Part 2: Abdominal Viscera

On the left side of the abdominal cavity, identify the spleen. The spleen lies in the superficial leaf of the greater omentum. (See DG Figs. 4-9B and 4-11)

• Comment: Note that the part of the greater omentum that attaches the spleen to the stomach is called the gastrosplenic ligament.

• Dissection Note: Typically, the spleen is abnormally enlarged in the cadavers due to barbituate use during euthanasia.

  Related Learning Objective

  • D5.3

   

Just caudal to the diaphragm, within the abdominal cavity, identify the liver and its lobes. On the right side, name/identify the right medial, right lateral, and caudate lobes. On the left side, name/identify the left medial and left lateral lobes. Between the left and right sides, identify the quadrate lobe. (See Dg Figs. 4-11, 4-16, and 4-17)

• Comment: Note that in cats, the divisions between some lobes of the liver may be less distinct than in dogs. Most often in cats the quadrate lobe and right medial lobes of the liver are fused.

• On the right side, on the caudate lobe, identify the caudate process (with renal impression) and the papillary process of the caudate lobe.

  • The caudate process caps the cranial end of the right kidney; this creates what is called the renal impression. (See DG Fig. 4-17, “Renal fossa”)

  • The papillary process can be seen through the lesser omentum in the lesser curvature of the stomach (which will be discussed with the stomach).

• Recall that the omental bursa has a communication with the main peritoneal cavity via the epiploic foramen. This is an opening caudomedial to the caudate lobe of the liver, at the level of the cranial duodenal flexure. Attempt to find this opening and pass a finger through it.

Identify the gall bladder in the fossa between the right medial and quadrate lobes of the liver. The gall bladder will usually look like a small, greenish colored sac. (See DG Fig. 4-17)

• Gently tip the liver cranially (toward the diaphragm) and carefully look for bile passages extending from each lobe of the liver (hepatic ducts) and from the neck of the gall bladder (cystic duct). These drain bile from the liver and gall bladder to the common bile duct. (Typically they are a greenish color and can be somewhat fragile, so dissect carefully!) (See DG Fig. 4-18A)

• The cystic duct and the hepatic ducts will join to form the bile duct (aka common bile duct). Identify the bile duct and carefully dissect its course. The bile duct will travel to the descending duodenum where it terminates on the major duodenal papilla. (See DG Fig. 4-18A)

Caudal to the liver, identify the stomach and its parts: cardiac part, fundus, body, and pyloric part. Note that these parts blend with each other and are more regional descriptions rather than specific structures. (See DG Figs. 4-9, A & B, 4-11, 4-13, and 4-19)

• The cardiac part is small and is the part nearest the entrance of the esophagus into the stomach (usually on the left side). (See DG Fig. 4-19)

• The fundus is the dome-shaped region off to the left side of the cardiac part. When the fundus is distended with food it can be quite large. (See DG Fig. 4-19)

• The body is the large middle portion of the stomach between the fundus and pyloric part. (See DG Fig. 4-19)

• After the body, there is a ‘bend’ in the stomach which indicates the transition to the pyloric part on the right side. (See DG Fig. 4-19)

  • Dissection Note: As you observe the pyloric part of the stomach note that it has several parts. The pyloric antrum is the initial part of the pyloric region that is thin-walled. It then starts to funnel down into the pyloric canal. The pyloric canal is the narrow passage between the pyloric antrum and the pylorus (sphincter).

  • In the pyloric part of the stomach identify the pylorus (sphincter). The pylorus is the sphincter, or muscular constriction, that allows passage of food from the stomach into the duodenum.

Identify the greater & lesser curvatures of the stomach.

• The lesser curvature of the stomach is the more cranial bend/curve of the stomach that lies between the esophagus and the pylorus. (The lesser curvature is smaller and has a decreased angle as compared to the greater curvature.) The lesser curvature is where the lesser omentum (aka ventral mesogastrium) is attached, and also where you can see the papillary process of the caudate lobe of the liver.

• The greater curvature of the stomach is the more caudal bend/curve of the stomach extending from the esophagus, along the fundus, body and pyloric part to the pylorus. The greater curvature is larger than the lesser curvature and is where the greater omentum (aka dorsal mesogastrium) is attached to the stomach.

Open the stomach with a single incision along the parietal/ventral surface (midway between the greater and lesser curvatures). Remove the contents of the stomach and observe the interior rugae (longitudinal folds of mucosa) and the pylorus (sphincter).

Reflect the greater omentum cranially and the main intestinal mass (mostly jejunum) to the left side to expose the duodenum on the right side of the abdominal cavity. The duodenum marks the initial part of the small intestine. The small intestine includes the duodenum, jejunum, and ileum.

On the right side, after the pylorus, identify the duodenum and trace it to identify its parts. (See DG Figs. 4-11 and 4-13)

• The duodenum begins at the pylorus and then curves to the right to course caudally. This first curve/bend in the duodenum is called the cranial duodenal flexure.

