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HUBS192 > GI PHYSIOLOGY II - SECRETION > Flashcards

GI PHYSIOLOGY II - SECRETION Flashcards

1
Q

TRUE/FALSE: the GI tract secretes and then reabsorbs around 8L of fluid per day?

A

true

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2
Q

what is secretion? what is absorption?

A
  • secretion = movement of solutes and water from body to lumen
  • absorption = movement of solutes and water from lumen to body
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3
Q

what is endocrine secretion? what is exocrine secretion?

A
  • endocrine = ‘secretions’ move into the body and not secreted as much
  • exocrine = secretions produced by epithelia and move into the lumen
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4
Q

what are the 3 components of exocrine secretion?

A
  • mucous
  • electrolyte solution
  • digestive enzymes
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5
Q

what are the functions of the 3 components of exocrine secretion?

A
  • mucous: protection, lubrication and aids mechanical digestion
  • electrolyte solution: dilution, provides optimal pH and essential for chemical digestion
  • digestive enzymes: chemical digestion and aids absorption
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6
Q

what are the volume of electrolyte solution approximately that is secreted per day?

A
  • plasma: total 3L
  • saliva: 1.5L
  • stomach: 3L
  • pancreas: 1.5L
  • liver: 0.5L
  • small intestine: 1.5L
    –> 8L perday from 3L of plasma meaning that reabsorption is important
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7
Q

what are the approximate pH of each region of the GI?

A
  • plasma: 7.4
  • saliva: 7.6
  • stomach: 1
  • pancreas: 7.8
  • liver: 7.5
  • small intestine: 7.5
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8
Q

what are the 2 types of salivary secretion? what are their rate of secretion?

A
  • basal (resting) secretion: 0.3mL/min
  • stimulated secretion: 1.5mL/min
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9
Q

what are the composition of saliva?

A
  • mucus
  • dilute solution of NaHCO3/NaCl
  • digestive enzymes
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10
Q

what are the function of NaHCO3/NaCl in saliva?

A
  • dilution of food
  • ensure optimal pH for digestive enzymes
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11
Q

what are the 2 salivary enzymes?

A
  • lingual lipase
  • alpha-amylas
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12
Q

what are the functions of salivary secretion?

A
  • aids
  • hygiene
  • digestion
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13
Q

What do salivary secretions aid in (2)?
What are their roles in hygiene (2)?
What are their roles in digestion(3)

A
  • Talking
  • Chewing and swallowing
  • Irrigation
  • Xerostomia - dry mouth
  • Dissolving food for taste
  • Lingual lipase for fats
  • alpha amylase for starch
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14
Q

what regulates the salivary secretion?

A
  • nervous: visual, smell or taste stimuli
  • autonomic nervous system: both parasympathetic and sympathetic
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15
Q

what stimulates the secretion of copious quantities of salivary fluid?

A

parasympathetic

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16
Q

what stimulates the secretion of small volumes of viscous salivary fluid?

A

sympathetic

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17
Q

where are salivary secretions released? what are the names of these? what proportion of the total volume are these?

A
  • sublingual 5%
  • submandibular 70%
  • parotid 25%
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18
Q

what is the amount of gastric secretion per day?

A

2-3L

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19
Q

what is the rate of secretion between meals? mostly what from where?

A
  • slow rate of 15-30mL/hour
  • mostly mucous and bicarbonate
  • from surface epithelium cells
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20
Q

in stomach, where secretes what during eating?

A
  • surface epithelial cells secrete bicarbonate and mucous
  • parietal cells secrete acids and intrinsic factor
  • chief cells secrete pepsinogen
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21
Q

what is the rate of gastric acid secretion while eating?

A

150mL/hour

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22
Q

what is the function of gastric mucous?

A

provide protection against abrasion and acid

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23
Q

what is the function of gastric intrinsic factor?

A

stabilise vitamin B12 and facilitates its absorption in small intestine

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24
Q

what is the function of pepsinogen?

A
  • inactive form of pepsin - a gastric proteolytic enzyme
  • converted to active form pepsin by acid
  • starts digestion of protein
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25
Q

what is the function of gastric acid?

A
  • dilute food
  • denature protein
  • activates pepsinogen to pepsin
  • creates optimum pH for pepsin action
  • protection against foreign bacteria
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26
Q

what is the source of acid in stomach?

A
  • carbonic anhydrase –> form H2CO3
  • dissociation of H2CO3 to give H+ and HCO3-
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27
Q

how does H+ being secreted into stomach?

A
  • H+ - K+ ATPase on apical membrane of parietal cells
  • pump H+ into lumen in exchange with K+
  • K+ return to lumen through membrane channel
28
Q

what is the source of chloride in stomach

A
  • anion counter transporter at serosal membrane of parietal cells ejects HCO3- into interstitial fluid
  • inports Cl- ions into cells
29
Q

how does chloride being secreted into stomach?

A
  • Cl- diffuse across cell
  • then enters lumen via Cl- channel in apical membrane
30
Q

TRUE/FALSE: gastric secretion coordinated with eating and arrival of food

A

true

31
Q

what are the 3 phases of gastric secretion? what percentage of secretion associated with meals is related to each phase?

