There are more than 9,000 kinds of birds in the world, and bird tracks can be seen in grasslands, shrubs, water surfaces, woods and other places. I don't know if you have observed that some birds will "throw objects" anytime and anywhere, why is this?
It turns out that birds have a short rectum, can not store a lot of feces, and at any time to defecate weight loss is conducive to flight. Although the size of birds is not large, the digestive system is very developed, consisting of the mouth, esophagus, sac, stomach, intestines and cloaca. These digestive organs are different in both structure and physiological function than the digestive organs of mammals.
oral cavity
Birds have no teeth, lips, gums and cheeks in their mouths, only beaks and tongues, so birds eat without chewing, and this simple and lightweight structure greatly reduces the weight of the head at the front of the neck of the bird, reducing the burden on its flight. The shape of the beak and tongue of birds varies depending on the species, feeding habits and feeding styles, such as the flattened beak and flat tongue of a duck, which makes it easy to feed on aquatic plants and plankton in the water.
esophagus
The esophagus, located between the bird's pharynx and glandular stomach, on the dorsal side of the trachea, is accompanied by the trachea and is a muscle-based duct that is easily dilated. The esophagus is divided into two parts, the esophagus of the neck and the esophagus of the thorac, and birds without sacs are difficult to distinguish between the neck and the chest from the appearance. The diameter of the esophagus is related to the size of the food swallowed by birds, and the esophagus itself has no digestive function, and its main function is to transmit food from the pharynx to the stomach.
craw
The sac is a cystic structure specialized by partial esophagus, which is similar in structure to the esophagus, and is mainly used for temporary storage and softening of food, and the degree of development of bird sacs is consistent with its habits. For example, the sacs of the gannets are very developed, because the fish is a hard food, and the hard food is softened and expanded in the sacs; there are also some birds whose sacs are more peculiar, such as the pigeon's sacs are bilateral sacs, and penguins do not even have sacs.
stomach
The stomach of the bird consists of the glandular stomach of the front and the musculature of the posterior part. There are digestive glands in the gland stomach that secrete digestive juices, which have the function of digesting food. The stomach, also known as the sand sac, is equivalent to the teeth of birds, which contains swallowed sand and gravel, which is mainly used to grind food. In general, the glandular stomach of birds is relatively small, it is not easy to retain more food, it is only responsible for secreting and supplying gastric juice. When the gastric juice is mixed with food, it flows into the stomach and muscle, and then the real digestive effect begins.
intestines
The intestines of birds are divided into small intestine, cecum and large intestine (rectum), which continues until it is adjacent to the cloaca and the cecum, after which it turns into the large intestine. The large intestine of birds is very short and opens directly to the cloaca. Among them, the small intestine is the longest section of the digestive tract and is the main place where food is digested and absorbed, while the large intestine is extremely short, does not store feces, but has the effect of absorbing water, which can reduce the weight burden for the birds.
cloaca
The cloaca is connected to the rectum in front of the cloaca and the cloaca posteriorly, which is a common channel of the three systems of digestion, urinary and reproduction. The interior is divided into three parts: fecal tract, cloaca and tract by two circular folds. The fecal tract communicates with the rectum and receives waste products excreted from the large intestine; The vas deferens and ureteral openings are in the cloaca, which receives urine excreted from the kidneys and sperm and eggs from the reproductive glands; The anal tract is the last segment of the digestive tract, which is opened outside the body with a cloaca hole for temporary storage and excretion of waste.
Although researchers have now studied birds in depth, there are many kinds of bird groups, and there is still a lot of research space, hoping that people can discover more secrets about birds in the future.
This article was scientifically checked by Huang Shaohua, a senior teacher of the second middle school in Chaisang District, Jiujiang City, Jiangxi Province.