4. Anatomy Flashcards
What are the 4 layers of the GI tract, from innermost to outermost?
Mucosa, submucosa, external muscle layers, serosa.
What 3 layers does the mucosa of the GI tract contain? Give 2 functions of each layer.
Epithelial layer - selectively permeable barrier, facilitated transport and digestion of food, promotes absorption, produces hormones, produces mucus.
Lamina propria - contains lymphoid nodules and macrophages, produces antibodies (mainly IgA which is resistant to proteases) to protect against bacterial and viral invasion.
Muscularis mucosae - layers of smooth muscle orientated in different directions keeps epithelium in contact with gut contents and helps keep crypt contents dynamic..
What does the submucosal layer of the GI tract contain?
Dense connective tissue, blood vessels, glands, lymphoid tissue, submucosal (Meissner’s) plexus.
What does the external muscular layer of the GI tract contain?
Inner circular muscle, myenteric (Auerbach’s) plexus, outer longitudinal muscle.
What does the serosal layer of the GI tract contain?
Blood and lymphoid vessels and adipose tissue.
What is the serosal layer of the GI tract continuous with?
Mesenteries.
What type of epithelium is found in the oesophagus and distal anus?
Stratified squamous epithelium.
What type of epithelium is found lining the whole GI tract except the oesophagus and distal anus?
Simple columnar.
What is an enterocyte?
A simple columnar cell.
Where in the GI tract are enterocyte the predominant cell?
Small intestine and colon.
What two layers do enterocytes need to transport nutrients through? Therefore what lies immediately below the enterocyte?
Apical membrane and basolateral membrane.
Blood vessels and lymphatics.
What is found on the surface of enterocytes?
Microvilli.
Where are goblet cells found?
Scattered in between enterocytes, increasing in number from the duodenum to the colon.
Give 2 reasons why goblet cells secrete mucus into the GI tract.
Act as a lubricant to reduce friction.
To protect against chemical damage due to acidity.
To form a physical barrier to protect against bacterial inflammation.
What cells are found lining the gastric mucosa and gastric pits? What do they secrete?
Gastric surface mucous cells (foveolar cells).
Secrete mucus/HCO3 that forms a barrier to stomach acid.
Where in the GI tract are villi found?
Small intestine.
Where in the GI tract are crypts found?
Small intestine and colon.
Crypts contain specialised cells including stem cells. Where in the crypt are they located and what is their function?
Base of crypts.
Constantly divide to replace epithelia every 2-4 days.
Crypts contain specialised cells including paneth cells. Where in the crypt are they located and what is their function?
Base of crypts.
Secrete antibacterial proteins to protect the stem cells.
Crypts and gastric glands contain specialised cells including enertoendocrine cells. Where in the crypts are they found and what is their function?
Between enterocytes deeper in the crypts and gastric glands.
Secrete hormones such as gastrin, cholecystokinin and secretin, that control the function of the gut.
What is the role of gastrin?
Peptide hormone that stimulates secretion of gastric acid.
What is the role of cholecystokinin?
Causes the release of digestive enzymes from the pancreas and bile from the gallbladder.
What is the role of secretin?
Secretin helps regulate the pH of the duodenum by inhibiting the secretion of gastric acid from the stomach and stimulating the production of bicarbonate from the pancreas.
What disease causes crypt alteration, cryptitis and crypt abscesses (neutrophils in lumen)?
Inflammatory bowel disease
