Physiology of the GI tract and intro to Gut Microbiome Flashcards
what are the 3 basic movements that take place along the GI tract?
- peristalsis
- segmentation
- migrating motor complex (MMC)
peristalsis involves what?
entire GI tract, starting with esophagus
what is peristalsis?
waves of smooth muscle contractions that propel food bolus throughout GI tract
what type of movement can be stimulated or promoted by distention of smooth muscle cells?
peristalsis
what is the function of peristalsis?
propel food further along GI tract
what involves contraction behind (proximal) the food bolus and relaxation in front (distal) of the food bolus
peristalsis
where does segmentation occur?
within SI and LI
how is segmentation produced?
produced by the coordination of smooth muscle cells and interstitial cells of Cajal (ICC)
what is the function of segmentation?
promote mixing the food particles to increase interaction between the villi of the enterocytes and various food particles to promote absorption
where does migrating motor complex occurs?
within stomach and SI (and a few other locations)
what is migrating motor complex?
Small movement, almost a vibration, that occurs predominantly during fasting 1.5-2 hr intervals
the movement of migrating motor complex is promoted by ?, secreted by? located in the ?
motilin
Mo-cells
duodenum
what is the function of migrating motor complex?
suspected that it is a self-cleaning mechanism, as this movement causes small food particles and bacteria to be dislodged from the intestinal wall and prevents bacteria from traveling from LI into SI
what is the pacemakers of the GI?
interstitial cells of cajal (ICC)
what is interstital cells of Cajal?
Form a network with each other and smooth muscle cells via gap junctions, as well as enteric motor neurons
what generate slow waves and can cause spike potentials that do trigger smooth muscle contractions
the interstitial cells of cajal
excitability of smooth muscles can be increased by additional factors such as:
- Muscle stretch (distention)
- Acetylcholine
- Other GI hormones
excitability of smooth muscles can be decreased by additional factors such as:
- Norepinephrine (causes hyperpolarization)
Enteric Nervous System is composed of ?
sensory, motor, and interneurons
the ENS is organized into ?
Submucosal plexus and myenteric plexus
submucosal plexus is located ?
Located between the layers of submucosa and circular muscle (only present in SI and LI)
what is the function of submucosal plexus?
Function to regulate motility, local blood flow, regulate secretions and epithelial cell function
myenteric plexus is located ?
Located between longitudinal and circular muscles (entire GI)
what is the function of myenteric plexus?
Function to regulate motility
what are some examples of nerves that connect CNS and ENS
○ Vagus Nerve
○ Pelvic Splanchnic Nerves
○ Thoracic Sympathetic Trunk
what is key when it comes to transport throughout the GI tract
timing
what happens if food is transported too quickly
may not have enough time to digest or absorb it
what happens when the food is transported too slowly
it may irritate the local or neighboring mucosa
what secretions promotes motility?
○ I-cells – cholecystokinin
○ Enterochromaffin cells – serotonin
○ G-cells – gastrin
○ Mo-cells – motilin
- Beta-pancreatic cells – insulin
what secretions reduces motility?
○ S-cells – secretin
○ D-cells – somatostatin
○ Pancreatic cells - Pancreatic peptide YY
○ Alpha-pancreatic cells – glucagon
what is digestion?
breaking down macromolecules into smaller molecules to increase absorption
what are the 2 major types of digestion?
mechanical digestion and chemical digestion
what is mechanical digestion?
physically cutting, crushing, and churning food so that the volume of each food particle decreases
what is the chemical digestion?
chemical processes that allows absorption of food particles
what is enzymatic digestion
enzymes break macronutrients down into smaller and smaller particles through the process of hydrolysis
what is lipid solubilization?
emulsifiers (bile salts, lecithin) secreted by the liver emulsify ingested lipids so that enzymes can break them down to smaller, absorbable molecules
what is the carbohydrate digestion?
begins in the mouth with salivary amylase (minority), further broken down by pancreatic amylase and brush border enzymes within SI (majority of CHO digestion)
what is protein digestion?
begins in the stomach with HCL and pepsin, further digested by pancreatic enzymes and brush border enzymes
what is fat digestion?
begins in the stomach with HCl and lipase (minority), further digested by pancreatic lipase and emulsified by bile acids released by the liver (majority of lipid digestion)
what is absorption?
movement of any substance across the mucosal epithelium of the alimentary tract and into the bloodstream (most substances) or lymphatics (lipids)
where does absorption largely takes place in?
in the small intestine
effective absorption is dependent on
a large surface area at the apex of the epithelial cell
only what can be transported across the epithelial cells of the small intestine, in terms of carbohydrate?
monosaccharides
what transports glucose and galactose from lumen into enterocyte
Na+/glucose (galactose) co-transporter
what is the passive transport of fructose from lumen into enterocyte
GLUT-5
what transports the monosaccharides from enterocyte into blood stream (hepatic portal vein)
GLUT-2 and GLUT-5 basolateral side
majority of protein is absorbed in the ?
duodenum and jejunum
what are the transporters of protein absorption?
Na+ symporters and PepT1 transporter
what transports dipeptides and tripeptides into enterocyte
PepT1 transporter
which protein transporter relies in H+ instead of Na+ concentration gradient
PepT1 transporter
nucleic acids are broken into ? and further broken into ? and ? via digestion
nucleotides
nucleoside
phosphoric acid
how are fat absorbed?
passive diffusion
what are chylomicron?
FFA’s and cholesterol are coated with proteins, more cholesterol and phospholipids
what is steatorrhea
impaired fat digestion and absorption result in high amount of fat in the stool
where are vitamins absorbed?
Majority absorbed in duodenum (upper SI), however vitamin B12 is absorbed in the ileum
For absorption, Most of the B-vitamins and vitamin C require what
Na+ cotransporters for absorption
where does iron get absorbed?
Occurs within duodenum via divalent metal transporter 1 (DMT1) – Fe2+ (ferrous) enters enterocytes
What is the microbiome?
The collection of all organisms living on and in a given environment or habitat
what is the human microbiome project
the catalog of the microbes in human and their genes
what bacteria are in the oral cavity?
spirochaetes
what bacteria are in the stomach
Helicobacter pylori
what bacteria are in the small intestine
lactobacili, gram positive cocci
what are the major compositions of the gut microbiome
firmicutes and bacteroidetes
what is bacteriostatic?
Mechanism of action interferes with bacterial cell activity (including replication) without directly causing death
what is bactericidal?
○ Mechanism of action directly kills the bacteria
what does the broad spectrum mean?
Antibiotic is able to effect different types of bacteria’s including gram positive, gram negative, and others (spirochetes, atypical)
what is antibiotic associated diarrhea?
○ Caused by disruption in normal gut microbiome
§ C. difficile accounts for 10-25% of AAD cases
