Upper GI Flashcards
What are the 4 layers of the GI tube?
- Mucosa
- Submucosa
- Muscularis externa
- Adventitia or serosa
What is the basic structure of the mucosa of the GI tube?
- Epithelium - rests on basal lamina
- Lamina propria - contains CT, glands, blood vessels, lymphatic tissue
- Muscularis mucosae - inner circular and outer longitudinal layers of smooth muscle, contraction produces local movement of mucosa to facilitate absorption and secretion
What is the basic structure of submucosa in the Gut tube?
Dense irregular CT
Blood and lymphatic vessles
Submucosal nerve plexus
Glands present in only esophagus and duodenum
What is the basic structure of the muscularis externa of the GI tube?
Inner circular and outer longitudinal smooth muscle layers - stomach has extra layer
Contraction results in peristalsis
Myenteric nerve plexus between inner and outer muscular layers
What is the basic structure of the adventitia of a standard GI tube?
Adventitia - CT only, present in extraperitoneal portion of GI tube (rectum and esophagus)
Serosa - CT covered by simple squamous epithelium, present in peritoneal cavity
What is part of the enteric nervous system?
Autonomics:
Parasympathetic preganglionic axons and postglanglionic neurons
Sympathetic postganglionic axons
Visceral afferent dendrites
Plexuses:
Myenteric plexus
Submucosal plexus
What is the myenteric plexus and where is it located?
Between inner and outer layers of the muscularis externa
Controls peristalsis
What is the submucosal plexus?
Regulates glandular secretion in mucosa and submucosa, blood flow, and muscularis mucosae
Visceral afferents monitors chemistry of gut contents and mechanical stimulation of mucosa
What is achalasia?
Dysfunction of myenteric plexus causes constriction of the lower esophageal sphincter
What is Hirschsprung’s Disease?
Cognenital megacolon
Absence of enteric nerves in portion of bowel
What is the function of the esophagus? How does that connect to its lining?
Transport masticated food to stomach
Epithelial lining must resist abrasion
What layers does the esophagus contain?
Mucosa
Submucosa
Muscularis externa
Adventitia
Serosa
What is in the mucosa of the esophagus?
Nonkeratinized stratified squamous - protects from abrasion
Lamina propria - cardiac glands concentrated proximally and distally. Glands secrete mucus for lubrication and neutralization of stomach acid
Muscularis mucosae contains only longitudinal fibers
What is the submucosa of the esophagus?
Contains esophageal glands proper (seromucous) - serous and mucous secretions
Also secretes pepsinogen and lysozyme
What is in the muscularis externa of the esophagus?
Transition from striated to smooth muscle
What is in the adventitia and serosa of the esophagus?
Thoracic esophagus - adventitia
Abdominal esophagus - serosa
What is the gastroesophageal junction?
Transition in function from transportation to digestion
Transition from stratified squamous epithelium to secretory gastric epithelium
see “z-line” in gross anatomy
What is barrett’s esophagus?
Metaplastic columnar epithelium with goblet cells in distal esophagus, usually near gastroesophageal junction
Due to chronic insult from gastric secretions (stomach acid) - GERD or frequent vomiting
Increased risk of adenocarcinoma
What are the regions of the stomach?
Cardia - region around gastroesophageal junction
Fundus - makes up bulk of stomach
Pylorus - region around pyloric sphincter and gastroduodenal junction
What are the rugae of the stomach?
Longitudinal folds that allow for distension
Formed by muscosa and submucosa
What are the functions of the stomach?
Temporary storage
Secretion of gastric juice
Formation of chyme - product of gastric churning and chemical digestion
What layers does the stomach have?
Mucosa
Submucosa
Muscularis Exzterna
What is in the mucosa of the stomach?
Epithelium - simple columnar that are surface mucous cells and form pits
What are gastric pits?
Formed by invagination of surface epithelium into the lamina propria
Lined by simple columnar epithelium and surface mucous cells that secrete bicarbonate rich protective mucus
What are the gastric glands? What types of cells do they contain?
Empty into the gastric pits
Contains 3 regions:
1. Isthmus - contains regenerative stem cells
- Neck - contains mucous neck cells that secrete lubricating mucus that lubricates chyme. Also parietal cells that secrete HCL and gastric intrinsic factor, which binds to B12 for absorption by ileum
- Base - Contains chief cells that secrete pepsinogen and converts to pepsin when mixes with acid. Also contains enteroendocrine cells that secrete hormones
What are cardiac glands?
In cardia region of stomach
Shallow pits and long, coiled glands
Predominantly surface mucous cells
What are pyloric glands?
In pyloric region
Deep pits and short glands
Mainly mucous neck cells that secrete lysozyme
What are the protective mechanisms of the gastric epithelium?
- Rapid turnover of surface epithelial cells ensures damaged cells replaced with healthy ones
- Epithelial cells secrete mucous that is bicarbonate rich to raise pH of surface cells and protect them from acid
- Mucous neck cells secrete mucous that lubricates chyme to prevent abrasion in peristalsis and gastric churning
**If these break down, erosion or ulceration of gastric mucosa can occur
What is the gastroduodenal junction?
Transition in mucosa from secretory to absorptive
Pyloric sphincter - thickening of middle circular layer of muscularis externa
Duodenal glands (Brunner’s glands) - in submucosa of duodenum and secrete bicarbonate mucus
