Digestion - Small Intestines: Accessory Secretory Organs Flashcards
after how long is acidic chyme emptied from the stomach to the duodenum ?
3-4 hours via pyloric valve
what occurs if there is stomach acid in the intestine?
small intestine secretes secretin
what does secretin do
induces bicarb secretion from pancreas and liver to neutralize intestinal acid
what is the mesentery
an extension of the peritoneum that suspends the bulk of the intestine away from the body. holds blood and lymphatic vessels between its 2 sheets
what are vili
projections into the lumen covered predominantly with mature, absorptive enterocytes along with interspersed mucus-secreting goblet cells
how much do vili increase surface area?
600x to 200-500m^2
what are crypts of lieberkuhn
tubular invaginations of the epithelium around the vili, lined with younger epithelial cells that are involved in secretions
what is found at the base of the crypts of lieberkuhn?
stem cells to continually divide and provide all the epithelial cells in the crypts and on the vili
what are paneth cells?
antimicrobial cells that secrete alpha defensins which insert into microbial membranes to form pores (lyses them)
where are paneth cells
at the bottom of the crypts of lieberkuhn
what is celiac disease
gluten enteropathy that results from type IV hypersensitivity to gluten that affects 1/133 americans
what does gluten do in celiac disease
erroneously activates T cells (type IV) that damage intestinal vili, makes them stubby
why is anemia found in celiac disease sometimes?
malabsorption of iron, folic acid, and vitamin B12
symptoms of celiac disease
commonly asymptomatic, could be chronic diarrhea with pale, loose and greasy stool. weight loss, fatigue, failure to thrive in children
what are enterogastrones?
hormones released by the upper intestinal mucosa (duodenum) in response to dietary lipids that INHIBIT gastric motility and secretion.
what are the enterogastrones?
- CCK 2. secretin 3. gastric inhibitory peptide
what are enterogastrones stimulated by
- luminal fatty acids (CCK) 2. acid in duodenum (secretin) 3. hyperosmotic solutions like glucose (gastric inhibitory peptide)
when is secretin released
in response to pH of 4-4.5 in the duodenum, stimulates pancreas and bile ducts to release a flood of bicarbonate
what makes secretin?
in the cytoplasmic secretory granules of S cells in the mucosa of the duodenum
how is gastric inhibitory peptide made?
synthesized as a 153aa prohormone and cleaved to active 42aa peptide by K cells in the mucosa of the duodenum
what stimulates gastric inhibitory peptide?
glucose induced hyperosmolarity of the duodenum, and GIP stimulates insulin secretion
what stimulates release of CCK?
fatty and amino acids
what does CCK stimulate
release of pancreatic enzymes and contraction of the gallbladder
what does the pancreas secrete in response to CCK
- trypsin (protein) 2. chymotrypsin (protein) 3. carboxypeptidase (protein) 4. lipase (fat) 5. amylase (sugar) 6. ribonuclease 7. deoxyribonuclease
what synthesizes CCK?
I cells in the mucosal epithelium of the small intestine, secreted into the duodenum
what is preprocholecystokinin?
the gene product that undergoes posttranslational modification into family of CCK hormones that all have the same active moiety
what does CCK do as a neuropeptide?
acts as a hunger suppressant by binding to receptors widely distributed in the CNS
what role does CCK play in drugs?
major role in inducing drug tolerance to opioids like morphine and heroin
what roles does CCK play?
- stimulates release of pancreatic enzymes 2. contraction of gallbladder 3. slows stomach speed of digestion 4. hunger suppressant 5. induces drug tolerance
what occurs if there is fatty acids in the duodenum
CCK is released and increases in concentration in the plasma. this causes gallbladder contraction which increases bile release into the common bile duct. simultaneous relaxation of sphincter of Oddi allows increased bile flow into the duodenum.
what is in bile
- bile salts 2. excess cholesterol 3. lecithin (a phospholipid) 4. bicarb 5. bile pigments (from RBC breakdown) 6. trace metals
what do bile salts do
emulsify fats
what is the duct of santorini
an extra accessory pancreatic duct other than the main pancreatic duct that exits directly at the minor duodenal papilla and bypasses the ampulla of vader
what is the duct of wirsung?
the major pancreatic duct that carries pancreatic digestive enzymes
where does the duct of wirsung end?
it meets the common bile duct at the ampulla of vater, both exiting at the major duodenal papilla
what is the ampulla of vater?
