Digestive Tract

Question 1

Lamina Propria

Answer 1

CT between the epithelium and the muscularis mucosa

Question 2

Muscularis Externa

Answer 2

Circular and longitudinal smooth muscle.

Question 3

Serosa or Adventitia

Answer 3

Serosa= simple squamous epithelium (the visceral peritoneum) and its underlying CT found on the abluminal surface of most of the gut. When there is no serosa, there is adventitia comprised of loose CT.

Question 4

Esophagus

Answer 4

Non-Keratinized stratified squamous. Mucous glands in the sub mucosa for lubrication. Muscalaris externa is skeletal muscle in the proximal 1/3 transitioning to smooth muscle. In the thorax there is an adventitia circumferentially and only in the abdomen is there a serosa covering the anterior and lateral surfaces.

Question 5

Gastro-Esophageal Junction

Answer 5

Abrupt transition from non-keretinized stratified squamous to simple columnar.

Question 6

Stomach

Answer 6

Storage up to 1.5 liters without a change in intraluminal pressure. Mechanical mixing. Early enzymatic digestion. Epithelium specialized to produce HCl, enzymes, hormones, protraction from acid. Surface mucous cells produce an alkaline mucous protective layer. Thickened muscalaris externa and three layers for protection. Distal end of the stomach, the circular muscle layer is thickened to produce the pylorus.

Question 7

Parietal (oxyntic) cells

Answer 7

Red due to mitochondria. Intercellular canalicular system which serves to increase the SA where HCl and intrinsic factor (a glycoprotein necessary for vitamin B12 absorption in the ileum) are produced. These cells contain the enzyme carbonic anhydrase which combines CO2 and H2O to produce H2CO3, which rapidly dissociates into H+ and HCO3-. H+ is actively pumped out of the canaliculi.

Question 8

Chief (zymogenic) Cells

Answer 8

Proenzyme pepsinogen which is converted by the acidic medium in the gastric lumen into pepsin, a proteolytic enzyme which breaks down proteins into smaller peptides. They also secrete lipase and leptin. Basal= basophilic due to RER. Vesicle containing pepsinogen is eosinophilic in apical.

Question 9

Enteroendocrine Cells

Answer 9

Secrete the hormone gastrin as well as serotonin, VIP, somatostatin, and others into the blood at the basal surface of the cell. Gastrin is produced mainly in the antral (distal) portion of the stomach and stimulates acid secretion by the parietal cells in the body of the stomach.

Question 10

Mucous Neck Cells

Answer 10

Produce a unique mucous.

Question 11

Stem Cells

Answer 11

Replenish and differentiate.

Question 12

Surface Mucous Cells

Answer 12

Sticky mucous. Bicarbonate rich in the high pH environment.

Question 13

Small Intestine

Answer 13

Longest portion of GI. Duodenum, jejunum, and ileum. Terminates at the ileocecal valve, or the entrance to the colon. Muscalaris mucosa produces movement to mucosal villi while the muscalaris externa moves the intestinal contents not only distally, but in an alternating antegrade/retrograde fashion that prolongs contact and mixes.

Question 14

Duodenum

Answer 14

Begins just distal to the pyloris and ends at the duodenojejunal junction (marked by the ligament of Treitz. Receives secretions from the liver and gallbladder through the common bile duct. Chemical and enzymatic reactions occur to prepare the contents for digestion. Pancreas secretes alkaline secretions as do the submucosal glands of Brunner (identifying feature of the duodenum). Pancreas secretes enzymes that break down proteins and carbohydrates, while the bile emulsifies fats.

Question 15

Glands of Brunner

Answer 15

Distinctive feature of the duodenum. Secretes alkaline secretions.

Question 16

Plicae Circulares

Answer 16

Throw up the intestinal mucosa into grossly visible folds.

