GI Secretions Flashcards
What does mouth secrete?
- Saliva
- lingual lipase
- salivary alpha amylase
- R-proteins=transcobalamin-1 (TC-1)
What does esophagus secrete?
Electolytes and mucus
What does stomach secrete?
- HCl
- intrinsic factor
- pepsinogens
- gatric lipase
- mucus
- gastrin
- somatostatin
- histamine
What does liver and gallbladder secrete?
- Bile and buffers (electrolytes)
What does pancreas secrete?
-
Exocrine gland
-
buffers and enzymes
- typsin, chymotrypsin, procarboxypeptidase, lipase, colipase, proelastase, alpha amylase
- monitor peptie
- trypsin inhibitor; stimulates CCK
-
buffers and enzymes
-
Endocrine gland
- insulin
- glucagon
- somatostatin
What enzymes/secretions are located in the small intestine ?
- Buffers- mucus and electrolytes
- enterokinase
- brushborder disaccharides
- brush border peptidases
- secretin
- gastrin
- CCK, VIP, GIP, motilin, 5HT, somatostation
What is gastin? SIte of secreiton? Stimuli? Action?
- Site of secretion: G-cells in antrum of stomach and in duodenum
- Stimuli- stretch, peptides, amino acids, vagus (through GRP)
- Action- stimulate gastric H, increase lower GI motility, increase gastric mixing
Secretin?
Site of secreiton, primary stimuli, general actions?
- Site of secretion
- s-cells in duodenum
- Primary stimuli
- acidic chyme
- Aciton
- increase pancreatic, biliary and intestinal buffers
- decrease gastric H
What is cholecystokinin (CCK)
Site, primary stimuli, action?
- Site
- I-cells of duodenum and jejunum
- Stimuli
- small epptides, amino acids and fats
- Actions
- increase pancreatic enzyme secretion
- contracts gallbladder
- relaxes sphincter of oddi
What is GIP?
Site, Sitmuli, action?
Glucose Insulinotropic Peptide
- Site
- Duodenum and jejunum
- Stimuli
- fatty acids
- glucose
- amino acids
- Action
- increase pancreas insulin secretion
- decrease gastric H
What is motilin?
Site
Stimuli
Action
- Site
- m-cells of duodenum
- Stimuli
- fasting
- Action
- stimulates phase III MMC contractions
What is GLP-1 and peptide YY?
Site? Stimuli?Action
Glucagon-Liek Peptide
- Site
- mainly jejunum/lower SI (GLP-1)
- Jejunum/ileum (peptide YY)
- Stimuli
- chyme
- Actions
- Satiety
- decrease hypothalamic NPY
- Satiety
What is ghrelin?
Site, stimuli, action?
- Site
- oxnytic cells of stomach
- Stimuli
- fasting
- Action
- hunger- increase hypothalamic NPY
What is leptin?
- Produced in adipose tissues nad considered counterpart of ghrelin
- when you eat, glucose and insulin increase circulating leptin which decreases appetite by suppressing NPY in the arcuate nucleus
- much longer process becaue this is stimulated by GLUCOSE and insulin ALREADY in blood
What hormones supress hypothalamic NPY?
GLP-1
Leptin
peptide YY
What hormones stimualte NPY?
Ghrelin
What are the salivary glands?
Parotid gland (serous fluid c amylase)
Submandibular gland (mixed serous/mucous fluid)
Sublingual gland (mucus fluid)
Glands are highly dependent on ____ ____
blood flow
How are salivary glands activated?
PSNS activated during feeding to increase blood flow to glands
salivary glands are ____ glands
exocrine
- Make secretions and secrete into ducts
Is saliva alway constituted the same?
No, varies based on flow of saliva
Low flow rate has lower conc of Na, Hco, Cl and K
High rates have much higher concentration of all electrolytes
What is electrolyte is higher in saliva?
What type of solution is saliva?
Potassium much higher in saliva (20mEq)
Saliva is a hypotonic solution
What is found in saliva?
