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Lecture 19

BIO210Y5 Lecture Notes - Lecture 19: Submucous Plexus, G Cell, Gastrin

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Sanja Hinic- Frlog

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Lecture 19B Notes – Digestive System Regulation
Liver bile production is key for lipid digestion
Cirrhosis of the liver is hardening of the tissue of the cells
oHepatocytes are dying faster than they can be replaced
If there is too much bile, you can have gall bladder stones they can block passageways in the digestive
Protein Digestion and Absorption
The low pH in addition to mixing of the stomach helps denature the proteins
Carbohydrate Digestion and Absorption
Inhibiting gastrin is important to decrease motility to decrease pH
Digestive system lets body know that you’re close to nutrient digestion so insulin needs to help deal with a lot
of sugar that is being absorbed (works with GIP)
Lipid Digestion and Absorption
Bile is important for lipid digestion
Gastrin, Secretin, GIP, CCK, and VIP
G cells in the pyloris of the stomach secrete gastrin and release it and also in the duodenum increases
stomach motility once the food has reached the stomach
Also stimulating gastric acid to lower the pH and other enzymes that help digestion of macromolecules
Once chyme reaches the duodenum multiple hormones and enzymes are released
Releasing GIP is a signal that body is close to nutrient absorption so body needs to deal with a lot of glucose
so insulin is released
Secretin and CCK buffer the system and produce bile
VIP dilates the capillaries around the digestive system to increase the surface are to take up as much nutrients
as required
Gastric secretion is divided into 3 different phases
Local Coordination
Phase 1 is cephalic phase emotional connection with food so your stomach is already becoming a favourable
environment for the food you are seeing
CNS activates the submucosal plexus that activates the muscles in your stomach and the chief cells, parietal
cells and mucous cells, and G cells to start doing their thing and start creating a favourable environment
The gastric phase is when you obtain the food
Subconsciously you are adding the stretch and the chemoreceptors food has reached the stomach so your
stomach has expanded
oThis process keeps going for 3-4 hours to make sure that you have the most effective digestion and
most effective environment for digestion
The last phase is the intestinal phase you’ve reached the small intestine from pyloric sphincter (duodenum)
oThe chyme is moving into the small intestine and CCK, GIP, and Secretin are activated to stop the
mixing and low pH to calm your stomach down (inhibition myenteric plexus)
Focused on bringing in enzymes that will help you digest and absorb the nutrients before they enter the
The duodenal stretch receptors prevent further movement of the stomach
CCK is the key once it is in the duodenum to releasing the bile from the opening that pancrease and gall
bladder share this emulsifies lipids
Parietal cell stimulation secretin release pH increases chief cell inhibition
Defecation Reflex
There are 2 different loops that control the movement of the feces into the rectum and the anal canal
There are 2 sphincters internal open the anal canal and external releases the feces
The short reflex loop is the stimulation of stretch receptors when the food reaches the rectum and you increase
local peristalsis when the myenteric plexus is stimulated
oInternal sphincter is relaxed and the feces goes through into the anal canal
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