8.6: The Large Intestine Flashcards
(30 cards)
Name the key structures of the large intestine
Cecum
Appendix
Ascending colon
transverse colon
descending colon
sigmoid colon
rectum
anal canal
How does the large intestine mix contents?
Haustral contractions undergo the segmenting of contents
What is the function of goblet cells in the large intestine?
They secrete mucus to lubricate feces and protect the epithelium
What is absorbed in the large intestine?
Water, electrolytes, short chain fatty acids
What is the role of bicarbonate ions in the colonic epithelium?
to neutralise acidic bacterial products
How is water absorbed in the colonic epithelium?
It is absorbed osmotically with Na+ and Cl-
How are short chain fatty acids absorbed in the colonic epithelium?
via monocarboxylate transporters, which are important for colonocyte energy
How is sodium and chloride absorbed in the colonic epithelium?
Na+ is actively absorbed via epithelial sodium channels
Cl- passively follows sodium absorption or exchanged with bicarbonate
What is the role of colonic bacteria in fermentation?
colonic bacteria ferments carbs and fiber, to produce short chain fatty acids like acetate, propionate and butyrate
What are the primary functions of the large intestine?
storage of faeces before defecation and drying by removing liquid and leaving solid faecal matter
What does faeces consist of?
fluid and solids, including bacteria, mucus, undigested fibre, unabsorbed biliary components, fat
What are haustra?
pouches of the colon ceen from the caecum to the rectum
What are taeniae coli?
3 separate bands of longitudinal muscle that are gathered into haustral pouches
Where is the myenteric plexus located?
beneath the taeniae coli
What does the histology of the large intestine consist of?
mucosa, submucosa, muscularis externa, but no villi
What does the lack of villi mean for the large intestine?
It has a lower surface area
What are the two types of movements in the large intestine that allow motility, describe them
Haustral contractions - slow segmenting movements that occur in the haustra that aid in the absorption of water and electrolytes
mass movements - peristaltic waves waves that propel faecal matter over longer distances, occurring 1-3 times a day, facilitating the elimination of waste from the colon
How are haustral contractions initiated?
by the colonic pacemakers signaling to smooth muscle cells
What are some qualities of haustral contractions
segmental
slow
non-propulsive
How is the large intestine’s motility regulated by intrinsic innervation?
Via the myenteric plexus concentrated beneath the taenia coli, through the enteric NS, coordinates local reflexes within the intestinal wall including peristalsis and segmentation
How is the large intestine’s motility regulated by extrinsic innervation?
It involves parasympathetic fibres from the vagus nerve and sympathetic fibres from the spinal cord, which influence enteric neuron activity and smooth muscle contraction by coordinating responses to stimuli like food intake/stress
What does the interplay between intrinsic/extrinsic innervation allow?
efficient movement/processing of faecal material through large intestine
What is the gastrocolic reflex
a physiological response characterised by the stimulation of colonic motility following ingestion of food
List the steps of the gastrocolic reflex
- food enters the stomach
- release of gastrin and activation of the extrinsic autonomic nerves
- stimulation of colon motility
- pushes contents into rectum, urge to defecate
