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Physiology Exam 5 > Digestive System > Flashcards

Digestive System Flashcards

1
Q

What are the exocrine secretions of the GI tract?

A

HCl, H2O, HCO3-, bile, lipase, pepsin, amylase, trypsin, elastase, and histamine***** secreted into lumen of GI tract

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2
Q

What are the endocrine secretions of the GI tract?

A

Stomach and small intestine secrete hormones to help regulate GI sx: gastrin, secretin, CCK****, GIP, GLP-1, guanylin, VIP and somatostatin

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3
Q

Where does max abs occur?

A

SI

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4
Q

What lines the lumen of GI tract?

A

Mucosa (made of simple columnar epithelium)

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5
Q

What is the thin layer of smooth muscle responsible for the folds that increase SA for absorption?

A

Muscularis mucosae

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6
Q

What is the submucosa?

A

Thick, highly vascular layer of CT

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7
Q

What is the importance of the muscularis layers contracting?

A

Move food through the tract, pulverize/mix food -> helps facilitate enzymes

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8
Q

How is the GI tract extrinsically innervated?

A
  • PNS increases motility/GI secretions

- SNS reduce peristalsis/secretory activity

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9
Q

What enzyme catalyzes partial digestion of starch?

A

Salivary amylase (mixed with food during mastication/chewing)

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10
Q

What are the 3 phases of deglutition/swallowing?

A

1) Oral phase - voluntary
2) Pharyngeal/esophageal phases - involuntary
3) Larynx is raise, epiglottis covers entrance to respiratory tract

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11
Q

What moves food from esophagus to stomach?

A

Peristalsis

-After food passes -> LES constricts

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12
Q

What happens if LES is not working?

A

Regurgitation of chime which is acidic -> acid reflux

-In pregnancy high estrogen -> LES loosens

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13
Q

What is the most distensible part of GI tract?

A

Stomach (empties into duodenum)

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14
Q

What are the fx of stomach?

A

Stores food
Initiates digestion of proteins (pepsinogen -> pepsin)
Kills bacteria
Moves food/chyme -> intest

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15
Q

What do gastric glands secrete?

A

Gastric juices

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16
Q

What do goblet cells secrete?

A

Mucus

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17
Q

What do parietal cells secrete?

A

HCl and intrinsic factor*********

  • Requires B12
  • Blocked by proton pump inhibitors
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18
Q

What do chief cells secrete?

A

Pepsinogen (zymogen) -> Pepsin

-Activated by HCl (pepsin is more active at pH of 2)

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19
Q

What do enterochromaffin-like cells (ECL) secrete?

A

Histamine and serotonin

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20
Q

What do G cells secrete?

A

Gastrin

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21
Q

What do D cells secrete?

A

Somatostatin

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22
Q

What do stomach cells secrete?

A

Ghrelin (desire to eat)

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23
Q

How do parietal cells produce HCl?

A
  • Secrete H+ into gastric lumen by primary active transp (ATPase pump)*****
  • Takes in Cl- against its electrochemical gradient, by coupling its transport w/ HCO3-
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24
Q

What is HCl production indirectly stimulated by?

A

Gastrin and ACh

-Both stimulate release of histamine -> stimulates parietal cells to secrete HCl

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25
Q

Does HCl denature or hydrolyze ingested proteins?

A

Denatures (alters tertiary structure) -> more digestible

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26
Q

What is inactivated by acidity of stomach?

A

Carb digestion by salivary amylase

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27
Q

What are the only commonly ingested substances absorbed in stomach?

A

Alcohol and aspirin

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28
Q

What are peptic ulcers?

A

Erosions of mucous membranes of stomach/duodenum produced by HCl

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29
Q

What is Zollinger-Ellison syndrome?

A

Ulcers of duodenum produced by excessive gastric acid secretions
-Prone to stomach cancer

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30
Q

What is helicobacter pylori?

A

Bacterium that resided in GI tract that may produce ulcers

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31
Q

What is acute gastritis?

A

Histamine released by tissue damage/inflammation -> further acid secretion

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32
Q

What are some protective mechanisms of stomach?

A
  • Parietal and chief cells impermeable to HCl
  • Alkaline mucus contains HCO3-
  • Tight junctions between adjacent epithelial cells
  • Rapid rate of cell division (entire epithelium replaced in 3 days)
  • Prostaglandins (NSAIDs) inhibit gastric secretions
33
Q

What is absorbed in duodenum/jejunum?

A

Carbs, AAs, lipids, iron, Ca2+

34
Q

What is absorbed in ileum?

A

Bile salts, vitamin B12****, electrolytes, H2O

35
Q

What are brush border enzymes?

A

Microvilli have these; not secreted into lumen (remain attached to membrane w/ active sites exposed to chyme)

36
Q

Which enzymes does absorption require?

A

Both brush border enzymes and pancreatic enzymes

37
Q

What are the 2 major types of contactions in the SI?

A

1) Peristalsis - slow movement

2) Segmentation - contraction of circular smooth muscle (mix chyme)

38
Q

What starts contractions of intestinal smooth muscles?

A

Occur automatically in response to endogenous pacemaker activity

39
Q

What is the rhythm of contractions paced by?

A

Slow waves - graded depolarizations produced by interstitial cells of Cajal

40
Q

What triggers APs of smooth muscle contractioN?

A

Opening of VG Ca2+ channels -> inward flow of Ca2+

41
Q

What does the LI absorb?

