GI TBL 23

Question 1

Gut tube consists of the _____, ______, and ______ that opens via the ______ duct to the yolk sac.

Answer 1

Gut tube consists of the cranial foregut, caudal hindgut, and midgut which opens via the vitelline duct to the yolk sac.

Question 2

Gut tube-derived GI tract extends from the _____ to the _______.

Answer 2

esophagus to the anal canal

Question 3

After obliteration of the yolk sac in (time), the foregut forms the (3) to the origin of the (3), which are also foregut-derived.

Answer 3

week 4
foregut forms the esophagus, stomach, and portion of the duodenum proximal to the origin of the gallbladder, liver, and pancreas, which are also foregut-derived.

Question 4

Discuss the 90⁰ clockwise rotation of the stomach and where the original left side and right side face.

Discuss the formation of the greater and lesser curvature.

Answer 4

after the stomach rotates 90⁰ clockwise around its longitudinal axis, its original left side faces anteriorly and its original right side faces posteriorly.

During the rotation, the original posterior wall grows faster than the original anterior wall and thereby creates the greater and lesser curvatures of the stomach.

Question 5

rotation of the stomach around its anteroposterior axis moves its distal portion to the (direction) and (direction) and its proximal portion to the (direction) and (direction).

Answer 5

rotation of the stomach around its anteroposterior axis moves its distal portion to the right and upward and its proximal portion to the left and downward.

Question 6

What creates the characteristic C-shaped loop of the duodenum?

Answer 6

the rotation pulls the duodenum to the right and creates its characteristic C-shaped loop.

Question 7

Arterial supply to foregut, midgut, and hindgut derivatives. Discuss said arterial relation to the ABDOMINAL aorta.

Answer 7

the celiac artery, superior mesenteric artery (SMA) and inferior mesenteric artery (IMA) are unpaired branches of the abdominal aorta.

Celiac artery–> foregut derivatives
Superior mesenteric artery–> Midgut derivatives
Inferior Mesenteric Artery–> Hindgut derivatives

Question 8

SMA occupies the ______ of the INTESTINAL LOOP.

What forms the intestinal loop?

Answer 8

SMA occupies the long axis of the intestinal loop.

Elongation of the midgut forms the intestinal loop.

Question 9

(speed) growth of (organ) temporarily reduces the capacity of the abdominal cavity.

What does the intestinal loop do to continue growing?

Answer 9

Rapid growth of the liver temporarily reduces the capacity of the abdominal cavity .

Intestinal loop herniates into the connecting stalk to continue growing.

Question 10

Intestinal loop makes a (directional movement) around the (artery) before returning to the abdominal cavity.

Answer 10

intestinal loop makes a counterclockwise rotation around the SMA before returning to the abdominal cavity.

Question 11

The midgut forms (7).

Answer 11

Distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and transverse colon.

Question 12

(directional movement) of the intestinal loop establishes the spatial relations of the (2).

Answer 12

Counterclockwise rotation of the intestinal loop establishes the spatial relations of the small intestine (duodenum, jejunum, and ileum) and large intestine (colon and rectum).

Question 13

Discuss the role of the allantois (describe) in week 3.

Answer 13

allantois, an endodermal diverticulum from the yolk sac, enters the caudal aspect of embryo via the connecting stalk to form the cloaca in week 3.

Question 14

What forms the anorectal canal?

Answer 14

Terminal hindgut enters the posterior portion of the cloaca that forms the anorectal canal.

Question 15

What forms the anal membrane?

What happens to create the anal opening and discuss what happens after the anal opening begins to form.

Answer 15

Ectoderm and underlying endoderm of the anterior surface of the anorectal canal form the anal membrane.

When the membrane ruptures to create the anal opening, the ectoderm proliferates inward to line the inferior half of the anal canal.

Question 16

Hindgut forms the (4)

Answer 16

Hindgut forms the descending colon, sigmoid colon, rectum, and superior half of the anal canal.

Question 17

How does an omphalocele form and what are the consequences?

Answer 17

The origin of the defect is a failure for the bowel to return to the body cavity from its physiological herniation during the 6th to 10th week.