• After the cranial duodenal flexure, trace the duodenum caudally on the right; this is the descending part of the duodenum.

  • There are two duodenal papillae that empty into the descending duodenum, the major duodenal papilla and the minor duodenal papilla. We will only dissect/look for the major duodenal papilla but you should be aware of which ducts empty into the duodenum at each papilla. The bile duct empties into the duodenum at the major duodenal papilla, right alongside the pancreatic duct. The larger accessory pancreatic duct empties into the duodenum at the minor duodenal papilla (just caudal to the major). These papilla will be dissected on a demonstration specimen for you to view.

    • • Make an incision (~4cm long) into the free border of the proximal portion of the descending duodenum. Use a scalpel handle to scrape away the mucosa inside the duodenum to search for the duodenal papilla. The papilla will look like a small, raised nodule inside the lumen of the duodenum that remains in place after the mucosal lining is scraped away. (See DG Figs. 4-13, 4-18A, and 4-19)

        • •  Identify the major duodenal papilla; this is where the pancreatic duct and bile duct open into the duodenum.

          • Comments: Roughly 2cm caudal to the major duodenal papilla, note that you may see the minor duodenal papilla; this is where the accessory pancreatic duct opens into the duodenum. If possible, view the minor duodenal papilla on demonstration specimens.  Note that in the cat specimens the minor duodenal papilla may be very small or absent. The accessory pancreatic duct (and minor duodenal papilla) are only present in cats about 20% of the time.

• The duodenum will then curve to the left; this curve/bend in the duodenum is called the caudal duodenal flexure. (See DG Fig. 4-13)

• After the caudal duodenal flexure, trace the duodenum as it continues cranially as the ascending part of the duodenum. The ascending part of the duodenum is usually quite short and terminates at the duodenojejunal flexure where the intestine curves again and becomes the jejunum. (See DG Fig. 4-13)

• Identify the short connecting mesentery attached to the duodenum, the mesoduodenum.

  • Comment: You may also note that the ascending duodenum is secondarily attached to the mesocolon of the descending colon via the duodenocolic fold.

    Related Learning Objective

    • D5.3

     

Identify the pancreas. The pancreas is lobulated and composed of a left lobe, body, and right lobe. (See DG Figs. 4-13, 4-29, and 4-34)

• Locate the right lobe of the pancreas along the dorsomedial aspect of the descending duodenum where it is enclosed in the mesentery attached to the duodenum (mesoduodenum).

  • Comment: As previously mentioned, the pancreatic duct empties into the descending duodenum alongside the bile duct at the major duodenal papilla and the accessory pancreatic duct empties into the duodenum at the minor duodenal papilla.

• Trace the right lobe of the pancreas cranially to locate the body which lies near the pylorus of the stomach.

• Continue tracing the body of the pancreas to the left lobe which is found between the peritoneal layers making up the deep leaf of the greater omentum (caudal to the stomach).

After the duodenojejunal flexure, identify the jejunum. The jejunum is the longest part of the small intestine and forms the majority of the loops/coils found in the ventrocaudal part of the abdominal cavity.

• Identify the long mesentery (aka mesojejunoileum) connecting to the jejunum and ileum.

  • Identify the root of the mesentery which is a short (connecting) peritoneal attachment to the abdominal wall. Vessels and nerves pass through the mesentery to supply the large and small intestines, and the mesentery is where you will find (cranial) mesenteric lymph nodes. The root of the mesentery anchors the jejunum to the dorsal body wall.

    • • Using blunt dissection, look for and identify (cranial) mesenteric lymph nodes along the vessels in the mesentery connecting to the jejunum.

        Related Learning Objectives

        • D5.2
        • D5.3

         

Trace the jejunum to its termination as the ileum on the right side of the abdomen. The ileum is the short, terminal part of the small intestine; it passes cranially on the right side of the abdomen. (See DG Figs. 4-13, 4-21, 4-29, 4-31, 4-32, and 4-34)

• Dissection Note: It can sometimes be hard to distinguish the transition from jejunum to ileum. Often, it can be helpful to move on to identify the cecum and then ‘back-up’ to the ileum to identify it. There is also an antimesenteric vessel that can be used to approximate the length of the ileum. The fold of connecting mesentery between the ileum and cecum (called the ileocecal fold) can also be used to approximate the length of the ileum, particularly in the cat.

• The ileum joins the large intestine at the ileal orifice (aka ileocolic orifice). (This will be discussed further after the cecum and colon are identified.)

Identify the cecum. The cecum is a small, blind-ended pouch. In the dog it can be S-shaped, but it is more comma-shaped in the cat. (See DG Figs. 4-13, 4-21, 4-29, 4-31, 4-32, and 4-34) The cecum is part of the large intestine which also includes the colon and rectum. The cecum is found on the right side of the abdomen at the junction of the ileum and the colon.

