Anatomy Of The Abdominal Viscera- Midgut And Hindgut

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Anatomy Of The Abdominal Viscera- Midgut And Hindgut

3/22/10 11:00 AM

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What are the organs of the foregut?
Abdominal part of the esophagusStomachDuodenum (proximal to the point of entry of the pancreatic and bile ducts)PancreasLiverGallbladder
What are the organs that are created from the embryonic midgut?
Duodenum (distal to the point of entry of the bile and pancreatic ducts)JejunumIleumCecumAppendixAscending colonProximal 2/3 of transverse colon
What are the organs that are created from the embryonic hindgut?
Distal 1/3 of transverse colonDescending colonSigmoid colonRectumAnal canal
What is the fxn of the small intestine?
Secretion of digestive enzymes, absorption of most of the food
Most bowel sounds are produced by _______
Peristaltic activity in the ileum and jejunum
T/F.  The jejunum and the ileum are retroperitoneal, and are therefore the most immobile parts of the digestive tract.
FALSE.  They are peritoneal, so they are the most mobile parts of the digestive tract.
The jejunum and ileum are suspended to the posterior abdominal wall by _____
Mesentery (fold of peritoneum that is fan-shaped)
T/F.  There is a sharp demarcation b/t the jejunum and the ileum.
FALSE.  No sharp demarcation.
What are the 4 characteristic features of the jejunum?
1. Circular folds are numerous2. Only a few arterial arcades3. Less fat is present in the mesentery4. Only solitary lymphoid nodules present
What are the 4 characteristic features of the ileum?
1. Circular folds are few or absent2. Numerous arterial arcades3. More fat is presnet in the mesentery4. Peyer's patches are present (aggregates of lymphoid nodules)
What is the main role of the large intestine?
Formation, transport, and evacuation of feces (through absorption of water and secretion of mucus); also excretes calcium, magnesium, and iron from the body.
What are 4 features of the large intestine that distinguish it from the small intestine?
1. Teniae coli (ribbon-like bands of outer coat of longitudinal muscle)2. Haustra (sacculations of the intestine produced by the teniae)3. Semilunar folds (located on interior, corresponding to the haustra)4. Epiploic appendices (fat-filled bags of peritoneum hanging off of the large intestine)
Large intestine consists of ______
Appendix, cecum, ascending colon, R colic (hepatic) flexure, transverse colon, L colic (splenic) flexure, descending colon, sigmoid colon, rectum, anal canal 
Which is more superior- right or left colic flexure?
Left colic flexure
Which structures of the large intestine are retroperitoneal?
Ascending colon and descending colon and upper portion of the rectum, so no a mesentery(and lower portion of rectum + anal canal are not part of the peritoneal cavity)
Which structures of the large intestine are peritoneal?
Appendix - MesoappendixCecum - no mesenteryTransverse colon - transverse mesocolonSigmoid colon - sigmoid mesocolon
Gutters of the abdomen
1. R paracolic gutter (right of the ascending colon)2. L paracolic gutter (left of the descending colon)3.  Gutter to the right of the attachment of the mesentery (to posterior abdominal wall)4. Gutter to the left of the attachment of the mesentery (to the posterior abdominal wall)
Subphrenic spaces of the abdomen
L and R subphrenic spaces, below the diaphragm and on either side of the falciform ligament (which connects the liver to the diaphragm)
T/F.  Abdominal gutters are important because they all communicate with the pelvis.
FALSE.  All but the gutter to the right of the attachment of the mesentery communicate with the pelvic cavity.
Why are abdominal gutters important?
Sites of potential accumulation of infected peritoneal fluid or tumor cells.
What are the teniae coli?
3 longitudinal muscles that the run along the large intestine,beginning at the base of the appendix 
The teniae coli are named for ______
Their relationship with peritoneal attachments on the transverse colon
What are the 3 teniae coli?
1. Omental teniae (attachment to greater omentum)2. Free teniae (no peritoneal attachment)3. Mesocolic teniae (attachment to transverse mesocolon)
At the rectosigmoid junction, the teniae coli spread out to form the longitudinal muscle layer of the retum
What is the cecum?
A sac-like structure which lies below the opening of the ileum into the large intestine; it is the thinnest-walled structure of the large intestine, so if something obstructs the large intestine distal to the cecum, it could rupture
What is the appendix?
Outpocketing of the inferior portion of the cecum; opens into the cecum ~1 inch below the ileal orifice
What is the ileal orifice?
The opening of the ileum into the cecum
What is unique about the ileal orifice?
It sometimes has a labial form, in which superior and inferior lips meet on both sides to form a frenulum; also surrounded by a muscular sphincter
What are the 2 forms of the ileal orifice?
Labial formPapillary form
Which is the most commonly seen form of the ileal orifice?
Postmortem = labial formIn vivo = papillary form
What is intussusception?
Invagination of one area of the intestine into the lumen of an adjoining segment; most commonly invagination of the ileum into the cecum/colon
Why is the ileocolic form of intussusception the most common?
Because of the larger size of hte large intestine/colon to the small intestine/ileum
Why is intussusception dangerous?
When it occurs, there is a grave risk of cutting off the blood supply to the gut an developing gangrene; fatal if not treated in 2-5 days
Intussusception is more common in children.  Why?
Because of the relatively larger size of the large intestine as compared to the small intestine, or due to the infection of Peyer's patches and intrusion into gut lumen.
Where is the position of the appendix?
Generally in the RLQ, but position can be variable.  However, position of the base attachment to the cecum is pretty fixed.  Draw a line between ASIS and umbilicus, and 1/3 of the way from the ASIS is McBurney's point - location of appendix.
What is a common place for the appendix to be located?
