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Anatomy Unit 3 > TBL 19 > Flashcards

TBL 19 Flashcards

1
Q

What arteries supply the foregut, midgut and hindgut?

A

celiac artery: foregut
SMA: midgut
IMA: hindgut

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2
Q

What forms the intestinal loop? What occupies the long axis of the loop?

A

Rapid elongation during midgut development

SMA

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3
Q

How is the intestinal loop attached to yolk sac?

A

its apex by the vitelline duct to the yolk sac

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4
Q

What causes reduction of the capacity of the abdominal cavity? What happens as a response?

A

Elongation of the loop and expansion of the liver cords temporarily reduces the capacity of the abdominal cavity so the loop enters the stalk and later returns to the cavity.

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5
Q

How does an omphalocele form and what are the consequences?

A

Omphalocele involves herniation of abdominal viscera through an enlarged umbilical ring. The viscera (may include liver, small and large intestines, stomach, spleen, gallbladder) are covered by amnion. Results because failure of bowel to return to the body cavity from its physiological herniation during the 6th-10th weeks.

High rate of mortality –> severe malformations (cardiac anomalies, neural tube defects)

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6
Q

What forms an ileal (Meckel) diverticulum?

A

when the vitelline duct persists forming an outpocket of the ileum

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7
Q

What does the counterclockwise (180) rotation of the intestinal loop cause?

A

The intestinal loop makes a counterclockwise rotation around the SMA during herniation. The transverse colon passes anterior to the duodenum.

The completion of the counterclockwise rotation determines final deposition of the midgut and hindgut derivatives in the abdominal cavity.

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8
Q

What are derivatives of the midgut? hindgut?

A

Midgut: distal duodenum, jejunum, ileum, cecum, appendix, ascending colon and proximal 2/3 of transverse colon

hindgut: distal 1/3 of transverse colon, descending colon, sigmoid colon, rectum, and upper anal canal

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9
Q

Why are most gut atresias and stenoses caused by vascular accidents? Why is proximal duodenal atresia an exception?

A

From the distal portion of the duodenum cadually, gut atresias and stenoses are thought to be caused by vascular accidents that resulted in compromised blood flow and tissue necrosis in a section of the gut resulting in defects.

Atresias in the upper duodenum are due to a lack of recanalization.

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10
Q

How does Hirschsprung disease cause congential megacolon and where does it most commonly occur?

A

Congenital megacolon is due to an absence of parasympathetic ganglia in the bowel wall (Hirschsprung disease = aganglionic megacolon).

In most cases, the rectum is involved and in 80% the defect extends to the midpoint of the sigmoid.

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11
Q

What is allantosis?

A

Allantosis is a slender endodermal diverticulum of the distal hindgut that extends into the connecting stalk. The proximal part of the allantosis forms the cloaca

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12
Q

What divides the endoderm-lined cloaca into urogenital and anorectal portions?

A

MESODERM-derived urorectal septum

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13
Q

What contributes to the periarterial plexuses on the branches of the celiac trunk to the foregut-derived viscera?

A

greater splanchnic nerves (t5-t9) which synnapse in the celiac ganglion

postsynaptic sympathetic fibers

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14
Q

Where do the greater splanchnic nerves synapse? (T10-T11)

A

superior mestenteric ganglion

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15
Q

What do branches of the SMA convey to the midgut derivatives?

A

Plexuses of postsynaptic sympathetic and visceral sensory fibers

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16
Q

Where is visceral pain from the midgut derivatives referred to? What is it perceived as?

A

umbilical region

dull, diffuse pain

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17
Q

What do vagus nerves do?

A

Vagus nerves contribute to the celiac trunk

vagal fibers also join the SMA plexus to the midgut derivatives

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18
Q

What do the parasympathetic and sympathetic fibers do ENS-regulated GI tract?

A

peristalsis and glandular secretion are:

accelerated– parasympathetic
decelerated – sympathetic

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19
Q

What nerves synapse in the inferior mesenteric ganglion?

