ANSC 2202 - Distal GI Tract

Liver (and its functions)

• Largest gland in the body

• Accessory organ

• Functions:

  • Clears out drugs and toxins

  • Formation of bile (for breakdown of fats)

How does the liver vary in size across species?

• Carnivore: 3-5% of body weight

• Omnivores: 2-3%

• Herbivores: 1-1.5%

4 Lobes of the Liver

• Left

• Right

• Quadrate

• Caudate

What do capillaries in the liver and intestines do?

• Absorb nutrients from digestion

Liver: the Porta

• Where blood vessels and nerves enter the liver

  • Portal vein

Gallbladder

• Stores bile

• Common bile duct: liver to duodenum

• HORSES & RABBITS DO NOT HAVE A GALLBLADER

Small Intestine parts

• 3 Parts:

  • Duodenum

  • Jejunum

  • Ileum

How does the small intestine vary in size across species?

• Horses: 80+ feet

• Dogs: 3-4x body length

• Sheep & Goats: 25x body length

Dueodenum

• Relatively short

• Receives ingesta (food) from the pylorus

• Anchored to the body

• Adjacent to the pancreas

  • Sigmoid loop

Pancreas

• Exocrine:

  • Secretes through duct

  • Produces enzymes that aid in digestion

    • specifically of carbohydrates, fats, and proteins

      • The insides/lining of our organs are considered external surfaces, so endocrine secretes onto them.

• Endocrine:

  • Secretes into blood

  • Secretes hormones

    • insulin, glucagon, and gastrin

Jejunum

• Longest part of the small intestine

• Great range of motion

Jejunal Arcades

• Blood vessels attached to the jejunum

Mesentery

• Attaches jejunum to the body wall

  • Connective tissue

• Carries blood vessels, lymphatics, and nerves to the digestive organs

Ileum

• Short

• Empties into the cecum

• Ileocecal fold

  • Connection between ileum and cecum

Large Intestine

• Absorbs water

What does the large intestine do in horses?

• Fermentation

Parts of the Large Intestine

• Cecum

• Colon

• Rectum

How does the large intestine vary in size across species?

• Carnivores: relatively small

• Herbivores: large and complex

  • All animals, to some capacity, can break down fiber in the large intestine

Ruminants are ____ fermenters

• Foregut (Rumen)

Horses are ____ fermenters

• Hindgut (cecum and colon)

Cecum

• Latin: blind

  • Pouch that does not connect to anything at the end

• At the junction of the ileum and the colon

• Functions:

  • Water absorption

  • Fermentation

Cecum species variation

• Dogs: S-shaped

• Ruminants and pigs: relatively small

• Horses: comma shaped, 3 ft long

Colon (3 parts)

• Ascending (beginning part)

  • Spiral colon (ruminants and pigs) 

  • Horses = large colon

• Transverse (between ascending and descending)

  • Hard to identify in our species

• Descending (ending part)

  • Longest part

  • Horses = small colon

• Note that the ascending, transverse, and descending names are typically used for humans and arent very meaningful for the direction in animals.

Spiral Colon

• Ruminants and Pigs

• 3 Parts:

  • Centripetal coils: inwards

  • Central flexure: where coil folds upon itself

  • Centrifugal coils: outwards

    • (Centrifugal spins things in a circle and throws them to the outside!)

Pig: Spiral Colon

Equine Colon: Large Colon

• Ascending is called the “large colon”

• 10-12 ft long, double horseshoe (two u-shapes)

• Can hold over 20 gallons

• Functions in fermentation

  • 10¹⁰ (10^10) bacteria per mililiter

• Only attached to the body wall in one place

  • This leads to a lot of issues

Equine Colon: Small Colon

• Descending colon is called the “small colon”

• About 11.5 ft long

• Where fecal balls are formed

Rectum

• From descending colon to anus

• Within pelvic cavity

• Dorsal to reproductive organs

  • Shortest part of entire GI

Anus

• Caudal most opening of the gastrointestinal tract

Anal sacs/glands

• In dogs and cats

• Secretes an “evil-smelling” fluid

• Probably territorial marker

• Can become impacted or inflamed

  • Typically in dogs—causes them to scoot around

Colic

• In horses, abdominal pain

• Has many, many causes in both small and large intestine

  • Torsion

  • Entrapment

  • Tumors

  • Inflammation

  • Gas distention

• Treatment involves rehydration (difficult), pain medication, or surgery

Terms