VM520 Systems 2: Digestion Metabolism and Nutrition - Structure and Function of the Small Intestine and Pancreas

Structure and Function of the Small Intestine and Pancreas in Domestic Animals

Introduction

• Topic: Structure and Function of the Small Intestine and Pancreas

• Instructor: Dr. Mahesh S. Deokar

• Goals of the Lesson:

  • Describe topography of the small intestine in healthy animals, emphasizing its adaptation for nutrient absorption and interaction with digestive enzymes.

  • Explain the intricate structure and function of the small intestine components, focusing on specific adaptations of different domestic species.

  • Discuss the structure and function of the pancreas, including its dual role in both endocrine and exocrine systems.

Small Intestine Overview

• General Structure: The small intestine is a convoluted tube that plays a crucial role in digestion and absorption, consisting of three main segments:

  • Duodenum: The first section, approximately 25-30 cm long, is subdivided into three parts: descending, transverse, and ascending. The duodenum receives chyme from the stomach and secretions from the pancreas and liver, which aid in digesting proteins, fats, and carbohydrates.

  • Jejunum: The middle section, around 2-3 meters long in carnivores, is primarily involved in the absorption of nutrients due to its extensive vascular supply and large surface area, provided by villi and microvilli.

  • Ileum: The final section, approximately 3-4 meters long, opens into the cecum. It is responsible for the absorption of vitamin B12 and bile salts, and may also absorb any remaining nutrients not absorbed by the jejunum.

Feline and Canine Anatomy

• Feline (Cat) Abdominal Viscera:

  1. Heart

  2. Diaphragm

  3. Liver

  4. Small Intestine includes duodenum, jejunum, ileum with a focus on lymphatic drainage in absorption.

  5. Spleen

  6. Urinary Bladder

• Canine (Dog) Abdominal Viscera:

  1. Liver

  2. Stomach

  3. Spleen

  4. Small Intestine with notable differences in segment lengths compared to felines.

  5. Urinary Bladder

Small Intestine in Horses

• Duodenum: This structure consists of shorter sections: descending, transverse, and ascending, which are adapted to accommodate the larger volume of fibrous feed processed in equines.

• Jejunum: Located mostly in the left dorsal abdomen, high mobility is afforded due to the long mesentery, enabling it to adapt to content volume. The jejunum is rich in blood supply, which is vital for nutrient absorption.

• Ileum: This section opens into the cecum and may exhibit adaptations such as the presence of Peyer's patches for immune function.

Small Intestine in Ruminants

• Duodenum: Similar to horses, featuring segments that allow for processing of complex carbohydrates from fibrous plant material.

• Jejunum: Highly flexuous, positioned in relation to a modified large intestine, known as the spiral colon, which assists in further breakdown and fermentation of food.

• Ileum: Opens into the cecum with adaptations like a thicker lining to facilitate nutrient absorption.

Small Intestine in Pig

• Duodenum: Consists of three similar parts: descending, transverse, ascending, comparable to other species.

• Jejunum: Predominantly situated on the right side but changes depending on stomach distention, impacting digestion and absorption efficiency during feeding.

• Ileum: Opens into the cecum; its position shifts depending on stomach conditions, emphasizing the adaptability of pigs in processing food of varying types.

The Pancreas Overview

• Location: The pancreas is located in the craniodorsal part of the abdominal cavity, in close association with the duodenum, liver, and stomach, and plays a pivotal role in digestion and metabolic regulation.

• Structure: This organ consists of a body with two lobes:

  • Body: Serves as the central connection point for both lobes, facilitating the flow of digestive enzymes.

  • Right Lobe: Also referred to as the head, associated with the duodenum, playing a critical role in regulating digestive processes.

  • Left Lobe: Known as the tail or gastrosplenic portion, connects to the stomach and is involved in the endocrine secretion of hormones like insulin and glucagon.

Exocrine Functions of the Pancreas

• Digestive Enzymes Produced:

  • Amylase: Breaks down carbohydrates into simple sugars for absorption.

  • Lipase: Aids in fat digestion by breaking down triglycerides into fatty acids and glycerol.

  • Proteases: Including trypsinogen, chymotrypsinogen, and carboxypeptidase, which are essential for breaking down proteins into peptides and amino acids for absorption.

• Regulation: Hormones like cholecystokinin stimulate gallbladder contraction and pancreatic enzyme secretion, while secretin regulates bicarbonate secretion, aided by nervous system signals that enhance digestive efficiency.

Blood Supply to the Pancreas

• Supplied by a network of arteries:

  • Hepatic artery ➔ Gastroduodenal artery ➔ Cranial pancreaticoduodenal artery, providing ample oxygen and nutrients necessary for pancreas function.

  • Cranial mesenteric artery ➔ Caudal pancreaticoduodenal artery, ensuring consistent blood flow during digestion.

Variations in the Pancreas among Species

• Cats: Characterized by a larger pancreatic duct than dogs and the presence of an accessory duct in approximately 20% of individuals, influencing enzyme delivery.

• Dogs: Exhibit larger main and accessory pancreatic ducts, enhancing digestive enzymes distribution.

• Cattle: Present a rare primary duct and frequent occurrence of accessory ducts, which can affect nutrient absorption due to variations in digestive process efficiency.

• Horses: Notable for a large pancreatic duct, with a smaller accessory duct that assists in digestion and enzyme delivery.

• Pigs: Have a significant accessory pancreatic duct that allows for effective enzyme secretion during digestion.

Conclusion and Next Steps

• Students are encouraged to reach out with further questions to Dr. Deokar via email, fostering an interactive learning environment.

• The next session will delve into the intestinal phase of digestion and explore liver functions, linking to the comprehensive digestive system of domestic animals.