GI TBL 26

Question 1

Discuss where the greater splanchnic nerve synapse and how the periarterial plexuses are formed and where?

Answer 1

greater splanchnic nerves (T5-T9) synapse in the celiac ganglion and postsynaptic sympathetic fibers with accompanying visceral afferent fibers form periarterial plexuses on branches of the celiac trunk to the foregut-derived viscera.

Question 2

Discuss where the lesser splanchnic nerves synapse.

Answer 2

lesser splanchnic nerves (T10-T11) synapse in the superior mesenteric ganglion.

Question 3

Branches of the SMA convey plexuses of postsynaptic sympathetic fibers, visceral afferent fibers, and presynaptic fibers of the vagus nerves to the (7)

Answer 3

midgut-derived duodenum, jejunum, ileum, cecum, appendix, ascending colon, and transverse colon.

Question 4

visceral pain from the midgut derivatives is perceived as (characterize) and (location).

Answer 4

dull, diffuse pain in the umbilical region of the abdominal wall.

Question 5

Where do the least splanchnic and lumbar splanchnic nerves synapse?

Answer 5

least splanchnic (T12) and lumbar splanchnic (L1-L2) nerves synapse in the inferior mesenteric ganglion.

Question 6

Periarterial plexuses on the branches of the IMA transport postsynaptic sympathetic fibers to the (3)

Answer 6

Periarterial plexuses on the branches of the IMA transport postsynaptic sympathetic fibers to the hindgut-derived descending colon, sigmoid colon, and rectum.

Question 7

Vagus nerves synapse with the enteric neurons of the (2)

Answer 7

foregut and midgut derivatives.

Question 8

Presynaptic parasympathetic fibers of the pelvic splanchnic nerves arise from (location) and synapse (location).

Answer 8

Presynaptic parasympathetic fibers of the pelvic splanchnic nerves arise from spinal cord segments S2 to S4 and synapse with the ENS visceral motor neurons of the hindgut derivatives.

Question 9

Visceral afferent fibers from the DRG at S2 to S4 join the (nerves).

Answer 9

pelvic splanchnic nerves

Question 10

Visceral pain from the inferior half of the sigmoid colon and the rectum is conveyed to the (location).

Answer 10

DRG at S2-S4.

Question 11

Pain from posterior thighs and perineum is perceived as (characterize).

Answer 11

dull and diffuse

Question 12

Visceral afferent fibers from the DRG at T12-L2 are transported (fibers) to (2).

Answer 12

Visceral afferent fibers from the DRG at T12-L2 are transported by postsynaptic sympathetic fibers to the descending colon and superior half of the sigmoid colon.

Question 13

Visceral pain from descending colon and superior half of the sigmoid colon is perceived as (characterize) and (location)

Answer 13

Dull, diffuse pain in the pubic region of the abdominal wall.

Question 14

Why can visceral pain from diverticulosis of the sigmoid colon be referred to the pubic region of the abdominal wall or to the perineum and posterior thighs?

Answer 14

Visceral pain from superior half of sigmoid colon is referred to pubic region of abdominal wall via Visceral afferent fibers from the DRG T12-L2.

Visceral pain from inferior half of sigmoid colon, perineum, and posterior thighs is relayed by visceral afferent fibers from the DRG at S2 to S4.

Question 15

Discuss the length of jejunum and ileum. What quadrants are they in?

Answer 15

Jejunum and ileum are 6-8 m long and reside in all four abdominal quadrants.

Question 16

Discuss the attachment of the jejunum and ileum to the posterior abdominal wall.

Answer 16

Mesentery of the small intestine, which is derived from the dorsal mesentery, does the attachment.

Question 17

Intestinal branches of the retroperitoneal SMA course within the mesentery to supply (2).

Intestinal branches form (structures and course).

Answer 17

Intestinal branches of the retroperitoneal SMA course within the mesentery to supply the jejunum and ileum.

