Physiology 3120 Lecture Notes - Lecture 61: Ileocecal Valve, Enteric Nervous System, Ileum
2 May 2018
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Human Physiology Lecture 61
Gastrointestinal Physiology- Large Intestine
- Function: finish absorption & produce vitamins & form feces
Large Intestine
- Ileum connects to the large intestine
- Ilocecal valve, which prevents the back flow of large intestine contents into the ileum
o Do not want to have bacteria laid in contents because bacteria love to live in large intestine
▪ DON’T WANT IT COMING BACK INTO THE SMALL INTESTINE
o Gatekeeper!
- Note: there are bacteria that live in the stomach, but we do not want it there (bad bacteria-H. pylori)
- If there is an over growth of bacteria in the small intestine (there is some bacteria in the small
intestine) leads to disease affecting the function of the small intestine
- VERY good to have a huge microbiome within our large intestine
o We thrive when we have more bacteria present in the large intestine
- Appendix
o Finger like projection
o Size dependent on the individual (variable)
o Need it BUT we can live without it
▪ Do better digestively when you have it – prefer to keep it
o Part of the immune system, contains a lot of bacteria ready to repopulate our large intestine
if necessary
- Transverse, ascending, descending colon
- Haustra = bubble like structures where the circular muscle is more contracted and then relaxed, then
contracted
o Individual bubbles
o DO NOT HAVE THIS IN THE SMALL INTESTINE
- As the contents of your large intestine pass from haustra to haustra, the contents will flip and turn as
it moves forward due to the ridges that force the content to move around as they exit one haustra to
the next
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Large Intestine Motility
- Due to the haustra we have special motility pattern that happens in the large intestine and not any
other region of the digestive tract
- Gastroileal Reflex
o Presence of food in the stomach stimulates the opening of the ileocecal valve
▪ Upper digestive tract in your stomach, if you have eaten a meal, it will trigger the
valve to open
▪ If we have contents within the small intestine still remaining, these products can
easily exit the small intestine to the large intestine permitting the small intestine to
receive the next meal
▪ = enteroenteric reflex (one part of the digestive tract triggers another part of the
digestive tract to do something different)
• Can be contained within the digestive tract neurons (enteric nervous
system) – does not have to reflex to the CNS
o Do not want the large intestine contents from going into the small intestine
▪ Ilececal valve is triggered to open at the right time
- Gastrocolic Reflex
o Reduces in its ability to due it as an adult and older children
o Strong reflex as a baby
▪ When a baby eats food, the colon is stimulated to empty
▪ Baby produces poop as soon as it eats
- Haustral Churning
o Mixing of large intestine contents from one haustra to the next
o As you are flipping the contents, it allows for maximal absorption of water, that the large
intestine needs to absorb
▪ We absorb water in the small intestine BUT the chyme that gets into the large
intestine is very liquefied – we want to keep the water content
▪ Main job of large intestine: absorb the water BUT not too much, it leads to problems
in removing the chyme (constipation)
• Good balance of absorbing the right amount of water through the action of
haustral churning
- Peristalsis & Mass Peristalsis
o Unidirectional movement of lumen contents out of the large intestine
o Peristalsis pushing from ascending, transverse, to descending colon
o Mass peristalsis = forceful contraction to allow for the evacuation of the large intestine
contents
▪ Feeling you get that you should visit the bathroom
Bacteria of the large intestine
1. Fermentation of undigested carbohydrate: bacteria ferment undigested carbohydrates in the chyme
o Gas byproducts produced including hydrogen, carbon dioxide, methane
▪ Some individuals have the ability to produce methane BUT not everyone does
▪ Different bacteria composition is important for the different types of byproducts
due to fermentation
▪ These gases contribute to flatus in the colon
find more resources at oneclass.com
find more resources at oneclass.com