Question 17

Intestinal SA

Answer 17

Lots of folding, like plicae circulares. Villi projections of the mucosal epithelium. Further projections of the apical cell membrane of enterocytes into microvilli. 1500 fold increase in SA.

Question 18

Jejunum

Answer 18

Largest amount of absorption occurs in the proximal region. SA is maximized by plicae and villi and longer villi. Gradual change to the ileum. Absorption takes place on the apical surface with monosaccharides and amino acids entering the capillaries and fat products (mainly chylomicrons) entering the lymphatics.

Question 19

Villous Architecture

Answer 19

The villi are mucosal finger-like projections into the intestinal lumen. Epithelium consists of enterocytes with microvilli on their apical surface forming the brush border aka striated border with mucous filled goblet cells interspersed.

Question 20

Core of the Villi

Answer 20

Lamina Propria containing capillaies, lymphatics, nerves, smooth muscle cells, and typical CT cells (leukocytes, plasma cells, macrophages, etc).

Question 21

Crypts of Lieberkuhn

Answer 21

Intestinal glands burrowing into the lamina propria of the mucosa. The mitotic activity which replenishes the enterocytes occurs only in the depths of these glands. The cells then migrate towards the lumen reaching the tips of the villi where they are sloughed off, replacing the entire epithelium every 3-6 days.

Question 22

Paneth Cells

Answer 22

Located in the crypts and have granules containing lysozyme secreted to protect against bacterial infection.

Question 23

Ileum

Answer 23

Not distinctly different from the jejunum. Less need for absorptive SA and the plicae and villi decrease in frequency and length. Increase in lymphoid tissue signaling and immunological activity. Sometimes, collection of lymphoid tissue are visible to the naked eye “Peyer’s patches.” Microscopically, there are lymphoid follicles in the lamina propria and submucosa. Epithelium contain “M” cells. The absorption of vitamin B12 and the reabsorption of bile acids occur in the distal ileum.

Question 24

Peyer’s Patches

Answer 24

Collections of lymphoid tissue visible to the naked eye.

Question 25

“M” Cells

Answer 25

Endocytose intestinal antigens, transporting them via macrophages and lymphocytes to the lymph nodes to induce an antibody response (IgA) by plasma cells.

Question 26

Colon

Answer 26

Absorb water and electrolytes from liquid intestinal content that enters through the ileocecal valve. The most water absorption occurs in the small intestine but that which occurs in the colon is responsible for the consistency of a formed stool from a semi-liquid substance. Simple columnar epithelium. Microvilli but no villi. Glands with many goblet cells for lubrication. There are lymphoid nodules in the lamina propria and submucosa and a dramatic increase in lymphoid nodules in the vermiform appendix hinting at an immunological function.

Question 27

Taeniae coli

Answer 27

Three separated, segregated bands of longitudinal smooth muscle. Distinctive. Positive ID in surgery. Converge at the blind end of the cecum at the base of the appendix.

Question 28

Haustra

Answer 28

Between the taeniae the colonic walls bulge out forming sacculations.

Question 29

Rectum

Answer 29

Distal end of the colon. Longitudinal smooth muscle are once again circumferential (ie no taeniae). the rectum ends at the level of the pelvic diaphragm where the mucosa is thrown up into longitudinal folds.

Question 30

Digestive Epithelium

Answer 30

Simple columnar.

Question 31

Rectal Columns of Morgagni

Answer 31

Mucosa is thrown up into longitudinal folds.

Question 32

Anus

Answer 32

Terminal portion about 4 cm. Epithelium changes to stratified squamous. Then keratinized stratified squamous. Thickened circular smooth muscle fibers thickened to internal anal sphincter.

Question 33

Meissner’s Plexus

Answer 33

Neural cell bodies located in the submucosa.

Question 34

Auerbach’s plexus

Answer 34

Ganglia located between two layers of the muscularis externa.

Question 35

Somatostatin

Answer 35

Inhibition of other endocrine cells. Produced in the pulorus duodenum.