WK 4 - 2 Structures of the digestive system-mesenteries

Digestive System Overview

General Information

  • Course Code: BM1002

  • Instructor Email: alexandra.trollope@jcu.edu.au

Learning Objective

  • Objective: To describe the organization of the parietal and visceral peritoneum, the greater and lesser omentums, and mesenteries, as well as their roles and relationships within the human body.

Abdominopelvic Cavity

The abdominopelvic cavity houses numerous vital organs and structures that are essential for digestion and overall bodily function. The following structures are included in the abdominopelvic cavity:

  • Liver: A vital organ responsible for detoxification, protein synthesis, and the production of biochemicals necessary for digestion.

  • Stomach: An organ responsible for breaking down food and mixing it with digestive juices.

  • Mesocolon: The fold of peritoneum that connects the colon to the posterior abdominal wall.

  • Transverse Colon: The middle section of the large intestine that absorbs water and nutrients.

  • Greater Omentum: A large fold of peritoneum extending from the stomach, it plays roles in fat storage, immune response, and protection of abdominal organs.

  • Parietal Peritoneum: This serous membrane lines the abdominal cavity and provides support to the abdominal organs.

  • Lesser Omentum: A double layer of peritoneum that extends from the liver to the lesser curvature of the stomach.

  • Mesentery Proper: A fold of peritoneum that attaches the small intestine to the back wall of the abdomen.

  • Diaphragm: A muscle that separates the thoracic cavity from the abdominopelvic cavity and aids in respiration.

  • Urinary Bladder: Stores urine before it is expelled from the body.

  • Pancreas: An organ with both endocrine and exocrine functions, essential for digestion and blood sugar regulation.

  • Duodenum: The first part of the small intestine, playing an important role in the chemical digestion of food.

  • Jejunum: The second part of the small intestine where most nutrient absorption occurs.

  • Ileum: The final section of the small intestine, continuing the process of nutrient absorption.

  • Rectum: The final section of the large intestine that stores feces before elimination.

  • Peritoneal Cavity: The potential space between the parietal and visceral layers of peritoneum that contains serous fluid.

  • Visceral Peritoneum: The layer of peritoneum that covers most abdominal organs, providing protection and support.

  • Peritoneum: The serous membrane that forms the lining of the abdominal cavity and surrounds the peritoneal cavity.

Types of Peritoneum

Parietal Peritoneum:

  • Lines the abdominal cavity and forms a protective layer for the organs within.

Visceral Peritoneum:

  • Covers the viscera (internal organs), providing a smooth surface to reduce friction from movements during digestion.

Retroperitoneal:

  • Describes organs located external or posterior to the peritoneum; these include the kidneys and aorta.

Intraperitoneal:

  • Refers to organs completely covered by visceral peritoneum, including the stomach and most of the intestines.

Organ Locations

Intra- or Retro

  • Intraperitoneal Organs: Include the stomach, transverse colon, jejunum, ileum, and sigmoid colon; these organs are freely mobile due to mesenteric attachments.

  • Retroperitoneal Organs: Include the duodenum, ascending colon, rectum, and descending colon; these organs have a fixed position due to their external location relative to the peritoneum.

Mesentery

Structure and Function

  • Definition: A mesentery consists of two sheets of serous membrane with loose connective tissue in between. It supports the intestines and contains blood vessels, lymphatics, and nerves that supply the digestive organs.

  • Roles:

    • Provides the necessary attachment for organ mobility within the abdominal cavity, allowing for movements during digestion.

    • Facilitates the transmission of blood vessels and nerves between the folds of the mesentery, ensuring adequate supply to the digestive organs.

Omenta and Mesentery

Components

  • Falciform Ligament: A ligament that attaches the liver to the anterior abdominal wall and diaphragm.

  • Greater Omentum: A significant fold of peritoneum that hangs down from the stomach, covering the intestines, and providing insulation and cushioning to abdominal organs.

  • Lesser Omentum: Connects the stomach and proximal part of the duodenum to the liver.

  • Mesentery Proper: Attaches the small intestine to the posterior abdominal wall and provides a pathway for blood vessels and nerves.

Development of Mesenteries

Key Points

  • There is a trade-off between mobility and fixation in long tubes like the gut, which allows for freedom of movement during digestion while maintaining structural integrity.

  • Mesenteries support and stabilize gastrointestinal (GI) tract organs, allowing vessels to travel within their folds without encumbering digestive processes.

  • Derivatives of the dorsal mesogastrium include the greater omentum and mesentery proper, which arise from embryonic structures during development.

  • Derivatives of the ventral mesogastrium include the lesser omentum (including the hepatoduodenal and hepatogastric ligaments), falciform ligament, and the ligamentum teres (round ligament of the liver).

Embryological Development

  • At 4 weeks of gestation, the digestive tube is suspended in the coelom via dorsal and ventral mesentery, which is crucial for proper organ development.

  • The ventral mesentery disintegrates except where vital blood vessels and visceral organs develop, particularly along the paths of umbilical arteries and veins.

  • As the embryo grows, the stomach and liver experience a rotation to the right, leading to the formation of pockets that enable the development of greater and lesser omentum.

  • The pancreas and liver originate from epithelial pockets that grow into the dorsal and ventral mesenteries, respectively, highlighting the importance of mesenteric structure in organ development.