Anatomy of Canine GI

External abdominal oblique m, internal abdominal oblique m, transversus abdominis m, rectus abdominis m

Muscles of the abdomen and linea alba

Cranial epigastric a, branches of the thoracic and abdominal aorta

Vasculature supplying the abdominal muscles

Ventral branches of thoracic and lumbar nerves, nT13, nL1, nL2, nL3, nL4

Innervation of abdominal muscles

Caudoventral, ventrolateral

The ventral branches of the thoracic and lumbar nerves run in a ___ pattern and supply the ___ parts of the abdominal wall.

nT13

Costoabdominal n.

nL1

Cranial iliohypogastric n.

nL2

Caudal iliohypogastric n.

nL3

Ilioinguinal n.

nL4

Lateral cutaneous femoral n.

Mesothelial lining

Covers and compartmentalizes the body cavities

Pleural cavities, mediastinum

Three spaces of the thoracic cavity

Peritoneal cavity, retroperitoneal cavity

Two spaces of the abdominal cavity

Peritoneum

Serous membrane of the abdominal cavity that covers most of the abdominal viscera and a large portion of the abdominal wall

Compartmentalizes the abdominal cavity into the peritoneal and retroperitoneal cavities

Helps suspend, support, and attach the organs of the peritoneal cavity

Parietal peritoneum

Not in contact with the organ

Visceral peritoneum

In direct contact with the organ

Connecting peritoneum

Connects the layers of peritoneum (i.e. visceral to parietal or visceral to visceral peritoneum)

Includes the mesenteries, omenta, ligaments, and folds of peritoneum

Peritoneal cavity

Space between the visceral and parietal peritoneum

Has a small amount of fluid

Mesentery

Connecting peritoneum between the intestinal (or reproductive) tract and the body wall

Contains the blood vessels, nerves, and lymphatic structures that are associated with organs

Mesenteric lymph nodes

Lie along the vasculature in the mesentery near the jejunum

Meso-

The folds of mesentery are named based on the organ they connect to. What prefix is used to describe them?

Root of the mesentery

Dorsal attachment to the body wall

L1

At what spinal level is the root of the mesentery for horses?

L2

At what spinal level is the root of the mesentery for canines and ruminants?

Omenta

Connecting peritoneum between the stomach and an abdominal organ or the body wall

Greater omentum

Connects the dorsal abdominal wall to the greater curvature of the stomach

Has a lace-like appearance due to streaks of fat around the blood vessels

Has two leaves and a space

Covers the intestines

Greatly elongated in carnivores

Superficial/parietal leaf, deep/visceral leaf, omental bursa

What are the two leaves and the space of the greater omentum?

Lesser omentum

Connects the lesser curvature of the stomach to the liver

Omental bursa

Pouch within the greater omentum

Has an opening called the epiploic foramen

Epiploic foramen

Opening in the omental bursa between the caudate process of the liver, ventral to the caudal vena cava, and dorsal to the portal vein

Clinical relevance in domestic horses

Gastrosplenic ligament, nephrosplenic ligament

Ligaments associated with the omentum

Gastrosplenic ligament

Attaches the stomach to the hilus of the spleen

Nephrosplenic ligament

Attaches the spleen to the kidneys

Clinical relevance in domestic horses

Falciform ligament

Thin, sickle-shaped fold of peritoneum that attaches the liver to the ventral abdominal wall and diaphragm

Extends cranially from the umbilicus and is dorsal to the linea alba between the left and quadrate lobes of the liver

Fat-filled in adults

Routinely trimmed during surgery to prevent it from prolapsing into the suture line along the linea alba

Umbilical vein

What does the falciform ligament contain pre- and perinatally?

Round ligament of liver

What does the falciform ligament contain in adults?

Peritoneal effusion

What is the fat in the falciform ligament commonly misinterpreted as by inexperienced interpreters?

Peritonitis

Inflammation of peritoneum

Cervical, thoracic, and abdominal parts

Three parts of esophagus

Esophageal hiatus at diaphragm

Where does the esophagus enter the abdomen?

Dorsal

The esophagus follows along the ___ [dorsal or ventral] border of the liver to the stomach

Oral

Connects to pharynx

Aboral

Connects to stomach

Outer layer, muscular layer

Tissue layers of esophagus

Outer layer of esophagus

Loose connective tissue (adventitia) in the neck

Serosa in the thorax (mediastinal pleura) and abdomen (peritoneum)

Muscular layer of esophagus

Contains striated muscle

Certain species (e.g. cats, pigs, horses) have areas of smooth muscle as well

Peristalsis

How is the food bolus transported?

