Lecture 22: THE SMALL INTESTINE Flashcards
What are the regions of the small intestine (in order)?
Duodenum, jejunum and ileum
What is the largest region of the small intestine?
Ileum
What is the total length of the small intestine?
About 6m
Where is the initial segment of the small intestine?
Retroperitoneal
What is the small intestine held in place by?
Mesentery
What does the mesentery allow?
Movement, but prevents the small intestine from getting tangled
What does the mesentery contain?
Arteries, veins, nerves and lymphatics
What is delivered to the small intestine?
Chyme which is acidic
What is needed because of chyme being acidic?
Protect the epithelium and neutralise pH
How is the epithelium protected?
By mucous secreting cells and glands in the submucosa (specifically in the duodenum)
How is pH neutralised?
By bicarbonate (HCO3-) from the pancreas
What are plicae circulares?
Permanent folds of the small intestined
What is the structure of plicae circulares?
Core of submucosa with overlying mucosa
Where are villi found?
On the surface of the plicae circulares
What does the muscularis mucosae allow?
Villi to wiggle back and forth
What are villi?
Folds of the mucosa
What is the core of each villus?
FCT (lamina propria)
What do villi contain?
Vessels
What vessels do villi contain?
Lymph lacteal and capillary network
What is drained into the lymph lacteal?
Products of fat digestion
What is drained into the capillary network?
Products of protein and carbohydrate digestion
What enters the mesenteric veins?
Nutrient rich, deoxygenated blood absorbed in the small intestine
What do mesenteric veins drain into?
Hepatic (liver) portal vein
What do lymph lacteals drain into?
The cisterna chyli, thoracic duct and then left subclavian vein
What is the epithelium of the small intestine?
Simple columnar
What is on the apical surface of the small intestine cells?
Microvilli to increase the surface area further
What do microvilli form?
A brush border
What is glycocalyx?
A network of glycoproteins and branched filaments
What does the glycocalyx do?
Tether enzymes
What does contact digestion involve?
Enzymes attached to the brush border
What is the plasma membrane?
A barrier which is selectively permeable (lipid soluble things can travel through it)
What does the plasma membrane have?
Proteins (channels and transporters)
How are tight junctions described?
Very tight
What junctions are between small intestine epithelial cells?
Tight junctions
What may diffuse through tight junctions?
Small molecules (down a concentration gradient)
What are the cells of the small intestine epithelium?
Enterocytes, goblet, stem, paneth and endocrine
What are enterocytes?
Absorptive cells which have a microvilli brush border
What do goblet cells do?
Secrete mucous for protection
What do stem cells do?
Make all cell types
What do paneth cells secrete?
Granules and antibacterial enzymes
What do endocrine cells do?
Secrete hormones
What is found in an intestinal crypt?
Paneth cells at the base, stem cells above and epithelial cells further above
