AS Lecture 7 - The Large Intestine Flashcards
What is the cecum?
Blind pouch just distal to ileocecal valve - larger in herbivores
What is the appendix?
Appendix is thin finger like extension of caecum - not physiologically relevant in humans
What are the functions of the colon?
Reabsorption of electrolytes and water Elimination of undigested food and waste
What is the structure of the colon?
1.5m long and 6cm in diameter Ascending: RHS, from cecum to hepatic flexure Transverse: hepatic flexure to splenic flexure, hanging off stomach from greater omentum Descending: from splenic flexure to sigmoid colon Sigmoid colon from descending colon to rectum
Where does the colon’s blood supply come from and what is a complication that can arise?
Proximal transverse colon uses middle colic artery
Distal third of transverse perfused by inferior mesenteric artery
Region between these two is sensitive to ischemia
What is the layout and features of the colon?
Peritoneum carries fatty tags and the muscle coat has 3 thick longitudinal bands (taeniae coli), the gut wall is pouched in appearance (haustra) Many nodules of lymphoid tissue
What is the function of Fatty tags/appendices epiploica?
May have protective function against intraabdominal infections
What is the function of the taenia coli?
Necessary for large intestine motility
What does the colon absorb and where?
Colon absorbs electrolytes and water, more in proximal colon Large intestine can reabsorb around 4.5 l
What is the rectum and what is its histology?
Dilated distal portion of alimentary canal Has transverse rectal folds in its submucosal and absence of taenia coli in its muscularis externa
What is the function of the transverse rectal folds?
Store the faeces until allowed to remove it - with sphincter under conscious control
Fill in the blanks of the general plan of the gut tube
How is the colon similar to the small intestine?
Enterocytes and goblet cells are abundant, as well as crypts Stem cells are also found in the crypts
How is the large intestine mucosal layer organised?
Mucosa is smooth as it has no villi (smaller SA) Enterocytes have Microvilli (short, irregular) and are concerned with reabsorption of salts Water is absorbed passively following the electrolytes
What are the levels of goblet cells like in the crypts of the large intestine?
Higher number of goblet cells, which increases the further down the gut, as it facilitates the passage of increasingly solid faeces Dominated by goblet cells
What is the abundance of Paneth cells and enteroendocrine cells in the colon?
None in colon, fewer enteroendocrine cells than in SI
What are the muscle layers of the large intestine?
Muscularis externa - consists of inner circular and outer longitudinal layer Cicular muscles segmentally thickened Longitudinal layer in taenia coli (in between layer is thin) Bundles of muscle from taeniae coli penetrate the circular layer at irregular intervals
How are the haustra distributed in the large intestine?
Shorter than circular muscle layers, Haustra can contract individually Apart from rectum and anal canal, they are substantial and continuous