Development Of The GI system Flashcards

1
Q

What is the midgut?

A

Begins inferior to the major duodenal papilla & ends at the junction between the 2/3 & distal 1/3 of the transverse colon.

  • Duodenum (inferior to the major duodenal papilla),
  • Jejunum,
  • Ileum,
  • Cecum,
  • Appendix,
  • Ascending colon, and
  • Right two-thirds of the transverse colon.
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2
Q

What are the supplies and drainages of the midgut?

A

Arterial supply : Superior mesenteric artery (SMA)

Venous drainage: Superior mesenteric vein

Lymphatic drainage : Superior mesenteric nodes

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3
Q

Describe the medgut development

A

Midgut elongates to form a U shaped loop which is suspended by the dorsal mesentery. It communicates with the umbilical vesicle (yolk sac) via the narrow omphaloenteric (vitelline) duct . Ventrally the loop projects into the umbilical cord [6th week→physiological umbilical hernia – because peritoneal cavity is smaller]

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4
Q

Describe the midgut loop function

A

Midgut loop has cranial and caudal limbs. The cranial limb grows rapidly and gives rise to the distal part of the duodenum, jejunum, and part of the ileum. The caudal limb gives rise to the rest of the ileum, cecum, appendix, ascending colon and proximal 2/3 of the transverse colon.

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5
Q

Describe the first rotation of the midgut

A

Within the umbilical cord midgut loop rotates 90 degrees anticlockwise around the axis of superior mesenteric artery

Rotation brings cranial limb to the right & caudal limb to the left

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6
Q

Describe the second midgut rotation

A

10Th week midgut returns to the abdominal cavity

Further 90 degrees anti-clockwise rotation occurs as the midgut
returns to the abdomen. Cranial limb returns first, occupies the
central and left part of abdomen

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7
Q

Describe the third midgut loop rotation

A

Another rotation of the viscera for 90 degrees for a total of 270 degrees.

Large intestine returns to abdomen and occupies right side.

Cecum and appendix descend to right lower quadrant of the abdomen

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8
Q

What is the impact of non-rotation of the midgut?

A

Non-rotation – caudal limb returns first →small intestine lies to the right, generally asymptomatic

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9
Q

What is the impact of reversed midgut rotation?

A

Reversed rotation – midgut loop rotates in a clockwise direction. Duodenum lies anterior to transverse colon posterior.

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10
Q

What is a Subhepatic Cecum and Appendix?

A

– Cecum gets adhered to the liver / doesn’t descend to the iliac fossa. May cause difficulty in diagnosis of appendicitis

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11
Q

What is a Mixed Rotation and Volvulus?

A

– cecum lies inferior to the pylorus and is fixed to the posterior abdominal wall by peritoneal bands.

– may cause duodenal obstruction.[due to failure of midgut loop to complete the final 900 rotation]

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12
Q

What is cecal diverticulum?

A

Cecal diverticulum – 6th week on the caudal limb of the midgut. Appendix remains narrow but increases in length. Cecum undergoes differential growth, appendix enters its medial side

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13
Q

What is Omphalocele?

A

Embryological defect: Persistence of the abdominal herniation.

Size of the hernia depends upon its contents

•In contrast to umbilical hernia it is covered by fetal membranes.

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14
Q

What is an umbilical hernia?

A

Embryological defect:
Incomplete closure of the umbilical ring

Clinical presentation:
•It appears as a soft swelling covered by skin.
•It protrudes during crying ,coughing and straining.
• Can be easily reduced through the fibrous ring at the umbilicus
•The hernia can contain omentum and small portions of the small intestines.

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15
Q

What is Gastroschisis?

A

Due to defect near the median plane of the abdominal wall.

Viscera protrudes into the amniotic cavity. Anomaly is due to incomplete closure of lateral folds during 4th week of development [1 in 10,000]

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16
Q

What Meckels Diverticulum? What is the Rule of 2’s?

A

A Meckel’s diverticulum is a fingerlike projection from the ileum,
representing retention of the embryonic Omphaloenteric duct (intestinal stalk/vitelline duct ).

“Rule of 2s”:
Approximately 2 feet proximal to the ileocecal junction. It occurs in 2% of the population.
It occurs 2x as often in males as in females.
It is most commonly about 2 inches long.
It can contain 2 kinds of secretory tissue: gastric and pancreatic (it still remains unknown why).
It can mimic the signs of 2 problems: appendicitis and peptic ulcer.
It can produce periumbilical pain and internal bleeding.

17
Q

What is the significance of Meckeks Diverticulum in the population?

A

In 2 - 4% of the population a small portion of the omphaloenteric [vitelline duct] may persist giving rise to an Ileal (Meckel’s) diverticulum.

It is located 40 - 60cm from the ileocecal valve on the anti-mesenteric border of the ileum. May be asymptomatic, may contain gastric or pancreatic tissue. May become infected→symptoms resemble appendicitis.

18
Q

Describe the umbilical fistula

A

Omphaloenteric duct remains patent forming a communication between the umbilicus and intestinal tract .

Clinical signs:
• Fecal discharge at the umbilicus
• Infection at the umbilical stump

19
Q

What is the hindgut?

