Physiology of the Gastrointestinal Tract and Introduction to Gut Microbiome Flashcards
(122 cards)
1
Q
Big picture functions of the GI Tract?
A
- Transporting food by-products
- Breaking down and absorbing food by-products
- Decontaminating the food and maintaining appropriate relationship with live non-human cells
2
Q
3 basic movements that take place along the GIT?
A
- Peristalsis
- Segmentation
- Migrating motor complex (MMC)
3
Q
Waves of smooth muscle contraction that propel food bolus throughout entire GI tract?
A
Peristalsis
4
Q
What produces rhythm of peristalsis? Where is it located?
A
Interstitial cells of Cajal (ICC) - in myenteric plexus
5
Q
Peristalsis involves _____ behind (proximal) the food bolus and _______ in front (distal) of the food bolus
A
Contraction; Relaxation
6
Q
Function of peristalsis?
A
Propel food further along the GI tract
7
Q
Some problems with Peristalsis? (3)
A
- Esophageal spasms
- Atonic colon
- Gastroparesis
8
Q
Coordination of smooth muscle cells and interstitial cells of Cajal?
A
Segmentation
9
Q
Where does segmentation occur?
A
Within the Small and Large Intestines
10
Q
Function of segmentation?
A
Promotes mixing food particles to increase their interaction between villi and promotes absorption
11
Q
Small movement, almost a vibration, that occurs predominantly during fasting 1.5-2 hr intervals
A
Migrating motor complex (MMC)
12
Q
Where does MMC occur mainly?
A
Stomach and Small Intestine
13
Q
What is MMC movement promoted by?
A
Motilin - secreted by Mo-cells in teh duodenum
14
Q
Function of MMC?
A
Self-cleaning mechanism = dislodges food and bacteria from walls
15
Q
What may a lack of MMC cause?
A
SIBO
16
Q
What are the “pacemakers of the GI Tract”?
A
Interstitial Cells of Cajal (ICC)
17
Q
Where are ICC’s found?
A
Throughout the entire GI Tract
18
Q
ICC’s form a network with each other and smooth muscles via _______, as well as ______
A
Gap junctions; enteric motor neurons
19
Q
What triggers smooth muscle contractions of ICCs?
A
Spike potentials
20
Q
Additional factors that can increase the excitability of smooth muscle? (3)
A
- Muscle stretch (distention)
- Acetylcholine
- Other GI hormones
21
Q
What can decrease excitability of smooth muscles? What does it cause?
A
Norepinephrine - causes hyperpolarization
22
Q
What is the enteric nervous system composed of?
A
Sensory, motor, and interneurons
23
Q
What is the enteric nervous system organized into? (2)
A
- Submucosal plexus and Myenteric plexus
24
Q
Where is the Submucosal plexus located?
A
Located between the layers of submucosa and circular muscle (only present in SI and LI)
25
Function of the submucosal plexus? (4)
- Regulate motility
- Regulate local blood flow
- Regulate secretions
- Regulate epithelial cell function
26
Where is the Myenteric plexus located?
Between longitudinal and circular muscles (entire GI)
27
What is the function of the myenteric plexus?
Regulate motility
28
Nerves that connect the ENS and CNS? (3)
- Vagus Nerve
- Pelvic Splanchnic Nerves
- Thoracic Sympathetic Trunk
29
Secretions promoting motility? (5)
- I-cells = CCK
- Enterochromaffin cells = serotonin
- G-cells = gastrin
- Mo-cells = motilin
- Beta-pancreatic cells = insulin
30
Secretions reducing motility? (4)
- S-cells = secretin
- D-cells = somatostatin
- Pancreatic cells = Pancreatic peptide YY
- Alpha-pancreatic cells = glucagon
31
What is digestion?
Breaking down macromolecules into smaller molecules to increase absorption
32
Two types of digestion?
1. Mechanical
2. Chemical
33
What is mechanical digesiton?
Physically chewing/cutting/crushing/churning food to decrease vol and increase SA
34
Parts of the GI tract that help with mechanical digestion?
Mouth and Stomach
35
What is chemical digestion?
Chemical processes that allows absorption of food particles
36
Two types of chemical digesiton?
1. Enzymatic digestion
2. Lipid solubilization
37
What is enzymatic digestion?
Enzymes break macronutrients down into smaller and smaller particles through the process of hydrolysis
38
What is lipid solubilization?
