Transcription
This is CH weight embryo in the gastrulation period. You see here, here is ectoderm, this one is mesoderm, and this one is endoderm. Here is yolk sac and here is amniotic cavity. You see here, craniocaudal folding or flexure. This endoderm, this endoderm becomes primitive gut. Is it clear? This endoderm becomes primitive gut.
This is coronal section, and you see ectoderm, amniotic cavity, notochord, mesoderm, and endoderm. Here is yolk sac. Lateral folding of the three-layer embryonic germ layer makes digestive tract or primitive gut. Have a look here.
[Music] [Music] Sure, what's happened? There are two foldings in the three-layer germinal disc at the third week of intrauterine life. Craniocaudal folding is related to the elongation of the neural tube. Elongation of the neural tube. Neural tube is a part of the ectoderm. It's a part of the ectoderm, and elongation of this part of the ectoderm makes craniocaudal folding. Development of somites. Somites are parts of the parts of the intraembryonic mesoderm, okay? And development of somites make lateral folding of the three-layer germ disc. After these two foldings end, the endoderm on the roof of the yolk sac becomes primitive gut. Endoderm makes primitive digestive tube, primitive gut.
After this folding, these two foldings, allantois enters into the connecting stalk, goes on the ventral surface, goes to the ventral surface. The yolk sac and the allantois remain outside of the embryo, outside of the embryo. Here is allantois, okay? And here is yolk sac.
This primitive gut has four regions. This primitive gut has four regions. Foregut. [Music] Gut from stomodeum or prechordal plate or oropharyngeal membrane to the respiratory bud or lung bud. The first part, the first part of the primitive gut becomes pharyngeal gut from primordial aorta to the lung bud, respiratory bud. This part is called pharyngeal gut. From respiratory bud to the liver bud or hepatic bud or hepatic diverticulum is called forgot. It's called foregut. Third part, from hepatic bud or liver bud begins as midgut. Here is midgut. And fourth part is hindgut. In the adult, the border between midgut and hindgut is, yeah, which part of transverse colon? Right two-thirds and left one-third of the transverse colon is the border between midgut and hindgut.
All structures that develop from foregut are supplied by celiac trunk. All structures that developed from foregut are supplied by celiac trunk. All structures that developed from the midgut are supplied by superior mesenteric artery. And all structures that developed from hindgut are supplied by inferior mesenteric artery.
After craniocaudal folding and lateral folding of the three-layer, three-laminar germ disc, endoderm becomes epithelium of the digestive tract. Digestive tract from stomodeum to the lung bud. This part is called pharyngeal gut. And from respiratory bud to liver bud, this part is called foregut. From liver bud, okay, to the border between right two-thirds and left one-third of transverse colon is called midgut. You see here, after foldings of the trilaminar germ disc and forming of primitive gut, just midgut has connection with the yolk sac. This connection is called vitelline duct. The midgut remains temporarily connected to the yolk sac by means of vitelline duct or yolk stalk. This stalk is called vitelline duct.
At the beginning of primitive gut, there is a stomodeum. At the beginning of primitive gut, there is stomodeum, and on the end of the primitive gut, there is cloacal membrane. Cloacal membrane. Here, here is stomodeum, and here is cloacal membrane.
In the embryonic period, we can see two mesenteries: dorsal mesentery and ventral mesentery. Dorsal mesentery extends from the lower part of the esophagus to the rectum. This is dorsal mesentery that develops two: greater omentum, mesentery proper, transverse mesocolon, and sigmoid mesocolon. You know, dorsal mesentery becomes greater omentum, mesentery proper, transverse mesocolon, and sigmoid mesocolon. You see here.
And ventral mesentery is a derivative of transverse septum. Septum transversum is the main part of the diaphragm. Septum transversum is a horizontal septum, mesodermal septum, that this septum is formed by mesoderm at the level of T3 to H, C3 to C5 somites. At the level of C3 to C5 somites. If I ask you which nerve is a motor nerve of the diaphragm, you answer me phrenic nerve. And if I ask you what are the segments of the phrenic nerve, you answer me C3, C4, and C5 segments of the spinal cord. Yeah.
