 primary germ layers, endoderm derivatives, first the contents, formation of endoderm, formation of digestive tract from endoderm, then respiratory tract, endocrine system, auditory system, and the urinary system. First the endoderm, endoderm is actually the innermost membrane or layer of cells which is formed during the gestulation process. So endoderm is the layer of cells which is formed during the gestulation process and is the innermost position. In gestulation we know that there are three layers formed. Three layers are formed in most of the animals. The outer layer is actually the ectoderm. The lower layer is the mesoderm and the middle layer is the endoderm. When we read these general concepts, the endoderm is a digestive tract. So we are confined to the digestive tract and endoderm is formed by the endoderm. But the endoderm is not only a digestive tract but also other body organs. If we look at the body organ formed by the endoderm, that is the digestive tract. There are two portions of the digestive tract which are not synthesized by the endoderm. One is the oral cavity and the other is the mouth. This endoderm will not be formed. Similarly, the other digestive tract's end position is the anus. The anus and the oral cavity or the mouth portion are not actually found by the endoderm. The other portions are esophagus, stomach, small intestine, large intestine. All the digestive tract portions are all synthesized by the endoderm. Apart from this, the different glands of the endoderm are formed by the endoderm. Similarly, liver and pancreas. The main vessel of the liver is the metabolic factory of our body. There are many mechanisms involved in the body. But the important role of the liver is to digest our food. So the liver is also formed by the endoderm. The formation of the liver is also endoderm. The liver contains gallbladder which is also synthesized by the endoderm. Similarly, the pancreas is also synthesized by the endoderm. The second important system is the respiratory tract. In the respiratory tract, we see different parts of the lungs. The lungs have different parts in which we track bronchi and alveoli. These are portions where they are synthesized. They are actually formed by the lungs. Then the endocrine glands. Those endocrine glands are synthesized by the endoderm. They are the thyroid, parathyroid gland, parathyroid gland, parathyroid gland, thymus and the pancreas. The pancreas and the endocrine gland are also produced by the insulin. These four important glands are actually formed during development by the endoderm. Similarly, the auditory canal. If we look at the auditory tube, which is also called auditory canal, and then the tympanic cavity. These two things, tympanic cavity and auditory canal, they are both found by the endoderm. If we look at it a little bit, the auditory tube that is going out of our ears is the auditory tube. There is a tympanic membrane. The tympanic membrane is actually in the cavity. So we give the cavity the name of the tympanic cavity. Then the urinary and genital systems. Our urinary system is the urinary bladder. The urinary bladder is the endoderm that is synthesized. This is important in formation. Endoderm is derived from this. Similarly, in females, the vagina and the urethra. So the vagina or the urethra are the portions synthesized by the endoderm. So it means that the endoderm doesn't make a digestive system, but rather it makes a body organ.