Intestino e cloaca de Gallus gallus domesticus

Abstract

The alimentary canal is important for the processes of transport, digestion, nutrient absorption, and waste elimination. The video presented aims to demonstrate the morphology and describe the main functions of the intestinal segments (small and large) and to report some curiosities and zootechnical applications. This material was produced by academics from the extension project "Knowing, respecting and producing birds: didactic and alternative models in the teaching and learning process", linked to the discipline Comparative Anatomy of Domestic Animals (BA066) of the Zootechnics Course at the Federal University of Paraná (UFPR). The small intestine of birds begins after the gizzard (gastric ventricle) and can be sequentially segmented into the following portions: duodenum (descending and ascending); jejunum and ileum. The ascending portion of the duodenum receives secretions from the liver (bile) and pancreas (pancreatic juice) through ducts, which are quantitatively larger and distinct compared to mammals. The ascending and descending portions of the duodenum form the U-shaped duodenal loop, and between them, in the mesoduodenum, lies the pancreas. Further along is the jejunum, an important segment for food absorption. Regarding the topography of this segment, there are literary discrepancies concerning its termination and the beginning of the ileum. Some describe it as ending at the vitelline diverticulum, while another description refers to the ileocecal folds. It is important to mention that the vitelline diverticulum ("Meckek's diverticulum") is a remnant of the yolk sac, responsible for nourishing the embryo during development inside the egg. In adult birds, it remains as a small dilation in the intestine, although not always perceptible. The last portion of the small intestine is the ileum, also responsible for the final absorption of nutrients and bile salts. The large intestine of birds is formed by two ceca and a rectum. The ceca are responsible for the microbial fermentation of fiber and the production of B vitamins and vitamin K. After the ileocecal junction, the intestine continues into the rectum, which extends to the cloaca. It is interesting to note that several academic books also describe this last portion as the colon. This region is responsible for water reabsorption and the direction of feces. Since birds do not have a urinary bladder, it is in the rectum that the mixing of feces with uric acid occurs, allowing for greater water conservation. The cloaca is important for receiving contents from the digestive, urinary, and reproductive systems. Morphologically, it is segmented respectively into: coprodeum, urodeum, and proctodeum; however, in the digestive system, its function is to allow the elimination of feces.