Organ-specific immunity: GUT - Anatomy Flashcards
Name three distinctive features of the mucosal immune system
- Anatomical feature
- Effector mechanism
- Immunoregulatory environment
Where can you find mucosal tissue?
Lung and gut
Where can you find epithelial tissues?
- Lung
- Gut
- Vagina
Name three anatomical features of the mucosal immune system
- Interaction mucosal epithelia and lymphoid tissue
- Discrete compartments lymphoid tissue/organized structures such as PP
- Specialized antigen-uptake mechanisms
What is special about the lymph nodes in the gut?
Lymph nodes are quite far out–> cells have to travel far
What is an example of the specialized antigen-uptake in the gut?
M cells –> allow for selective uptake of antigens
Name two effector mechanisms of the mucosal immune system
- Activated/memory T cells predominate even without infection
- Memory T cells have a slightly more activated phenotype
Name two examples of the immunoregulatory environment of the mucosal immune system
- Active down regulation of immune responses predominates
- Inhibitory macrophages and tolerance inducing DCs
Why do the memory T cells have a slightly more activated phenotype?
Lamina Propria is full of memory cells, which are needed to respond to the exterior
What is the function of Tregs?
Maintaining tolerance to harmless exogenous antigens
Name the intestinal segments of the small intestine
- Stomach
- Duodenum
- Jejunum
- Ileum
What is the function of the stomach?
Stores, stirs and mixes food with gastric juices it secretes before emptying it into the duodenum
What is the function of the duodenum?
Anterior section of small intestine; secretions from liver and pancreas are added
What is the function of the jejunum?
Middle section of small intestine; majority of nutrients are absorbed here
What is the ileum?
Terminal part of small intestine
What are the intestinal segments of the colon?
- Cecum
- Vermiform appendix
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Anus
What is the function of the cecum?
Anterior part of the large intestine, receives food particles from the ileum
How is the gastric acid from the stomach neutralized in the duodenum?
By glands that make alkaline substances
What is the function of the vermiform appendix?
Tubular extension of the cecum; blinde darm
Vermiform appendix doesn’t really serve a purpose anymore
What is the function of the ascending colon?
First segment of the colon; absorbs water from food residues before it is secreted
What is the function of the transverse colon?
Second segment of the colon. Right colon mainly enables absorption of water
Which segments of the colon form the right colon?
- Ascending colon
- 1/2 of the transverse colon
What is the function of the descending colon?
Third segment of the colon; stores waste before elimination
What is the function of the sigmoid colon?
Fourth segment of the colon; carrier waste to rectum
What is the rectum?
Terminal section of large intestine preceding the anus
What is the function of the anus?
Terminal orifice of the digestive tube controlled by a sphincter enabling ejection of fecal matter
Which parts of the colon are involved in excretion of fecal matter?
- Sigmoid colon
- Rectum
What is the function of tight junctions in the gut?
Zipper between cells to make sure there is really a barrier to the exterior
Where are the majority of the nutrients absorbed in the intestine?
Jejunum
Where can we find the lymphoid structures in the gut?
Peyers Patches
Where are the Peyers Patches situated?
Directly underneath the epithelium
How do DCs and T- and B cells interact with each other in the Peyers Patches?
DCs migrate to T cell area within the patch to initiate a T cell response and subsequently a B cell response in the B cell area
What makes Peyers patches different from colonic patches?
PP have an organized structure of T- and B cell areas
Which immune cells are present in the other parts of the lamina propria?
Memory T- and B cells, macrophages, monocytes and DCs
Why are the immune cells in the lamina propria of the different parts of the intestine different from each other?
They are adapted to the sight they are in
What does IEL mean?
Intra-epithelial lymphocytes
Where are IEL situated?
In between the epithelial cells of the small intestine
What is the function of IEL?
Barrier function of the epithelium
Where do the lymphatics of the lamina propria drain to?
Mesenteric LNs
Will all the mucosal tissue see the same type of antigen?
No.
What type of antigens travel through the small intestine?
- Food proteins
- Bacteria
What can said about the overall bacterial load and diversity of bacteria in the small intestine?
Both are lower
What type of antigens travel through the large intestine?
Bacteria
Which part of the small intestine already contains a higher bacterial load and increased diversity?
Ileum
Which part of the intestine contains the highest bacterial load and diversity?
Colon
Histology: characteristics of the duodenum (2)
- High leaf-like villi
- Brunner glands in submucosae
What is the function of these Brunner glands?
Anti-acid function
Histology: characteristics of the jejunum (4)
-High folds
- High villi that decrease in height closer to the ileum
- Crypts become deeper closer to the ileum
- No glands
Histology: characteristics of the ileum (3)
- Fewer to no folds
- Villi decrease in length
- Increasing lymphoid tissue
Histology: characteristics of the colon (4)
- No folds
- No villi
- Deep crypts
- Lymphoid follicles
Why do we have high leaf-like villi and folds in the duodenum and part of the jejunum?
Surface enlargement for nutrient uptake
Why does the colon not have villi?
No surface enlargement is needed
Why do you need muscle in the intestine?
Peristaltic movement
How long does regeneration from crypt to tip of the villus take?
36h
How long does it take to renew the epithelium of the whole GI-tract?
2-4 days
To what does the term ‘lamina propria’ refer to?
All the tissue that’s under the epithelial layer except for the PP
What are crypts?
Basis of where the villus starts to form (sites where you have the stem cells of the epithelium)
Why do we have microvilli?
To avoid direct attachment of bacteria to the epithelium
True or false: “If you don’t see regularity of the crypts , something is totally off in the intestine”
True. The crypts need to be very well organized in the colon
What is happening in the colon if you don’t see regularity of the crypts?
Tissue distruction
What are the subtypes of the epithelial cells in the intestine? (2)
- Goblet cells
- Paneth cells
Where can you find paneth cells?
Only in the small intestinal crypts
Whatis the function of goblet cells?
Mucus production
What structure can be found in paneth cells and what is their function?
Granules filled with anti-microbial substances –> keep the crypt clean of bacteria
What is an unique feature of paneth cells opposed to other epithelial cells?
Paneth cells can sense what is seen to activate TLR/PRR if it can’t get rid of it itself
What tissues are included in GALT?
Tissue directly under the epithelium:
- Peyers patch
- Colonic patch
- Isolate lymphoid follicles
Do mesenteric LNs fall under the associated-lymph node tissue nomenclature?
No. They are just lymph nodes
What is the function of the dome area in the PP?
Contains the DCs, picks up antigens –> migration to the T cell area
Which cells are mainly present in the dome area of the PP?
Phagocytes, DCs
What is meant with ‘regional adaptation of lymph nodes’?
