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GIT Flashcards

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1
Q

What is a criteria for substances to be absorbed by small intestine

A

Water soluble

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2
Q

Describe the 3 types of gi motility

A

Segmentation:

  • not moving, churning effect
  • non propulsive contraction
  • at small and large intestine

Peristalsis: propulsive force to move luminal contents

Tonic contraction: relatively prolonged contraction to isolate and divide segments, occurs at sphincters

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3
Q

How does esophagus prevent retrograde movement of esophageal or gastric contents

A

Tonic contraction (prolonged contraction) of upper and lower esophageal sphincter

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4
Q

How is tone of les controlled

A

Modulated by swallowing centre controlling involuntary movement of smooth muscle. Increase tone by cholinergic agonist, a adrenergic agonist, gastrin, substance p (increase pain). Decrease tone by b adrenergic agonist, dopamine, cck, coffee, nicotine

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5
Q

Function of gastric motility between meals

A

Clear undigested debris and slough epithelial cells

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6
Q

What are the 3 relaxations involved in gastric motility after a meal

A

Reflex, adaptive, feedback

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7
Q

Timing for gastric emptying of solids

A

Half life is 2 hours. Initial lag phase of about 1 hour (extensive mixing and retropulsion at stomach). Linear emptying phase for 1 or more hours until stomach empty.

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8
Q

Tell me about liquid emptying

A

Isotonic saline/water empty rapidly. First order kinetics between volume and rate. When nutritional value increases, higher the caloric density, slower the emptying due to feedback from small intestine. Maximum inhibition at 1M/18% glucose. Fructose less inhibition on gastric emptying compared to glucose and xylitol. 200kcal/h into duodenum

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9
Q

How do the 2 types of abnormal gastric emptying work

A

Projectile vomiting not accompanied by nausea: vomit centre in medulla activated by afferent fibres. Caused by irritation due to injury or increase in intracranial pressure.

Nausea: chemoreceptor trigger zone in brainstem activated by afferent fibres from GIT or circulating vomit inducing agents eg apomorphone

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10
Q

What is the function of migrating motor complex (90-120 minutes per cycle) in intestine

A

Housekeeping during interdigestive period: clear undigested debris and slough epithelial cells, and inhibit migration of colonic bacteria into distal epithelium

Mmc is depressed when food enters

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11
Q

What is the main function of the small intestine

A

Process and absorb nutrients. Does so by mixing chyme with digestive juices and bile, propelling chyme in caudal direction and bringing chyme in contact with microvilli

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12
Q

What is the function of gastrin in small intestine

A

Stimulate motility, increase mucin and intestinal juice production, promote relaxation of ileocecal sphincter

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13
Q

What is intestinointestinal reflex

A

Severe distension or injury to any part of the small intestine inhibit motility in rest of small intestine

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14
Q

What is the gastroileal reflex

A

Chyme in stomach triggers increased motility in ileum

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15
Q

Ileogastric reflex

A

Distension of ileum inhibit gastric motility

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16
Q

How does distension of proximal colon affect ileocecal sphincter

A

Contraction to prevent food from moving backwards from colon to small intestine

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17
Q

Why is transit in large intestine slow

A

No villi hence small absorptive area. Hence slow transit to aid microbial digestion of complex carbohydrates to volatile scfa for absorption and aid absorption of water and electrolytes

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18
Q

What is the effect of distension of rectal wall on anal sphincters

A

Relaxation of internal anal sphincter (involuntary). Contract external anal sphincter (voluntary) with the tensing of abdominal muscles.