A

least splanchnic nerves (T12) and lumbar splanchnic nerves (L1-L2)

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20
Q

What do periarterial plexuses on branches of the IMA do?

A

convey postsynaptic sympathetic fibers to the hindgut derivatives

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21
Q

How do hindgut derivatives refer pain?

A

Proximal hindgut derivatives (distal 1/3 of transverse colon, descending colon and superior half of sigmoid colon) refer visceral pain to the hypogastric region via visceral sensory fibers from DRG at T12-L2, which accompany the postsynaptic sympathetic fibers from the inferior mesenteric ganglion

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22
Q

What are pelvic splanchnic nerves? What accompanies these nerves?

A

Pelvic splanchnic nerves arise from spinal cord segments S2 to S4, which consist of presynaptic parasympathetic fibers that synapse with enteric ganglia in the hindgut-derived viscera.

Visceral afferent fibers from DRG at S2-S4 accompany the pelvic splanchnic nerves

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23
Q

What provides parasympathetic innervation to the midgut derivatives?

A

vagus nerves!

24
Q

Where is visceral pain from the inferior half of the sigmoid colon, rectum and upper anal canal referred to?

A

posterior thighs and perineum

25
Q

How does referral of visceral pain differ after diverticulosis develops in the upper half or lower half of the sigmoid colon?

A

Diverticulosis is a disorder in which multiple false diverticula develop along the intestine.
Upper half –> epigastric region
Lower half –> thigh/ perineum

26
Q

What is the anatomical significance of the jejunum and ileum?

A

They are 6-8m long and occupy all four abdominal quadrants.

The jejnum and ileum are attached to the posterior abdominal wall by the mesentery of the small intestine, a derivative of the dorsal mesentery.

27
Q

Branches of which artery supply the jejunum and ileum? Within the mesentery what happens to these branches?

A

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

Within the mesentery, intestinal branches form loops or arcades. Straight branches (vasa recta) from the arcades supply capillaries in the walls of the jejunum and ileum

28
Q

Compare the arterial aracades and vasa recta of the jejunum and ileum.

A

Vasa recta
Jejunum: long
ileum: short

Arcades
Jejunum: a few large loops
Ileum: many short loops

29
Q

What are the symptoms of ileus, how can it be diagnosed early, and how is early diagnosis related to treatment?

A

Ileus is obstruction of the intestine. It is accompanied by severe colicky pain, along with abdominal distension, vomiting, and often fever and dehydration.

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

30
Q

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

A

It occurs in 1-2% of the population. It is when there is a remnant of the proximal part of the embryonic yolk stalk. An ileal diverticulum may become inflamed and mimics the pain produced by appendicitis.

31
Q

What happens to the plicae circulares in the jejunum?

A

They are more numerous and well developed

32
Q

What do simple columnar epithelium do in villi and intestinal crypts? What do the epithelium consist of?

A

Simple columnar epithelium lines the villi of the small intestine mucosa. They dip between the villi to form the intestinal crypts.

Consists of goblet cells and enterocytes (absorptive cells).

33
Q

Describe the jejunum layers.

A

Microvilli–> intestinal crypts.
These crypts fill the lamina propia and extend to the muscularis mucosae. Visceral peritoneum or serosa covers the muscularis externa.

34
Q

What is found in the lamina propia of the ileum and jejunum?

A

Capillaries and large lymphatic capillaries (lacteals)

Lacteals absorb digested lipids while other digested nutrients are absorbed by the capillaries

35
Q

What are Paneth cells?

A

Paneth cells reside at the base of the intestinal crypts and are especially numerous in the ileum.

Paneth cell cytoplasm contains reddish pink secretory granules that contain lysozyme.

The antimicrobial actions of Paneth cells (and selectively differentiated plasma cells) provide a main line of defense against pathogen invasion of the ileum.

36
Q

What is a special characteristic of the ileum?

A

extensive MALT resides in the ileal submucosa and occupies half of the ileal circumference

37
Q

Compare ratios of enterocytes and goblet cells in the three segments of the small intestine.

A

Decrease enterocytes and increase goblet cells as you travel from duodenum to ileum

38
Q

What are stimuli that cause massive mucous secretion by the goblet cells?