At the third week, septum transversum is a mesodermal septum that is formed at the level of C3 to C5 somites, and these somites become spinal cord segments. Yeah. Similar to spinal cord segments. From septum transversum, the liver bud, liver bud goes to the septum transversum because, because at first, diaphragm is at the level of septum transversum. If you see here, diaphragm is at the level of septum transversum. And with enlargement and development of the liver, liver, liver descends. And mesodermal, mesodermal structures around the liver makes ventral mesentery.
Ventral mesentery has two parts. One part between liver and anterior abdominal wall that is called falciform ligament. Inferior border of the falciform ligament, there is vitelline, sorry, there is umbilical vein. Left umbilical vein. After birth, this umbilical vein, this umbilical vein becomes, this umbilical vein becomes ligamentum teres. I told you, in the inferior border of the falciform ligament, there is umbilical vein. After birth, this umbilical vein becomes ligamentum teres hepatis, or round ligament of the liver.
A part of ventral mesentery is located between the lesser curvature of the stomach and the liver. Here, this part of ventral mesentery is called lesser omentum. And in the free border of the lesser omentum, there are three structures: hepatic artery proper, common bile duct, or CBD, and portal vein.
Foregut begins at the level of lung bud or respiratory bud and ends at the level of liver bud. From here to here is foregut. At first, liver bud or hepatic bud is at the level of septum transversum and enters into the septum transversum. Okay? But after elongation of the esophagus and stomach, stomach descends into the abdominal cavity. And this part of diaphragm that hepatic bud emerged from, this part descends into the abdomen. You see here.
Foregut develops to the primordial pharynx and derivatives and lower respiratory system, esophagus, and stomach. Duodenum proximal to the opening of the bile duct and liver and pancreas. All structures are developed by foregut, by foregut. I told you all derivatives of the foregut are supplied by celiac trunk. Here is celiac trunk. Here is superior mesenteric for supplying midgut. And this is inferior mesenteric artery for supplying hindgut.
When the embryo is approximately four weeks old, respiratory diverticulum, respiratory diverticulum or lung bud appears at the ventral wall of the foregut. Yeah, I told you last semester about respiratory system. This is respiratory bud. Respiratory bud descends and then divides into two branches, and each branch divides into two branches and makes lung. And lung formation, there are four stages. Who can tell me four stages for lung development? Pseudoglandular is the first stage. Canalicular is the second stage. Terminal sac is the third one. And alveolar stage is the fourth. I told you these stages are important. Do you remember? Yeah.
From lung bud, two lungs and tracheobronchial tree developed. And esophagus is posterior to this lung bud or respiratory bud. At first, you see here, esophagus is very, very short. And diaphragm is at the level of transverse septum, septum transversum. Yeah. Here, with elongation of the esophagus, with elongation of the esophagus, stomach and diaphragm enters into the abdomen. You know that tracheoesophageal septum is a septum between esophagus and trachea. I told you last semester, this septum separates esophagus from trachea. And there are many congenital malformations such as tracheoesophageal fistula. Yeah. I told you at first, esophagus is a short structure, but with descending of the heart and lungs, this structure, this organ extends length, reaches its final relative length to the seventh week. The seventh week, the esophagus goes to the abdominal cavity. Its epithelium and glands are derived from endoderm that proliferates and partly or completely obliterates the lumen of the esophagus.
Lumen of all parts of the digestive tract. What's the origin of epithelium of digestive tract? You, I told you at the first, this session is very important. You understand, epithelium of all parts of the digestive tract is formed by endoderm, except, except lower part of the anal canal. Yeah. And beginning part of the oral cavity.
The muscular coat, which is formed by surrounding visceral mesoderm, splanchnic mesoderm, is striated in its upper two-thirds and smooth muscle in the lower one-third. Striated muscle on the upper two-thirds is from branchial arches four and sixth. And muscular coat or mesenchyme of the lower one-third of the esophagus is derived from splanchnic mesoderm around the primitive gut. [ __ ] mesoderm. You see here, four layers of the esophagus, similar to stomach, small intestine, large intestine. Yeah. Mucosa, submucosa, muscularis externa, and adventitia. Here is formation of these four layers. Lumen of this mucosa is formed by endoderm, and glands are derived from endoderm. Okay? But connective tissue and muscular tissue are derived from mesoderm. Most part of the digestive tract, this connective tissue and muscular tissue are derived from splanchnic mesoderm around the primitive gut.
