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Medical Physiology > Digestion - Small Intestines: Accessory Secretory Organs > Flashcards

Digestion - Small Intestines: Accessory Secretory Organs Flashcards

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USMLE® Step 1 flashcards
1
Q

after how long is acidic chyme emptied from the stomach to the duodenum ?

A

3-4 hours via pyloric valve

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2
Q

what occurs if there is stomach acid in the intestine?

A

small intestine secretes secretin

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3
Q

what does secretin do

A

induces bicarb secretion from pancreas and liver to neutralize intestinal acid

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4
Q

what is the mesentery

A

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

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5
Q

what are vili

A

projections into the lumen covered predominantly with mature, absorptive enterocytes along with interspersed mucus-secreting goblet cells

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6
Q

how much do vili increase surface area?

A

600x to 200-500m^2

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7
Q

what are crypts of lieberkuhn

A

tubular invaginations of the epithelium around the vili, lined with younger epithelial cells that are involved in secretions

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8
Q

what is found at the base of the crypts of lieberkuhn?

A

stem cells to continually divide and provide all the epithelial cells in the crypts and on the vili

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9
Q

what are paneth cells?

A

antimicrobial cells that secrete alpha defensins which insert into microbial membranes to form pores (lyses them)

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10
Q

where are paneth cells

A

at the bottom of the crypts of lieberkuhn

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11
Q

what is celiac disease

A

gluten enteropathy that results from type IV hypersensitivity to gluten that affects 1/133 americans

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12
Q

what does gluten do in celiac disease

A

erroneously activates T cells (type IV) that damage intestinal vili, makes them stubby

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13
Q

why is anemia found in celiac disease sometimes?

A

malabsorption of iron, folic acid, and vitamin B12

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14
Q

symptoms of celiac disease

A

commonly asymptomatic, could be chronic diarrhea with pale, loose and greasy stool. weight loss, fatigue, failure to thrive in children

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15
Q

what are enterogastrones?

A

hormones released by the upper intestinal mucosa (duodenum) in response to dietary lipids that INHIBIT gastric motility and secretion.

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16
Q

what are the enterogastrones?

A
  1. CCK 2. secretin 3. gastric inhibitory peptide
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17
Q

what are enterogastrones stimulated by

A
  1. luminal fatty acids (CCK) 2. acid in duodenum (secretin) 3. hyperosmotic solutions like glucose (gastric inhibitory peptide)
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18
Q

when is secretin released

A

in response to pH of 4-4.5 in the duodenum, stimulates pancreas and bile ducts to release a flood of bicarbonate

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19
Q

what makes secretin?

A

in the cytoplasmic secretory granules of S cells in the mucosa of the duodenum

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20
Q

how is gastric inhibitory peptide made?

A

synthesized as a 153aa prohormone and cleaved to active 42aa peptide by K cells in the mucosa of the duodenum

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21
Q

what stimulates gastric inhibitory peptide?

A

glucose induced hyperosmolarity of the duodenum, and GIP stimulates insulin secretion

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22
Q

what stimulates release of CCK?

A

fatty and amino acids

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23
Q

what does CCK stimulate

A

release of pancreatic enzymes and contraction of the gallbladder

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24
Q

what does the pancreas secrete in response to CCK

A
  1. trypsin (protein) 2. chymotrypsin (protein) 3. carboxypeptidase (protein) 4. lipase (fat) 5. amylase (sugar) 6. ribonuclease 7. deoxyribonuclease
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25
Q

what synthesizes CCK?

A

I cells in the mucosal epithelium of the small intestine, secreted into the duodenum

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26
Q

what is preprocholecystokinin?

A

the gene product that undergoes posttranslational modification into family of CCK hormones that all have the same active moiety

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27
Q

what does CCK do as a neuropeptide?

A

acts as a hunger suppressant by binding to receptors widely distributed in the CNS

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28
Q

what role does CCK play in drugs?

A

major role in inducing drug tolerance to opioids like morphine and heroin

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29
Q

what roles does CCK play?

A
  1. stimulates release of pancreatic enzymes 2. contraction of gallbladder 3. slows stomach speed of digestion 4. hunger suppressant 5. induces drug tolerance
30
Q

what occurs if there is fatty acids in the duodenum

A

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.

31
Q

what is in bile

A
  1. bile salts 2. excess cholesterol 3. lecithin (a phospholipid) 4. bicarb 5. bile pigments (from RBC breakdown) 6. trace metals
32
Q

what do bile salts do

A

emulsify fats

33
Q

what is the duct of santorini

A

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

34
Q

what is the duct of wirsung?

A

the major pancreatic duct that carries pancreatic digestive enzymes

35
Q

where does the duct of wirsung end?

