Anatomy of Ruminant GI

Rumen, reticulum, omasum, abomasum

Four chambers of the stomach

Forestomach

First three chambers of stomach make up this

Non-glandular

Involved in fermentation of complex carbohydrates

Serosa covers most of the surface of the rumen and reticulum (but not the dorsal surface)

Is the abomasum glandular or non-glandular?

Glandular

Abomasum

4th chamber of stomach

Glandular

Similar to the function of the carnivore’s stomach

Cranial

Spatial relationship:

Diaphragm, liver, reticulum

Left of midline

Spatial relationship:

Rumen, spleen

Right of midline

Spatial relationship:

Intestines, colon, omasum, abomasum, pancreas

Ventral

Spatial relationship:

Omentum

Caudal

Spatial relationship:

Uterus, bladder

Rumen

First chamber of stomach

Sometimes called the paunch

Site for fermentation of cellulose; fermentation performed by microorganisms

Left

Which half of the abdomen does the rumen almost completely fill?

7th ICS to pelvic inlet

Location of rumen

Left and right longitudinal/ruminal pillars

Separate the dorsal and ventral sacs

Cranial pillar

Separates ruminal atrium from dorsal sac

Caudal pillar

Helps form caudal blind sacs

Dorsal and ventral coronary pillars

With the caudal pillar, they make the caudodorsal blind sac and the caudoventral blind sac, respectively

Left and right accessory pillar

Extension of the cranial pillar

Ruminal grooves

External and correspond with internal pillars

Where blood vessels attach to supply and drain the rumen

Named after the pillars

Dorsal sac, ventral sac with ruminal recess, cranial sac/ruminal atrium, caudodorsal blind sac, caudoventral blind sac

List the ruminal sacs

Cardia

The esophagus opens at the ___ of the rumen.

Cardia

At the junction of the rumen and reticulum

Discharges into both chambers

Gastric/esophageal groove

Three segments: Reticular, omasal, and abomasal grooves

Opening of the esophagus initiates the gastric groove

Bypasses rumen, reticulum, omasum; sucking reflex causes the groove to close and milk to run to the abomasum

Associated with the orifices between compartments of the complex stomach

Reticular, omasal, abomasal grooves

Three segments of gastric groove

Ruminal mucosa

Lined by stratified squamous epithelium

Most of it has a distinctive papillary appearance —> Increases surface area for absorption

Ruminal papillae

Increased surface area

Largest in the blind sacs

Fewest in the ventral sac

Reticulum

Cranial to rumen

Involved in fermentation

Breaks down complex food

Catches material that is too large and sends it back to the mouth via regurgitation

Ruminoreticular fold

Separates the rumen and reticulum

Roughly U-shaped

Reticular mucosa

Lined by stratified squamous epithelium

Distinctive honeycomb appearance

Increases surface area for absorption

Reticulum

Lies to the left of the median plane between ribs 6 and 7

Close to diaphragm and xiphoid process

Hardware disease

Metal punctures reticulum —> punctures the wall during contractions

Can lead to pericarditis due to proximity of diaphragm and heart

Ruminal contractions

Mix forestomach content, move content forward to the omasum or backward for rumination, and aid in removing gases from the rumen

Primary contractions

Associated with ruminal mixing

Contractions

Related to rumination

Secondary contractions

Related to eructation of gas

Ruminal atrium

Where does the reticular content move to when a reticular contraction occurs?

Dorsal sac

Which contracts first: dorsal sac or ventral sac?

Craniocaudal

In what direction do the sacs in the rumen contract?

2-5 contractions every 2 minutes

Normal rumen contraction rate

Paralumbar fossa

Between the dorsal sac and left flank

Can insert a trocar in case of extreme bloat

Regurgitation

Reticular contraction floods the region of the cardia

Coordination of stomach movements with the thoracic wall and throat

Ingesta is drawn into the esophagus, carried orally by an antiperistaltic wave

Eructation

No reticular involvement in contractions

Originate in the ventral sac to the dorsal sac

Force ruminal gas forward to the cardiac region

Omasum

Lies right of midline

Deep to ribs 8-11

Follows dome of the diaphragm

Omasum

Lined by stratified squamous epithelium —> Occupied by crescent-shaped laminae that arise from the sides and the greater curvature

Plays a role in water absorption and digestion

Biphasic

Omasal contractions are ___.

Abomasum

Lies on the ventral floor, close to midline

Tucked in close to the rumen and omasum

Abomasal atony

Loss of motility and function is a significant in displaced abomasum

Leads to the accumulation of liquid and gas

Left displaced abomasum (LDA)

Distends in space between rumen and reticulum to the left body wall

Right displaced abomasum (RDA)

Emergency

Can create abomasal volvulus

Percussion

Listening for pings produced from a gas interface

9-13

What ribs should you concentrate on when percussing the abomasum?

Greater omentum

Composed of two serosal sheets

Reflected at the descending duodenum

Superficial leaf

Serosal sheet of greater omentum

Attaches to left longitudinal groove

Deep leaf

Serosal sheet of greater omentum

Attaches to right longitudinal groove

Supraomental recess

Space above the deep leaf of the greater omentum

Opens caudally and contains the intestines

Lesser omentum

Arises from the liver

Connects reticulum, omasum, abomasum, and duodenum to the liver

Intestines

Mostly contained on the right side of midline

Duodenum

Starts right of median plane

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

Part of duodenum in order

Jejunum

Forms coils

Lies in the supraomental recess

Ileum

Short

Identified by the ileocecal fold

Primary site of infection for Johne’s disease in ruminants

Johne’s disease

Caused by Mycobacterium paratuberculosis

Usually infected as calves from contaminated feces, milk, or colostrum

Onset of clinical signs between 2-6 years

Harbors in the small intestine

Causes gradual thickening of the intestines, reducing the nutrients cows can absorb

Periodic to persistent pipe-stream diarrhea and progressive weight loss

No treatment

Cecum

Blind sac at the level of the ileocecocolic junction

Cecum and colon junction is marked by the entrance of the ileum

Projects caudally from the supraomental recess

Proximal loop (S-shaped), spiral loop, distal loop (U-shaped)

Segments of ascending colon

Centripetal coils, central flexure, centrifugal coils

Parts of spiral loop of ascending colon

Transverse colon

Crosses right to left in front of the root of the mesentery

Descending colon

Turns caudal toward pelvis

Liver

Almost entirely on right side

Four lobes

Runs caudodorsally from ribs 6-12

Left, right, caudate, quadrate

Lobes of bovine liver

Liver biopsy

ICS 10 at the level of the ventral end of the tuber coxae; needle directed toward the opposite olecranon

Gallbladder

Present in ruminants

Between the right and quadrate lobes of the liver

Bile duct

Formed by cystic duct and hepatic duct

Enters the duodenum distal to the pylorus

Spleen

On left side of rumen

Located from costochondral junction 7 to dorsal part of rib 12

Pancreas

Pink and yellow in color

Two lobes and a body