Involuntary defecation if pressure > 55mmhg

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19
Q

What are 3 factors that can result in diarrhoea

A

Inflammation, leading to malabsorption, increasing intestinal lumen pressure. Increased bowel motility, increasing risk of diarrhea

Failure to absorb nutrient molecules effectively, osmotic action of carbs and proteins draw water into colon resulting in distension of rectal wall triggering defecation reflex

Excess secretion by small intestinal mucosa. Usually secrete large amounts of water but 99% reabsorbed. Diarrhoea if secretion exceeds absorption

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20
Q

How much saliva is produced per day

A

1-1.5L

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21
Q

Is it true that glands have a low rate of blood flow and metabolism

A

No! High rates, blood flow to glands 10 times that of blood flow to actively contracting skeletal muscle

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22
Q

At what ph is alpha amylase active

A

Ph 4-11

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23
Q

What is the ph of saliva

A

pH6.2 to 7.5

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24
Q

What is the function of parietal cells in stomach

A

Secrete HCl that kills bacteria (except helicobacter pylori which neutralises acid, and that activates pepsinogen secreted by chief cells to pepsin to digest bacteria

Secrete intrinsic factor for absorption of vitamin b12

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25
What happens when rate of secretion from blood to gastric juice increase
Ph of gastric juice decreases as more h+
26
Why is there hypokalemia in prolonged vomiting
K+ in gastric juice is always greater than in blood plasma. Vomiting lead to loss of H+ (alkalosis). H+/K+ exchange mechanism, shift of K+ out from plasma and interstitial fluids into urine ie increased renal excretion of K+
27
What is basal and stimulated rate of gastric acid secretion
Basal: 1-5mM/hour | Max stimulated: 6-40mM/hour
28
What are the stimulators of hcl secretion
Histamine and adrenaline (act through cAMP, stress) | Gastrin and acetylcholine (act through Ca2+, relaxation, digestion and basal hcl respectively)
29
What are inhibitors of hcl secretion
Omeprazole, prostaglandins, histamine antagonists, anticholinergics, gastrin antagonists
30
At what ph is pepsinogen most active
<3, converted by HCl. | Inactivated irreversibly at alkaline duodenum ph
31
Where is intrinsic factor-b12 complex absorbed
Terminal ileum. Loss of terminal ileum lead to pernicious anemia. IF complexes with B12 to make it resistant to digestions. IF produced at fundus of stomach
32
Why is the stomach better protected against acid than the small intestine
Mucin is insoluble in acidic pH + cannot be destroyed by pepsin (hence resistant to acid digestion) and is precipitated out. Stomach has lower ph (2 when empty 5-6 when full) and is hence better protected
33
How is mucin secretion regulated
Same as HCl: gastrin and ach stimulate Mucin not secreted during stress, only hcl Also mechanical stimulation
34
How do prostaglandins affect gastric mucosal cells
Local paracrine effect ie affect cells in close proximity
35
What is the function of prostaglandins
Stimulate mucin, phospholipid and bicarbonate secretions. Enhance mucosal blood flow. Stimulate mucosal cell turnover. Directly inhibit parietal cell secretion (HCl!!) Hence prostaglandin deficiency due to cox inhibitors lead to stomach ulcer Prostaglandin also sensitive nociceptors but this is in neurophysio teehee
36
What can reduce HCO3- secretion from mucus in gastric
``` Adrenergic agonists (increase hcl secretion) Aspirin and NSAIDS via inhibition of prostaglandins which stimulate HCO3- secretion ```
37
How many days does it take to replace the entire mucosa
1-3 days (high replacement rate = high growth rate)
38
How to treat ulcers
Neutralise HCL via antacids, prevent acid secretion (omeprazole, irreversible or cimetidine, reversible), antibiotics (for helicobacter pylori), prostaglandin agonists (increase mucin, decrease hcl)
39
Why is fat digestion in the stomach minimal
High acidity in stomach inhibits fats from forming emulsion, hence insoluble and cannot be digested (stomach only absorb highly fat soluble substances)
40
What causes heartburn
Increase in gastric acid secretion, backflow into esophagus around region of heart. Backflow of acidic chyme from stomach into esophagus. Could be due to coffee which decreases tone of LES (relaxation), or tight clothing which prevents distension of proximal stomach, hence chyme spills upward past LES
