EMBRIOLOGISISTEM DIGESTIVUS

disampaikan pada kuliah blok Sistem Digestivus 1FK UNISMA, 2014

Reza Hakim

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PENDAHULUAN- Pembentukan BodyCavities -

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1. Pembagian Gut Tube

• Embryo folding (cephalocaudal+lateral) menyebabkan sebagian yolk sac masuk ke dalam embrio membentuk primitive gut.• Alantois dan sisa yolk sac tetap di luar embrio.• Foregut & hindgut blind-ending tube (di bagian

cephal & caudal dari embrio)• Midgut sementara masih terhubung dengan

yolksac (melalui vitelline duct)

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1. Pembagian Gut Tube

4 Sections of Development1. Pharyngeal gut bagian dari foregut2. Foregut memanjang ke bawah sampai liver outgrowth3. Midgut caudal dari liver hingga 2/3 colon transversum4. Hindgut setelah (akhir) midgut hingga membran kloaka

Endoderm membentuk epithelial lining & sel-sel khusus untuk parenkim kelenjar. Stroma kelenjar berasal dari mesoderm.

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Transverse sections through embryos at various stages of development(A) The intraembryonic cavity, bordered by visceral and somatic layers of lateral plate mesoderm, is in open communication with the extraembryonic cavity. (B) The intraembryonic cavity is losing its wide connection with the extraembryonic cavity. (C) At the end of the fourth week, visceral mesoderm layers are fused in the midline and form a double-layered membrane (dorsal mesentery) between right and left halves of the body cavity. Ventral mesentery exists only in the region of the septum transversum (not shown)

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- Pembentukan BodyCavities -

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2. Mesenterium

= double layers of peritoneum that enclose an organ and connect it to the body wall. Peritoneal ligaments are double layers of

peritoneum (mesenteries) that pass from one organ to another or from an organ to the body wall.

Mesenteries and ligaments provide pathways for vessels, nerves, and lymphatics to and from abdominal viscera.

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Primitive dorsal and ventral mesenteriesThe liver is connected to the ventral abdominal wall and to the Stomach by the falciform ligament and lesser omentum, respectively. The superior mesenteric artery runs through the mesentery proper and continues toward the yolk sac as the vitelline artery.

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3. Esophagus

Embryo 4 weeks old : the respiratory diverticulum (lung bud) appears at the ventral wall of the foregut at the border with the pharyngeal gut.

The tracheoesophageal septum gradually partitions this diverticulum from the dorsal part of the foregut (respiratory) Ventral portion & Dorsal portion (esofagus).

With descent of the heart & lungs, esophagus lenghtens rapidly.

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Successive stages in development of the respiratory diverticulum and esophagus through partitioning of the Foregut. (A) At the end of the third week (lateral view). (B,C) During the fourth week (ventral view)

12Variation of esophageal atresia and / or transesophageal fistula

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4. Stomach

4 weeks : Appear as a fusiform dilatation of the foregut.

↓Different rates of growth in various regions

appearance & position change greatly↓

Rotates around a longitudinal & anteroposterior axis

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4. Stomach

The stomach rotates 90° clockwise around its longitudinal axis:

left side face anteriorly right side face posteriorly.

During this rotation, the original posterior wall of the stomach grows faster than the anterior portion, forming the greaterand lesser curvatures.

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4. Stomach

The cephalic and caudal ends of the stomach originally lie in the midline, but during further growth, the stomach rotates around an antero-posterior axis :

the caudal /pyloric part moves to the right and upward the cephalic or cardiac portionmoves to the left &

slightly downward

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A–C Rotation of the stomach along its longitudinal axis as seen anteriorly. D,E Rotation of the stomach Around the anteroposterior axis. Note the change in position of the pylorus and cardia

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4. Stomach

Rotation about the longitudinal axis pulls the dorsal mesogastrium to the left, creating a space behind the stomach Omental Bursa (lesser peritoneal sac). This rotation also pulls the ventral mesogastrium to the right.

As this process continues in the fifth week of development, the spleen primordium appears as a mesodermal proliferation between the two leaves of the dorsal mesogastrium.

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4. Stomach

Lengthening and fusion of the dorsal mesogastrium to the poste-rior body wall also determine the final position of the pancreas.

Initially, the organ grows into the dorsal mesoduodenum, but eventually its tail extends into the dorsal mesogastrium.

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Transverse sections through the region of the stomach, liver, and spleen, showing formation of the omental Bursa (lesser peritoneal sac), rotation of the stomach, and position of the spleen and tail of the pancreas between the two Leaves of the dorsal mesogastrium. With further development, the pancreas assumes a retroperitoneal position.

