorbed food. These nutrients are further
processed in the liver as they circulate through the sinusoids. The nutrient molecules
(proteins, carbohydrates, fat) undergo further enzymatic digestion termed, intermediate
metabolism, by enzymes secreted from liver hepatocytes. The fully metabolized nutrients become
amino acids (units of protein), simple sugars and fatty acids that are utilized by the
body for energy and building blocks.
artery, C=portal vein, D=liver, E=Vena cava
In addition to intermediate metabolism the liver also
produces bile and stores it in the gall bladder. The liver also manufactures and stores
glycogen, which is the only storage form of sugar in the body.
Main functions of the liver:
The liver has dozens of important functions in the
body. Many of its functions are related to the numerous liver enzymes. Some enzymes
"break down" molecules while others work to "combine" molecules and form new
essential substances for the body.
Below are some of the non digestive functions of
1) detoxification of most medicines, alcohol and harmful substances from the
2) production of blood clotting factors
3) storage of glycogen (the only storage
form of sugar in the body)
4) destruction of old non functional red blood cells
5) storage of vitamins and minerals
6) removal of hormones from there body
7) formation of urea (thus removal of ammonia from the body)
8) formation of plasma
proteins globulin and albumin (used for the building blocks of the body and the immune
Don't forget about
of rumen, b=rectum, c=spiral colon
Ruminates provide milk, meat and wool for much of
the world. They do this by converting food that is useless for carnivores into energy.
Ruminants have a unique digestive system that
allows for the digestion of hay, grass, corn cobs, and even a small amount of urea
(i.e. chicken droppings!). They convert these substances to proteins, vitamins, fatty acids, methane gas and
Ruminates have three extra "stomachs" where
millions of bacteria and protozoa (single celled organism) live. These microorganisms
produce special enzymes that breakdown cellulose (plant fiber).
The rumen stomachs and
cross sections of stomachs
A=interior of rumen, B=interior of reticulum, C=interior of omasum, D=abomasum,
E=caudal diverticulum of rumen, F=reticulum
Only ruminant animals have thes microorganisms to digest cellulose
living in the three extra digestive "vats".
three specialized stomachs of ruminants are termed the forestomachs (i.e.
located before the true stomach, not 4 stomachs)
The most cranial stomach is the reticulum, it's lining looks like a honeycomb.
largest compartment, the rumen occupies an area from the diaphragm to the pelvis,
primarily on the left side of the abdomen. In a large cow the rumen can hold up to 150
liters It is partially divided into two chambers by muscular pillars and within each
chamber is a diverticulum. These separations distribute the weight more evenly, think how
hard it would be for a wild ruminant to run and jump if there was a hundred pound ball
food churning in the rumen! Most of the fermentation (microbial digestion) takes place in
The omasum is a rounded compartment, filled with muscular laminae which descend
from the top downward. The lamina have been compared to the pages of a book in appearance.
The lamina are covered with papilla and function to grind food.
The last stomach,
the abomasum is the true stomach and is similar in function to the monogastric stomach.
For the successful digestion of roughage, like
hay, the food needs to be exposed to the microbes for long periods. To achieve this
ruminants regurgitate their food and chew it again, this is
rumination. They have to
eructate or belch to release the huge quantities of methane gas produced by microbial
g) What would happen if a cow did not
Ruminates also secrete copious amounts of saliva,
which is needed for the rumination process. A 190 liters
of salvia was
measured in a day, via
cannulation of salivary ducts in dairy cow.
It is sometimes possible to feel/palpate the ruminations
of cattle by placing your hand in their paralumbar fossa (flank region) and waiting to feel
the contractions (lifting) of abdominal muscles which signal the rumination. Normally
cattle ruminate about 3 times a minute after eating. Ruminant animals need to spend about 8
hours a day ruminating to digest and utilize their food. When cattle are stressed or sick
they stop ruminating. Often the first question the bovine practitioner asks
cattleman/dairyman when called out to treat a sick cow is "is she still
Members of the equine family are monogastric
herbivores. They have a specialized fermentation vat, the cecum, for the microbial
digestion of cellulose. The cecum in the horse is very different than in carnivores. All
food traveling through the intestines must enter the cecum, via the ileocecal valve. This
allows roughage to be digested by the enzymes of the bacteria and protozoans living in the
cecum. The cecum extends from the flank region to the diaphragm and is coma shaped, it
holds about 15 quarts in the average horse.