hepatopancreatic ampulla that is formed by the union of the duct of wirsung (pancreatic duct) and the common bile duct
where does the duct of santorini exit?
bypasses the ampulla of vater and exits at the minor duodenal papilla
what is a part of the endocrine pancreas?
alpha, beta, delta, PP, and epsilon cells
what do alpha cells secrete
glucagon
what do beta cells secrete
insulin
what do delta cells secrete
somatostatin
what do PP cells secrete
pancreatic polypeptide
what do epsilon cells secrete
ghrelin
what do sympathetic alpha2 receptors do to the pancreas?
stimulate alpha cells inhibit beta cells
what do parasympathetic M3 receptors do to the pancreas?
inhibit alpha cells stimulate beta cells
what does the exocrine pancreas secrete?
bicarb and digestive enzymes
what hormones influence exocrine pancreas secretion?
secretin and CCK
what cells secrete bicarb?
centroacinar cells
what cells secrete digestive enzymes
acinar cells
how much does the exocrine pancreas secrete?
1L/day into the duodenum
what is the make up percentage of pancreas
90% is exocrine glands 2% is endocrine glands 8% is blood vessels and interstitial fluid
what is the sympathetic innervation of the pancreas?
post-ganglionic fibers from celiac and superior mesenteric plexi to INHIBIT PANCREATIC SECRETIONS (inhibits beta cells, stimulates alpha)
what is the parasympathetic innervation of the pancreas?
vagus nerve, stimulates pancreatic secretion (inhibits alpha, stimulates beta)
describe the structure of the exocrine glands
similar to salivary glands, terminal acini that secrete pancreatic enzymes. acinar cells connected to ductal cells by centroacinar cells that secrete pancreatic HCO3
what do the acinar cells secrete?
pancreatic enzymes. proteases require activation in duodenum amylases and lipases are secreted in active form
what do the centroacinar cells secrete?
aqueous components , isotonic solution containing Na, Cl, K, HCO3
how are pancreatic enzymes synthesized?
in the RER, packaged by the golgi, then concentrated into zymogen granules.
how does CCK lead to pancreatic enzyme release
CCK allows fusion of zymogen granules in the acinar cells with the plasma membrane for release into the acinar lumen
what ionic concentrations in pancreatic fluid vary with flow rate?
Na and K remain isotonic to plasma Cl and HCO3 vary with flow rate
what modifies the initial isotonic solution
ductal cells apical Cl/HCO3 exchanger basolateral Na/K ATPase
how is pancreatic secretion made?
- hydration of metabolic CO2 is catalyzed by carbonic anhydrase to carbonic acid
- carbonic acid dissociates to H and HCO3
- protons transported to plasma using basolateral Na/H antiport (temporary acidification of venous blood)
- HCO3 is exchanged for Cl by apical antiport
- basolateral Na/K ATPase ejects Na to decrease Na concentration intracellularly
THE NET SECRETION IS OF BICARB INTO PANCREATIC DUCTAL JUICE AND ABSORPTION OF PROTONS LEADING TO ACIDIFICATION OF PANCREATIC VENOUS BLOOD
what occurs at low flow rates?
pancreatic cells secrete an isotonic solution comprising Na, Cl and water
what occurs when pancreas stimulated by secretin?
composition changes, remains isotonic with Na, HCO3 and water.
describe pancreatic juice composition
Na and K concentrations stay constant, HCO3 and Cl concentrations vary – bicarb concentration peaks at flow rates above 30microL/min
what regulates acinar cell enzymatic secretions?
acinar cells have CCKa and Ach muscarinic receptors
what does Ach binding to muscarininc receptors on acinar cells do?
stimulates and potentiates CCK secretion (vagovagal reflex)
what stimulates CCK secretion from I cells?
amino acids (phenylalanin, tryptophan, methionine), small peptides and fatty acids
what if phenylalanine is in the small intestine?
I cells are triggered to release CCK. Ach potentiates CCK secretion and increases IP3 and Ca. causes release of enzymes.
what regulates ductal cell aqueous secretions?
have receptors for CCK, Ach, secretin
what triggers release of secretin
luminal H+ (acidic chyme from stomach)
IS THE MAJOR STIMULUS OF AQUEOUS HCO3 RICH SECRETIONS
provides rapid neutralization of acidic chyme for action of pancreatic enzymes
what inhibits pancreatic secretions?
fat in the distal SI signals the end of the intestinal stage of digestion VIA peptide YY, ileal endocrine cells, and somatostatin