Omphalocele is associated with high rate of mortality and severe malformations such as cardiac and neural tube defects. Some live-born infants will have chromosomal abnormalities.

Question 18

Why are most gut atresias and stenoses caused by vascular “accidents”?

Answer 18

Vascular accidents that result in compromised blood flow and tissue necrosis in a section of the gut tissue may lead to a gut atresia and/or stenoses.

Accident- E.g. malrotation of intestinal loop

Note: Atresia is a condition in which an orifice or passage in the body is (usually abnormally) closed or absent.

Intestinal atresia is a broad term used to describe a complete blockage or obstruction anywhere in the intestine.

Stenosis refers to a partial obstruction that results in a narrowing of the opening (lumen) of the intestine.

Question 19

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

Answer 19

Congenital megacolon is due to the absence of parasympathetic ganglia in the bowel wall.

In most cases the rectum is involved and may extend to the midpoint of the sigmoid.

Hirschsprung disease (HD) is a motor disorder of the gut, which is caused by the failure of neural crest cells (precursors of enteric ganglion cells) to migrate completely during intestinal development. Mutations in the RET gene which is involved in crest cell migration may be the causative action. The resulting aganglionic segment of the colon fails to relax, causing a functional obstruction.

Question 20

What cell types/tissue characterize the esophageal mucosa?

The cell type is involved in the most common site of what cancer type and why?

Answer 20

Nonkeratinized stratified squamous epithelium and a richly vascular lamina propria.

Nonkeratinized stratified squamous epithelium abruptly changes to simple columnar epithelium at the esophagogastric junction (Z line), the most common site of esophageal carcinomas.

Question 21

Discuss the muscular mucosae.

Answer 21

muscularis mucosae is a longitudinal layer of smooth muscle that separates the mucosa and submucosa of the GI tract.

Question 22

What creates folds in the mucosa? Discuss the function.

Answer 22

Periodic contraction of the muscularis mucosae creates folds in the mucosa that assist peristaltic propulsion along the GI tract

Question 23

Discuss the spatial relation of the submucosa.

Discuss the submucosal glands of the esophagus.

Answer 23

Submucosa is between the muscularis mucosae and bi-layered muscularis external.

Submucosal glands of the esophagus produce mucus to lubricate the apical surface of the lining epithelium.

Question 24

In the PROXIMAL two-thirds of the esophagus, the muscularis external consists (2).

Answer 24

of an inner circular layer of smooth muscle and an outer longitudinal layer of skeletal muscle.

Question 25

In the DISTAL two-thirds of the esophagus (tissue) replaces (tissue)

Answer 25

smooth muscle replaces the skeletal muscle of the outer layer.

Question 26

Why do cancers in the thoracic portion of the esophagus have a high metastatic potential?

Answer 26

a layer of loose connective tissue (adventitia) covers the muscularis externa in the thoracic portion of the esophagus

Cancers of this portion of the esophagus have high metastatic potential.

Question 27

What is Barrett’s esophagus?

Answer 27

Metaplasia- stratified squamous to simple columnar epithelium- resulting from a response injury or esophagitis above the gastroesophageal junction.

Question 28

What conditions are typically associated with the most common cause of esophagitis?

Answer 28

Most common cause is reflux of gastric content into the lower esophagus- impairing its ability to repair the esophageal mucosa.

Conditions associated include GERD, hiatal hernia, incompetent lower esophageal sphincter.

Question 29

What forms rugae and discuss what occurs as the stomach fills to the rugae.

Answer 29

macroscopic folds of the mucosa and submucosa in the stomach form rugae that flatten as the stomach fills.

Question 30

Discuss the spatial relation of SIMPLE COLUMNAR epithelium and LONG GASTRIC GLANDS.

What cell types do the long gastric glands contain?

Answer 30

Simple columnar epithelium of the stomach regularly dips to join the long gastric glands that extend through the lamina propria to the muscularis mucosae.

Long gastric glands contain mucous cells, parietal cells and chief cells.