- Electrolytes
- salivary alpha amylase
- lingual lipase
- transcobalamin I (TC1)
- mucus
What is salivary alpha amylase?
Stach digestion
- Starch is glucose molecule with alpha linkages<– amylase breaks down alpha linkages
WHat is lingual lipase
- starts lipid digestion
- made on cells of tongue! (von Ebner’s glands)
- being lipid digestion before going to stomach
- active at low pH and can hydrolyze dietary triglycerides in the stoamch, yielding free fatty acids and diglycerides
What is transcobalamin-1 (TC-1)
- Protein that binds to vitamin b12
- essential vitamin that we need to absorb
- have multiple systems to protect b12 from proteases in system and make sure it’s absorbed
- protects b12 from stomach pepcids
What is innervation for secretion of saliva?
PSNS through facial (submax and sublingual) and glossopharyngeal nerve (parotid)
How does saliva amount vary with SNS vs PSNS
SNS- dries up (small blip by squishing of myoepithelial cells)
PSNS- increases saliva
What increases salivary flow?
- PSNS, Ach
- CNS (cephalic phase)
- sensory sitmulation- smelling somethign delicious and start salivating
- Nausea
- Esophageal distenstion
- from secondary esophageal peristalsis b/c of dry food
- Chewy, flavorful foods
- Dry, acidic, alkaline foods
- Meats, sweets, bitter foods
What decreases salivary flow?
- Sympathetic, NE
- Hormones (ADH, Aldosterone)
- any trigger to retain fluid when dehydrated
- Sleep
- Dehydration
- Drugs
- aging
What does saliva do?
- Taste- digesting some nutrients
- coagulation factors- ex- licking wounds
- antimicrobial action
- protection- cools down hot foods
- digestion- amylase, lipase
- lubrication- for food bolus to stomach
- oral hygiene- taking bacteria out of mouth
- during sleep, bacteria allowed to bloom, why you have bad breath in the morning
- having bacteria in mouth increases risk of cavities
What type of cells is saliva secreted from?
acinar cells
What are the gastric secreitons?
- HCl
- Intrinsic Factor
- Pepsinogens
- Gastrin- ONLY one secreted into blood as hormone
- Lipase
- Other- peptide, histamine, somatostatin
- Mucus
hipglom
What is HCl?
- secreted from parietal cells
- 1.5-2%concentration
- increases SA
- Having food in staomch stimulates vagal actions and secretes HCl
Intrinsic factor?
- Secreted by parietal cells
- 2nd line defense vitamin B12
- Helps prevent b12 being digested by proteases
- as gastric juices mixing, b12 exposed to IF and binds to site where pancretic proteases normally attack
- TC1 protects b12 in stomach, IF helps during digestion
What are pepsinogens?
- Enzymes secreted from chief cells
- start protein digestion
What is gastric lipase?
- Also comes out with chief cells (along with pepsinogens)
- continues lipid digestion
Where is histamine secreted from in stomach? Action?
Where is somatostatin secreted in stomach? Action
- Histamine- mast cells
- increases HCl
- Somatostatin- endocrine cells
- decreases Hcl
What does mucus in gastric secretions do?
- Lubricate stomach
- also stick to cells and trap HCO3 to protect lumen of stomach
What is gastrin in stomach
- Only hormonal secretion of stomach
- secreted into blood
- hormones= blood
- located in narrow region of antrum
- increase HCl
- stimulates motility
Where is gastin released from?
- G-cells in antrum of stomach and duodenum
- major function of gastrin is to stimulate H secretion from parietal cells
- pareital cells are between mucous and chief cells
What are stem/regenerative cells in stomach?
Differentiate to repalce other cells in glands
What are mucous neck cells?
Protect gastric mucosa by secreting mucous
What do parietal cells secrete?
HCl, and intrinsic factor
What do chief cells secrete?
Pepsinogen and gastric lipase
What do endocrine cells in stomach secrete?
Somatostatin
What do mast cells in stomach secrete?
Histamine
What is on lumen side of parietal cell?