A

Little abs fx

-Absorbs H2O, electrolytes, vitamin B comp, vitamin K and folic acid

42
Q

What does the LI secrete?

A

H2O via active transport of NaCl into intestinal lumen

43
Q

What are some major liver fx?

A

1) Detoxification of blood (production of urea)
2) Carb metabolism (blood glucose -> glycogen and fat)
3) Lipid metabolism (triglycerides/cholesterol/ketone bodies)
4) Protein synthesis (albumin)
5) Secretion of bile

44
Q

Where is bile pigment (bilirubin) produced?

A

Spleen, bone marrow and liver

-Liver produces/secretes 250-1500 mL bile/day

45
Q

Free bilirubin + glucuronic acid to form?****

A

Conjugated bilirubin (bilirubin glucuronide) -> secreted into bile

46
Q

Conjugated bilirubin is converted by bacteria in intestine to?

A

Urobilinogen -> absorbed by intestine and enters hepatic vein
-Recycled/filtered by kidneys and excreted in urine

47
Q

What happens to iron after hemolysis of RBCs?

A

Recycled to bone marrow

48
Q

What are bile acids derivatives of?

A

Cholesterol

49
Q

What does liver remove cholesterol for?

A

Fat emulsification

50
Q

3 ways liver can detoxify blood?

A
  • Excretion into bile
  • Phagocytosis by Kupffer cells
  • Chemical alteration of molecules (ammonia by deamination of AAs -> urea -> urine)
51
Q

How are steroid hormones/drugs inactivated by liver?

A

Conjugated -> anionic -> can be transported into bile by multispecific organic anion transport carriers

52
Q

Steroid and xenobiotic receptors stimulate?

A

Production of cyto P450 -> detox******

53
Q

How does liver regulate blood [glucose]?

A

1) Glycogenesis/lipogenesis
2) Glycogenolysis/gluconeogenesis
3) Has enzymes for FAs -> KBs

54
Q

Where are albumin/most plasma globulins produced?

A

Liver

-immunoglobulins NOT PRODUCED IN THE LIVER*****

55
Q

Where is bile stored/concentrated?

A

Gallbladder

56
Q

2 roles of pancreas?

A

1) Exocrine - acini -> pancreatic juice

2) Endocrine -> islets of langerhans -> insulin/glucagon

57
Q

What does pancreatic juice contain?

A

H2O, HCO3- and digestive enzymes

58
Q

What are most pancreatic enzymes produced as?

A

Zymogens

-Enterokinase activates trypsin -> activation of other p.enzymes

59
Q

What are the 3 phases of extrinsic control of gastric function?

A

1) Cephalic
2) Gastric
3) Intestinal

60
Q

What is cephalic phase stimulated by?

A

Sight/smell/taste of food

61
Q

What happens in cephalic phase?

A 
Activation of vagus:
Chief cells -> pepsinogen
G cells -> gastrin
ECL cells -> histamine
Parietal cells -> HCl (indirectly)
62
Q

What stimulates gastric phase?

A

Arrival of food in stomach

63
Q

What is gastric secretion stimulated by?

A

1) Distension
2) Chemical nature of chyme: G cells -> gastrin, chief cells -> pepsinogen, ECL cells -> histamine (-> HCl)
3) + feedback (more HCl and pepsinogen -> more polypeptides and AAs)

64
Q

What hormones inhibit gastric activity?

A

Neg. feedback by D cells -> somatostatin (inhibits gastrin), CCK, and GLP-1****

65
Q

What happens in the intestinal phase?

A

Inhibits gastric activity when chyme enters SI

66
Q

What stimulates smooth muscle contraction above the bolus?

A

ACh and substance P

67
Q

What stimulates smooth muscle relaxation below bolus?

A

NO, VIP and ATP

68
Q

What stimulates intrinsic afferents, which send impulses into intrinsic NS and activates motor neurons of the intestine?

A

Serotonin

69
Q

What 2 enzymes is the secretion of pancreatic juice/bile stimulated by?

A

1) Secretin

2) CCK

70
Q

What is secretin triggered by? What does it stimulate?

A

Response to acid

Stimulates: HCO3- production by pancreas, HCO3- secretion by liver into bile

71
Q

What is CCK triggered by? What does it stimulate?

A

Response to fat/protein content of chyme

Stimulates: p.enzymes production, contraction of sphincter of Oddi, enhances secretin

72
Q

What is the only way we can abs sugars during digestion of carbs?

A

Pancreatic amylase digests starch -> oligosaccharides -> hydrolyzed by brush border enzymes

73
Q

Where does digestion/absorption of protein start?

A

In stomach when pepsin digests proteins -> polypeptides

  • In duodenum/jejunum
  • Cleaved by endopeptidases
74
Q

How are free AAs absorbed?

A

Cotransport w/ Na+

75
Q

How are dipeptides/tripeptides transported?

A

Secondary active transport using a H+ gradient -> cytoplasm -> hydrolyzed into free AAs -> blood

76
Q

How are lipids digested/absorbed?

A

1) Emulsification (bile salt micelles)

2) Pancreatic lipase and colipase hydrolyze triglycerides -> free FAs and monoglycerides

77
Q

What happens to the remnants of cholesterol after lipoprotein lipase hydrolyze triglycerides to free FAs and glycerol for use in cells?

A

Taken to liver -> VLDLs (take triglycerides to cells) -> LDLs (take cholesterol to organs/blood vessels)

78
Q

What transports excess cholesterol back to liver?

A

HDLs

Physiology Exam 5 (5 decks)

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