The Abdomen
3.7 Vessels
similar to that of the dog and cat. No renal pelvis is present in cattle (Figure 3.28a).
The renal artery, vein, and ureter in goats and cattle can be identified at the hilus, an indenta- tion where the renal vein and ureter leave the kidney and the renal artery enters (Figure 3.28).
Identify the renal cortex, renal medulla, renal crest, renal pelvis, and renal sinus on median and sagittal sections of the goat or
sheep kidney (Figure 3.29a, b). No calyces are present in small ruminants.
vessels can be hard to identify. Generally, arteries are best identified on target struc- tures supplied.
3.7.1 Arteries
Goal: Identify the aorta, celiac, and cra- nial mesenteric arteries.
Arteries that supply the abdominal viscera comprise paired and unpaired vessels that originate from the abdominal aorta.
The unpaired arteries include (i) celiac, (ii) cranial mesenteric, and (iii) caudal mesenteric arteries. Paired arteries include (i) lumbar, (ii) phrenicoabdominal, (iii) renal, (iv) gonadal (testicular or ovar- ian), and (v) deep circumflex iliac arteries.
Your instructor may ask you to identify some of these arteries. Apart from the aorta, celiac, cranial mesenteric, and renal arteries, we tend not to trace other arteries of the abdo- men if they are not injected.
A brief discussion of the abdominal arter- ies follows.
The celiac artery gives three major branches:
splenic, left gastric, and hepatic arteries.
Their names indicate their target organs. Each of the aforementioned three branches of the celiac artery gives several named branches.
There are usually variations in the origin of branches from the celiac, left gastric, and hepatic arteries. Thus, there is little practical benefit in identifying these branches or trac- ing their origin. However, you can easily identify the right ruminal artery (from the splenic) coursing on the right longitudinal groove of the rumen. Likewise, the left ruminal artery (from the left gastric) runs in the left longitudinal groove.
Arteries running on the greater curvature of the abomasum are the right and left gas- troepiploic arteries which anastomose end- to-end about midway along the greater curvature. They originate from the hepatic and left gastric arteries, respectively. The left and right gastric arteries anastomose on the lesser curvature of the abomasum. The right gastric artery is a branch of the hepatic artery.
The cranial mesenteric artery supplies the small and large intestines except for the most caudal segment of the transverse and descending colon, which are supplied by the caudal mesenteric artery. Branches of the cranial mesenteric artery include caudal pan- creaticoduodenal, middle colic, ileocolic, right colic, colic branches, mesenteric ileal branch, and cecal arteries. There is no need to identify these branches.
The caudal mesenteric artery gives rise to the left colic and cranial rectal arteries. The left colic artery supplies the descending colon. The cranial rectal artery supplies the first part of the rectum.
Paired arteries include phrenicoabdominal, renal, gonadal (testicular or ovarian), lumbar, and deep circumflex iliac arteries. The renal arteries could be identified on isolated kidney or a dorsal view of the aorta. The gonadal arteries are discussed with the pelvis. There is no need to identify these arteries.
Identify the celiac, cranial mesenteric, and renal arteries by making a longitudinal inci- sion of the dorsal wall of the abdominal aorta (Figure 3.30). Insert your probe on the closely associated celiac, cranial mesenteric, and renal arteries from proximal to distal, respectively.
3.7.2 Veins
Goal: Identify the caudal vena cava and portal vein.
Venous return from the abdominal viscera (stomach, small intestine and the majority of large intestine, and the spleen) is high in fat and toxic contents. It drains into the portal vein which carries venous blood from the gastrointestinal tract to the liver for detoxification.
It is important to understand that blood from the gastrointestinal tract traverses two capillary beds, one in the gastrointestinal tract and the other in the liver. From the liver, detoxified blood reaches the caudal vena cava via the hepatic veins.
You have identified the cauda vena cava in the thorax and could do so on the visceral
surface of the liver. Follow its termination into the right atrium of the heart. The caudal vena cava drains blood from the pelvis, hind limbs, and from paired organs (kidney, adre- nal, and gonads.)
Hepatic veins that drain into the caudal vena can be demonstrated by opening the dorsal portion of the caudal vena that trav- erse the liver.
Your instructor may ask you to identify the portal vein and or its branches. It is formed by the merger of the cranial mesenteric, caudal mesenteric, splenic, and gastrodu- odenal veins.
3.7.3 Lymphatics
Goal: Understand the major lymph cent- ers of the abdomen. Identify the jejunal (mesenteric) lymph nodes (Figure 3.22).
The function of the lymphatic system is to carry large particles that are too bulky to be drained by veins. Lymphatic vessels start as small lymph capillaries and ultimately merge to form large lymphatic vessels (e.g., thoracic duct, intestinal, lumbar, and other trunks).
The thoracic duct joins the large veins near the thoracic inlet.
Lymph passes through lymph nodes for fil- tration before joining the venous system.
Lymphocenters consist of a single lymph node or multiple nodes.
Lymph from the abdomen is drained by three large lymphocenters: (i) celiac, (ii) cra- nial mesenteric, and (iii) caudal mesenteric lymphocenters.
Large numbers of lymph nodes are associ- ated with each of the centers. Note that each of these lymphocenters drains an area supplied by similarly named unpaired arteries (celiac, cranial, and caudal mesenteric arteries).
Lymph nodes of the celiac lymphocenter receive lymph from organs and lymph nodes associated with the celiac arteries. The nodes include gastric (in ruminants, these are referred to as the various ruminal, reticu- lar, etc. nodes), hepatic, splenic and (pan- creaticoduodenal lymph nodes drain to the colic or intestinal trunk).
The nodes of the cranial mesenteric lym- phocenter receive lymph from the cecal, colic, and jejunal lymph nodes. The jejunal lymph nodes (also called mesenteric lymph
Descending colon
Dorsal sac of the rumen
Aorta opened dorsally
Cranial Liver
Diaphragm (tendinous part) Spleen
Renal aa.
Sheep
Descending duodenum
Cranial
mesenteric a. Celiac a.
Figure 3.30 Isolated sheep abdominal viscera: dorsal view. The dotted circles show the location of the origins of the celiac, cranial mesenteric, and renal arteries on the floor of the abdominal aorta.
nodes) are very long and are in the mesojeju- num close to the mesenteric border of the jejunum (Figure 3.22).
The caudal mesenteric lymph nodes are associated with the descending colon and caudal mesenteric artery.