GI 3 Flashcards
What do the barriers in the GI tract function to do?
protect the GI tract
Physical Barrier in the GI tract
mucus layer, formed by the mucins from Goblet cells in the intestinal epithelium
Junctions b/n cells in the intestinal epithelium?
tight junctions
Paneth cells
secrete AMP (antimicrobial peptides) into the intestinal lumen and acts as a chemical barrier
Digestive secretions
gastric acid, saliva, and bile can act as a barrier in the GI tract
Largest immunological compartment in the body?
GI tract
Two Types of Immune System
- Innate
- Adaptive/Acquired
Innate Immune Systems
broad specificity, first line of defense
includes macrophages, dendritic cells, and intestinal epithelial cells
Adaptive Immune System
specific to antigen; have to be induced
Intraepithelial Lymphocytes
adaptive immune cells present in the intestinal epithelium [and lamina propria]; lymphatics drain to the mesenteric lymph node
Peyer’s Patches
aggregated follicles of lymphoid nodules; contain lymphocytes (naive B and T cells)
M cells
microfold cells; uptakes antigen at epithelial surface (lumen) and presents antigen to B and T cells, which are transported to mesenteric lymph node and undergoes differentiation
Gut-Associated Lymphoid Tissue (GALT)
includes intraepithelial lymphocytes, lymphocytes in the lamina propria, andlymphoid nodules (isolated or aggregated)
What is an aggregated patch of lymphoid nodules called?
Peyer’s Patch
Gut Microbiota Functions (4)
- Support digestion and absoprtion
- Maintain intestinal mucosa barrier
- Shape the host immune system
- Prevent colonization by pathogens
How much more bacteria is encoded in bacteria vs. the host?
100 times more
Dysbiosis
an imbalance (either in number or type) of microbial communities that are associated with a disease outcome
Examples of Diseases that can cause Dysbiosis (4)
- Necrotizing enterocolitis
- IBD
- IBS
- GI cancer
What are the three ways dysbiosis can have distant effects?
produce metabolites, stimulate cytokine secretion, or secrete pathogen associated microbial peptide into the blood
Organs possibly affected by dysbiosis
heart, liver, brain, prostate, kidney, lung, islet cells
Gut-Brain Axis
considered potentially relevant in diseases such as Parkinson’s and Alzheimer’s
Intestinal Dysbiosis in Animals can affect what? (3)
- Animal Health
- Production
- Food Safety
6 Factors that control Microbiota Composition
- Maternal Effect
- Host Genetics
- Diet
- Antibiotic Use
- Fasting (incl. travel stress)
- Age
How can we improve disease prevention and treatment with the gut microbiota?
probiotics, or prebiotics based treatment
fecal transplants
3 Sensory Systems responsible for detecing changes in/near GI Wall
- Neural sensation
- Endocrine
- Immune
4 Effector Systems
- Nervous System
- Endocrine
- Immune System
- Non-Immune Defense System
Motility
contraction and relaxation of the wall and sphincters of the gastrointestinal tract
3 Functions of GI Motility
- Break up food and mix it with secretions
- Propel food bolus
- Retain ingested food at specific points for digestion, absorption, or storage
unitary smooth muscle
gap junctions between individual smooth muscle cells to spread the electrical signal very quickly and helps with synchronous contractions (grouped into branching bundles)
Interstitial Cells of Cajal
cells closely associated with the motor neurons of the GI tract and connect to ICCs and SMCs via gap jxns
Pacemaker of the GI Tract?
Interstitial Cells of Cajal
Do interstital cells of Cajal have neurotransmitter receptors?
yes - can get signals from motor neurons for contraction
Slow Wave (Basic Electric Rhythm)
oscillating depolarization and repolarization of the [resting] membrane electric potential in the smooth muscle
If there are more negative ions inside the cell than outside the cell, is the membrane potential positive or negative?
negative
Can basic electric rhythm generate phasic contractions?
No, only weak contractions - it needs contribution of action potentials from other timuli (ex: motor neurons) to reach threshold
Origin of basic electric rhythm?
Interstitial Cells of Cajal (the pacemaker)
What controls the contractile parameters of frequency, propagation velocity and direction?
slow wave (basic electric rhythm)
Basic Electric Rhythm
Slow Wave
Slow Wave
Basic Electric Rhythm
Do slow waves require neural or hormonal input to occur?
No, they’re independent
Effect of Excitatory Molecules on Slow Wave
elevates baseline membrane potential and increases the chance of an action potential
Are slow waves consistent throughout the entire GI tract?
no
What part of the GI tract has the lowest BER frequency?
stomach
2 Types of Contractions
- Tonic (sustained)
- Phasic (rhythmic)
What type of contraction can occur without an action potential?
tonic contraction
Tonic contraction
maintain constant level of weak contraction w/o regular periods of relaxation (minutes to hours)
Examples of Tonic Contractions in the GI (5)
lower esophageal sphincter, pylorus, fundus/body of stomach, ileocecal sphincter, internal anal sphincter
Phasic Contractions
periodic contractions followed by relaxation (seconds)
Can phasic contractions occur without an action potential?
no
Examples of Phasic Contractions in the GI (3)
esophageal body, distal stomach, intestines
myogenic
smooth muscle contractions independent of neural input or membrane voltage
