Digestive_system_III_F2020

Ruminant Stomach Overview

• Complex Stomach Structure

  • Composed of four compartments:

    • Forestomachs (Non-glandular):

      1. Rumen

      2. Reticulum

      3. Omasum

    • Stomach (Glandular):4. Abomasum

Ruminant Stomach Functions

1. Rumen:

   • Functions as fermentation vat.

   • Houses bacteria and protozoa that breakdown ingested foods and produce volatile fatty acids.

2. Reticulum and Omasum:

   • Responsible for mechanical breakdown of fermented ingesta.

3. Abomasum:

   • Glandular region responsible for enzymatic digestion.

   • All forestomachs covered by stratified squamous epithelium.

Detailed Compartments of the Rumen

• Rumen Characteristics:

  • Largest of the four compartments, filling the left half of the abdomen.

  • Acts as a fermentation vat for microorganisms to break down cellulose.

  • Divided by grooves into dorsal and ventral sacs:

    • Grooves:

      • Longitudinal

      • Cranial

      • Caudal

• Rumen Papillae:

  • Mucosal projections giving a 'pile rug' appearance, aiding nutrient absorption.

Development and Anatomy in Ruminants

• Preruminant Calf at Birth:

  • Rumen size: 80% of total stomach volume post-weaning reduces to 25%.

  • Reticulum 5%, Omasum 10%, Abomasum 7% initially, shifting post-weaning.

Reticulum Overview

• The second forestomach.

  • Has a honeycomb appearance internally.

  • Heavy materials enter the reticulum from the rumen.

Omasum Characteristics

• The third of the forestomachs.

  • Known as the “Butcher's Bible” due to the page-like appearance of muscular laminae.

  • Omasal laminae covered with short papillae projecting into the interior.

Abomasum Description

• Fourth compartment lined with glandular mucosa resembling the simple stomach of carnivores.

• Esophageal Groove:

  • Channel from the cardiac opening to the abomasum.

  • In suckling ruminants, this chamber bypasses the rumen, reticulum, and omasum.

Intestinal Structure

Small Intestine

• Principal site of digestion and absorption.

  • Extends from pylorus to large intestines, divided into:

    1. Duodenum

    2. Jejunum

    3. Ileum

• Features enhancing digestion and absorption:

  • Extended length (approximately 3.5 times longer than body length).

  • Mucosal plicae and villi increase surface area significantly.

Microanatomy of Small Intestine

• Histological Organization:

  • Composed of tunica mucosa, submucosa, muscularis, and serosa.

    • Mucosa:

      • Epithelium (simple columnar with microvilli), goblet cells (for mucous production), and endocrine cells.

  • Villi increase surface area and enhance nutrient absorption through additional structures.

Large Intestine Overview

• Extends from the ileum to the anus; functions primarily to dehydrate fecal contents by absorbing water.

Cecum Characteristics

• Communicates with ascending colon at the cecocolic orifice.

• Variations across species:

  • Horse: Very large cecum with two openings.

  • Other species: Typically have single cecocolic opening.

Ascending Colon Variations

• Carnivores: Short and straight.

• Pigs and Ruminants: Forms a coil, known as spiral colon.

• Horse: Forms a double horseshoe-shaped loop.

Accessory Organs

Pancreas

• Functions:

  • Exocrine: Produces digestive proenzymes.

  • Endocrine: Produces hormones like insulin and glucagon.

• Regions: Body near pylorus, right lobe on right abdomen, left lobe corresponding.

Pancreatic Ducts

• Main Duct: Opens with the bile duct in the duodenum.

• Accessory pancreatic duct also opens in the duodenum.

Liver Overview

• Largest gland in the body; capable of full regeneration.

• Functions in carbohydrate, protein, and fat metabolism, production of bile, storage, filtration, and detoxification of foreign substances.

• Located in the cranial abdomen between diaphragm and stomach.

Liver Structure

• Lobation:

  • General lobation pattern includes left, quadrate, right, and caudate lobes.

  • Gall bladder sits between right and quadrate lobes.

Hepatic Blood Flow

• Blood Supply:

  • Hepatic artery (oxygen-rich) and portal vein (nutrient-rich from the digestive tract).

• Drainage: Hepatic veins carry blood from the liver to the caudal vena cava.

Biliary System

• Bile: Secretion from liver cells into the duct system aids digestion.

• Gall Bladder: Stores bile (absent in horses).

• Ducts include cystic duct, hepatic ducts, and the bile duct, which carry bile to the duodenum.