Behind the cecum (retrocecal appendix)
Appendix is retroperitoneal/peritoneal.
Peritoneal, connected to the ileum by mesoappendix (which contains the appendicular artery).
What is diverticulosis?
Outpocketings (diverticula) of the mucosal lining of the intestine, typically on the sigmoid colon.  Can become infected and rupture, and can result in erosion/hemorrhage of arteries on the colon.
Diverticulosis usually occurs in what group of people, and what prevents it?
Usually occurs in middle-aged or elderly peopleDiet high in fiber is said to prevent diverticulosis
What is the cause of diverticulosis?
Weak spots in the mucosal lining of the wall of the colon, usually along the lines where the arteries pierce the wall
What is a colonoscopy?
Procedure in which a flexible instrument (colonscope) is inserted through the anal canal and rectum to observe the inside of the colon.  Minor procedures such as biopsies and removal of polyps can be carried out by this procedure.
Removal of a portion/entire colon (may be necessary in severe inflammation/ulceration of the colon and rectum), may also remove anal canal.  If removing anal canal, need to also do an ileostomy to establish an opening b/t the ileum and the anterior abdominal wall.
What is the pelvic diaphragm?
Composed of 2 muscles (2 on each side), makes up the floor of the pelvic cavity and separates the pelvic cavity from the perineum below.
What is the most important muscle of the pelvic diaphragm?
Levator ani muscle.
What structures pass through the pelvis?
The rectum passes through the pelvic cavity, but as it passes through the pelvic diaphragm it becomes the anal canal.
Describe the anatomy of the rectum.
Rectum is about 5 inches long, begins at the rectosigmoid junction (at the 3rd piece of the sacrum) and ends anteroinferior to the tip of the coccyx as it passes through the levator ani muscle (of the pelvic diaphragm) to become the anal canal.
The junction of the rectum with the anal canal is marked by a _________
Sharp 80-degree bend, so rectum looks S-shaped from lateral view.
T/F.  The entire rectum is covered by peritoneum.
FALSE.  The lower 1/3 of the rectum is not covered by peritoneum, it's subperitoneal and not in the peritoneal cavity.
What structures are posterior to the rectum?
Sacrum & coccyx
What structures are anterior to the rectum?
Rectovesical pouch (may contain portions of sigmoid colon and ileum) --> upper 2/3 of rectumLower 1/3 of rectum -->urinary bladder, seminal vesicles, ductus deferens, ureters, prostate, and the rectovesical septum (tissue separating the rectum from the urinary bladder)
What is the clinical significance of these relationships?
1) When the rectum has to be removed, it can be done without damaging prostate or urethra due to the rectovesical septum2) If the rectal cancer penetrates the posterior wall of the rectum, it can involve the sacral plexus of nerves3) Pathological thickening of ureters can be felt through the rectal wall4) Enlargement of prostate can be felt through the rectal wall5)Enlargment of seminal vesicles can be felt through the rectal wall
Palpation of the prostate gland
Insert finger into anal canal, palpate the prostate through the anterior wall of the rectum.  Prostate gland may be enlarged due to benign prostatic hypertrophy (BPH) or a tumor.  Tumor is hard and irregular, and BPH prostate is elastic.
What structures are posterior to the rectum in the female?
Sacrum and Coccyx
What structures are anterior to the rectum in the female?
Rectouterine pouch (superior 2/3 of rectum), may contain portions of the sigmoid colon and ileumInferior 1/3 of rectum - vagina 
Structure of the rectum
There are 3 transverse rectal folds (superior transverse rectal fold, middle transverse rectal fold, and inferior transverse rectal fold) at 3 lateral flexures in the rectum.  Project into the lumen, and are permanent.  These serve to support the feces prior to defecation. Ampulla of the rectum = superior to and supported by the levator ani muscles of the pelvic diaphragm
What is the ischioanal fossa?
Wedge-shaped space lying on either side of the anal canal (and below the levator ani mm) filled with connective tissue and fat body that allows the anal canl to become distended during the evacuation of feces
What happens when an abscess in the ischioanal canal forms?
An abscess (collection of pus) can form in the ischioanal canal when hardened feces (due to chronic constipation) tears the lining of the anal canal, allowing infection to spread into the ischioanal fossa (through a fistula, abnormal passageway).  Abscess can rupture on the surface of skin or into the rectum.
T/F.  An abscess in the ischioanal fossa is limited to only one side.
FALSE.  Can spread to other ischioanal fossa through the postanal space that connects the 2 fossa.  Get a horseshoe shaped abscess.
Describe the structure of the anal canal.
Begins at the point where the rectum passes b/t the levator ani mm., and ends at the anus.  Surrounded by 2 sphincters- external anal sphincter and internal anal sphincter.
Internal anal sphincter
Thickening of the circular smooth muscle of the GI tract.  It is an INVOLUNTARY sphincter.  Sympathetic innervation maintains its tone, Parasympathetic innervation inhibits tone (so it can relax and let feces pass through).
External anal sphincter
VOLUNTARY sphincter.  Innervated by inferior rectal nerve and perineal branch of S4.  Maintains continence of the feces and supports the perineal body/pelvic floor.
What is the pectinate line?
An irregular line (resembles teeth of a comb) that marks a change in the lining of the anal canal.  Above the pectinate line is true mucosa, and below the pectinate line is skin.
Mucosa above the pectinate line is thrown into ____________
Vertical folds called anal columns.
What are anal valves?
Unite the lower ends of anal columns with folds of mucosa.  Tearing of anal valves is very painful.
What are anal sinuses?
Superior to the anal valves, secrete mucus to help with evacuation of feces.
What nerve(s) innervate the external anal sphincter?
1) Inferior rectal (anal) nerve2) Perineal branch of S4
What supplies the external anal sphincter?
Inferior rectal artery