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82 Tasks for the Veterinary Assistant

found in the body. The innate system is often the first body, with a few that are superficial enough to be felt if
line of defense and is composed of white blood cells enlarged. The popliteal lymph node is found caudal to
known as granulocytes; neutrophils, eosinophils, and the knee; the axillary is found in the armpit; the inguinal
basophils, and the white blood cell known as a mono- is found in the groin; and the submandibular is found
cyte. These blood cells circulate through the body and beneath the jaw.
take care of bacteria, parasites, allergens, and viruses as Diseases of the lymph system include lymphoma, a type
they come upon them or are called to the location by of cancer that is systemic and fatal. A biopsy of a swollen
cells in the tissues known as mast cells. These cells will lymph node can determine if it is cancer or some other
destroy pathogens either by ingesting them or by lymphadenopathy or disease of the lymph node. Cancers
releasing granules that destroy chemically. of the bone marrow can affect the production of white
The other response is from the adaptive system. The and red blood cells, either too few or too many or cells
adaptive system is largely made up of white blood cells that don’t do their jobs correctly. Autoimmune conditions
called lymphocytes. Lymphocytes are unique because make the blood cells attack “self” or normal body cells
they can adapt to whatever the body needs in the way of because they don’t recognize it as being part of the body.
defense against a pathogen. They are the cells that pro-
duce long‐term immunity to diseases. For example, one
type of lymphocyte will produce a receptor to detect Digestive System
antigens that are unique to a pathogen the body has
dealt with before. That lymphocyte will stimulate another The role of the digestive system is to take in food and
type of lymphocyte to produce antibodies against the extract the nutrients to nourish the body and then elim-
pathogen. These lymphocytes are very long lived and will inate the waste or unusable remainder. In the animal
take care of that pathogen at any time it enters the body. kingdom, some animals have one‐compartment stom-
Another type of lymphocyte roams throughout the achs called monogastric, or there are ruminant animals
body and attacks non‐self cells like cancer and new path- with four‐compartment stomachs. Cats, dogs, pigs,
ogens. If this occurs that lymphocyte will call for rein- horses, and most pocket pets are monogastric. Cows,
forcements and the different types of lymphocytes will sheep, goats, deer, and camelids are ruminants.
come to its aid. This lymphocyte can kill non‐self cells The digestive system starts with the mouth and the
and pathogens by releasing a chemical. taking in of food or prehension. Every animal has some
One way that innate and adaptive immune systems teeth; Table 5.1 shows the dental makeup and number
work together is by monocytes presenting antigens to for each animal.
lymphocytes. Monocytes phagocytize a pathogen, The teeth are used to break the food down into
meaning they encircle and destroy it. In the process they smaller parts. The tongue assists with keeping it in the
take a piece of the pathogen, called an antigen, and mouth and rolls the food around as it mixes with saliva.
poke it through their cell wall. They then travel to the The chewed food is swallowed and moves down the
lymph nodes where the lymphocytes hang out, and a esophagus to the stomach. In the monogastric stomach
specific type of lymphocyte will intercept the monocyte, the food is exposed to stomach acids that break it down
take the antigen, and produce a receptor for that specific further (Figure 5.15).
antigen. This lymphocyte will then move into the body Peristaltic waves move the material from the stomach
looking for that pathogen. When it finds it, it will attach into the small intestine where the nutrients are absorbed.
to the pathogen and destroy it, or signal that it needs The small intestine has three parts: the duodenum,
help. More lymphocytes will converge on the area. Some jejunum, and ileum. Finally, the undigestible material
will replicate and produce more lymphocytes with that continues to move into the colon or large intestine. The
receptor to kill more of the pathogen and others will colon also has three parts: ascending, transverse, and
produce lymphocytes that can produce antibodies for descending colon. In the colon, water is removed and
future use. These are the lymphocytes used to produce feces formed. The feces move into the sigmoid flexure
immunity against diseases by vaccinations. A small and finally into the rectum. The anal sphincters control
amount of antigen for a specific disease is introduced to the passage of feces into the environment which is called
the body. The lymphocytes that produce antibodies defecation or defecating.
become involved in the destruction of the “pathogen.” In ruminants, the chewed food goes to the rumen
Lymphocytes are produced in the bone marrow like where it is exposed to bacteria to ferment the cellulose
the other blood cells; however, they are released early in in foliage to break it down, then it goes into the retic-
their maturation which allows them to change or to rep- ulum (Figure 5.16). The remaining solids are regurgi-
licate themselves. They circulate in the bloodstream and tated and chewed again, this is referred to as cud. The
tissues, but most are sequestered in the lymph nodes. finer food particles move into the omasum for further
This allows large numbers to be deployed when needed. processing. The final stop is in the abomasum or true
There are thousands of lymph nodes throughout the stomach where digestive enzymes breaks the food into its