A

Cholinergic stimulation, bacterial and endotoxin exposure cause massive mucous secretion by goblet cells

39
Q

What causes easy recognition of the colon during surgery?

A

omental appendices and haustra

40
Q

What is the appendix? What is its relation to McBurney’s point?

A

It is a blind diverticulum from the posteromedial aspect of the cecum.

McBurney point: point that is 1/3 distance from the ASIS and umblicus. it is surface indicator indicator for the appendix in the lower right quadrant of the abdominal cavity

41
Q

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

A

afferent pain fibers enter the spinal cord at the T10.

later, severe pain results from irritation of the parietal peritoneum lining the posterior abdominal wall. extending the thigh at the hip joint elicits pain.

42
Q 
What branches of the SMA supply the 
cecum
appendix
ascending colon
transverse colon?
A

cecum = ileocolic

appendix = appendicular

ascending colon= right colic and ileocolic

transverse colon= middle colic

43
Q

What branches of the IMA supply the
descending colon
sigmoid colon
rectum?

A

descending colon: left colic and sigmoid

sigmoid: sigmoid
rectum: rectal (superior, middle, inferior)

44
Q

Describe the series of anastomotic arcades that form the marginal artery of the colon.

A

branches of the SMA anastamose with each other and with the right branch of the middle colic artery . This first series of anastomotic arcades is continued by the left colic and sigmoid arteries to form a continuous arterial channel to form the MARGINAL ARTERY!

45
Q

Where does lymph from the midgut and hindgut drain

A

midgut: superiro mesenteric lymph nodes –> (efferent lymph) thoracic duct
hindgut: inferior mesenteric lymph nodes –> (efferent lymph) thoracic duct

46
Q

What is the importance of the transverse and sigmoid mesocolon?

A

transverse mesocolon: enables free mobility of the transverse colon and it usually hangs to the level of the umbilicus

sigmoid mesocolon: mobility to the sigmoid colon but it usually remains in the left lower quadrant

47
Q

Why do mesenteries not form along the ascending and descending portions of the colon?

A

During development, ascending and descending portions of the colon only protrude partially into the parietal peritoneum. So visceral peritoneum covers their anterior and lateral surfaces but mesenteries do not form.

48
Q

What is the ratio of the absorptive cells to goblet cells in the colon?

A

It is much less in the colon than the small intestine. Thus, rich mucous secretion protects and lubricates the colonic epithelial surface.

49
Q

What is the function of the epithelium of the colon?

A

Water and electrolytes are absorbed across the epithelium and a vast bacterial population on the apical surface of the epithelium is engaged in nonenzymatic digestion.

50
Q

What does the muscularis externa of the colon consist of?

A

inner circular layer of smooth muscle and outer longitudinal layer of nonuniform thickness

51
Q

What are taeniae coli?

A

They are three equidistant longitudinal bands of smooth muscle that are interconnected by a thin layer of longitudinal smooth muscle

Tonic contraction of the taeniae coli form haustra

52
Q

What are omental appendices?

A

They are pockets of white fat in the serosa forming intermittent, pendulous bulges covered by visceral peritoneum.

53
Q

What differentiates the appendix from the colon? What is its function?

A

appendix lacks taeniae coli and contains a discontinuous ring of lymphoid nodules in the submucosa

assumed to be vestigial but abundant lymphoid tissue in its wall and production of B-lymphocytes in germinal centers of nodules = immunologic defense function?

54
Q

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

A

Diverticula: herniations of mucosa and submucosa through the muscularis externa of the colon

Diverticulitis: inflammation of the diverticula that can lead to perforations, tears, bleeding and infection. Symptoms: cramps, bloating, and constipation, blood in stool. Severe cases require surgery.

55
Q

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

A

Acute appendicitis first affects the mucosa, where edema and leukocyte infiltration may occur. Penetration of other layers –> abscess, necrosis, perforation into the peritoneal cavity –> peritonitis –> PAIN

Anatomy Unit 3 (9 decks)

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