Question 31

Parietal cells (actively/passively) transport (ions) into (location) to unite with (ions) to form _____.

Chief cells secrete ______. Discuss the evolution of said (____).

Answer 31

Parietal cells actively transport hydrogen ions into the glandular lumens that unite with chloride ions to form hydrochloric acid

Chief cells secrete pepsinogen that is converted by the acidic environment of the glandular lumens to pepsin, the active digestive enzyme.

Question 32

What forms the serosa of the stomach?

Answer 32

mesothelium encloses the outer layer of loose connective tissue thus forming the serosa of the stomach.

Note: Serous membrane (or serosa) is a smooth membrane consisting of two layers of epithelial cells (as membranes), which secrete serous fluid.

Question 33

(Muscle type) forms the uni/bi/tri-layered muscularis EXTERNA.

Answer 33

smooth muscle forms the bi-layered muscularis externa

Question 34

What creates the pyloric sphincter?

Answer 34

thickening of the inner circular layer creates the pyloric sphincter.

Question 35

Why does destruction of parietal cells lead to pernicious anemia?

Answer 35

Pernicious anemia—a form of megaloblastic anemia—is an autoimmune disease resulting in marked atrophy of gastric mucosa, destruction of parietal cells.

Parietal cells produce IF (intrinsic factor) which is required for the absorption of Vitamin B12 (“Cobalamin). Cobalamin is essential for erythrocyte synthesis in bone marrow and normal neurological function.

Note: pernicious anemia- In the “classic” advanced case of vitamin B12 or folate deficiency, the patient presents with severe anemia and macrocytic red cells (mean corpuscular volume (MCV) >100 fL) with or without varying neurologic disturbances. A macrocytic anemia.

Question 36

Why is projectile vomiting a symptom of pyloric stenosis?

Answer 36

Pyloric stenosis is characterized by extreme narrowing of the pyloric lumen and passage of food is obstructed resulting in projectile vomiting.

Question 37

What forms plicae circulares in the small intestine.

Answer 37

macroscopic folds of the mucosa and submucosa form plicae circulares in the small intestine.

Question 38

Discuss the components which contribute to forming the villi and the spatial orientations.

Answer 38

finger-like projections of the mucosa form villi and the simple columnar epithelium dips between the villi to form intestinal crypts that extend through the lamina propria to the muscularis mucosae.

Question 39

What increases the surface area for absorption? (3)

Answer 39

plicae circulares, villi, and intestinal crypts increase the surface area for absorption.

Question 40

Plicae circulares are most numerous were?

Answer 40

plicae circulares are most numerous in the jejunum.

Question 41

What muscle forms the uni/bi/tri-layered muscular externa of the small intestine?

Answer 41

smooth muscle forms the bi-layered muscularis externa of the small intestine.

Question 42

______ glands filling the _______ of the duodenum are distinctive for this portion of the small intestine.

Answer 42

mucous glands (of Brunner) filling the submucosa of the duodenum are distinctive for this portion of the small intestine.

Question 43

Mucous glands (of Brunner) secrete _________ to buffer the acidic discharge from the stomach.

Answer 43

glands secrete mucous with high bicarbonate ion concentrations to buffer the acidic discharge from the stomach.

Question 44

What cell types forms the intestinal crypts?

Answer 44

simple columnar epithelium dips between the villi to form the intestinal crypts.

Question 45

Discuss the absorption of digested lipids and other digested nutrients into the lymphatic system.

Answer 45

large lymphatic capillaries (lacteals) in the lamina propria absorb digested lipids and the microvascular capillaries absorb other digested nutrients.

Question 46

Epithelium consists of what other cell types? (2)

Answer 46

epithelium consists of goblet cells and absorptive cells (aka enterocytes).

Question 47

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

Answer 47

Ratio of Goblet cells: enterocytes is smallest in the duodenum
Ratio of Goblet cells: enterocytes is greatest in the ileum.

Note: The relative number of goblet cell gradually increases towards the distal end of the small intestines.

Question 48

Discuss the location of Paneth cells and what they contain.