Cranial sphincter, lower esophageal sphincter

Two sphincters

Upper esophagus

Where is the cranial sphincter located?

Cardiac, caudal

Other names of lower esophageal sphincter

Cranial sphincter

Pharyngeal muscles

Gastroesophageal junction

Where is the lower esophageal sphincter located?

Lower esophageal sphincter

Muscle layer at the gastroesophageal junction

Lower esophageal sphincters

Certain species (e.g. horses) have strong ___ that make vomiting impossible.

Sphincter

Ring of muscle around an opening, often to protect or close the opening

Dogs

Which species?:

Simple stomach with short intestine

Ruminants

Which species?:

Complex stomach and forestomach fermentation

Horses

Which species?:

Simple stomach and hindgut fermentation

Visceral peritoneum/serosa, smooth muscle, submucosa, mucosa

Layers of stomach

Submucosa

Which layer of the stomach forms rugae?

Mucosa

Which layer of the stomach has gastric pits?

Parietal surface

Which surface of the stomach faces the liver?

Visceral surface

Which surface of the stomach faces the intestines, pancreas, and greater omentum?

Cardiac part

Part of stomach where esophagus enters

Secretes mucus

Fundus

Dome-shaped blind area in stomach; left and dorsal to the cardia

Secretes mucus, HCl, and proteolytic enzymes

Body

Large middle portion of stomach

Secretes mucus, HCl, and proteolytic enzymes

Pylorus/pyloric part

Distal third of stomach as measured along the lesser curvature

Secretes mucus

Pyloric sphincter controls outflow

Material and function

What is the position of the carnivore stomach influenced by?

Empty stomach

Small and lies to the left (full or empty stomach?)

Full stomach

Extends caudally and ventrally (full or empty stomach?)

Dorsally, left

When filled with food, the fundus projects ___ [dorsally or ventrally] and to the ___ [left or right]

Left to right

Does the stomach move left to right or right to left?

9th ICS

At which ICS is the cardia fixed?

Right

The pylorus is on the ___ [left or right] of midline.

Left, ventrally

The greater curvature of the stomach faces ___ [left or right] and ___ [dorsally or ventrally]

Adds secretions to ingesta; digests food; absorbs nutrients, salt, and water

Actions of small intestine

Duodenum, jejunum, ileum

Three segments of small intestine

Duodenum

First segment of small intestine

Abdominal roof by mesoduodenum

Attachment of duodenum

Secretes mucus to buffer ingesta

Action of duodenum

Pancreatic ducts, bile duct

What is the duodenum a site of entry of?

Duodenoncolic fold

Connects ascending duodenum to descending colon

Surgical relevance

Cranial duodenum, cranial duodenal flexure, descending duodenum, caudal duodenal flexure, ascending duodenum

Cranial duodenum

(In duodenum)

Very short in the dog

Between pylorus and cranial duodenal flexure

Cranial duodenal flexure

(In duodenum)

Passes dorsally and to the right at the 9th ICS

Descending duodenum

(In duodenum)

Continues to 4th to 6th lumbar vertebrae

Right of midline

Caudal duodenal flexure

(In duodenum)

Crosses midline to the left

Ascending duodenum

(Part of duodenum)

Runs cranially

Short and lies to the left of the root of the mesentery (left of midline)

Terminates at the duodenojejunal flexure

Jejunum

Second segment of small intestine

Longest portion of small intestine

Loose mesentery allows for movement

Ventral

The jejunum occupies the ___ [dorsal or ventral] portion of the abdomen in carnivores.

Ileum

Third segment of small intestine

Shortest portion of small intestine

Ileocecal fold

The ileum is sometimes indistinguishable from the jejunum, but it is discernible by what structure?

Ileocecocolic junction

Area comprised of the junctions between the ileum, cecum, and ascending colon

Ileocolic

In carnivores, the ileocecocolic junction consists of the ___ junction and the cecocolic junction.

Ileocecal

In ruminants and equids, the ileocecocolic junction consists of the ___ junction and the cecocolic junction.

Ileocolic orifice

What orifice do carnivores have in the ileum?

Ileal papilla

Contains the ileocolic sphincter

Resorbs water

Action of large intestine

Cecum, colon, rectum

Three components of large intestine

Cecum

(In large intestine)

Blind sac

Site for fermentation (in hindgut fermenters)

May play a role in immune defense