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Flashcards in Midgut & Hindgut Embryo Deck (26):

Adult derivatives of the mid-gut

duodenum distal to the common bile duct (2-4 part), jejunum, ileum, cecum, appendix, ascending colon, proximal transverse colon


blood supply to the midgut



Midgut herniates into

the umbilical cord, forms a u-shaped loop. The two ends of the loop are connected by the dorsal mesentary.


When does mid-gut herniation happen?

Beginning of week 6


Two parts of mid-gut loop, which grows faster

Cranial and Caudal, the Cranial grows faster and has many folds. These folds become the small intestine. This growing also causes a 90 degree counterclockwise loop, so the loop now sits in a transverse plane.


When does the midgut return to the abdomen

week 10. During the return the small intestine becomes central and the large intestine becomes peripheral.


Rotation of small intestine as it returns into the abdomen

180 degree rotation, causes the large intestine to cross over the small intestine. In adult the transverse colon crosses anterior to the small intestine.


Fixation of organs

What causes things to be intra/retro peritoneal


Line of attachment of small intestine mesentary

Starts Left upper quadrant at duodenaljejunal junction, ends Right Lower Quadrant at ileocecal junction


When does decal diverticulum appear, what is it primordial of, where does it appear

Week 6, primordial of cecum and appendix.
Appears on the antimesenteric border.


How does appendix attach

In variable positions to the cecum


Hindgut derivatives

Left transverse colon, descending colon, sigmoid colon, rectum, superior portion of anus, epithelial lining of urinary bladder, most of the urethra


Blood supply of hindgut



What is the cloaca

Expanded distal hindgut, lined with endoderm. The allantois empties into the cloaca.


Two components of cloacal membrane

endoderm of cloaca, ectoderm of proctodeum (anal pit)


What fuses with the cloacal membrane

The distal urorectal septum, to create the anal membrane (bottom of anal canal), urogenital membrane (bottom of urogenital sinus) and the perineal body which sits between the rectum and sinus.


What is created when the cloaca is partitioned?

The dorsal anus/rectum and ventral urogenital sinus. Infolding of lateral cloacal wall come in to attach to descending urorectal septum.


When/how does anal membrane disappear?

Through cell apoptosis, by the end of week 8. Now the rectum is connected to the amniotic cavity.


Germ layers of anal canal

Top 2/3 from hindgut --> endoderm
Bottom 1/3 from proctodeum --> ectoderm
Junction between the two called the pectinate line/anal membrane


Anal sphincter develops from

Splanchnic mesoderm, induced by HOX genes


Arterial supply to anal canal

Upper 2/3 --> Superior Rectal Artery (branch of IMA)
Lower 1/3 --> Inferior rectal artery (Branch of internal pudendal artery, which is a branch of the iliac)


Lymphatic drainage of anal canal

Upper 2/3 --> Inferior mesenteric lymph node
Lower 1/3 --> Superficial inguinal lymph nodes
Can tell where cancer is coming from in anal canal, if you can palpate which lymph nodes are swollen


Innervation of anal canal

Upper 2/3 --> Autonomics. Sympathetics T1-L1, Parasympathetic S2-S4, Involuntary
Lower 1/3--> Inferior rectal nerve, branch of pudendal nerve (S2, S3, S4), Voluntary control


Omphalomesenteric Duct

The space in the umbilical cord that the midgut herniates into


After rotation of the midgut, where is the small intestine in relation to SMA?

It sits behind the SMA


Meckel's diverticulum

Clinical abnormality
Diverticulum of the ilium, can attach to the anterior abdominal wall.