Most organs in the body cavity are directly or indirectly connected with the outside world, including digestive system, respiratory system, urinary system and reproductive system. According to its morphological structure, it can be divided into lumen organs and parenchymal organs. The lumen organs are connected with the outside world through pipelines; The parenchymal organs are mainly glands, and there are catheter openings on the wall of the lumen organs.

From the perspective of individual development, most digestive and respiratory systems are derived from endoderm; The respiratory organ is another tube protruding from the upper part of the primitive digestive tube to the ventral side. The urinary and reproductive organs originated from the urogenital ridge of mesoderm and evolved into urinary and reproductive systems with different functions. But men still have common discharge tubes. So some people call the urogenital system urogenital system.

Extended data:

The digestive function of human stomach is mainly reflected in two aspects. First, the grinding of food, whether there is food or not, the grinding of stomach always exists, about three times a minute; The second is to dissolve food through stomach acid and promote digestion.

Various physiological movements of the stomach are mainly completed by the myogenic layer. The muscular layer of the stomach wall is very developed and consists of three layers of smooth muscle. Smooth muscle has great ductility, and it can grow to 2~3 times as long as it is.

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