Diaphragm is a septum between thorax and abdomen. This dome-shaped muscle is formed by four parts. I will ask you, how many parts are there in the formation of the diaphragm? Four parts. First and main part is septum transversum. Mesenchymal partition between embryonic thorax and abdomen in the third week. This septum transversum is at the level of C3 to C5 segments or somites. Second part of diaphragm is pleuroperitoneal membranes. With formation of the lungs in the thoracic cavity and descending of the lungs, posterior mesoderm of the thoracic wall makes a fold inferior to the lung bud and makes a fold that is called pleuroperitoneal membrane. Is it clear? You imagine this is mesoderm. This is mesoderm of the thorax. Okay? And from here, from here, lung bud descends in the thorax. Under this descending [Music] that's under this area, there is a fold here. There is a fold here that is called pleuroperitoneal fold. Okay? Pleuroperitoneal fold. And here is septum transversum. Okay? This septum transversum and this fold attached together, pleuroperitoneal fold and septum transversum on each side attached together and make, and make second part of the diaphragm, pleuroperitoneal membranes. Is it clear?
Mesentery of the esophagus. At first, mesentery of the esophagus is the third part of the diaphragm. And with enlargement of the body, myoblasts of the cervical somites make muscular part of the diaphragm. Diaphragm has four origins. First part is septum transversum. That septum transversum becomes central tendon of the diaphragm. Pleuroperitoneal membranes. These are mesenchymal membranes that descending of lungs make these pleuroperitoneal membranes from thoracic wall. Dorsal mesentery of the esophagus and mesenchyme of the body wall from cervical somites make muscular part. These four parts attached together and make diaphragm.
In the formation of the diaphragm, maybe pleuroperitoneal membranes cannot connect to the, cannot attach to the transverse septum and make an opening that is called Bochdalek or diaphragmatic hernia. Bochdalek or diaphragmatic hernia. There are many congenital malformations or hernias in the diaphragm. If between sternal, between external origin and costal origin of the diaphragm, if between these two parts, there is an opening, this opening is opening for descending of superior epigastric artery. Superior epigastric artery is a branch of internal thoracic artery. Is a branch of internal thoracic artery. And internal thoracic artery is a branch of the subclavian artery. Yeah. This herniation is called parasternal hernia of Morgagni. Parasternal hernia of Morgagni.
Here, another hernia in the diaphragm is esophageal hernia. Dilation of the esophageal opening in the diaphragm makes esophageal hernia. And pleuroperitoneal canal or foramen of Bochdalek is the most common site for diaphragmatic hernia. You see here, Bochdalek hernia at birth, small intestine and stomach and other structures of the abdomen goes to the thorax. And left lung cannot dilate, cannot open. And respiration makes failure. This is a common congenital malformation of the diaphragm. And the foramen of Bochdalek, and foramen of Bochdalek is formed by pleuroperitoneal membrane. Yeah. Bochdalek hernia is coming on the left side. Why? Why it's coming on the left side? I think because this part, this side is one of the, because on the right side, there is a big or large liver. Okay? On the right side, liver is a big structure that inhibits herniation of the abdominal organs into the thorax. Is it clear? Yeah. Is it clear?
Next part of the digestive tract is stomach. Stomach is a dilated part of the digestive tract. Begins its development from foregut in the fourth week as a fusiform dilation. Fusiform dilation. Yeah. But posterior border of this fusiform organ develops more than anterior border. Is it clear? This is fusiform organ, but posterior border develops more than anterior border. And makes greater curvature posteriorly and lesser curvature anteriorly. Is it clear? Yeah.
During the next two weeks, the dorsal border of the stomach grows faster than its ventral border and makes greater curvature on the posterior part. Here, you see here, this is fusiform organ that posterior border develops faster. Okay? And makes greater curvature. And anterior border makes lesser curvature. There are two rotations in the development of the stomach. You imagine I'm stomach. Okay? On the posterior border of me, there is two-layer dorsal mesogastrium. Yeah. Dorsal mesogastrium is posterior to me, and anterior to me, there is ventral mesogastrium. In the ventral mesogastrium, there is liver. Yeah. Do you remember? Yes. Is liver that makes ventral mesogastrium divides to two parts: between liver and stomach, lesser omentum. Between liver and anterior abdominal wall, there is falciform ligament. Is it clear?
