Anatomy Flashcards
Small Intestine
a specialized tubular structure within the abdominal cavity in continuity with the stomach proximally and the colon distally.
Small Intestine
250 cm in the term newborn to about 600 to 800 cm in the adult.
The caliber of the small intestine gradually diminishes from prox- imal to distal, and there is a fourfold reduction in surface area from the distal duodenum to the terminal ileum.
duodenum
most proximal portion of the small intes- tine. It begins with the duodenal bulb, travels in the retroperitoneal space around the head of the pancreas, and ends on its return to the peritoneal cavity at the ligament of Treitz.
Jejunum and Ileum
The proximal 40% of the mobile small intestine is the jejunum, which occupies the left upper por- tion of the abdomen.
The remaining 60% of small intestine is the ileum, and it is normally situated in the right side of the abdomen and upper part of the pelvis.
There is no distinct anatomic demar- cation between the jejunum and ileum, but the jejunum tends to be thicker, is more vascular, and has a greater diameter than the ileum.
Jejunum and Ileum
The jejunum and ileum are freely mobile in the abdominal cavity and are attached to the posterior abdominal wall by the intestinal mesentery.
The entire length of jejunum and ileum is suspended in this mesentery, except for the distal terminal ileum at the cecum, which is retroperitoneal.
Colon and Rectum
colon is a tubular structure about 30 to 40 cm in length at birth and measuring some 150 cm in the adult
The colon begins at the IC valve and ends distally at the anal verge.
It consists of 4 segments: cecum and vermiform appendix, colon (ascending, transverse, and descending portions), rectum, and anal canal.
The diameter of the colon is greatest in the cecum (7.5 cm) and nar- rowest in the sigmoid (2.5 cm) until it balloons out in the rectum just proximal to the anal canal.
Cecum
The cecum is the most proximal portion of the colon. It is about 6 to 8 cm in length and breadth and lies in the right iliac fossa, projecting downward as a blind pouch below the entrance of the ileum. The large diameter of the cecum makes it suscepti- ble to rupture with distal obstruction and permits tumors to grow to substantial size before producing symptoms of obstruction. The cecum is normally nonmobile because it is fixed in position by a small mesocecum; anomalous fixation, however, occurs in 10% to 20% of the population, predominantly women, predis- posing them to cecal volvulus.
ascending colon
The ascending colon is narrower than the cecum and extends about 12 to 20 cm from the level of the IC valve to the inferior surface of the posterior lobe of the liver, where it angulates left and forward, forming the hepatic flexure. The ascending colon is covered with peritoneum in about 75% of individuals and thus is usually considered to reside in the retroperitoneum.
transverse colon
The transverse is the longest (40 to 50 cm) and most mobile segment of the colon. It lies between the hepatic and splenic flexures and drapes itself across the anterior abdomen and anterior to the stomach. The phrenocolic ligament anchors the colon at the splenic flexure, but the transverse colon is so mobile that in the upright position it may actually dip down into the pelvis. Abdominal or pelvic surgery that results in adhesion formation can fix the position of the normally mobile transverse colon.
descending and sigmoid
The descending colon is about 25 to 45 cm in length and trav- els posteriorly and then inferiorly in the retroperitoneal compart- ment to the pelvic brim. It emerges from the retroperitoneum into the peritoneal cavity as the sigmoid colon, an S-shaped redundant segment of variable length, tortuosity, and mobility. The mobility of the sigmoid colon renders it susceptible to vol- vulus, and because it is the narrowest part of the colon, tumors and strictures of this region typically cause obstructive symptoms early in the course of disease.
rectum
The rectum is 10 to 12 cm in length and begins at the peri- toneal reflection, follows the curve of the sacrum passing down and posteriorly, and ends at the anal canal. The rectum narrows at its junction with the sigmoid, expanding proximal to the anus. The rectum lies entirely below the peritoneum in close relation- ship with the structure of the pelvis.
Anal Canal
Anal canal is 2 cm long in the infant and 4.5 to 5 cm long in the adult. It occupies the ischiorectal fossa, passing inferi- orly and outward toward the anal opening
The proximal duodenum receives arterial blood
right gastric artery, supraduodenal artery, right gastroepiploic artery, and superior and inferior pancreaticoduodenal arteries.
Venous drainage is via the SMV and the splenic and portal veins.
SMA delivers oxygenated blood
distal duodenum, jeju- num and ileum, ascending colon, and proximal two thirds of the transverse colon.
arterial supply of the anal area is from
superior, middle, and inferior hemorrhoidal arteries, which are branches of the inferior mesenteric, hypo- gastric, and internal pudendal arteries,
The wall of the small intestine and colon is composed o
4 layers: mucosa (or mucous membrane), submucosa, muscularis (or muscularis propria), and serosa
The epithelium of the small intestine is composed of various cell types:
absorptive cells (columnar cells), secretory cells (goblet cells), undifferentiated cells, tuft cells, M cells, cup-like cells, and enteroendocrine cells.
Omphalocele
known as exomphalos, occurs with a frequency of 1.5 to 3 in 10,000 births
male predominance and occurring more frequently when the mother is younger than 20 years or 35 years of age or older, and in pregnancies with multiple gestations.
congenital hernia involving the umbilicus.
