PBL 4 Flashcards
What are Haustrations?
Mixing movements that occur in the large intestine
Where the 3 longitudinal teniae coli contract at the same time
These call the unstimulated portion to bulge outwards into Haustrations
What is use of Haustrations?
Allow fecal matter to all be gradyllary exposed to the mucosal surface, allowing for absorption
What is a mass movement?
A modified type of peristalsis that occurs in the colon
Where are I cells found and what do they secrete?
Found in the small intestine, they secrete CCK
Name two incretin hormones?
Where are they secreted
GIP (gastrin inhibitory peptide) - dueodenum and jejunum
GLP-1 (glucagon like peptide 1) - small and large intestines
Where is motilin secreted?
In the duodenum and jejunum
How is motility in the gut controlled by the ENS by local reflexes?
Behind the bolus:
- Excitation of inner circular muscle - by Ach and substance P
- Inhibition of outer longitudinal muscle - by NO and VIP
In front of bolus
- Excitation of outer longitudinal muscle - by Ach and substance P
- Inhibition of inner circular muscle - by NO and VIP
What effect does noradrenaline have on the motility of the gut
Reduces motility
What is the effect of CCK on the sphincter of oddi?
CCK acts on local enteric nerves to cause release of inhibitory neurotransmitters NO and VIP to the sphincter of oddi
This causes the sphincter to relax, so bile and pancreatic juices can come through the ampulla of vater
How do enterochromaffin cells control GI tract motility?
Enterochromaffin cells are present in the GI tract and are stimulated by chemicals or mechanical touch
Enterochromaffin cells release 5-HT which plays a big role in contraction and relaxation of the gut wall
What neurotransmitter is released from enterochromaffin cells?
Serotonin
How do opiates lead to constipation?
Opiates act on Mu Receptors present in the GI Tract
This results in G protein activation which acts through second messengers to reduce nerve signals
Decreased excitatory nerve signals leads to a decrease in gut motility
Decreased gut motility leads to increased transit time so more water is absorbed, causing greater compaction of feces
How does Imodium relieve diarrhoea?
It is an opoid mu receptor agonist
Therefore acts to inhibit gut motility by decreasing the activity of the myenteric plexus
How do the external and internal anal sphincter differ in their control?
Internal sphincter - autonomically controlled
External sphincter - somatically controlled
What are the two reflexes in the defection reflexes mediated by?
Short reflex - ENS myenteric nervous system
Long reflex - vagus nerve
Why is the colour of feces brown?
Because of stercobilin and urobilin
What type of antibody is present on the simple coloumnar epithelium in the gut?
IgA
How can C.Diff infection be treated?
Fecal Transplant therapy
How does a healthy microbiome help in immunity
Gut bacteria stimulate the secretion of antimicrobial peptides from paneth cells
Where are stem cells found in the gut?
At the bottom of crypts in between paneth cells
What is gut associated lymphoid tissue?
Pop up lymph nodes within the gut which contain an abundance of immune cells
What is special about the dendritic and macrophage cells lining the gut epithelium
They are able to ‘sample’ bacteria, taking it into the lymph node to see if it is friendly or not
What is cell atrophy?
Cell shrinking?
What is the difference between cell hypertrophy and hyperplasia?
Hypertrophy - cell increase in size
Hyperplasia - increase in the number of cells due to cell division
