GI HISTOLOGY - A13 GI Lecture IV-Large Intestine

Question 1

Main layers of the digestive tract wall?

Answer 1

Mucosa: Lining epithelium, connective tissue, smooth muscle.Submucosa: Dense irregular connective tissue.Muscularis: Two layers of smooth muscle.Serosa: Mesothelium with connective tissue.Adventitia: Connective tissue attachment.

Question 2

Main structures of the large intestine?

Answer 2

Cecum with vermiform appendix.Colon: Ascending, transverse, descending, sigmoid.Rectum.Anal canal.

Question 3

Primary functions of the large intestine?

Answer 3

Reabsorption of water and electrolytes.Elimination of waste.Secretion of mucus for waste elimination.

Question 4

Structure of the mucosa in the large intestine?

Answer 4

Simple columnar epithelium (colonocytes).Irregular microvilli for fluid absorption.No plicae circulares or villi.

Question 5

Types of cells in the mucosal epithelium of the large intestine?

Answer 5

Columnar absorptive cells (colonocytes).Goblet cells for mucus.Enteroendocrine cells.Stem cells for regeneration.

Question 6

Colon subdivisions?

Answer 6

Ascending: Connects to cecum.Transverse: Crosses abdomen.Descending: Leads downwards.Sigmoid: Connects to rectum.

Question 7

Intestinal glands in large vs small intestine?

Answer 7

Longer, closely packed glands (crypts of Lieberkühn).Extend through full mucosa thickness.

Question 8

Predominant cell type in the colon?

Answer 8

Simple columnar absorptive cells (4:1 ratio to goblet cells).

Question 9

Key features of enterocytes and goblet cells?

Answer 9

Enterocytes: Apical striated border of microvilli.Goblet cells: Apical mucin granules.

Question 10

Turnover time for intestinal epithelial cells?

Answer 10

Absorptive and goblet cells: ~6 days.Enteroendocrine cells: Up to 4 weeks.

Question 11

Submucosa characteristics?

Answer 11

Dense irregular connective tissue, blood and lymphatic vessels.Houses submucosal plexus and lymphatic tissue.

Question 12

Muscularis externa characteristics?

Answer 12

Inner circular and outer longitudinal muscle layers.Longitudinal bands (teniae coli) form haustra coli.

Question 13

Appendix structure vs colon?

Answer 13

Many lymphatic nodules in submucosa.Covered by serosa continuous with mesentery.

Question 14

Role of myenteric plexus?

Answer 14

Located between muscle layers, regulates gastrointestinal motility.

Question 15

Significance of teniae coli?

Answer 15

Form haustra coli, present on cecum and colon, absent on rectum.

Question 16

Rectum features?

Answer 16

Dilated distal portion of alimentary canal.Transverse and longitudinal folds present.

Question 17

Serosa of appendix epithelium?

Answer 17

Simple squamous epithelium (mesothelium) facing peritoneal cavity.

Question 18

Lamina propria composition?

Answer 18

Dense irregular connective tissue, lymphatic nodules.Contains blood vessels, nerve fibers, ganglion cells.

Question 19

Mucosa characteristics in large intestine?

Answer 19

Simple columnar epithelium, lacks villi, longer glands.Smooth surface with crypts, mostly goblet cells.

Question 20

Anal canal structural features?

Answer 20

Upper part has anal columns.Stratified squamous epithelium, internal and external anal sphincters.

Question 21

Epithelium change at recto-anal junction?

Answer 21

Simple columnar to stratified cuboidal/squamous at pectinate line.Keratinized stratified squamous at anus.

Question 22

Hemorrhoidal venous plexus significance?

Answer 22

Located in submucosa, can develop varicosities leading to internal hemorrhoids.

Question 23

Colorectal polyps significance?

Answer 23

Asymptomatic masses, >95% colorectal cancer arises from polyps.Regular screening and removal is best prevention.

Question 24

Risk factors for colorectal cancer?

Answer 24

Age >50, adenomatous polyps, diet, related diseases, family history.

Question 25

Hirschsprung disease symptoms?

Answer 25

Ganglionic megacolon, absence of enteric neurons.Symptoms: abdominal distention, constipation, vomiting.

Question 26

Four layers of gastrointestinal tract?

Answer 26

Mucosa: Simple columnar epithelium.Submucosa: Supportive layer.Muscularis: Peristalsis and segmentation.Serosa/Adventitia: Outermost protective layer.

Question 27

Histologic layers of large intestine?

Answer 27

Mucosa: Simple columnar epithelium, lamina propria.Submucosa: Connective tissue, blood vessels.Muscularis: Inner circular, outer longitudinal layers.

Question 28

Zones of epithelium in rectum and anal canal?

Answer 28

Rectum: Simple columnar epithelium.Anal canal: Stratified cuboidal/squamous.At anus: Keratinized stratified squamous.