• The cecum opens into the ascending colon via the cecocolic orifice. Note that this orifice is distinct in the dog and less distinct in the cat.

  Related Learning Objectives

  • D5.2
  • D5.3

   

Identify the colon and its parts: ascending, transverse, descending, and right & left colic flexures. The colon is found dorsally within the abdominal cavity suspended from the dorsal body wall by mesentery known as the mesocolon. (See DG Figs. 4-13 and 4-31)

• Attached to, and communicating with, the cecum, identify the short ascending colon on the right side. (Note that in cats, the ascending colon is particularly short.)

  • Trace the ascending colon as it courses cranially and curves to travel to the left side of the body; this curve/bend is the right colic flexure.

• Make one small incision into the initial part of the ascending colon to observe the ileal orifice (aka ileocolic orifice) and the cecocolic orifice (distinct in the dog; less so in the cat). (See DG Fig. 4-21)

  • Using a forceps and probe, clean out any debris in the lumen of the intestines and cecum in this area.

  • Pass a probe through the opening between the ileum and the colon. This is the ileal orifice (aka ileocolic orifice).

  • Pass a probe through the opening between the cecum and the ascending colon. This is the cecocolic orifice.

• After the right colic flexure, the colon is continued as the transverse colon; identify the transverse colon as it travels from the right side to the left side of the abdominal cavity.

  Related Learning Objectives

  • D5.2
  • D5.3

   

  • Comment: Note that this region of the large intestine is cranial to the root of the mesentery.

  • Trace the transverse colon to the left side of the body where it curves caudally; this curve/bend is the left colic flexure.

• Identify the final part of the colon, the descending colon. The descending colon is the longest part of the large intestine and courses caudally into the pelvic inlet where it is then continued as the rectum.

• Identify the short mesocolon attaching to the ascending, transverse and descending colon.

Identify the terminal part of the large intestine, the rectum, as it passes through the pelvic region. The rectum will pass feces on through the anal canal and anus to be expelled from the body.

Dorsally in the abdominal cavity, identify the kidneys (right & left). The kidneys are dark brown in color and will be partially/mostly surrounded by fat. Mainly the ventral surface of the kidneys are covered by peritoneum, which is why they are considered to be retroperitoneal organs. The right kidney is located further cranially than the left. (See DG Figs. 4-9, A & B, 4-12, 4-13, and 4-22)

• In the middle of each kidney, on the medial border, identify the hilus. The hilus is the indentation in the kidney where renal vessels and nerves, as well as the ureter, communicate with the kidney. (See DG Fig. 4-23B, “renal hilus”)

Using blunt dissection, work through the fat and fascia near the hilus of each kidney to identify the renal a. and associated renal vein. Next, identify the ureters (left and right) and trace them caudally toward the urinary bladder. (Do this on both left and right sides.) (See DG Figs. 4-9, A & B, 4-12, 4-22, and 4-23A)

Near the cranial aspect of each kidney, identify the adrenal glands (left & right). Use blunt dissection with the tip of a scissors to uncover the adrenal glands in the fascia and fat just cranial, and slightly medial, to each kidney. (See DG Figs. 4-12, 4-22, and 4-27) Note that the adrenal glands are also considered to be retroperitoneal organs.

• On the left side, dissect between the left kidney and the aorta to locate the left adrenal gland.

• On the right side, dissect between the caudal vena cava and the caudate lobe of the liver to locate the right adrenal gland.

Using your fingers to dissect, free the left kidney from the surrounding fat, fascia, and peritoneum; DO NOT remove it, and do not cut its vascular attachment. Make a longitudinal incision through the lateral border to the hilus (dividing the kidney into dorsal and ventral halves). (See DG Fig. 4-23B)

• Open the kidney and identify the renal cortex, renal medulla, and renal pelvis. (See DG Fig. 4-23B)

  • Within the kidney, the outer (peripheral) layer is the renal cortex.

  • The more central, inner layer is the renal medulla.

  • The renal pelvis is the expanded part of the ureter within the kidney.

Using your fingers to dissect, free the right kidney from the surrounding fat, fascia, and peritoneum; DO NOT remove it, and do not cut its vascular attachment. Make a transverse incision through it at the hilus (dividing it into cranial and caudal halves). (See DG Fig. 4-23C)

• Open the kidney and again identify the renal cortex, renal medulla, and renal pelvis, as you did on the left kidney. (See DG Fig. 4-23C)

• In addition, identify the renal crest; this is the ridge formed by the medulla projecting into the renal pelvis, where urine is excreted from the kidney into the renal pelvis. (See DG Fig. 4-23C)

(Optional) In demonstration specimens, take a closer look at the left kidney to identify the renal pyramids (of the medulla), the renal sinus and pelvic recesses. (See DG Fig. 4-23, A-E)