Small Bowel Flashcards
What is the function of the small bowel?
To absorb nutrients, salt and water
What are the dimensions of the small bowel?
Approx. 6m long & 3.5cm in diameter.
Which artery supplies the jejunum and the ileum?
Superior mesenteric artery
What are the two functions of the mesentery?
Suspends small & large bowel from posterior abdominal wall
anchoring them in place
whilst still allowing some movement
Provides a conduitfor blood vessels, nerves & lymphatic vessels.
Which part of the GI tract is the only place where villi are found?
In the small intestine
Which nervous plexus innervate the villi?
Submucosal plexus - meissners plexus
Which cell type are the villi of the small bowel dominated by?
dominated by enterocytes (columnar absorptive cells)
Which cells do the crypts of Lieberkühn - epithelium include?
Stem cells
Paneth Cells
Where are the Crypts of Lieberkühn found?
In the base of the epithelial villi
What are villi mucosa lined with?
Simple columnar epithelium consisting of:
primarily enterocytes (absorptive cells) scattered goblet cells enteroendocrine cells
What is the life span of an enterocyte?
1-6 days
Which are the most abundant cell in the small bowel?
Enterocytes
What is the purpose of the villi on the enterocytes?
To increase the surface area for absorption by at least 500 fold
What are enterocytes specialised for?
Specialised for absorption & transport of substances.
What structures make up the brush border?
Microvilli
What is the surface of the microvilli covered in?
Glycocalyx
What is the glycocalyx?
A rich carbohydrate layer on the apical membrane which serves as protection from digestional lumen yet allows for absorption
What does the gllycocalyx trap?
An unstirred layer
What is the unstirred layer?
a layer of water and mucous which helps to regulate the rate of absoprtion from intestinal lumen
Which side of the goblet cells fo mucus containing granules accumulate on?
The apical end - this causes the goblet shape to form
What is mucous?
A glycoprotein which helps to facilitate the passage of material through the bowel
What happens to the abundance of goblets cells along the length of the bowel?
increased - abundance of goblet cells along entire length of bowel
Low in duodenum, higher in colon
Where are most enteroendocrine cells found?
found in lower parts of the crypts
What do enteroendocrine cells secrete?
Hormones to influence gut motility eg histamine
Where are paneth cells found?
At the bases of crypts
What do paneth cells contain?
Large, acidophilic granules
What do the granules in paneth cells contain?
antibacterial enzyme lysozyme (protects stem cells)
Glycoproteins & zinc (essential trace metal for a no. of enzymes)
Which cells in the small bowel engulf bacteria and protozoa?
Paneth cells
Why are epithelial stem cells essential in the GI tract?
Epithelial stem cells are essential in the GI tract to continually replenish the surface epithelium