Histology of the Esophagus and Stomach

Question 1

what are the 4 layers of the GI tract?

Answer 1

• mucosa
• submucosa
• muscularis externa
• serosa

Question 2

3 components mucosa

Answer 2

1. stratified squamous—oral cavity, oropharynx, esophagus, anal canal
2. simple columnar—stomach, small intestine, large intestine, rectum
3. functions:
   a. selective permeable barrier
   b. transport, digestion, absorption
   c. produce hormones

Question 3

submucosa

Answer 3

i. connective tissue—contains glands, blood vessels, nerves

Question 4

muscularis externa

Answer 4

i. Circular layer—inner layer is arranged around the tube’s lumen
ii. Longitudinal layer—fibers of the outer layer are disposed along the tube
1. These can contract and the circular layer reduces the diameter of the lumen
2. Contraction of the fibers of the longitudinal layer shortens the tube

Question 5

lamina propria of mucosa

Answer 5

i. consisting of a vascularized connective tissue
1. vascularized loose connective tissue
2. lymphatic nodules and scattered immunocompetent cells—lymphocytes, plasma cells, and macrophages
3. in the small intestine and large intestine, lamina propria is a relevant site of immune responses—Peyer’s patches and GALT

Question 6

muscularis mucosa of the mucosa

Answer 6

1. a thin double layer of smooth muscle is often present for local movement of the mucosa
2. increases contact area with food
3. propel and mix food in GI tract

Question 7

adventitia

Answer 7

a. Outside the peritoneal cavity
b. Binds to the body wall
c. Loose CT
d. Blood vessels, nerves

Question 8

serosa

Answer 8

a. Within the peritoneal cavity
b. Loose CT
c. Simple squamous epithelium
d. Blood vessels, nerves, adipose tissue

Question 9

extrinsic innervation of the GI tract

Answer 9

a. voluntary
i. Sympathetic—decreases motility/secretions
ii. Parasympathetic (Vagus N)—increases motility/secretions

Question 10

intrinsic/enteric innervation of the GI tract

Answer 10

i. Distinct, interconnected neuronal circuits
ii. Submucosal plexus—Meissner
iii. Myenteric (Auerbach plexus)
1. b/w the inner and outer layers of muscularis externa
2. peristaltic contractions move food bolus
3. secretory activity of mucosal and submucosal glands

Question 11

esophagus

Answer 11

a. hollow muscular tube that is about 25 cm long
b. lies posterior to the trachea in the thoracic cavity, except for its distal end, which passes thru the diaphragm into the abdominal cavity
c. carries food from the oropharynx to the stomach by a strong peristaltic reflex
d. lower esophageal sphincter (LES) is just anterior to the gastroesophageal junction
i. helps prevent regurgitation of stomach contents thru contraction and must relax to allow food passage with swallowing
e. upper esophageal sphincter (UES) is near the cricopharyngeus muscle

Question 12

GERD

Answer 12

1. UES—anatomically defined, cricothyroid
   a. Participates in initiation of swallowign
2. LES—funcitonally defined, gastroesophageal sphincter
   a. Prevents gastric reflux
   b. GERD: change in epithelium to columnar (like stomach), chronic esophagitis/ulceration, dysphagia, fibrosis

Question 13

Barrett’s Esophagus:

Answer 13

i. Condition in which an abnormal columnar epithelium replaces the stratified squamous that normally lines the distal esophagus
ii. Most severe histologic consequence of chronic gastroesophageal reflux and predisposes to the development of adenocarcinoma and ulcers

Question 14

mucous cells of the stomach

Answer 14

a. the mucosa in the fundus has 2 types of mucus producing cells:
i. surface mucous cells lining the pit
ii. mucous neck cells located at the opening of the gastric gland into the pit
b. both cell types here produce mucins which are glycoproteins with high molecular mass
c. a mucous layer with a lot of water forms an insoluble gel that attaches to the surface of the gastric mucosa to form a protective barrier
i. traps bicarbonate and neutralizes environment adjacent to the apical region of the surface mucous cells to an alkaline pH

