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lsm3214 > GIT > Flashcards

GIT Flashcards

1
Q

Where is HCL secreted and by what cell?

A

In the stomach, by the parietal cells

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2
Q

How does parasympathetic activity affect the slow waves and action potential of smooth muscles?

A

Parasympathetic = rest = higher height of slow waves = more peaks > threshold = more action potentials and more contractions

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3
Q

How does sympathetic activity affect the slow waves and action potential of smooth muscles?

A

Sympathetic = stress = lower height of slow waves = less peaks > threshold = less action potentials and contractions (to avoid resource competition!)

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4
Q

What is the function of the upper esophageal sphincter and what is it made of?

A

Skeletal muscles, controlled by the swallowing center, it contracts to prevent entry of air into the esophagus during breathing and protects the airway from aspiration of food

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5
Q

What is the function of the lower esophageal sphincter and what is it made of?

A

Cardiac sphincter, non-controllable, it contracts to prevent reflux of gastric contents into the esophagus (acidic, damaging!)

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6
Q

What is receptive relaxation?

A

In relation to gastric motility, receptive relaxation is the decrease in proximal gastric tone to facilitate smooth swallowing and prevent discomfort with initial food intake.

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7
Q

What is adaptive relaxation?

A

In relation to gastric motility, adaptive relaxation is relaxation of proximal stomach to accomodate for the inflow of food.

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8
Q

What is feedback relaxation?

A

In relation to gastric motility, feedback relaxation is ongoing relaxation of stomach muscles to accomodate the bolus and deliver contents to the duodenum.
- Proximal stomach: maintain minimal changes in intra-gastric pressure
- Distal stomach: Grind & disperse food, then pass to duodenum at suitable rate for optimal mixing and absorption.

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9
Q

What is small intestine segmentation?

A

Alternating contractions and relaxations of adjacent small intestine segments to mix chyme thoroughly with digestive enzymes.

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10
Q

What is small intestine peristalsis?

A

Coordinated contraction and relaxation of circular and longitudinal muscles to propel the bolus along the entire length of the intestine.

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11
Q

What is the function of HCl?

A

Kill bacteria in ingested food and activates pepsinogen into pepsin

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12
Q

What is the function of pepsinogen?

A

Backup method of protein digestion

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13
Q

Does pepsin work under high or low pH

A

Pepsin activity increases as pH decreases

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14
Q

How does the body protect our stomach lining given HCl secretions?

A

At acidic environment, mucin precipitates so it cannot be digested by pepsin.

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15
Q

What is the function of intrinsic factors?

A

Promote Vitamin B12 absorption via formation of an IF-B12 complex that is resistant to digestion.

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16
Q

What cell secretes intrinsic factors?

A

Parietal cells.

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17
Q

What is the function of gastrin?

A

Regulates and stimulates HCl secretion
Promotes gastric and intestinal motility
Stimulates pancreatic secretion
Regenerates GI membrane growth

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18
Q

What cell secretes gastrin?

A

G cells

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19
Q

What is the function of prostaglandins?

A

Inhibit HCl secretion
Mediates gastric mucosal protection via
1. enhanced blood flow via vasodilation
2. higher mucosal cell turnover
3. Increased mucus, phospholipid, HCO3- secretion

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20
Q

What does the secretion of HCl acid require?

A

Requires H+ K+ exchange at the ATPase proton pump in the lumen

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21
Q

Is the K+ concentration higher in the lumen/gastric juice or the plasma?

A

K+ concentration is always higher in gastric juice/lumen than the plasma as K+ is used to exchange for Na+ via parietal cells.

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22
Q

What are the features of the gastric mucosal barrier?

A

A thick mucous layer that consists of mucins and HCO3-
- Mucous layer precipitates out at low pH, slowing down outward diffusion of HCO3-
- HCO3- protects inward diffusion of H+

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23
Q

What is the function of the gastric mucosal barrier?

A

To protect the stomach against HCl, pepsin and abrasion

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24
Q

What is HCO3- secretion reduced by?

A

cAMP and adrenergic agonists

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25
Q

What is HCO3- secretion stimulated by?

A

Ca2+ and cholinergic agonists

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26
Q

What is HCO3- secretion inhibited by?

A

Aspirin & NSAID

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27
Q

What is the function of the stomach?

A

The stomach functions primarily to hold food, although some digestion happens (salivary amylase, gastric pepsinogen, but no fat digestion as acidic environment causes fat coagulation).

