Upper GI Tract Str and Fxn Flashcards
Overall the structure of the GI tract is conserved – what are the 4 tunics?
- Mucosa
- Submucosa
- Muscularis externa
- Adventitia/Serosa
What are three distinct layers of the mucosa?
- Epithelium
- Lamina propria
- Muscularis mucosae
What type of epithelium is present in the esophagus and anal canal versus the stomach, small and large intestine?
Stratified squamous non-keratinizing epithelium lines the esophagus and anal canal and serves to protect against abrasion
Simple columnar epithelium lines the stomach, small intestine, and large intestine and functions to secrete, absorb and protect
What is the function of the submucosa?
Layer of loose collagenous and adipose supporting tissue
Contains blood vessels and lymphatics
Innervated by submucosal (Meissner’s) plexus
What is the function of the muscular external?
It mixes luminal contents and propels contents along GI tract
What does the muscularis externa consist of?
Inner circular layer and outer longitudinal layer of smooth muscle (also skeletal muscle in the anal sphincter and esophagus)
Innervated by the myenteric (Auerbach’s) plexus between the muscle layers
What functions to protect and is the outermost covering of the GI tract?
The adventitia/serosa
What is the differences between adventitia and serosa?
Adventitia is loose connective tissue layer OUTSIDE the peritoneal cavity
Serosa is simple squamous epithelium WITHIN the peritoneal cavity
What is parasympathetic vs sympathetic function of the enteric nervous system?
Parasympathetic stimulates secretion and peristalsis
Sympathetic represses peristalsis and activates activity of sphincters
Which cells secreted hormones?
Enteroendocrine cells
What are the different types of mucosa throughout the GI tract?
- Protective: stratified squamous epithelium mainly found in the upper GI and anus
- Secretory: found in the stomach, contains an abundance of tubular glands
- Absorptive: mucosa is folded into villi to maximize surface area; throughout the small intestine
- Absorptive/protective: lines the large intestine; produces mucin to help fecal movement and absorb water
What are the 2 clusters of mucosal glands in the esophagus called that help to propel food by secreting mucus?
Esophageal cardiac glands – these are located in the mucosa layer
What are the two physiological sphyincters?
Pharyngoesophageal sphincter – prevents reflux from esophagus into the pharynx
Gastroesophageal sphincter prevents reflux from the stomach into the esophagus
What are the 4 anatomical regions of the stomach?
Cardia–small area at gastroesophageal junction
Fundus–secretes acid and enzymes
Body –secretes acid and enzymes
Pyloris–regulates release of chyme into duodenum (pyloric sphincter), secretes gastrin
Which cells secrete histamine in response to the vagus nerve to increase acid secretion?
Enterochromaffin-type cells
What are the three regions of a gastric gland?
Isthmus, neck and base
What are the 6 different types of cell types that can make up gastric glands?
- Surface mucous/lining cells (gastric pit)
- Parietal cells (isthmus, neck and base)
- Neck mucous cells (neck and base)
- Chief cells (base)
- Enteroendocrine cells (base)
- Stem cells (neck)
How does the mucous in surface lining cells differ from mucous neck cells?
Mucous in surface lining cells is thick and dense while the mucous secreted by mucous neck cells is soluble
Surface lining cell mucous adheres to the mucosa and protects against acid digestion while the soluble mucous lubricates the stomach contents to aid in digestion
What are enteroendocrine cells?
They secrete hormone-like substances into the lamina propria to influence the activity of nearby (paracrine) or distant (endocrine) cells.
Hormones secreted: Gastrin, serotonin, enteroglucagon, somatostatin, histamine
How are parietal cells identified?
Cytoplasm stains heavily with eosin
What do parietal cells have a lot of?
Mitochondria that provide the energy for HCl secretion
Where are chief cells located and what do they do?
Columnar cells at the bottom of gastric glands
Secretory granules contain proenzymes–pepsinogen, rennin, gastric lipase
Granule release controlled by hormonal and neural action (binding of secretin and vagus nerve stimulation)
Where are stem cells most commonly found?
In the neck of the gastric gland
How often are gastric mucosa cells regenerated?
Every 3 days
Which two parts of the stomach are histologically indistinguishable?
Fundus and body – straight tubular glands
What are the three phases of a stomach’s response to a meal?
Cephalic phase: brain anticipates (30% total gastric acid)
Gastric phase: food enters stomach, increase in G cell activity (60% total gastric acid)
Intestinal phase: chyme released into duodenum, enterogastric reflex, CCK and secretin suppress gastric activity (10% total gastric acid)
Where are “wandering cells” located in the stomach? Give some examples.
Submucosa
Lymphocytes, eosinophils, mast cells, and plasma cells. Also adipose tissue.
How many gastric glands open up into each gastric pit?
1 - 7
What does the mucosa in the pyloris and cardiac regions of the stomach look like?
Pyloris: glands are branched and mucous neck cells predominate
Cardiac: shallower gastric pits and glands are highly coiled, abundance of enteroendocrine cells