General Pattern of GIT and Histology of the Pharynx & Oesophagus Flashcards
What are the four principal tissue layers of the GI tract?
Mucosa
Submucosa
Muscularis externa
Serosa/Adventitia
What are the functions of the mucosa?
Secretion (mucus, enzymes, hormones)
Absorption
Protection
What are the two layers of the muscularis externa?
Inner circular layer
Outer longitudinal layer
What is the submucosa composed of?
Dense irregular connective tissue with blood vessels, lymphatic vessels, nerves, and submucosal glands (in esophagus and duodenum).
What are the three components of the mucosa?
Epithelium
Lamina propria (connective tissue)
Muscularis mucosae (smooth muscle)
What is the role of Meissner’s plexus?
It regulates the activity of glands and smooth muscles in the submucosa.
What is the function of Auerbach’s plexus?
It controls GI tract motility (peristalsis).
What is the difference between serosa and adventitia?
Serosa: Covers organs within the peritoneal cavity (simple squamous epithelium + connective tissue).
Adventitia: Found where the GI tract is attached to adjacent structures (fibrous connective tissue).
What type of epithelium lines the esophagus?
Non-keratinized stratified squamous epithelium.
What is unique about the muscularis externa in the esophagus?
It transitions from skeletal muscle (upper 1/3) to mixed (middle 1/3) to smooth muscle (lower 1/3).
What is the function of esophageal glands proper?
They secrete mucus to facilitate food transport and protect the mucosa.
What are the three histological regions of the stomach?
Cardia
Fundus/Body
Pylorus
What are the main cell types in gastric glands and their secretions?
Parietal cells: HCl and intrinsic factor.
Chief cells: Pepsinogen.
Mucous neck cells: Mucus.
What is the function of rugae in the stomach?
They allow the stomach to expand and increase surface area for digestion.
What is the role of Brunner’s glands in the duodenum?
They secrete alkaline mucus to neutralize stomach acid.
What structures increase the absorptive surface area in the small intestine?
Plicae circulares
Villi
Microvilli
How does GERD lead to metaplasia in the esophagus?
Chronic acid reflux causes the stratified squamous epithelium to transform into columnar mucous-secreting epithelium (Barrett’s esophagus), increasing cancer risk.
How do NSAIDs damage the stomach lining?
They suppress protective prostaglandins and allow acid to damage the lamina propria.
What are the four types of glands in the GI tract?
Simple cellular glands (e.g., goblet cells).
Mucosal glands (in lamina propria).
Submucosal glands (e.g., esophageal and Brunner’s glands).
Extramural glands (e.g., pancreas, liver).
How does the autonomic nervous system regulate GI activity?
Parasympathetic (vagus): Stimulates secretion and motility.
Sympathetic: Inhibits digestion.
What is the significance of fenestrated capillaries in the mucosa?
They facilitate rapid absorption of nutrients into the bloodstream.
Why does the esophagus have lymphatic nodules in its lamina propria?
To provide immune defense against pathogens ingested with food (part of GALT—Gut-Associated Lymphatic Tissue).
Why does the muscularis externa of the esophagus transition from skeletal to smooth muscle?
Upper 1/3 is under voluntary control (swallowing), while lower 2/3 is involuntary (peristalsis).
What is the muscularis mucosae, and how does it function?
A thin layer of smooth muscle beneath the lamina propria; its contraction aids in local movement of the mucosa to enhance secretion/absorption.