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4. Stomach

As a result of rotation of the stomach about its anteroposterior axis, the dorsal mesogastrium bulges down.

It continues to grow down and forms a double-layered sac extend-ing over the transverse colon and small intestinal loops like an apron Greater Omentum.

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5. Duodenum

Terminal part of the foregut + cephalic part of midgutHubungan kedua part berada pada distal dari liver bud.Stomach rotates; Duodenum takes on C-shaped loop.

rotates to the right + Rapid growth of pancreas head = swing the duodenum to the right side of abdominal cavity.

Usia 2 bulan: obliterasi lumen duodenum oleh proliferasi sel-sel di dindingnya Terjadi rekanalisasi segera.

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6. Liver & Gallbladder

Pertengahan minggu ke-3: Liver primordium (dari endodermal epithelium) muncul pada ujung distal dari foregut.

Rapidly proliferating cells that penetrate the septum transversum, that is, the mesodermal plate between the pericardial cavity and the stalk of the yolk sac. The connection between the hepatic diverticulum and the foregut (duodenum) narrows, forming the bile duct.

A small ventral outgrowth is formed by the bile duct, and this outgrowth gives rise to the gallbladder and the cystic duct.

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7. Midgut

In the 5-week embryo, the midgut is suspended from the dorsal abdominal wall by a short mesentery and communicates with the yolk sac by way of the vitelline ductor yolk stalk.

Development of the midgut is characterized by rapid elongation of the gut and its mesentery, resulting in formation of the primary intestinal loop.

At its apex, the loop remains in open connection with the yolk sac by way of the narrow vitelline duct.

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7. Midgut

The cephalic limb of the loop develops into the distal part of the duodenum, the jejunum, and part of the ileum.

The caudal limb becomes the lower portion of the ileum, the cecum, the appendix, the ascending colon, and the proximal two-thirds of the transverse colon.

(A). Primary intestinal loop before rotation (lateral view). The superior mesenteric artery forms the axis of the loop. Arrow, counterclockwise rotation. (B) Similar view as in Ashowing the primary intestinal loop after 180° counter-clockwise rotation. The transverse colon passes in front of the duodenum

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7. Midgut Rotation

Coincident with growth in length, the primary intestinal loop rotates around an axis formed by the superior mesenteric artery.

When viewed from the front, this rotation is counterclockwise, and it amounts to approximately 270° when it is complete.

Even during rotation, elongation of the small intestinal loop continues, and the jejunum and ileum form a number of coiled loops.

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7. Midgut Herniation

The large intestine likewise lengthens considerably but does not participate in the coiling phenomenon.

Rotation occurs during herniation (about 90°), as well as during return of the intestinal loops into the abdominal cavity (remaining 180°).

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7. Midgut Retraction

During the 10th week, herniated intestinal loops begin to return to the abdominal cavity.

Although the factors responsible for this return are not precisely known, it is thought that regression of the mesonephric kidney, reduced growth of the liver, and expansion of the abdominal cav-ity play important roles.

The proximal portion of the jejunum, the first part to reenter the abdominal cavity, comes to lie on the left side.

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7. Midgut Retraction

Since the appendix develops during descent of the colon, its final position frequently is posterior to the cecum or colon.

These positions of the appendix are called retrocecalor retrocolic, respectively.

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8. Hindgut

The hindgut gives rise to the distal third of the transverse colon, the descending colon, the sig-moid, the rectum, and the upper part of the anal canal.

The endoderm of the hindgut also forms the internal lining of the bladder and urethra.

The terminal portion of the hindgut enters into the posterior region of the cloaca, the primitive anorectal canal (the allantois) enters into the anterior portion, the primitive urogenital sinus.

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(A)The hindgut enters the posterior por-tion of the cloaca, the future anorectal canal; the allantois enters the anterior portion, the future urogenital sinus. The Urorectal septum is formed by merging of the mesoderm covering the allantois and the yolk sac. The cloacal Membrane, which forms the ventral boundary of the cloaca, is composed of ectoderm and endoderm.(B) As caudal fold-ing of the embryo continues, the urorectal septum moves closer to the cloacal membrane.(C) Lengthening of the genital Tubercle pulls the urogenital portion of the cloaca anteriorly; breakdown of the cloacal membrane creates an opening for The hindgut and one for the urogenital sinus. The tip of the urorectal septum forms the perineal body.

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8. Hindgut

The cloaca itself is an endoderm-lined cavity covered at its ventral

boundary by surface ectoderm. This boundary between the endoderm and the ectoderm forms the cloacal membrane.

At the end of the seventh week, the cloacal membrane ruptures, creating the anal opening for the hindgut.

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