A
  • cephalic: head controls secretion - 20%
  • gastric: stomach controls secretion - 70%
  • intestinal: intestine controls secretion - 10%
32
Q

what does the cephalic phase basically do?

A

prepare for arrival of food

33
Q

what stimulate the cephalic phase?

A
  • higher centers (CNS): thoughts, smell, sight of food
  • chewing, tasting
34
Q

how does extrinsic parasympathetic nervous system respond to the stimuli during cephalic phase?

A
  • via ENS
  • stimulates parietal cells, chief cells and goblet cells
  • stimulate secretion of hormone gastrin
35
Q

what does hormone gastrin do?

A

release into blood then stimulates parietal cells and chief cells

36
Q

what does the gastric phase basically do?

A

ensure sufficient secretion to handle ingested food

37
Q

what stimulates the gastric phase?

A
  • stretch of stomach wall
  • products of digestion stomach lumen
  • elevated pH
38
Q

describe the nervous and hormonal regulation of gastric phase?

A
  • ENS local nervous reflex
  • external nervous reflex associated with parasympathetic nervous system
  • both above stimulate: secretion from gastric glands, motility and gastrin secretion
39
Q

what does intestinal phase basically do?

A

controls delivery to small intestine

40
Q

what stimulate the intestinal phase?

A

arrival in duodenum of:
- acidic chyme
- lipids and carbs

41
Q

describe nervous and hormonal regulation of intestinal phase

A
  • hormones involved: GIP, CCK, secretin
  • nerves: long reflex duodenum to brain to stomach
  • both activities above inhibit secretion and motility
42
Q

how much does pancreas secrete per day?

A

1-1.5L

43
Q

what are the 2 components of pancreatic secretion?

A
  • enzymes
  • alkaline fluid
44
Q

which structure secrete enzyme in pancreas?

A

acinar cell

45
Q

what are the pancreatic digestive enzymes?

A
  • lipolytic –> lipase/phospholipase
  • amylytic –> pancreatic amylase
  • proteolytic –> trypsin, chymotrypsin, carboxypeptidase
  • nucleolytic - ribonuclease/deoxyribonuclease
46
Q

what stimulate the secretion of digestive enzyme in acinar cells of pancreas?

A

hormone cholecystokinin (CCK)

47
Q

what stimulates CCK secretion?

A

arrival of lipids and carbohydrates in duodenum

48
Q

TRUE/FALSE: proteolytic enzymes secreted as inactive precursors and activated in the stomach?

A

FALSE
although proteolytic enzymes are secreted as inactive precursors, however they are activated in duodenum, not stomach

49
Q

name the precursors and proteolytic enzymes?

A
  • trypsin - trypsinogen
  • chymotrypsin - chymotrypsinogen
  • carboxypeptidase - procarboxypeptidase
50
Q

what does activation of the proteolytic enzymes involved?

A
  • enterokinase (enteropeptidase): structure bound to duodenal membrane and concerts trypsinogen into trypsin
  • then trypsin converts other enzymes to active form
51
Q

where is the alkaline fluid (HCO3 rich) produced?

A

duct cells in pancreas

52
Q

what stimulate the secretion of alkaline fluid/HCO3 in pancreas?

A

hormone secretin

53
Q

what stimulate the secretion of secretin?

A

arrival of acidic chyme in duodenum

54
Q

what are the functions of alkaline fluid?

A
  • neutralises acid chyme delivered from stomach
  • creates optimum pH for pancreatic and intestinal enzyme
55
Q

what is the amount of biliary secretion per day?

A

0.5L

56
Q

what are the products and what are their functions of the biliary secretion?

A
  • bile salts: fat digestion
  • HCO3- rich fluid: neutralise acid
  • bile pigments: waste product for excretion
  • cholesterol: excretion
57
Q

briefly describe the production of bile

A

constantly secreted by liver, stored and concentrated in gallbladder and delivered to duodenum through bile duct with arrival of food

58
Q

what initiate the delivery of bile?

A
  • CCK and secretin
59
Q

what events associated with CCK secretion?

A
  • respond to products of digestion in duodenum
  • contraction of gallbladder
  • relaxation of hepatopancreatic ampulla
60
Q

what does secretin do to bile?

A

mild stimulation of bile by liver

61
Q

what stimulates bile secretion?

A

bile itself (enterohepatic circulation)

62
Q

what does it mean by saying enterohepatic circulation of bile?

A

because bile is hard to produce metabolically, 95% of them is reabsorbed in ileum and then transported back to liver for another circulation

63
Q

what is the amount of secretion from small intestine per day and where is it secreted?

A

1.5L from crypts/glands

64
Q

what are the small intestinal secretion? what are their function?

A
  • mucous for lubrication
  • isosmotic fluid (mixture of NaCl and NaHCO3) to helps neutralise acid and dilute food to aid digestion
  • digestive enzymes
65
Q

what is the large intestine secretin and what does it do?

A

mucous for lubrication

HUBS192 (23 decks)

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