Intestinal branches form loops or arcades and straight branches (aka vasa recta) that course from the arcades into the walls of the jejunum and ileum.

Question 18

How would the mesentery of the small intestine help distinguish the jejunum and ileum during surgery?

Answer 18

Jejunum has less fat in mesentery, vasa recta are longer but less numerous, arterial arcades are in series, and wall is thick and heavy.

Ileum has more fat in mesentery, vasa recta are shorter and more numerous, arterial arcades run vertically, and wall is thin and light.

Question 19

What are the symptoms of ileus and how can it be diagnosed early?

Answer 19

Ileus is accompanied by a severe colicky pain, along
with abdominal distension, vomiting, and often fever and
dehydration.

If the condition is diagnosed early (e.g., using a
superior mesenteric arteriogram), the obstructed part of the vessel may be cleared surgically.

Note: Ileus is temporary absence of the normal contractile movements of the intestinal wall.

Question 20

What is the frequency of an ileal (Meckel) diverticulum and where is visceral pain from an inflamed diverticulum referred?

Answer 20

1–2% of the population.

An ileal diverticulum may become inflamed and produce pain mimicking that produced by appendicitis.

Vague pain in the peri-umbilical region because
afferent pain fibers enter the spinal cord at the T10 level.

Question 21

What enables recognition of the colon during surgery.

Answer 21

omental (epiploic) appendices and haustra

Question 22

Locate the transverse and sigmoid mesocolon.

Answer 22

Informational

Question 23

Ascending colon and descending colon lack mesenteries- discuss.

Answer 23

Ascending colon and descending colon lack mesenteries (i.e., they partially protrude into the parietal peritoneum and visceral peritoneum only covers their anterior and lateral surfaces).

Question 24

What forms the ileocolic artery and what does it supply (2). Right and middle colic artery supply (structures).

Answer 24

SMA generates the ileocolic artery to supply the cecum and appendix

Right colic artery to supply the ascending colon

Middle colic artery to supply the transverse colon.

Question 25

What generates the left colic artery and it supplies?

Sigmoid artery and superior rectal artery supply (structures)

Answer 25

IMA generates the left colic artery to supply the descending colon

Sigmoid artery to supply the sigmoid colon

Superior rectal artery to supply the retroperitoneal portion of the rectum

Question 26

Anastomoses between the (arteries) form the marginal artery of the colon (function)

Answer 26

Ileocolic, right colic, middle colic, left colic, sigmoid, superior rectal artery.

Marginal artery of the colon provides important collateral circulation to the large intestine.

Question 27

Lymph drainage from midgut/hindgut derivatives. Discuss further drainage.

Answer 27

midgut derivatives–> superior mesenteric lymph nodes

hindgut derivatives–> inferior mesenteric lymph nodes,

like the celiac nodes of the foregut-derivatives, efferent lymph from the mesenteric nodes empties into the thoracic duct.

Question 28

Why does pain from appendicitis usually commence as vague umbilical pain and become sharp local pain in the lower right quadrant?

Answer 28

The pain of appendicitis usually commences
as a vague pain in the peri-umbilical region because
afferent pain fibers enter the spinal cord at the T10 level.

Later, severe pain in the right lower quadrant results from irritation of the parietal peritoneum lining the posterior abdominal wall.

Extending the thigh at the hip joint elicits pain.

Question 29

How do histologic changes during the pathogenesis of appendicitis correlate with the accompanying sensations of visceral and somatic pain?

Answer 29

Acute appendicitis first affects the mucosa, where edema and leukocyte infiltration occur.

Penetration of other layers may lead to abscess,
necrosis, perforation into the peritoneal cavity, and a complication— peritonitis (inflammation of the peritoneum).

Question 30

What are the early symptoms of diverticulitis and when would surgical treatment be required?

Answer 30

Early symptoms are cramps, bloating, and constipation, often followed by blood in the stool. Antibiotic treatment is usually successful, but severe cases may need surgery

Question 31

Rectum follows (directional course). Discuss where it lies (location)

Answer 31

Rectum follows the curve of the sacrum and coccyx.

