Ruminant Stomach Anatomy Quiz

Stomach (Gaster)

• The stomach is a musculoglandular sac of the digestive tube.
• Classification according to compartments:
  • Monogastric: one compartment (dog, pig, horse)
  • Multilocular: more than one compartment (ruminants, 4 chambers)
• Classification according to mucous membrane type:
  • Simple: lined entirely with glandular mucous membrane (dog)
  • Compound (composite): partly glandular, partly non-glandular (pig, horse, ruminants). The non-glandular parts are esophageal or proventricular.

Anatomical Features

• The stomach has two orifices, two borders, and two surfaces.
• Openings:
  • Cardiac orifice (cardia): where the esophagus enters the stomach. Located to the left of the median plane.
  • Pyloric orifice (pylorus): where the stomach connects to the duodenum. Located to the right of the median plane, in contact with the liver's visceral surface.
• Borders:
  • Dorsal border (lesser curvature): concave, extends between the cardia and pylorus. In some species, it has an angular notch.
  • Ventral border (greater curvature): larger, extends from the cardia, through the fundus and then crosses the median plane to the pylorus.
• Surfaces:
  • Parietal (diaphragmatic) surface: directed craniodorsally and to the left, related to the diaphragm and left lobe of the liver.
  • Visceral (intestinal) surface: directed caudoventrally and to the right, related to the intestines, pancreas, and greater omentum.

Stomach Parts

• Body: the part of the stomach to the left of the angular notch.
• Fundus: the part of the body bulging above the level of the cardia. Separated from the cardia by the cardiac notch.
• Pyloric region: right to the body, divided into pyloric antrum and pyloric canal, ending at the pyloric sphincter.

Stomach Fixation

• Non-peritoneal fixation:
  • Attachment to the esophagus and duodenum.
  • Pressures of adjacent organs.
• Peritoneal fixation:
  • Through omenta and ligaments:
    • Greater omentum: attaches the greater curvature of the stomach to intestinal segments.
    • Gastrosplenic ligament: attaches the stomach to the spleen.
    • Gastrophrenic ligament: attaches the stomach to the diaphragm.
    • Lesser omentum: attaches the lesser curvature of the stomach and the cranial part of the duodenum to the liver.

Stomach Structure

• The stomach wall consists of mucous, muscular, and serous coats.
• Mucous coat:
  • Varies according to stomach type.
  • Glandular stomach: simple columnar epithelium with goblet cells.
  • Non-glandular stomach: stratified squamous cornified epithelium.
  • Glandular mucosa: divided into cardiac, fundic, and pyloric regions, glands opening into gastric pits.

Ruminant Stomach

• Consists of four chambers: rumen, reticulum, omasum (forestomachs), and abomasum (true stomach).
• Rumen, reticulum, and omasum have non-glandular mucosa.
• Abomasum has glandular mucosa.
• Relative position: rumen on left, reticulum cranially, omasum on right, abomasum ventrally.
• Capacity: in ox, 110-235 liters (rumen 80%, reticulum 5%, omasum 7%, abomasum 8%). In small ruminants, 16-30 liters.

Rumen

• Position: occupies left half of the abdominal cavity, extending from the diaphragm to the pelvic inlet.
• Surfaces: parietal (left), visceral (right).
• Has several ruminal grooves.
• Has dorsal and ventral curvatures.

Reticulum

• Position: most cranial chamber, spherical, intrathoracic part of the abdominal cavity. Located between the diaphragm and rumen.
• Surfaced: diaphragmatic, visceral.

Omasum

• Position: ventral in the intrathoracic part of the abdominal cavity, to the right of the median plane, between the rumen and right abdominal wall.
• Shape: spherical, larger than reticulum, in ox.
• Surfaces: visceral (left), and has two curvatures

Abomasum

• Position: most distal compartment, in the form of an elongated sac, lies chiefly on the abdominal floor, with the fundus on the left and the pyloric part on the right, and the body crosses the median plane from left to right. Closely relates to the ruminal recess.
• Shape: like a simple stomach, composed of fundus, body, and pyloric parts.
• Has two curvatures (greater and lesser) and two surfaces (parietal and visceral).

Liver

• The liver is the largest gland in the body.

• Functions: secretion of bile for fat digestion, metabolic process (fat, carbohydrates, protein), storage of fat, glycogen, and vitamins, blood formation (RBCs in fetal life), blood protein secretion, and secretion of heparin, detoxification.

• Position: generally in intrathoracic part of the abdominal cavity, mostly to the right of the median plane.

• Color: reddish-brown.

• Size and weight: depend on species, age, and condition of the animal. Greater in well-fed animals. Decreases with age.