A

Begins at the junction between the proximal 2/3 & distal 1/3 of the transverse colon, and ends midway through the anal canal.
• The left one-third of the transverse colon,
• Descending colon,
• Sigmoid colon,
• Rectum,
• Upper part of the anal canal.
• Endodermal lining of hindgut gives rise to the urinary bladder and most of urethra

20
Q

What are the supplies and drainages of the hindgut?

A

Arterial Supply : Inferior mesenteric
Venous drainage : Inferior mesenteric vein
Lymphatic drainage: Inferior mesenteric nodes

21
Q

Explain the rekation/orientation of cloaca to the hindgut

A

The Cloaca
• Due to folding of the embryo the allantois and the hind gut opens into the cloaca .

  • Therefore, the cloaca is terminal part of the hind gut before division into rectum, bladder and genital primordia.
  • It is an endoderm lined cavity that is in contact with the surface ectoderm at the cloacal membrane

Cloacal membrane:
•Endodermal component = cloaca •Ectodermal component = proctodeum

22
Q

What is the embryological significance of the cloacal partitioning?

A

Urorectal septum – mesenchymal tissue :

Divides tissue into :
•Ventral primitive urogenital sinus
•Dorsal primitive rectum and Cranial part of the anal canal

23
Q

What is the significanceof the cloacal membrane ?

A
•The urorectal septum fuses with the cloacal membrane •The cloacal membrane is divided into
Urogenital (UG) membrane, &
Anal membrane
Upper anal canal – hindgut
 Lower anal canal-proctodeum

•Mesenchymal proliferations produce elevations of the surface ectoderm around the anal membrane. The membrane is soon located at the bottom of the ectodermal depression –proctodeum. The anal membrane then ruptures at the end of the 8th week.

24
Q

Describe the development of the anal canal

A

• Superior 2/3 derived from the hindgut
• Inferior 1/3 derived from proctodeum
• Pectinate line – junction of the epithelia derived from the
ectoderm of the proctodeum and endoderm from the hind gut
• Pectinate line is the former site of the anal membrane

25
Q

What is the blood supply to the anal canal?

A

Blood supply to the anal canal :
Superior 2/3 supplied by the superior rectal artery – IMA Inferior 1/3 supplied by the inferior rectal artery – internal pudendal

26
Q

What is the innervation to the anal canal?

A

Above the pectinate line – autonomics

Below the pectinate line – inferior rectal nerves –pudendal n

27
Q

How are anal lesions classified?

A

Lesions are classified as low or high depending on whether the rectum ends superior or inferior to the puborectalis muscle, which maintains fecal continence and relaxes to allow defecation.

28
Q

What are the clinical features of low anorectal maalformations?

A
Clinical Features of low anorectal malformations:
• No anal opening
• Abnormal opening in the perineum
• Anal dimple/stenotic opening
• Bulge at the site of the anus
29
Q

What are the clinical features of high anirectal malformations?

A

• Generally present as fistulas that communicate with the urogenital system In the male it can present as rectourethral , rectovesical or rectoprostatic
In the female it can present as rectovestibular or rectovaginal
• Flat perineum
• No pigmentation or dimple at the site of the anus

30
Q

What are the comsequences if anirectal malformations/lesions?

A

M3conium is excreted at an abnormal opening

31
Q

What is the significance of the high anomaly- anorectal agenesis- with fistula?

A

Although the rectum ends blindly, there is usually a fistula to the bladder (rectovesical fistula) or urethra (rectourethral fistula) in males or to the vagina (rectovaginal fistula) or the vestibule of the vagina (rectovestibular fistula) in females.

Anorectal agenesis with a fistula is the result of incomplete separation of the cloaca from the urogenital sinus by the urorectal septum

32
Q

What is the signifucance of rectal atresia?

A

High anomaly

The anal canal and rectum are present but are separated .

Sometimes the two segments of intestine are connected by a fibrous cord, the remnant of an atretic portion of the rectum. The cause of rectal atresia may be abnormal recanalization of the colon or, more likely, defective blood supply

33
Q

Describe anal stenosis

A

Low anorectal abnormality

Anal Stenosis (narrowed anal canal)
In anal stenosis the anus is in the normal position, but the anus and anal canal are narrow . This birth defect is probably caused by a slight dorsal deviation of the urorectal septum as it grows caudally.
34
Q

What is membranous atresia?

A

Low anorectal

In Membranous Atresia the anus is in the normal position, but a thin layer of tissue separates the anal canal from the exterior.

The remnant of the epithelial anal plug is thin enough to bulge on straining and appears blue from the presence of meconium superior to it. This defect results from failure of the epithelial plug to perforate at the end of the eighth week.

35
Q

What is imperforate anus?

A

Low anorectal anomaly

The anal canal may end blindly or there may be an ectopic anus or an anoperineal fistula that opens into the perineum . The abnormal canal may, however, open into the vagina in females or the urethra in males .

More than 90% of low anorectal anomalies are associated with an external fistula.

36
Q

Describe Hirschsprung Disease (Congenital Megacolon8

A

Absence of autonomic ganglia in the Myenteric Plexus of the NARROWED segment.
Failure of migration of neural crest cells in weeks 5 - 7.

Incidence 1:5,000 births
Most common cause of neonatal intestinal obstruction
Aganglionic segment no peristalsis