At the fifth, at the fifth week of the intrauterine life, the fifth, the week five, in the dorsal mesogastrium, a mesodermal structure developed that is called spleen. And the dorsal mesogastrium, you imagine this border of the stomach, anterior border is lesser curvature, and posterior border is greater curvature. If this stomach makes a 90-degree rotation, okay, clockwise, clockwise. This rotation, for example, this is liver, my right hand is liver, and here is lesser omentum, and my left hand is spleen. Okay? And this is dorsal mesogastrium. Okay? If I rotate 90 degrees in this position, on the clockwise direction, yeah, liver goes to the right side of the abdomen, and spleen goes to the left side of the abdomen. And my right side, my left side becomes anterior surface of the stomach, and my right side becomes posterior surface of the stomach. Is it clear? This is first rotation of the stomach, 90 degrees clockwise. And the axis, on the axis of the craniocaudal axis of the stomach, there is first rotation. Second rotation of the stomach is at the anterior-posterior axis of the stomach. This lesser curvature that goes to the right side, okay? And this greater curvature that goes to the left side. After this anterior-posterior axis rotation of the stomach, change the position, and lesser curvature goes superiorly, and greater curvature goes inferiorly. Is it clear? Yeah. There are two rotations for stomach. First one is 90 degrees clockwise at the superior-inferior border. And second one is anterior-posterior axis rotation that makes lesser curvature superiorly and greater curvature inferiorly. After these rotations, left side of the stomach becomes anterior surface, and right side of the stomach becomes posterior surface. Is it clear? The effects of rotation on the stomach is ventral border or lesser curvature moves to the right, and dorsal border, greater curvature to the left. The original left side becomes the anterior surface, and original right side becomes posterior surface. This is first rotation. You see here. Okay? This is first rotation in the long axis of the stomach. After first rotation, I told you, spleen goes to the left side, side. And liver goes to the right side. Posterior to the stomach, posterior to the stomach and lesser omentum, there is lesser sac or omental bursa. And between greater curvature of the stomach and spleen, this part of dorsal mesogastrium becomes gastrosplenic ligament. Gastrolienal or gastrosplenic ligament. And between spleen and posterior abdominal wall or kidney, left kidney, there is lienorenal or splenorenal ligament. Here is omental bursa. Here is omental foramen. This is greater omentum. Lesser omentum. This is gastrolienal. And here is lienorenal ligament. Left vagus nerve is located on the left side of the stomach, and right vagus nerve is located on the right side of the stomach. After this clockwise rotation, left vagus becomes left vagal trunk, anterior vagal trunk. And right vagus becomes posterior vagal trunk. It's normal. Yeah. You see here. You read these parts. I told you these parts. This is falciform ligament between right and left lobes of the liver. And this ligament is ligamentum teres hepatis or round ligament of the liver. Free border of the lesser omentum. At first, is inferior border of the lesser omentum. After anterior-posterior axis rotation of the stomach, this border becomes right border. Okay? On the right border or anterior border of the omental foramen, there are three structures that you tell: common bile duct, portal vein, and hepatic artery proper.
Pyloric stenosis is a congenital malformation of the stomach. Occurs when the circular and to a lesser degree longitudinal muscles of the stomach in the region of the pyloric part or pyloric sphincter hypertrophies. And one of the most common abnormalities of the stomach in infants is stenosis of the pyloric part. And pyloric part is characterized by an extreme narrowing of the pyloric lumen, and passage of food is obstructed, and resulting in severe projectile vomiting. This is very, very important. Severe projectile vomiting. Vomiting is projectile. Okay? But this vomiting is milk. Milk. Infant after feeding, breastfeeding, okay? Makes epigastric bulging and projectile vomiting. Okay? If this vomiting becomes green, it's not completely milk. Becomes green with bile. This congenital malformation is stenosis of the duodenum. Stenosis of the duodenum. In the pyloric stenosis, this vomiting is projectile, and just there is milk. But in the duodenal stenosis, this is not completely milk. There are many bile in addition to the milk. Is it clear? And the duodenal stenosis or duodenal atresia. Okay. After 15 minutes, rest. Come back to the class.