- Tubulovesicles
- when not stimulated to secrete, vesicles fold inwards
- once stimulated, the vesicles come out and increase SA for secretion tremendously
- H-K ATPase pump on membrane
What is the rate limiting step in H transport?
H/K ATPase pump
What 3 things control stimulation of acid secretion at parietal cell?
- Histamine (significant, from enterochromaffin-like cell (ECL))
- Gastrin- through blood
- act directly on parietal cell or
- indirectly through ECL cell
- Ach (PSNS)
- vagal stimulation
- ACh can act directly on muscarinic receptor on parietal cell
- indirectly by stimulating ECL to stimulate histamine
*
How do we make HCl acid?
- First, CO2 in cell. CO2 metabolism H + HCO3
-
Then Sends H outside the cell and bring K in
- forcing H out into lumen against 10^6 gradient!
- need ATP, highly metabolic
- brings K into cell (also against gradient)
- K also leaks outside into lumen via separate channel
- Cl- leaks out into pariteal cell to establish electrochemical gradient created by excess H in lumen
-
HCO3 from breakdown of CO2
- Secreted by HCO3-Cl antiport pump
- Hco3 into blood
- Cl into parietal cell
- Blood coming out of stomach will be very alkaline (pH a little higher than normal)
What does gastric fluid ion concentration look like at low rate of secretion? High rate?
- At low rate, mostly Na and Cl in lumen. Very little H or K in gastric lumen
- At high rate, [H] increase significantly. Highest with [Cl]
What electolyte loss happens with vomiting over days?
Hypokalemia (both from gastric secretions and saliva)
Can have metabolic alkalosis
What is helicobacter pylori?
- Gram (-) bacteria, enters body through fecal-oral transmission
- once ingested, can get into mucus layer, infiltrate and make ureases that combine with CO2 and make ammonia
- this neutralizes the acid and protects the h. pylori
- This urease creates cytotoxic response
- inflames cell
- disrupts bicarb layer
- If h.pylori bloom, can disrupt mucus layer and cause chronic infammation of tissue–> ulcer
- Main cause of non-nsaid related gastric/duodenal
How do NSAIDs cause ulcers?
- NSAIDS are prostaglandin inhibitors
- prostaglandins are cytoprotective to stomach
- normally increase mucus production and reduce histamine secretion
- prostaglandins are cytoprotective to stomach
- Make helicobacter worse as well
What things stimulate gastric acid secretion?
Parasympathetic, ACh (vagus)
Gastrin
Histamine
What inhiibts gastric acid secretion?
- Secretin-
- g-cell to decrease gastrin
- Somatostatin-
- released form endocrine cells in gastric glands, act in paracrine manner (acts locally) through ECL
- Peptide YY-
- As chyme goes to jejunum, peptid YY secreted to decrease action in gastric.
- Prostaglandin
- local- acts on pareital cell to decrease histamine
What gets trapped in gastric mucus layer to neutralize acid?
HCO3
What is neural control of acid secretion?
- Cephalic phase via vagus
- PSNS excites pepsin and acid production
- as soon as last of chyme drips into duodenum, vagus nerve stops, G-cells in antrum stop gastin secretion into blood
- PSNS excites pepsin and acid production
- Gastric phase
- local nervous secretory reflexes
- vagus reflexes
- gastrin stimulation
- Intestinal phase
- nervous mechanism (enteric)
- hormonal mechanisms
What is located on small intestine lining?
Brush border villus cells
cypts of lieberkuhn
What is the brush border villus cell?
- Lining of all of small intestine in upper portion (crypts in lower) (abundant)
- Site of absorption
- high nutrient transport
- low permeability?
- “Wedge” in glycocalyx in brush border cells
- provides final digestion of carb/protein
- not possible if brush border lining disrupted
- extremely important that brush border is intact
What are cypts of lieberkuhn?