Emulsifiers secreted by the liver emulsify ingested lipids so that enzymes can break them down to smaller, absorbable molecules
39
Enzymes/secretions present in the mouth to aid in digestion? (3)
- Salivary amylase
- Mucus
- Water
40
Contributing organs/structures for digestion in the mouth? (2)
- Salivary glands
- Teeth
41
What is being digested in the mouth?
Carbohydrates (all other are being broken down into smaller particles)
42
Enzymes/secretions present in the stomach to aid in digestion? (3)
- HCl
- Lipase
- Pepsin
43
Contributing nerve for stomach digestion?
Vagus nerve promotes HCl release
44
What is being digested in the stomach?
Proteins, fats, carbs - limited digestion other than proteins
45
What is the most important site of chemical digestion?
Small intestine
46
Enzymes/secretions present in the small intestine to aid in digestion? (3)
- Bile acids
- Pancreatic enzymes
- Brush border enzymes
47
Contributing organs/structures to small intestine digestion?
- Liver contributes bile
- Pancreas releases numerous enzymes including lipase and amylase
48
What is being digested in the small intestine?
- Proteins (bb enz. Pancreatic enz.)
- Carbs (bb enz. and amylase)
- Lipids (lipase and bile acids)
49
The movement of any substance across the mucosal epithelium of the alimentary tract and into the bloodstream (most substances) or lymphatics (lipids)?
Absorption
50
What is absorption largely dependent on?
The health of the villus and microvilli of enterocytes in the small intestine
51
What occurs in carbohydrate digestion?
Polysaccharides are broken down into monosaccharides
52
What monosaccharides can be transported across the epithelial cells of the small intestine? (3)
Galactose, Glucose, Fructose
53
How are glucose and Galactose transported into the enterocyte?
Na+/glucose (galactose) co-transporter (SGLT1)
54
What does SGLT1 depend on?
High [Na+] in the lumen to power transport of hexose
55
How is fructose transported into the enterocyte?
GLUT-5 = passive transporter
56
How are the monosaccharides transported out the basolateral side of the enterocyte?
GLUT-2 and GLUT-5
57
Where are majority of proteins absorbed?
The duodenum and jejunum
58
Transporters for individual amino acids?
Na+ symporters
59
How are dipeptides and tripeptides transported into the enterocyte?
PepT1 Transporter
60
What does the PepT1 transporter rely on?
H+ concentration gradient
61
What happens to di- and tripeptides in the enterocyte?
They're hydrolyzed into amino acids
62
Nucleic acids are broken down into sugars, purines, and pyrimidines - how are the bases absorbed?
Nucleoside transporters
63
What fatty acids can passively diffuse through enterocyte (unmodified)?
FFAs that are 10-12 C long
64
What happens to fatty acids that are > 10-12 C long?
They're re-esterified once in the enterocyte
65
How is cholesterol transported into the enterocyte?
NPC1L1 transporter
66
What are FFA’s and cholesterol that are coated with proteins, more cholesterol and phospholipids
Chylomicron
67
Why does chylomicron enter the lymphatics?
Too large to pass between endothelial cells into blood stream
68
Impaired fat digestion and absorption resulting in high amount of fat in the stool
Steatorrhea
69
What are the fat soluble vitamins? What do they depend on for absorption?
A,D,E,K
Depend on incorporation into micelle
70
Where are most vitamins and nutrients absorbed?
Duodenum
71
Where is Vitamin B12 absorbed?
Ileum
72
What do most B vitamins and Vitamin C require for absorption?
Na+ co-transporter
73
Where does Iron absorption occur? Via what?
Occurs within duodenum via divalent metal transporter 1 (DMT1)
74
How is iron transported out of the enterocyte?
Ferroportin 1 and hephaestin
75
In the plasma Fe2+ is converted to Fe3+ and is transported by _____
transferrin
76
What is the microbiome?
The collection of all organisms living on and in a given environment or habitat
77
What organisms are most/least prevalent in the microbiome?
viruses > bacteria > fungi
78
What is the distribution of microbiota determined by? (4)
- pH
- O2 access
- temperature
- tropism
79
Most common bacteria in mouth?
Spirochaetes
80
Most common bacteria in the Esophagus?
Streptococci and Lactobacilli
81
Most common bacteria in the stomach?
H. pylori
82
Most common bacteria in the small intestine?
Lactobacilli
83
Most common bacteria in the large intestine?
- Bifidobacteria
- Lactobacilli
- Enterococci
84
Where is the most diversity in the microbiome in the body?