• Anatomical description: 2 surfaces, 2 borders, 2 extremist, parietal surface is convex and related to diaphragm, visceral surface in most species has a hilus separating cranial gastric surface and large caudal intestinal surface.

• Hepatic porta: a depression in visceral surface, where portal vein, hepatic artery, and hepatic nerve plexus enter.

• Lobation: divided by two imaginary lines into three lobes; right, intermediate, and left.

• Fixations:

  • Non-peritoneal fixation: pressure of surrounding viscera, continuation of hepatic veins into caudal vena cava, structures entering and leaving hepatic porta.
  • Peritoneal fixation: hepatogastric and hepatoduodenal ligaments (lesser omentum, connecting liver/porta to stomach/duodenum), coronary ligament (liver/diaphragm), right and left triangular ligaments (liver/diaphragm/sublumbar region), falciform ligament (umbilical fissure/sternal part of diaphragm), round ligament (umbilical vein), hepatorenal ligament (right lobe/caudate process/right kidney).

Pancreas

• Soft lobulated organ in intrathoracic part of cavity, mainly right of a median plane, associated with duodenum.
• Color: light with pink tinge.
• Formation: consists of body, right lobe, and left lobe. Body is the middle part against cranial part of duodenum. Right and left lobes are two branches digesting from the body to corresponding sides. Right lobe continues alongside the descending duodenum (except in horses).

Excretory and Duct system

• Excretory apparatus: consists of hepatic ducts uniting to common hepatic duct, Gall bladder has cystic duct connecting to common hepatic duct forming bile duct. Some species' bile duct opens with major pancreatic duct to duodenum.
• Vessels and Nerves: Nutritional arterial supply from hepatic artery and functional blood supply from portal vein; The hepatic veins join caudal vena cava. The lymph is drained by hepatic lymph nodes; hepatic plexus.
• Gallbladder: temporary storage and discharge of bile into duodenum.
• Position: lies in fossa on the visceral surface of the liver between quadrate and right medial lobes.
• Shape: pear-shaped or conical sac.
• Formation: consists of fundus, body, and neck (connects to cystic duct).
• Comparative: projects from ventral border of liver in ruminants (absent in equines and camel).

Spleen

• Position: intrathoracic part of the left abdominal cavity; position varies depending on stomach fullness (especially in dogs).
• Anatomical description: Two surfaces (parietal, visceral); two borders; two extremities; parietal surface is convex and relates to diaphragm; visceral surface in most species has a hilus.

Intestine

• Extends from the stomach to the anus.
• Comprises small and large intestines.
• Small intestine: duodenum, jejunum, and ileum. Duodenum is the fixed part, jejunum and ileum are mesenteric.
• Large intestine: cecum, colon, rectum, and anal canal.
• Canines have shortest intestine, followed by equines/pigs, ruminants.

Duodenum

• Extends from the pylorus to the duodenojejunal flexure.
• Consists of three parts (cranial, descending, and ascending duodenum).
• Has three flexures (cranial, caudal and duodenojejunal).
• Cranial part passes to the right on the liver, forming a cranial flexure continued as a descending duodenum..

Cecum

• Varies in size, shape, and position across species; lacks vermiform appendix in most domestic .
• Size depends on species (shortest in cats).
• Position: right side of abdominal cavity (except pigs)
• Communication: ileum joins cecum at ileocecal orifice (cecocolic in horses)
• Muscular bands: present only in pigs and horses

Colon

• Divided into ascending, transverse, and descending colon.
• Ascending colon (dog): simplest arrangement (as in humans), running cranially on the right, crossing the median plane to connect with the transverse colon, and proceeding caudally on the left as the descending colon.
• Ascending colon of pig: forms 3 spiral (cone) loops.
• Ascending colon of ruminants: three loops (proximal (S-shape), spiral, distal).
• Transverse colon: begins on the right side of the ascending colon and proceeds to the left side at the cranial mesenteric artery.
• Descending colon: lies in the left dorsal quadrant of body cavity; positioned caudally under the dorsal abdominal wall, attached to the mesocolon. It attaches to the ascending duodenum with the duodenocolic ligament and enters the pelvic cavity, turning to become the rectum. In ruminants, it presents as a sigmoid colon. In horses, it is long, with two bands, and coils easily distinguishable from jejunal coils.
• Rectum: continuation of descending colon as it enters the pelvis, has peritoneal and retroperitoneal parts, has no bands or sacculations. In horses, forms an expanded ampulla.

Anal Canal

• Short terminal portion of digestive tract.
• The anus is the terminal orifice, surrounded by external striated sphincter M. arising from caudal vertebrae, and internal sphincter as thickened continuation of circular smooth muscle of rectum.