small bowel Flashcards
- What is the general function of the small bowel?
- Approximately, how long is the small bowel and what is its diameter?
To absorb nutrients, salt and water
6m long 3.5cm in diameter
- What are the functions of the mesentery?
Suspends small and large bowel from the posterior abdominal wall, anchoring them in place whilst still allowing some movement
Provides a conduit for blood vessels, nerves and lymphatic vessels
it is also a fat store
- What are the functions of the mesentery?
Suspends small and large bowel from the posterior abdominal wall, anchoring them in place whilst still allowing some movement
Provides a conduit for blood vessels, nerves and lymphatic vessels
- What are the 3 main regions of the small intestine/bowel?
- What are the 6 layers of the small intestine from superficial to deep?
Duodenum , Jejunum , Ileum
Serosa, longitudinal muscle layer, circular muscle layer, submucosa, mucosa, lumen
- What innervates villi?
- How thick is the epithelium of villi what what cells are they dominated by?
Innervation from submucosal plexus (part of the enteric nervous system)
1 cell thick (dominated by enterocytes - simple columnar absorptive cells)
two features of the villi?
motile
have a rich blood supply and lymphatic drainage for absorption of digested nutrients
- What are villi (mucosa) lined with?
Simple columnar epithelium consisting of:
Primarily enterocytes Scattered goblet cells Enteroendocrine cells (hormone secreting cells eg GLP-1, serotonin)
- What types of cells does the epithelium of the Crypts of Leiberkuhn include?
- What is the most abundant type of cell in the small bowel?
Paneth cells (secretory cells- antimicrobial peptides and proteins) Stem cells
Enterocytes (tall columnar cells with microvilli and a basal nucleus)
- What are enterocytes cells specialised for and what are their lifespans?
- What is the cylindrical internal surface area of the small bowel?
- What increases the surface are of the small bowel and by how much?
Absorption and transport of substances
1-6 days (relatively short)
0.4m^2
Villi and microvilli
~500 fold ^
- What structure makes up the ‘brush border’?
- What is glycocalyx?
Microvilli - several thousand microvilli per cell
Rich carbohydrate layer on apical membrane of microvilli
- What is the purpose of glycoalyx?
- What is the “unstirred layer”?
Covers surface of microvilli
Serves as protection from digestional lumen yet allows for absorption
Traps a layer of water and mucous → regulates rate of absorption from intestinal lumen
- What is the second most abundant epithelial cell type?
- What is mucous and what does it do?
Goblet cells
Large glycoprotein that facilitates passage of material through bowel
- What happens to the number of goblet cells along the entire length of bowel?
Abundance increases along entire length of bowel
Low in duodenum and high in colon As more lubrication is needed further down the system
- What classification of epithelial cells are enteroendocrine cells and where are they most often found?
- What is the function of enteroendocrine cells?
Columnar epithelial cells
Lower parts of crypts
Hormone secretion for example to influence gut motility
- What do enteroendocrine cells have a high affinity for in terms of staining?
Chromium/silver salts (hence being called chromaffin cells in older textbooks)
- Where are Paneth cells exclusively found?
Bases of crypts
- What do Paneth cells contain that are important for their functions and what are some of these functions?
Large, acidophilic granules containing anti-bacterial lysozyme (protects stem cells) and glycoproteins and zinc (essential trace metal for a number of enzymes)
Engulf some bacteria and protozoa May have a role in regulating intestinal flora
- Why are epithelial stem cells essential in the GI tract?
- where do their daughter cells go
To continually replenish the surface epithelium as cells such as enterocytes have a very short life span
They continually divide by mitosis and migrate to the top of villus, replacing older cells that die by apoptosis → digested and reabsorbed
differentiate into various cell types (pluripotent)