A

it meets the common bile duct at the ampulla of vater, both exiting at the major duodenal papilla

36
Q

what is the ampulla of vater?

A

hepatopancreatic ampulla that is formed by the union of the duct of wirsung (pancreatic duct) and the common bile duct

37
Q

where does the duct of santorini exit?

A

bypasses the ampulla of vater and exits at the minor duodenal papilla

38
Q

what is a part of the endocrine pancreas?

A

alpha, beta, delta, PP, and epsilon cells

39
Q

what do alpha cells secrete

A

glucagon

40
Q

what do beta cells secrete

A

insulin

41
Q

what do delta cells secrete

A

somatostatin

42
Q

what do PP cells secrete

A

pancreatic polypeptide

43
Q

what do epsilon cells secrete

A

ghrelin

44
Q

what do sympathetic alpha2 receptors do to the pancreas?

A

stimulate alpha cells inhibit beta cells

45
Q

what do parasympathetic M3 receptors do to the pancreas?

A

inhibit alpha cells stimulate beta cells

46
Q

what does the exocrine pancreas secrete?

A

bicarb and digestive enzymes

47
Q

what hormones influence exocrine pancreas secretion?

A

secretin and CCK

48
Q

what cells secrete bicarb?

A

centroacinar cells

49
Q

what cells secrete digestive enzymes

A

acinar cells

50
Q

how much does the exocrine pancreas secrete?

A

1L/day into the duodenum

51
Q

what is the make up percentage of pancreas

A

90% is exocrine glands 2% is endocrine glands 8% is blood vessels and interstitial fluid

52
Q

what is the sympathetic innervation of the pancreas?

A

post-ganglionic fibers from celiac and superior mesenteric plexi to INHIBIT PANCREATIC SECRETIONS (inhibits beta cells, stimulates alpha)

53
Q

what is the parasympathetic innervation of the pancreas?

A

vagus nerve, stimulates pancreatic secretion (inhibits alpha, stimulates beta)

54
Q

describe the structure of the exocrine glands

A

similar to salivary glands, terminal acini that secrete pancreatic enzymes. acinar cells connected to ductal cells by centroacinar cells that secrete pancreatic HCO3

55
Q

what do the acinar cells secrete?

A

pancreatic enzymes. proteases require activation in duodenum amylases and lipases are secreted in active form

56
Q

what do the centroacinar cells secrete?

A

aqueous components , isotonic solution containing Na, Cl, K, HCO3

57
Q

how are pancreatic enzymes synthesized?

A

in the RER, packaged by the golgi, then concentrated into zymogen granules.

58
Q

how does CCK lead to pancreatic enzyme release

A

CCK allows fusion of zymogen granules in the acinar cells with the plasma membrane for release into the acinar lumen

59
Q

what ionic concentrations in pancreatic fluid vary with flow rate?

A

Na and K remain isotonic to plasma Cl and HCO3 vary with flow rate

60
Q

what modifies the initial isotonic solution

A

ductal cells apical Cl/HCO3 exchanger basolateral Na/K ATPase

61
Q

how is pancreatic secretion made?

A
  1. hydration of metabolic CO2 is catalyzed by carbonic anhydrase to carbonic acid
  2. carbonic acid dissociates to H and HCO3
  3. protons transported to plasma using basolateral Na/H antiport (temporary acidification of venous blood)
  4. HCO3 is exchanged for Cl by apical antiport
  5. 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

62
Q

what occurs at low flow rates?

A

pancreatic cells secrete an isotonic solution comprising Na, Cl and water

63
Q

what occurs when pancreas stimulated by secretin?

A

composition changes, remains isotonic with Na, HCO3 and water.

64
Q

describe pancreatic juice composition

A

Na and K concentrations stay constant, HCO3 and Cl concentrations vary – bicarb concentration peaks at flow rates above 30microL/min

65
Q

what regulates acinar cell enzymatic secretions?

A

acinar cells have CCKa and Ach muscarinic receptors

66
Q

what does Ach binding to muscarininc receptors on acinar cells do?

A

stimulates and potentiates CCK secretion (vagovagal reflex)

67
Q

what stimulates CCK secretion from I cells?

A

amino acids (phenylalanin, tryptophan, methionine), small peptides and fatty acids

68
Q

what if phenylalanine is in the small intestine?

A

I cells are triggered to release CCK. Ach potentiates CCK secretion and increases IP3 and Ca. causes release of enzymes.

69
Q

what regulates ductal cell aqueous secretions?

A

have receptors for CCK, Ach, secretin

70
Q

what triggers release of secretin

A

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

71
Q

what inhibits pancreatic secretions?

A

fat in the distal SI signals the end of the intestinal stage of digestion VIA peptide YY, ileal endocrine cells, and somatostatin

Medical Physiology (21 decks)

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