- Where secretions happen
- A lot of mucus, electolytes secreted out of crypts to help get pH up in stomach
- have CFTR (cystic fibrosis transmembrane conductance regulator) which secretes Cl into lumen of gut, Na and H2O to follow
- names CFTR becaues these are also located in pancreas/lung of CF patient and don’t work
- get very thick mucus without serous production
- have CFTR (cystic fibrosis transmembrane conductance regulator) which secretes Cl into lumen of gut, Na and H2O to follow
What are duodenal hormones released?
- Gastrin
- Secretin
- Cholecystokinin
- Glucose insulinotropic peptide (GIP)
What does gastin do in small intestine?
- Released in response to stretch
- secrete HCl at parietal cells
- increase motility in lower GiI
- part of gastrocolic reflex
- presence of PNS and gastrin coming out causing mass movement of colon
What is secretin’s role in duodenum?
- Secreted in blood in response to low pH
- responds to acid in chyme coming out
- goes to increase pancreatic and intestinal buffers
- important buffer acidic chyme
- as chyme comes out of pyloric sphincter, getting spurts of juices coming out of common bile duct (strong hco3 buffers) in order to decrease acidity
- out of stomahc 2–>4–> 7 by jejenum
- necessary to get pH up of chyme
What is cholecystokinin role in duodenum?
- Increases pancreatic enzyme
- need for digestion of carb/lipid/protein coming down in chyme
- rule of thumb- digestion in upper GI tract handle 25-30% digestion. Pancreatic enzymes are 75%
- need for digestion of carb/lipid/protein coming down in chyme
- gallbladder contraction
- increase bile production in liver
What is GIP role in duodenum?
- Increases insulin at pancrease
- secreted into blood
- Squirts of chyme into duodenum, hormones are all stimulate, GIP goes to blood (very early) and sitmulate insulin production. SO that when glucose comes into blood, very soon we have insulin available
- anticipatory response
- when glucose does come into cell, going to stimulate even more insulin
Pancreatic acini secrete ___and ___
enzymes and buffers
What duodenal secretion stimulates pancreatic acini to secrete enzymes? buffers?
CCK- enzymes
Secretin- buffers/electolytes
Proteases must be secreted in ____ form
zymogen
Trypsinogen is activated to trypsin in duodenum by ______
enterokinase
What proteases are activated by trypsin?
- Chymotrypsinogen
- Pro-carboxypeptidase
- Pre-co-lipase
Why do we want typsin only activated in duodenum?
Typsinogen can sponatenously activate to trypsin in pancreas and cause auto-digestion of pancrease–> pancreatitis
- Under normal circumstances, have trypsin inhibitor in pancrease so cells won’t get chewed up
- aka monitor peptide
Pancreatic lipase?
Active in cell but needs pre-co-lipase
Pancreatic amylase?
Starch digestion. Activated by Cl
What do proteases break down proteins to?
Oligopeptides
When chyme is lower in GI tract, pancreatic secretions ____
cease.
No vagal stimulation (no food/chyme in upper GI tract)
More local action, getting everything moving down the tract
Secretion of H and HCO3 into lumen in ileum helps reclaim ___,____ and ___ back into ECF
sodium, chlorid and water back into ECF!
What is the “hamster wheel” in lumen of ileum?
- In ileum and jejunum, secreiton of H and HCO3 allows absorption of Na and Cl from lumen (H/Na, and CL/HCO3)
- H and HCO3 that was just excreted forms to make H2O and CO2 in lumen
- H2O and CO2 absorbed by cell!
- then dissociates into H and HCO3 again and is used AGAIN to absorb more Na and Cl!
- aka hamster wheel…
Electrolyte movment in lumen of colon?
- Colon is speicalized for storage, slow movmeent and reclamation of Na and H2O out of cyme to make feces
- Aldosterone sensitive Na/K ATP-ase pump on ECF lumen
- ENaC- epithelium Na channel to get Na into ECF (brings H2O with it)
- Cl come sin via HCO3/Cl exchanger
- HCO3 stays in feces because it’s so distal
- K intralumen goes way up because of Na/K pump
- leaks into lumen and excreted in feces
- Only thing left in lumen is HCO3 and K (under normal circumstances)
- excreted in feces
