Week 11- Large Bowel Flashcards
What are the 4 parts of the colon?
Ascending
Transverse
Descending
Sigmoid
How does the transverse colon receive blood?
Via middle colic artery (branch of superior mesenteric)
How does the distal 3rd of the transverse colon receive blood?
Inferior mesenteric artery
Where are fatty tags found?
The peritoneum
Describe the muscle coat of the peritoneum
Has 3 thick longitudinal bands
What is the function of the large bowel?
Reabsorption of electrolytes & water, and the
elimination of undigested food and waste
How much water can the large bowel absorb?
4.5L (usually 1.5 L)
How is the rectum different to the large bowel?
Distinguished by transverse rectal folds in its submucosa and the absence of taenia coli in its muscularis externa.
What muscles are found in the anal canal?
Surrounded by internal (circular muscle) and external (striated muscle) anal sphincters.
Describe the mucosal structure of the large bowel
Similar to small bowel, enterocytes and goblet cells are abundant, crypts present where stem cells are found
Describe the mucosal layers of the large bowel
Mucosa
Submucosa
Muscularis (2 layers- circular and longitudinal muscles)
Serosa
Where are Meissener’s plexus found in the mucosal layers?
Submucosal plexus
How does the surface of the large bowel differ from the small bowel?
Has fewer villi (smaller surface area)
Enterocytes have some irregular villi that are mainly for salt reabsorption
How are crypts of the large bowel different to the small bowel?
They are dominated by goblet cells
How is water absorbed in the large bowel?
Passively- it follows electrolytes
Describe the distribution of goblet cells in the large bowel
Mainly in crypts, dont increase in abundance along the bowel , apical end filled with mucous granules
What stimulates goblet cells secretion?
Acetylcholine (parasympathetic and enteric nervous system)
Do you find paneth or enteroendocrine cells in the large bowel?
No
How does the glycocalyx in the large bowel differ to the small bowel? What is its function?
No digestive enzymes but does trap a layer of water and mucous (unstirred layer), serves as protection from digestional lumen yet allows for absorption. Regulates rate of absorption from intestinal lumen
Describe the muscle layers of the large bowel
Like the small bowel, muscularis externa consists of an inner circular and
outer longitudinal layer.
• Circular muscles segmentally thickened.
• Longitudinal layer concentrated in three bands- taenia coli
What is the tenia coli?
Longitudinal layer concentrated in 3 bands
Describe colonic contractions
Minimally propulsive, 5-10cm/hr