Omphalocele
It is covered by an avascular sac composed of fused layers of amnion and peritoneum
Prenatally, increased levels of maternal serum AFP suggest the possible presence of an omphalocele.
US during pregnancy allows the diagnosis of this abdominal wall defect in most infants, which may allow for karyotyping or amniocentesis if required
Operative treatment is required in all patients with omphalocele.
an abdominal wall defect most commonly located to the right of an intact umbilical cord
Gastroschisis
mothers younger than age 20
frequently in whites and in Hispanic infants than in other races or ethnicities.
Gastroschisis
abnormal body wall folding, disruption of the right vitelline artery, and failure of mesoderm formation.
in gastroschisis, a sac is absent, and the exposure of the viscera to amniotic fluid and a compromised blood supply results in bowel that is edematous, thickened, shortened, and covered in fibrinous exudate.
Prematurity is more common in children
Meckel Diverticulum
anti-mesenteric outpouching of the ileum that is usually found within 2 feet of the IC junction
1.2% to 2% of the population and has a male-to-female ratio of 3:1.3
true diverticulum, containing all 3 layers of bowel wall: mucosa, muscularis, and serosa
The length of the Md var- ies from 1 to 10 cm. Ectopic GI mucosa—duodenal, gastric, bili- ary, colonic, or pancreatic tissue—is present in about 50% of Md,
Meckel Diverticulum
Painless bleeding per rectum
infant or child with significant painless rectal bleeding although standard abdominal plain films, barium contrast studies, and US are seldom helpful in making the diagnosis; rarely, an enterolith (which is often indistinguishable from an appendicolith) or dilated bowel loops with air–fluid level within the Md may be seen on these conventional studies.
Omphalomesenteric (Vitelline) Cyst
more common in male sub- jects and is characterized by a mucosa-lined intestinal cystic mass within the center of a fibrous cord.
cyst may present as a pal- pable nodule within the umbilicus and be complicated by infection.
Patent Omphalomesenteric (Vitelline) Duct
a persistent connection between the distal ileum and umbilicus
foul-smelling
discharge from the umbilicus is typical. Common presenting symptoms include SBO, an acute abdomen, and umbilical abnormalities.
Ectopic tissue is seen in a third of cases
Definitive diagnosis can be made
by fistulography.
Omphalomesenteric Band
diagnosed when the solid cord con- necting the ileum to the umbilicus remains intact.
Malrotations
Rotation defects result from errors in the normal embryonic development of the midgut, which gives rise to the distal duo- denum, jejunum, ileum, cecum, and appendix, as well as the ascending colon and proximal two thirds of the transverse colon.
Enteric Duplication
Male individuals appear to be more commonly affected, at 60% to 80% of cases
The most common GI duplications are in the small intestine
Duplications consist of an epithelial lining from some portion of the GI tract and a smooth muscle wal
Intestinal Atresia and Stenosis
Intestinal atresia refers to a congenital complete obstruction of the intestinal lumen
Small bowel atresias are more common in black infants, low birth weight infants, and twins.
In the duodenum
atresia results from failure of recanaliza- tion of the solid stage of duodenal development
Clinically, the presentation is that of a proximal intestinal obstruction with bilious vomiting on the first day of life, usu- ally without abdominal distention.
Duode- nal obstruction is easily diagnosed by abdominal films revealing a typical “double bubble” sign with a paucity of small intestinal air
The classification system of Grosfeld and colleagues comprises 5 different types of jejunoileal and colonic atresia
In the “apple-peel” atresia or “Christmas tree” deformity (type IIIb), proximal atresia with wide separation of the bowel loops is associated with absence of the distal SMA. The distal ileum receives its blood supply by retrograde perfusion through the ileocolic artery. Type IIIb atresias account for less than 5% of all atresias. Atresias are far more common than stenoses, with a frequency ratio of 15:1. With the exception of multiple atresias and perhaps the apple-peel atresia, heredity appears to be of little significance in most cases.
Hirschsprung Disease
a congenital absence of ganglion cells in both the submucosal (Meissner) and myenteric (Auerbach) plexuses.
Two pathogenetic mechanisms have been proposed for HD: failure of migration of neural cells, and alteration of the colonic microenvironment.
Any full-term infant who does not pass meconium within the first 48 hours of life should be suspected of having this disorder.
The transition zone between the narrowed distal and dilated proximal intestine will be seen in the most common form of HD—the rectosigmoid form
Hirschsprung Disease
Dilation of the empty rectum by the first examiner usually results in explosive expulsion of retained fecal material and decompression of the proximal normal bowel.
Most commonly, infants younger than 6 months of age with HD will continue to have variable but significant constipation, punctuated by recurrent obstructive crises or bouts of fecal impaction, often with failure to thrive.
Hirschsprung Disease
Anal manometry is the most reliable method by which the gastroenterologist can make the diagnosis of ultrashort-segment
Suction biopsy of the rectal mucosa is the most reliable method of diagnosis, except in patients with ultrashort-segment HD.
Definitive treatment of HD is surgical. In all instances, biopsy of the muscularis propria of the bowel is indicated at the time of surgery to assess for the presence of ganglion cells in the myen- teric plexus and to delineate the proximal extension of agangli- onosis.
