The mesentery is a continuous, double-layered fold of the peritoneum, the membrane that lines the frog’s coelomic, or body, cavity. This structure is found in all vertebrates, providing a fundamental framework for internal organization. In the frog, understanding the mesentery is key to appreciating how the animal maintains a functional digestive system despite its dynamic movements and compact anatomy. It serves multiple purposes, including providing a protected route for the transport of necessary materials.
Anatomical Structure and Location
The mesentery is a delicate, often translucent membrane composed of two sheets of serous tissue derived from the peritoneum. It is a highly organized anatomical feature, most prominent as the membrane that holds the long, coiled small intestine.
It connects the entire length of the small intestine, and parts of the stomach and large intestine, to the dorsal body wall of the coelomic cavity. This attachment is critical because the digestive tract is significantly longer than the body cavity. Sections are sometimes named based on the organ they support, such as the mesogaster for the stomach and the mesentery proper for the small intestine.
Primary Function: Organ Support and Anchoring
The primary role of the mesentery is mechanical stabilization, serving as an anchor for the digestive organs within the body cavity. It firmly secures the long, looping small intestine to the fixed dorsal wall, preventing the entire tract from shifting freely. This is important for the frog, which engages in rapid movements like jumping and swimming that subject its internal organs to force.
By fixing the organs in place, the mesentery ensures the digestive system maintains its proper three-dimensional arrangement. This stabilization prevents the long intestinal loops from twisting around themselves, a potentially fatal condition known as volvulus. The supportive role of the mesentery also allows the intestines to perform the necessary muscular contractions, called peristalsis, without being displaced.
The mesentery also allows the digestive tract to have a degree of controlled mobility, which is necessary for efficient peristalsis and for accommodating changes in volume as food passes through. This balance between firm anchoring and controlled movement is a significant feature of the mesentery’s structural design. The membrane provides the necessary restraint while still allowing for the functional flexibility required by the digestive process.
Secondary Function: Pathway for Circulation
A second function of the mesentery is its role as a protected conduit for the circulatory and nervous systems. Major blood vessels travel within the two layers of the mesentery to supply and drain the digestive organs. Mesenteric arteries branch within the membrane to deliver oxygenated blood and nutrients to the intestinal wall.
Correspondingly, the mesenteric veins collect blood rich in newly absorbed nutrients from the small intestine. This nutrient-laden blood is then transported away from the digestive tract, primarily via the hepatic portal system, toward the liver for processing before entering the general circulation. The mesentery also contains lymphatic vessels, which collect tissue fluid and absorb dietary fats. Nerves housed in the membrane regulate the muscular contractions and glandular secretions of the digestive tract.