Superior third of rectum resides retroperitoneally and its inferior two-thirds resides in the pelvic cavity in a subperitoneal position.

Question 32

Pelvic diaphragm forms (boundary).

Answer 32

Pelvic diaphragm forms the inferior boundary of the abdominopelvic cavity.

Question 33

Discuss the puborectalis and what it forms.

Answer 33

Puborectalis of the pelvic diaphragm forms the puborectal sling that creates a right-angled turn of the rectum at its union with the anal canal.

Question 34

Anal canal resides in the (location and define).

Answer 34

Perineum, a shallow subcutaneous compartment inferior to the pelvic diaphragm

Question 35

Superior rectal artery supplies the (structure)

Middle rectal artery supplies the (structure).

Answer 35

Retroperitoneal rectum

Subperitoneal rectum

Question 36

(Fibers) convey visceral pain from the rectum to the posterior thighs and perineum.

Answer 36

visceral afferent fibers from the DRG at S2 to S4 in the plexus of the middle rectal artery

Question 37

Middle rectal artery and inferior rectal artery supply the (structures)

Answer 37

Middle rectal artery—> anal canal above pectinate line Inferior rectal artery–> anal canal below the pectinate line.

Question 38

What maintains tonic contraction of the internal anal sphincter?

What voluntarily contract the external anal sphincter?

Answer 38

Postsynaptic sympathetic fibers accompanying the superior and middle rectal arteries maintain tonic contraction of the internal anal sphincter

Somatic motor fibers of the inferior rectal nerve, a branch of the pudendal nerve (S2-S4), voluntarily contract the external anal sphincter.

Question 39

How is tonus of the internal sphincter inhibited and peristaltic contraction of the rectum and anal canal is evoked?

How is fecal continence is maintained?

Answer 39

Somatic motor fibers of the pudendal nerve supply the pelvic diaphragm and when distension of the rectum reflexively activates the pelvic splanchnic nerves, tonus of the internal sphincter is inhibited and peristaltic contraction of the rectum and anal canal is evoked.

Fecal continence is maintained by voluntary contraction of the pelvic diaphragm and external anal sphincter.

Question 40

Visceral afferent fibers accompanying the pelvic splanchnic nerve supply the (2).

Somatic afferent fibers of the inferior rectal nerve are locally sensitive to (3).

Answer 40

Anal canal above the pectinate line and below the pectinate line

Somatic afferent fibers of the inferior rectal nerve (cutaneous innervation below the pectinate line and external anal sphincter) are locally sensitive to touch, pain, and temperature.

Question 41

Above the pectinate line venous blood drains into (structure) and lymph drains into (structure).

Answer 41

Venous blood drains into the hepatic portal vein and lymph drains into the internal iliac nodes.

Question 42

Below the pectinate line venous blood drains into (structure) and lymph drains into (structure).

Answer 42

Venous blood drains into the IVC and lymph drains into the superficial inguinal lymph nodes.

Question 43

What are predisposing factors for hemorrhoids? Why is anesthesia employed during surgical treatment of external hemorrhoids?

Answer 43

Predisposing factors for hemorrhoids include pregnancy,
chronic constipation and prolonged toilet sitting and straining, and any disorder that impedes venous return, including increased intra-abdominal pressure.

Regarding pain from and the treatment of hemorrhoids,
it is important to note that the anal canal superior to the pectinate
line is visceral; thus it is innervated by visceral afferent
pain fi bers, so that an incision or needle insertion in this
region is painless. Internal hemorrhoids are not painful and
can be treated without anesthesia. Inferior to the pectinate
line, the anal canal is somatic, supplied by the inferior anal
(rectal) nerves containing somatic sensory fi bers. Therefore,
it is sensitive to painful stimuli (e.g., to the prick of a hypodermic
needle).