Large intestine
85
93.5% of gut bacteria belong to what phyla? (4)
- Firmicutes
- Bacteroidetes
- Proteobacteria
- Actinobacteria
86
What 2 bacteria contribute most to the gut microbiome?
Firmicutes and Bacteroidetes
87
Examples of Firmicutes? (2)
- Lactobacillus
- Enterococcus
88
Examples of Bacteroidetes? (2)
- Bacteroides
- Prevotella
89
Examples of Proteobacteria? (5)
- Helicobacter
- E. coli
- Shingella
- Salmonella
- Yersina
90
Example of Actinobacteria? (1)
- Bifidobacterium
91
8 functions of gut microbiome?
1. Harvesting energy
2. Strengthen gut integrity
3. Shape intestinal epithelium
4. Regulate immune function
5. Regulate intestinal motility
6. Protection against pathogens
7. Production of some nutrients
8. "Endocrine organ"
92
Gut microbiome development if C-section?
- Less Bacteroides
- More clostridium
93
Gut microbiome development if vaginal birth?
More characteristic of mothers microbiota
94
Gut microbiome development if breastfed?
Bifidobacterium high
95
Gut microbiome development if formula-fed?
- Bifidobacterium low
- higher diversity and altered ratios of other bacteria
96
Gut microbiome development if under-fed?
Increased entero-pathogens
97
What happens with a childs gut flora by 2.5 years old?
Composition, diversity, and functional capabilities similar to that of an adult
98
What factors can influence the composition of the gut microbiota?
- Genetics
- Diet
- Medications
99
Dietary impact on gut microbiome of diet rich in starch, fiber, and plants vs. sugar, starch, animal proteins
Starch/fiber/plant = Prevotella present
sugar/starch/animal = prevotella largely absent
100
Why is Prevotella important?
Produces short chain fatty acids (SCFA's)
101
Microbiome metabolites? (4)
- Short-chain fatty acids (SCFAs)
- Trimethylamine (TMA)
- Bile acids
- Indoles
102
Examples of SCFAs produced? (3)
Acetate, Propionate, Butyrate
103
When are SCFAs' produced?
During fermentation of indigestible carbohydrates (fibers)
104
How do SCFAs promote intestinal integrity? (4)
1. Regulating luminal pH
2. Regulate mucus production
3. Produce fuel for the epithelial cells
4. Modify mucosal immune function
105
How do SCFAs influence overall metabolism? (4)
1. Appetite regulation
2. Energy expenditure
3. Glucose homeostasis
4. Immuno-modulation
106
Microbiome metabolite that has been linked to increasing RF for atherosclerosis and thrombosis?
Trimethylamine (TMA)
107
Microbiome metabolite that has been correlated to changes in energy metabolism?
Bile acids
108
Microbiome metabolite that is produced by Trp metabolism and maintains intestinal barrier and influences immune function?
Indoles
109
What can be metabolized into TMAs?
- Choline
- Phosphatidylcholine
- L-carnitine
110
Healthy/Beneficial changes made by non-pathogenic E. coli?
Increase epithelial mucus secretion and reduce epithelial permeability
111
Healthy/Beneficial changes made by non-pathogenic Lactobacillus rhamnossus?
Increase expression of occludin and
ZO-1 proteins
112
Healthy/Beneficial changes made by non-pathogenic L. rheuteri?
Increase epithelial cell proliferation
113
Pathogenic changes in Salmonella entetica?
Reduced ZO-1 and occludin proteins and tight junction complexes
114
Pathogenic changes in Clostridium difficile?
Reduced mucin production
115
Pathogenic changes in Enterovirus E11?
Direct cytotoxicity
116
Bacteria increased when constipated? Decreased?
I: Bacteroides and Enterobacter
D: Bifidobacterium and Prevotella
117
Bacteria increased in diarrhea? Decreased?
I: Prevotella
D: Bifidobacterium, Bacteroides, Lactobacillus
118
Mechanism of action interferes with bacterial cell activity (including replication) without directly causing death
Bacteriostatic
119
Mechanism of action directly kills the bacteria
Bactericidal
120
Antibiotic is able to effect different types of bacteria’s including gram positive, gram negative, and others (spirochetes, atypical)
Broad spectrum
121
Negative effects of antibiotics on gut microbiome? (3)
- Reduce species diversity
- Altered metabolic activity
- Select the antibiotic-resistant organisms
122
When does antibiotic associated diarrhea (ADD) typically occur?
Initially during treatment or up to 2 months following discontinuation