41
How does small intestine have large surface area
Villi, microvilli, multiple folds
42
What does cck do
Inhibit gastric emptying, stimulate secretion mucus in small intestine, stimulate secretion of digestive enzymes from pancreas
43
What does secretin do
Regulate ph of duodenum bu inhibiting gastric acid secretion from parietal cells and stimulating HCO3- secretion
44
Where is hco3- produced
Crypts of lieberkuhn of duodenum (overlying intestinal glands) Vs brunner’s glands which are at submucosa of proximal duodenum and secrete mucin (coat duodenal epithelium to protect from acid chyme)
45
How much intestinal juice is produced a day
2-3L
46
How does stress lead to diarrhea
Stress lead to increased cAMP levels, activating cl- levels causing less fluid to be absorbed resulting in diarrhea
47
What is the ph of the large intestine
8-8.4. Buffer against H+ produced by bacterial fermentation
48
What stimulates small intestinal juice secretion
Gastrin, acetylcholine
49
What stimulates intestinal juice secretion at large intestine
Parasympathetic nerve impulses, mechanical and chemical irritation of mucosa
50
What is congenital cl- diarrhea
Lack hco3-/cl- exchanger. Small intestine has elevated cl- and depressed hco3- , resulting in osmotic movement, causing diarrhea
51
How does oral rehydration therapy work
Glucose concentration cannot excees 1mM. SGLT1 transporter. Use glucose to bring in sodium, bring in cl-, creating osmotic gradient to draw water in
52
What are the 3 phases of pancreatic secretion
Cephalic: vagal stimulation, activated by thought, smell, sight etc of food. Secretion of enzymes and bicarbonate Gastric: stimulated by gastric distension and food break down products. Release of gastrin that stimulates low volume high enzyme pancreatic secretion Intestinal: 70% of total pancreatic secretion. Stimulated by CCK and secretin from endocrine cells of duodenum and upper jejunum. Stimulate secretion of hco3-
53
What is the rate limiting step in carbohydrate absorption
Break down of oligosaccharides into monosaccharides by brush border disaccharides in SI. Enzyme activity greatest at brush border of jejunum
54
How does lactase deficiency lead to diarrhea when you take dairy
Accumulate lactose in bowel lumen. Lactic acid production plus accumulation of sugar increases lumen osmolality —> fluid accumulation —> fluid distension and enhanced peristalsis that reslts in watery diarrhea
55
What is protein in the jejunum for
Protein digested in colon provide ammonia for microflora/bacteria. About 10% of dietary protein
56
What does elevated cck stimulate
Contraction of gallbladder and relaxation of sphincter of Oddi for increased bile flow into common bile duct and duodenum
57
Where are primary bile acids actively reabsorbed
Terminal ileum
58
How are secondary bile acids formed
Via deconjugation and dehydrozylation of primary bile acids by intestinal bacterea
59
Why are bile salts more hydrophilic than bile acids
Bile salts are bile acids that have been conjugated with glycine or taurine. More hydrophilic, more able to form micelles for fat absorption
60
How much bile required per meal
4-8g
61
What are the 3 main pancreatic lipases
Glycerol ester hydrolase, cholesterol esterase, phospholipase a2
62
What is the rate limiting step in absorption of fat >95% absorption of triglycerides!
Migration of micelle from chyme to microvilli surface
63
What kinds of food will slow down gastric emptying
Solid meals, low volume meals, fat (slowest, tend to signal end of digestion hence slow down gastric emptying), proteins, chyme with high acidity or osmotic pressure
64
What kind of control is gastric emptying under
Neural - increase: anger - decrease: fear, pain Hormonal - increase: gastric - decrease: CCK, GLP-1
65
How are tonic contractions responsible for gastric emptying
Generate pressure gradient from stomach to small intestine
66
Does proximal or distal part of stomach have thicker muscle
Distal portion. Thicker muscle for more movement to squeeze chyme out. Strong peristaltic waves that increase in amplitude
67
What is the effect of a proximal gastric vagotomy
Decreased gastric distensibility (adaptive relaxation mediated by vago vagal reflex arc). This resuts in increased intra gastric pressure after meal ingestions, feeling of fullness
68
Which is most effective amino acid to curb cravings
L-tryptophan

Physio (3 decks)

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