Morphology of the GI system - Brodski

Question 1

Layers of the alimenary canal

Answer 1

In order from out to in:

Serosa

Longitudinal muscle layer of the muscularis

Myenteric (Auerbach’s) plexus

Circular muscle layer of muscularis

Submucosa and submucosal (Meissner’s) plexus (glands and ducts)

Muscularis mucosa

Lamina propria (lymph nodules)

Mucous epithelium

Question 2

What is the function of the Meissner’s submucosal Plexus

and Auerbach’s Myenteric Plexus

What happens when they are absent?

Answer 2

Submucosa: Secretory function, mucosal movement, and localized blood flow.

Aurerbach’s: Peristaltic Motility

Hirschsprung Disease is when they don’t interact

Achalasia is degeneration of myenteric plexus

Question 3

Layers of the esophagus

Answer 3

Mucosa:
Epithelium (stratified sqamous nonkeratinized)
Lamina propria
Muscularis mucosae (only) longitudinally oriented smooth muscle fibers

Submucosa:
Harbors glands

Muscularis externa:
Inner circular and outer longitudinal
upper third mostly skeletal
middle third skeletal and smooth
lowest third only smooth muscle

Question 4

Components of the mucosa of the stomach

Answer 4

Mucus Neck Cells:
Produce a soluble mucus that mixes with chyme, to reduce friction. Produced in the neeck of the fundic gland.

Parietal Cells:
Manufacture hydrochloric acid and gastric intrinsic factor
(Necessary for vitamin B12 absorption). Lack: pernicious anemia.

Chief Cells:
Manufacture pepsinogen, rennin (rennet), gastric lipase. Secretory vesicles in apical cytoplasm contain pepsinogen (activated by low pH in stomach lumen).

DNES (diffuse neuroendocrine secretory) Cells:
Manufacture endocrine, paracrine, and neurocrine hormones individually dispersed among other epithelial cells of mucosa. Also found in respiratory system and pancreas.

Regenerative Cells:
proliferate to replace all of the specialized cells.

Question 5

3 phases of HCl Production

Answer 5

1. CEPHALIC PHASE
   occurs before food reaches stomach
   mediated by vagus
   release of acetylcholine
   G cells also stimulated - gastrin release

2. GASTRIC PHASE
   gastric distention activates release of vagus acetylcholine
   peptides stimulate gastrin release
3. INTESTINAL PHASE
   peptides in duodenum stimulate duodenal gastrin release

Question 6

Overview of Hormones in GI tract (location, cell, action, etc.)

Answer 6

Question 7

Components of increased surface area in the small intestines

Answer 7

Surface absorptive cells (Upper half of gland, terminal digestion and absorption of water and nucleus)

Goblet cells (upper half of gland, more towards ileum)

DNES cells (1% of cells covering villi and intervillar surface)

Plicae circulares:
Transverse folds of submucosa and mucosa (Unlike rugae they are permanent)

Villi:
Epithelially covered protrusions of lamina propria

Microvilli:
Modifications of the apical plasmalemma of the epithelial cells covering the intestinal villi

Crypts of Lieberkuehn:
Invaginations of the epithelium into the lamina propria between the villi form intestinal glands
Also have specialized cells:
Regenerative Cells
Paneth Cells: Produce antibacterial lysozyme, localized at bottom of crypts, live for 20 days (as opposed to 3 days)

Question 8

Paneth Cells

Answer 8

Inside Crypts of Lieberkuehn only in the small intestines

Produce antibacterial lysozyme
localized at bottom of crypts
Rather long life span of 20 days

Question 9

Acinus of Exocrine Pancreas Cells and actions

Answer 9

Acinar cells (40-50/acinus) produce digestive enzymes:

Pancreatic amylase, pancreatic lipase, DNase, trypsinogen, trypsin inhibitor. Activation by CCK produced by DNES in small intestine (duodenum) and acetylcholin released by postganglionic parasympathetic fibers. Released in acidic conditions

Centroacinar cells (3-4/acinus, serous, bicarbonate-rich alkaline fluid, pale, low cuboidal):
 Buffering the acid chyme that inters the duodenum.
 Activation:
 Secretin:  produced by DNES cells of small intestine Acetylcholine?

Intralobar Ducts begin with terminus of centroacinar cells.

Question 10

Proteins and vitamins produced by the liver

Answer 10

Albumin (not a factor for liver function bc long half life and hypoalbumin can have many reasons.)

Blood clotting factors
(Factor VIII, produced also in the liver but not in hepatocytes)

Lipoproteins (in particular VLDLs)

Glycoproteins (e.g. iron transport)

Vitamin A:
Liver essential for uptake, storage and maintenance

Vitamin D (source: diet and synthesis in intestinal bacterial flora):
 Liver essential for metabolizing into active from

Vitamin K (source: diet and synthesis in intestinal bacterial flora):
 Biosynthesis of factor II, VII, IX, X depends on vitamin K (inhibits). Most important.

Vitamin B12
require gastric intrinsic factor produced in parietal cells
for absorption in terminal ileum

Question 11

Endocrine function of the kidney

Answer 11

Degradation of estrogens

Production of insulin-like growth factor 1: mediated growth hormone activity

Thyroid hormones: T4 is converted in the liver (and kidney) to the biological active form T3

Vitamin D is converted to active form

Degradatino of estrogens (gynecomastia is an increase in estrogens and decreased testosterone)

Question 12

Kupffer cells

Answer 12

Phagocytic cells located on sinusoidal walls that remove particulate material and old red blood cells from circulation.

Kupffer cells are members of the mononuclear phagocyte system