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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
Does HCl denature or hydrolyze ingested proteins?
Denatures (alters tertiary structure) -> more digestible
26
What is inactivated by acidity of stomach?
Carb digestion by salivary amylase
27
What are the only commonly ingested substances absorbed in stomach?
Alcohol and aspirin
28
What are peptic ulcers?
Erosions of mucous membranes of stomach/duodenum produced by HCl
29
What is Zollinger-Ellison syndrome?
Ulcers of duodenum produced by excessive gastric acid secretions -Prone to stomach cancer
30
What is helicobacter pylori?
Bacterium that resided in GI tract that may produce ulcers
31
What is acute gastritis?
Histamine released by tissue damage/inflammation -> further acid secretion
32
What are some protective mechanisms of stomach?
- 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
What is absorbed in duodenum/jejunum?
Carbs, AAs, lipids, iron, Ca2+
34
What is absorbed in ileum?
Bile salts, vitamin B12******************, electrolytes, H2O
35
What are brush border enzymes?
Microvilli have these; not secreted into lumen (remain attached to membrane w/ active sites exposed to chyme)
36
Which enzymes does absorption require?
Both brush border enzymes and pancreatic enzymes
37
What are the 2 major types of contactions in the SI?
1) Peristalsis - slow movement | 2) Segmentation - contraction of circular smooth muscle (mix chyme)
38
What starts contractions of intestinal smooth muscles?
Occur automatically in response to endogenous pacemaker activity
39
What is the rhythm of contractions paced by?
Slow waves - graded depolarizations produced by interstitial cells of Cajal
40
What triggers APs of smooth muscle contractioN?
Opening of VG Ca2+ channels -> inward flow of Ca2+
41
What does the LI absorb?
Little abs fx | -Absorbs H2O, electrolytes, vitamin B comp, vitamin K and folic acid
42
What does the LI secrete?
H2O via active transport of NaCl into intestinal lumen
43
What are some major liver fx?
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
Where is bile pigment (bilirubin) produced?
Spleen, bone marrow and liver | -Liver produces/secretes 250-1500 mL bile/day
45
Free bilirubin + glucuronic acid to form?******************
Conjugated bilirubin (bilirubin glucuronide) -> secreted into bile
46
Conjugated bilirubin is converted by bacteria in intestine to?
Urobilinogen -> absorbed by intestine and enters hepatic vein -Recycled/filtered by kidneys and excreted in urine
47
What happens to iron after hemolysis of RBCs?
Recycled to bone marrow
48
What are bile acids derivatives of?
Cholesterol
49
What does liver remove cholesterol for?
Fat emulsification
50
3 ways liver can detoxify blood?
- Excretion into bile - Phagocytosis by Kupffer cells - Chemical alteration of molecules (ammonia by deamination of AAs -> urea -> urine)
51
How are steroid hormones/drugs inactivated by liver?
Conjugated -> anionic -> can be transported into bile by multispecific organic anion transport carriers
52
Steroid and xenobiotic receptors stimulate?
Production of cyto P450 -> detox****************
53
How does liver regulate blood [glucose]?
1) Glycogenesis/lipogenesis 2) Glycogenolysis/gluconeogenesis 3) Has enzymes for FAs -> KBs
54
Where are albumin/most plasma globulins produced?
Liver | -immunoglobulins NOT PRODUCED IN THE LIVER*************
55
Where is bile stored/concentrated?
Gallbladder
56
2 roles of pancreas?
1) Exocrine - acini -> pancreatic juice | 2) Endocrine -> islets of langerhans -> insulin/glucagon
57
What does pancreatic juice contain?
H2O, HCO3- and digestive enzymes
58
What are most pancreatic enzymes produced as?
Zymogens | -Enterokinase activates trypsin -> activation of other p.enzymes
59
What are the 3 phases of extrinsic control of gastric function?
1) Cephalic 2) Gastric 3) Intestinal
60
What is cephalic phase stimulated by?
Sight/smell/taste of food
61
What happens in cephalic phase?
``` Activation of vagus: Chief cells -> pepsinogen G cells -> gastrin ECL cells -> histamine Parietal cells -> HCl (indirectly) ```
62
What stimulates gastric phase?
Arrival of food in stomach
63
What is gastric secretion stimulated by?
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
What hormones inhibit gastric activity?
Neg. feedback by D cells -> somatostatin (inhibits gastrin), CCK, and GLP-1******************
65
What happens in the intestinal phase?
Inhibits gastric activity when chyme enters SI
66
What stimulates smooth muscle contraction above the bolus?
ACh and substance P
67
What stimulates smooth muscle relaxation below bolus?
NO, VIP and ATP
68
What stimulates intrinsic afferents, which send impulses into intrinsic NS and activates motor neurons of the intestine?
Serotonin
69
What 2 enzymes is the secretion of pancreatic juice/bile stimulated by?
1) Secretin | 2) CCK
70
What is secretin triggered by? What does it stimulate?
Response to acid | Stimulates: HCO3- production by pancreas, HCO3- secretion by liver into bile
71
What is CCK triggered by? What does it stimulate?
Response to fat/protein content of chyme | Stimulates: p.enzymes production, contraction of sphincter of Oddi, enhances secretin
72
What is the only way we can abs sugars during digestion of carbs?
Pancreatic amylase digests starch -> oligosaccharides -> hydrolyzed by brush border enzymes
73
Where does digestion/absorption of protein start?
In stomach when pepsin digests proteins -> polypeptides - In duodenum/jejunum - Cleaved by endopeptidases
74
How are free AAs absorbed?
Cotransport w/ Na+
75
How are dipeptides/tripeptides transported?
Secondary active transport using a H+ gradient -> cytoplasm -> hydrolyzed into free AAs -> blood
76
How are lipids digested/absorbed?
1) Emulsification (bile salt micelles) | 2) Pancreatic lipase and colipase hydrolyze triglycerides -> free FAs and monoglycerides
77
What happens to the remnants of cholesterol after lipoprotein lipase hydrolyze triglycerides to free FAs and glycerol for use in cells?
Taken to liver -> VLDLs (take triglycerides to cells) -> LDLs (take cholesterol to organs/blood vessels)
78
What transports excess cholesterol back to liver?
HDLs

Physiology Exam 5 (5 decks)

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