Epithelial components of the organs of the digestive system are derived from the endoderm, whereas connective tissue and muscle components are derived from the mesoderm. At the 3rd-4th week of development, as a result of cephalocaudal and lateral foldings of the embryo, a portion of the endoderm-lined yolk sac cavity is incorporated in the embryo to form the primitive gut. Primitive gut is composed of four main regions: pharyngeal gut, foregut, midgut, and hindgut. The esophagus and stomach are derived from the foregut. The development of the esophagus is characterized by lengthening, widening, thickening, and histological changes. The development of the stomach is characterized by widening, thickening, and histological changes as well as positional changes. In the present study, we tried to review the morphological and functional development of the esophagus and stomach with the aid of pictures obtained from various stages of prenatal and postnatal development of the organs of rats. Previous reviews lack information on both histological and functional development of the organs. Development of the digestive tractThe digestive system consists of the digestive tube and its principal associated organs, namely, salivary glands, pancreas, liver, and gallbladder. It begins with the oral cavity and ends in the anal canal. The digestive tube is composed of the esophagus, stomach, small intestines (duodenum, jejunum, and ileum), and large intestines (cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal). The liver and pancreas are accepted to be associated glands bound to the digestive tube by excretory ducts. Epithelial components of the organs of the digestive system are derived from the endoderm, whereas connective tissue and muscle components are derived from the mesoderm. The organs of the body are formed by the proliferation, migration, and differentiation of the stem/progenitor and mature cells.The first 8 weeks of intrauterine development period is called as "organogenesis period" as well as "embryonic period". At the end of the 8th week, the embryo is approximately 30 mm in length and 2 g in weight. The heart is functional on the 4 th week. Primary brain vesicles are formed, and primary brain waves are detectable. At the end of this period, all of the body systems are formed but are not mature in morphological and functional manner. The development and growth of the organs continue during the fetal period. Most of the organs are fully developed at the postnatal period; still, volume increase is obvious through the puberty period. It is a matter of fact that morphological and functional maturation period is not uniform for all of the cell types.In this review, we aimed to outline brief information about the histological features and prenatal and postnatal morphological and functional development of the esophagus and the stomach. Recent reviews lack information on both histological and functional development of these organs.

The parenchyma of the liver and pancreas is derived from the endoderm, whereas the stroma is derived from the mesoderm. Both of them are derived from the endoderm of the foregut as the esophagus, stomach, and a part of duodenum. At the 3 rd -4 th of development, the liver, gallbladder and bile ducts become diverticulum hepaticum that is derived from the caudal portion of the foregut. There were inductive effects of septum transversum and cardiac mesoderm for the development of liver diverticulum. The pancreas arise from the endoderm of the foregut. The pancreas is derived from the fusion of the ventral and dorsal pancreas bulbs, which arise from the endoderm of the duodenum. The inductive effects of the notochord and dorsal aorta play a role in the development of the pancreas. In this manuscript, we attempted to review the morphological and functional development of the liver and pancreas with the aid of pictures obtained from various stages of prenatal and postnatal development in the organs of rats.

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Epithelial components of the organs of the digestive system are derived from endoderm whereas connective tissue and muscle components are derived from mesoderm. At the 3-4 th of development, as a result of cephalocaudal and lateral foldings of the embryo, a portion of the endoderm-lined yolc sac cavity is incorporated in the embryo to from the primitive gut. Primitive gut is composed of four main regions which are pharyngeal gut, foregut, midgut, and hindgut; respectively. Intestines are derived from foregut, midgut and hindgut. The development of the intestines is characterised by lengthening, widening, thickening, histological and positional changes. In this manuscript we tried to review the morphological and functional development of the small and large intestines with the aid of pictures obtained from various stages of prenatal and postnatal development the intestines of rats. Previous reviews lack of information on both histological and functional development of the small and large intestines. Keywords: Development, large intestines, small intestines ÖZSindirim sistemi organlarının epitelyal bileşenleri endodermden, bağ dokusu ve kas bileşenleri mezodermal kökenlidir. Gelişimin 3-4th haftalarında embriyonun büyümesi ile beraber sefalokaudal ve lateral yönlerde kıvrılması, endodermle döşeli vitellüs kesesinin bir bölümünün embriyo bedeni içinde kalarak primitive bağırsağı oluşturması ile sonuçlanır. Bağırsak HistolojisiBağırsak duvarı mukoza, submukoza, muskularis (muskularis eksterna) ve adventisya tabakalarından oluşur. Mukoza, epitel, lamina propriya ve muskularis mukozadan ibarettir. İnce bağırsaklarda tek katlı çizgili kenarlı, kalın bağırsaklarda tek katlı pirizmatik epitel özelliği gösteren yüzey epiteli absorbsiyondan sorumlu, pirizmatik şekilli enterositler dışında mukus salgılayan kadeh şekilli goblet hücrelerini de içerir. İnce bağırsaklarda mukoza ve submukoza katlanarak villusları oluşturur. Bağ dokusu özelliğindeki lamina propriya büyük ölçüde tubuler bağırsak bezleri ile işgal edilmiştir. İnce bağırsak bezlerinde enterosit ve goblet hücrelerinin yanı sıra paneth hücreleri, enteroendokrin hücreler, M hücreleri ve kök hücreler bulunur. Kalın bağırsak bezlerinde ise sağlıklı kişilerde paneth hücrelerine rastlanmaz. Mukozanın son katı olan muskularis mukoza içte sirküler, dışta longitudinal seyreden iki düz kas tabakasından oluşur. Orta yoğunlukta bağ dokusu submukozada submukozal sinir pleksusu (Meissner sinir pleksusu) bulunur. Duodenumda bu tabaka içinde Brunner bezleri olarak bilinen serömüköz bezler yer alır. Tunika mukoza ince bağırsaklarda sirküler ve longitudinal seyirli kas hücrelerinden oluşan iki tabakalı bir yapı gösterir. Kas tabakaları arasında myenterik sinir pleksusu bulunur. Kalın bağırsaklarda ise dış longitudinal kas tabakası üç bant şeklinde düzenlendiği için enine kesitte kesintili seyreder. En dış tabaka seroza özelliğindedir (1, 2). Primitif Bağırsağın GelişimiGelişimin 3-4. haftasında embriyonun büyümesi ile beraber sefalokaudal ve lateral yönlerde kıvrılması, endo...

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