Gastro Block 9: Response to infection and noxious substances

What are Peyer’s Patches?

• patches of tissue that sense and sample pathogens, antigens and particles within the gut lumen

Where are Peyer’s Patches found?

• located in the terminal ileum

• smaller versions are found in the colon

What are microfold cells?

• immune cells which transport bacteria, whole or antigen or particles and take them to the basolateral packet where they can be presented to underlying immune cells

Where are microfold cells found?

• found in follicle-associated epithelium in the gut

List the 7 resident immune cells of the gut muscosa:

1. macrophages

2. professional killing cells

3. recruited neutriphils

4. dendritic cells → initiate adaptive immunity by presenting antigens to T cells

5. mast cells → release histamines

6. T-lymphocyte populations

7. intra epithelial lymphocytes

If a pathogen is in the GI tract what happens?

• innervation in gut wall is stimulated so infectious agents are moved down bowel to be excreted

• mucus production is stimulated to make a barrier

• macrophages, neutrophils and dendritic cells encounter pathogen and present antigen to T cells

• adaptive immune response is activated → antibodies are made to combat pathogen

• IgA is produced by B cells

What are Paneth cells?

• specialised secretory epithelial cells found at base of crypts of Lieberkuhn

What is the function of Paneth cells?

• guard the gut by secreting antimicrobial peptides like alpha-defensins and lysozyme

• They provide critical niche signals (e.g., Wnt, Notch, EGF) to neighboring stem cells, enabling them to regenerate the intestinal lining

How many crypts are there per villus?

6-10

What signals cause damaged cells in the gut to endergo apoptosis?

• withdrawal of growth factors

• removal of nutrients

• removal of oxygen

• UV damage, chemo, viruses, inflammatory cytokines can cause apoptosis

List the steps of Apoptosis:

1. cell shrinks and blebs

2. DNA and mitochondria break down

3. inside of cell flips (cell membrane flips to show on the outside of cell)

4. immune surveillance cells are recruited to areas of inflammation and damage → immune cell engulf damaged cell

What mechanism prevents gaps in the GI barrier during shedding?

Zipper mechanism prevents gaps in the barrier and maintains barrier integrity and function when cells shed

What type of reflex is the vomiting reflex?

• involuntary reflex

How does the vomiting reflex get triggered?

• if the stimulus reaches a point strong enough to pass threshold potential and generate an action potential at the cells that lie within the vomiting centre, then you will be sick.

Where is the vomiting centre found in the brain?

Vomiting centre is in the medulla oblongata and lower pons regions of the brains stem

From which 4 areas does the vomiting centre receive signals from?

• gut

• higher brain

• blood

• CSF

What external influences can trigger the vomiting reflex?

• irritants in GI tract

• alcohol

• drugs

• allergens

• molds

• radiation

• physical bloating

What internal influences can trigger the vomiting reflex?

• motion sickness

• visual signs

• touch

• fear

• hormonal imbalances e.g. pregnancy

Describe the signals sent from the vomiting centre in the brain to the effectors:

• efferent response is relayed backdown to diaphragm + intercostal muscles + gut

• travel down PHRENIC nerve to diaphragm → contracts

• travel down VAGUS nerve to duodenum → contracts pyloric canal + antrum so food cannot go further down

• travel down vagus nerve to LOS to UOS + pharynx → relaxation of muscle

Where are contraction signals sent to?

1. diaphragm

2. pyloric canal

3. antrum

4. intercostal muscles

Where are relaxation signals sent to?

• LOS

• UOS

• oesophagus

• pharynx

What stops vomit from entering the lungs?

• Soft palate is raised

• epiglottis is moving over the trachea to prevent vomit coming out of your nasal passages or going into your lungs.