Question 15

chief cells

Answer 15

a. predominate in lower 1/3 of gastric gland
b. not present in cardiac glands and seldom in antrum
c. zymogen granules are observed in the apical region of the cell
i. pepsinogen—proenzyme stored in the zymogen granules—released into the lumen of the gland and converted in the acid environment of the stomach to pepsin which digests most proteins
ii. exocytosis of pepsinogen is stimulated by feeding

Question 16

parietal cells

Answer 16

a. secrete HCl and intrinsic factor
i. HCl—maintains pH
ii. Intrinsic factor—reabsorbs vitamin B12

Question 17

Autoimmune gastritis

Answer 17

i. Autoimmune gastritis is caused by autoantibodies to H/K ATPase, a parietal cell antigen, and intrinsic factor
1. Destruction of parietal cells cases a reduction in HCl (achlorhydria) and a lack of intrinsic factor
2. Resulting B12 deficiency disrupts the formation of RBC in the bone marrow leading to pernicious anemia

Question 18

secretion of Hal

Answer 18

i. Parasympathetic mediator is ACh and the peptide gastrin produced by enteroendocrine cells of the antrum—stimulate parietal cells to secrete HCl

Question 19

Helicobacter pylori

Answer 19

i. Gastric juice is a combo of:
1. An alkaline mucosal gel protective component produced by surface mucous cells and mucous neck cells
2. HCl and pepsin
ii. Protective component is always present
iii. Aggressive component is facultative b/c HCl and pepsin levels increase above basal levels after food intake
iv. Mucous blanket lining the epithelium is the site where the flagellated H. pylori resides
1. It survives and replicates in the gastric lumen
2. Presence leads to ulcers and increased likelihood of adenocarcinoma

Question 20

gastroendocrine cells

Answer 20

a. Fcn of GI tube is regulated by peptide hormones produced by these cells
b. Peptide hormones are synthesized and dispersed throughout the mucosa from the stomach thru the colon
i. MANY of these cells
c. These cells are part of diffuse endocrine system

Question 21

peptide hormones that are produced by gastroendocrine cells have what 3 functions?

Answer 21

i. Regulation of water, electrolyte metabolism, and enzyme secretion
ii. Regulation of GI motility and mucosal growth
iii. Stimulation of the release of other peptide hormones

Question 22

secretin

Answer 22

1. Released by cells in the duodenal glands of Lieberkuhn when gastric contents enter the duodenum
2. Secretin stimulate pancreatic and duodenal bicarb and fluid release to control the gastric acid secretion and regulate the pH of the duodenal contents
3. Secretin, together with CCK, stimulates the growth of the exocrine pancreas
   a. Secretin and ACh stimulate chief cells to secrete pepsinogen and inhibits gastrin release to reduce HCl

Question 23

gastrin

Answer 23

1. Produced by the G cells located in the lyploric antrum
2. 3 forms exist
3. fcn: stimulate HCl production by parietal cells
4. also activates CCK to stimulate gall bladder contraction

Question 24

CCK

Answer 24

1. Produced in duodenum
2. Stimulates gallbladder contraction and relaxation of sphincter of Oddi when protein and fat rich chime enters the duodenum

Question 25

glucose dependent insulinotropic peptide (GIP)

Answer 25

1. Formerly called gastric inhibitory peptide
2. Produced in duodenum
3. GIP stimulates insulin release when glucose is detected in small intestine

Question 26

motilin

Answer 26

1. Released cyclically every 90 min during fasting from upper small intestine and stimulates GI motility
2. Neural control mechanism regulates release of motilin

Question 27

ghrelin

Answer 27

1. Produced in stomach fundus
2. Binds to its receptor in GH secreting cells of the anterior hypophysis
3. Stimulates secretion of GH
4. Ghrelin plasma levels increase during fasting triggering hunger by acting on hypothalamic feeding ceters