Midgut & Hindgut Embryo Flashcards
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
SMA
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
IMA
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.