Answer 48

Paneth cells reside at the base of the intestinal crypts mainly in the ileum and contain reddish pink cytoplasmic granules filled with lysozyme.

Note: Paneth cells secrete antimicrobial peptides

Question 49

Discuss why ______ portion of the small intestine provides an antimicrobial line of defense.

Answer 49

extensive submucosal MALT also characterizes the ileum; thus, this portion of the small intestine provides an antimicrobial line of defense.

MALT- mucous associated lymphoid tissue

Question 50

What treatment effectively promotes healing of peptic ulcers?

Answer 50

Antibiotic treatment because a main cause for peptic ulcers is Helicobacter pylori infection.

Question 51

Discuss the absorptive:goblet cell ratio in the colon and the result.

Answer 51

the ratio of absorptive cells to goblet cells is significantly reduced in the colon; thus, a mucous blanket containing a vast microbial population (microbiota) covers the epithelial surface.

Question 52

What causes the concentration of fecal mass?

Answer 52

absorption of water and electrolytes across the colonic epithelium concentrates the fecal mass.

Question 53

Discuss the spatial relation of taeniae coli and the two muscle layers (name) of the muscularis externa.

Answer 53

the smooth muscle of the muscularis externa is organized into an inner circular layer and a thin longitudinal layer.

The taeniae coli interconnects the 3 bundles of longitudinal layer smooth muscle.

Question 54

What creates the colonic haustra?

Answer 54

tonic contraction of the taeniae coli creates the colonic haustra

Question 55

Define epiploic appendices.

Answer 55

pockets of white fat form intermittent bulges in the serosa called omental (epiploic) appendices.

Question 56

Does the mucosa of the COLON continue into the RECTUM?

Answer 56

YES. mucosa of the colon continues into the rectum.

Question 57

Discuss the characteristic ______ folds of the mucosa of the SUPERIOR HALF of the anal canal. The SUPERIOR HALF of the anal canal is derived embryologically from?

Answer 57

the superior half of the anal canal is hindgut-derived and observe the characteristic longitudinal folds of its mucosa (aka anal columns).

Question 58

What demarcates the superior and inferior halves of the anal canal?

Answer 58

inferior end of the anal columns denotes the pectinate line that demarcates the superior and inferior halves of the anal canal.

Question 59

Discuss the cell type transition which occurs at the pectinate line.

Answer 59

the pectinate line marks the transition from endoderm-derived simple columnar epithelium to the ectoderm-derived nonkeratinized stratified squamous epithelium.

Question 60

Discuss what forms the inner/external anal sphincter.

Answer 60

the inner circular layer of the muscularis externa thickens to form the involuntary internal anal sphincter and a circular layer of skeletal muscle forms the voluntary external anal sphincter.

Question 61

Discuss what forms the enteric nervous system and its enabling functions.

Answer 61

neural crest cell-derived visceral sensory neurons, interneurons, and motor neurons form the enteric nervous system (ENS) that enables local, reflexive regulation of the GI tract.

Question 62

More neurons in ENS or of the spinal cord?

Answer 62

together the ENS neurons outnumber the neurons of the spinal cord.

Question 63

Where do the neurons of the ENS organize? (location)

Answer 63

the neurons of the ENS organize into submucosal and myenteric plexuses.

Question 64

Discuss how motor neurons of the GI are activated.

Answer 64

local mechanical and/or chemical stimuli activate the sensory neurons that via the interneurons reflexively activate the motor neurons.

Question 65

What creates peristaltic propulsions along the GI tract?

Answer 65

reflexive activation in the myenteric plexus induces serial contractions of the muscularis externa that create peristaltic propulsions along the GI tract.

Question 66

(Reflexive/CNS) activation in the SUBMUCOSAL PLEXUS induces (function).

Answer 66

reflexive activation in the submucosal plexus induces secretion by the glandular epithelial cells of the GI tract.

Question 67

Discuss the role of the ENS neurons in activating _____-derived enteroendocrine cells.

Answer 67

neurons of the ENS also activate endoderm-derived enteroendocrine cells, which are diffusely scattered in the epithelium of the GI tract and produce ≥ 30 hormones.