Bat digestive system
Photos and Text: Kathy Coulombe and Sarah Winstanley
This shows displacement of the intestines in a female bat during pregnancy. Fetal bats are very large in proportion to the mother's body size.
This illustrates an inguinal hernia in a male Tadarida brasiliensis.
To dissect the digestive system, we made incisions into the abdominal sheath laterally on both sides (having already dissected the abdominal musculature in a previous lab). We removed the abdominal to expose the deep organs. We cut the diaphragm and ribcage medially and reflected them to expose the esophagus. We transected the esophagus as cranially as possible (around the level of C4). We removed the liver from the abdominal cavity with tweezers gently to bring out the rest of the digestive organs intact. After we had removed the intestines, we cut them (as caudally as possible). This enables us to stretch it out on a surface and examine the digestive organs.
Note that we performed this dissection on a different specimen than the one we used for all of our other dissections on Tadarida braziliensis. This was because we preserved the abdomen on our initial male specimen in order to study the indirect inguinal hernia more closely at a later date. The specimen we used for this dissection was female.
Our first observation was that the abdomen was distended. After we removed the abdominal wall, we observed that the uterus filled two thirds of the abdomen and confirmed our suspicions that this bat was pregnant. The muscle fibers around the uterus have different angles of orientation and run in different directions. We split the layers of the uterus and removed a single large foetus. Uncurling the fetus proved difficult, as it was tightly curled, with the transparent wings wrapped around the head. Claws were present on the distal end of the digits on the lower limb. The fetus was 12 mm in length.
The liver is divided into four lobes. Previous studies of the bat's liver indicate that the left central lobe of liver can be separate from other lobes or partially fused with right central lobe. [1] These claims could not be substantiated by our dissection as the liver was damaged by tweezers upon removal from the abdomen.
The pancreas is a short section of glandular tissue that looks similar to the white lumps of fat present in the bat, but that is located just caudally to the liver and remains on the mesentery of the duodenum after its removal (as opposed to fat). We had difficulty finding the pancreatic duct to confirm the connection of the pancreas.
The intestines of the specimen were severely displaced to the left of the abdomen due to the bat's advanced pregnancy at death. The intestines of Tadarida braziliensis are not divided into large and small intestines, and the cecum is absent. This anatomy corresponds in part to the diet of this species. Tadarida braziliensis is a faunivorous species whose diet consists only of insects. High protein diet allows for the easy digestion, and hence a relatively simple and less differentiated gut. This is in contrast with faunivores, which use long differentiated intestines to ferment the nutrients, which are difficult to process from the cellulose of plants for example. This specimen has a digestive tract that measures 100 mm, which is approximately nose-to-end-of-tail length of the animal. The length of the bat's GI tract is relatively short compared to the digestive tract of the rabbit, for example, whose intestines alone measure about twice the length of the rabbit itself. The short GI tract is unique in bats because of their mode of locomotion. In flight, bats need to be light enough to support their weight using their wings. The short tract limits the amount of stored food in the tract to a minimum. To compensate, bats do not eat one large meal a night, but eat smaller amounts more frequently.
1. Simmons, N. B. 1988. A reappraisal of interfamilial relationships of bats. In Bats: Phylogeny, Morphology, Echolocation and Conservation Biology. T. H. Kunz and P. A. Racey (eds.). Washington: Smithsonian Institution Press.