Horses have a complex large intestine which allows
the absorption of the feed processed by the cecum.
Other unique equine digestive feature include:
levels of amylase in saliva
2) absence of a gall bladder (there is a constant release of bile into the
3) a relatively small stomach with approximately a 3 to 4 quart capacity
Horses are "designed" to be grazers, to ingest small
volumes of feed frequently. If wild equine species are compared with todays horses
(that often spend many hours daily in stalls and are fed large "meals" of
carbohydrate rich food) it is easy to see why many domestic horses have digestive
h) What is the name of the most serious
New born animals (neonates) of different species
have very similar digestive tracts, in fact, a foal, puppy and calf are more like
one another than adults of their own species (relative to the digestive
for several adaptations it would be difficult for neonates to ingest enough nutrients for
They have relatively longer and more distendable intestines than adult animals,
this allows for a large capacity and more chance for absorption of nutrients.
They also have
special enzymes to digest milk sugars (lactase and maltose).
For the first day or so after
birth they can absorb maternal antibodies (large protein molecules in the "first
milk" of the mother) which fights off infection.
They also lack proteolytic enzymes,
so these antibodies are not destroyed.
i) What is the first milk called?
Neonates have a "suckling reflex" which
stimulates peristalsis and digestive secretions when suckling begins. The liver
does not become fully functional in neonates until several weeks after birth.
Although they have not ingested anything a newly born animal often has
bowel movements immediately after birth; this fetal fecal matter is called meconium.
A unique feature of young ruminates is
the esophageal groove. It is a groove like structure formed by contraction of smooth
muscle extending from the esophagus to the omasum. This temporary tube allows milk to bypass the rumen and
reticulum (which are useless for milk digestion). The groove is formed when the
calf suckles. The rumen doesn't become functional until a few months of age. The young
ruminant ingests the needed bacteria and protozoa by licking and chewing objects, by
grazing and by eating the mother's feces.
Clinical Anatomy and Physiology for
Veterinary Technicians by Colcilla and
Please answer these questions and return answers by e-mail to Dr.
Assignments will be “spot checked” and logged in and answered e-mailed
back to student after receiving assignment. The student is responsible
for noting the correct answers. The questions might be included on exams
system – chapter 11
1. What is another name for the digestive tract?
2. If the prehensile organ is severely damaged in
the horse what will probably happen?
3. Why are the teeth of cats pointed on the
4. Which domestic species has the most teeth?
5. What is floating of teeth? Why is it done?
6. Why do animals suffering from mega esophagus
7. Why is volatile fatty acids production essential
in ruminant species?
8. Where do ruminant species get most of their
9. Why does a liquid medication take effect quicker
than ingestion of a solid?
10. What hormone is secreted after ingestion of a
fatty meal to slow gastric emptying?
12. Why are there so many different pancreatic
13. How can elastase be identified as an enzyme?
14. If your cat had ileus would you need to change
the cat box often?
15. What is the cause (physiological mechanism)
that causes ascities in a patient with liver failure?
Answers to the italicized questions:
a) Give examples of monogastrics Dogs,
cats, humans, horses; ruminants: cows, sheep, goats.
b) Which species cool their body through help from the salivary glands? canines
- some rodents also wet their bodies by licking to cool themselves via
c) Why do animals salivate before vomiting? To protect esophagus from acidic
d) What does this mean in relation to house breaking puppies? Puppies have to go within
1/2 hour of eating and they can't hold it!
e) What is the cecum called in humans? appendix
f) Where are they absorbed? Via the lymphatics
g) What would happen if a cow did not eructate? Bloat
h) What is the name of the most serious equine disease? Colic
i) What is the first milk called? Colostrum