Absorption is minimal

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28
Q

What is the function of the small intestine?

A

Functions primarily to digest and absorb nutrients from ingested food (majority of absorption!)

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29
Q

What is the function of the large intestine?

A

Functions to compact passing material by absorbing water and electrolytes.

30
Q

What is the function of the pancreas?

A

The pancreas secretes digestive enzymes and bi-carbonate rich pancreatic juice into the duodenum of the small intestine to promote digestion

31
Q

What are the pancreatic enzymes secreted?

A

Pancreatic lipase, protease, amylase.

32
Q

What is the cephalic phase of pancreatic secretion?

A

Stimulated by sight, thought, smell, taste, enhanced by vagal stimulation
- leads to secretion of substantial amount of enzymes and HCO3-

33
Q

What is the gastric phase of pancreatic secretion?

A

Triggered by gastric distension which leads to gastrin release and low volume high enzyme secretion

34
Q

What is the intestinal phase of pancreatic secretion?

A

Responsible for 70% of pancreatic secretions

35
Q

What stimulates the intestinal phase of pancreatic secretion?

A

CCK & secretin hormones released from endocrine cells into the small intestine

36
Q

What is the function of CCK?

A

Increased secretion of pancreatic enzymes

37
Q

What is the function of secretin?

A

Increased secretion of HCO3-

38
Q

What is the pathway activated by secretin?

A

cAMP pathway

39
Q

What is the pathway activated by CCK?

A

Ca2+ pathway

40
Q

What does CCK secretion respond to?

A

Fats

41
Q

What does secretin secretion respond to?

A

low pH! (<4.5)

42
Q

What is the difference in nutrient absorption and selection in the duodenum, jejunum and ileum?

A

Duodenum & upper jejunum: Highly absorptive, low in selectivity and specificity
Lower jejunum & ileum: High affinity for specific molecules, allowing for better selectivity.

43
Q

Why is the small intestines absorptive capacity for Ca2+ and Fe2+ low?

A

Calcium & Iron are divalent cations that are larger in size due to the presence of hydrated water surrounding it. Hence, it is more poorly absorbed.

44
Q

What happens if your body fails to absorb water and electrolytes?

A

Rapid dehydration and circulatory collapse

45
Q

Does the small intestine secrete enzymes?

A

No, but digestion still occurs as enzymes are obtained from pancreatic secretion or release following cell death

46
Q

What pH is intestinal juice?

A

The intestinal juice is slightly alkaline

47
Q

What occurs in the luminal digestion phase of carbohydrate digestion?

A

Digestion begins with salivary amylase which is moved to the stomach with the food bolus.

Digestion continues until the acidic gastric environment inactivates amylase.

The food bolus moves on to the small intestine where it is mixed with pancreatic juice and pancreatic amylase. Amylase breaks carbohydrates into various dissacharides.

48
Q

What occurs in the mucosal digestion phase of carbohydrate digestion?

A

Dissacharides must physically contact disaccharidases located on the microvilli walls to be converted into monosaccharides.

Monosaccharides are absorbed and distributed to other parts of the body and out of enterocytes via passive diffusion!

49
Q

How is fructose absorbed in the small intestine?

A

Fructose is absorbed via facilitated diffusion.

50
Q

How is glucose absorbed in the small intestine?

A

Glucose absorbed via Na+ dependent glucose transporter.

51
Q

Which part of the small intestine has the highest capacity to absorb sugars?

A

Duodenum and upper jejunum

52
Q

Where does majority of protein digestion occur?

A

Duodenum and jejunum

53
Q

What is the end product of protein digestion?

A

Either amino acids or small polypeptides

54
Q

Where is bile formed?

A

Hepatocytes, using cholesterol as a precursor

55
Q

What is the function of bile?

A

Aid emulsification of dietary fats

56
Q

What is the mechanism of action for bile release?

A

Bile release is stimulated by increased CCK secretion –> sphincter relaxes + gallbladder contracts –> increase bile flow into the bile duct and duodenum.

57
Q

What is the composition of bile?

A

Bile acids, bile pigments, phospholipids, electrolytes

58
Q

What are 2˚ bile acids

A

1˚ bile acids deconjugated and dehydrolysed by intestinal bacteria

59
Q

What are the features of 2˚ bile acids?

A

Non-polar = fat soluble = can diffuse through the membrane

60
Q

What are bile pigments?

A

Bile pigments are waste products from hemoglobin metabolisis that are to be excreted

61
Q

How is urobilin obtained?

A

Urobilin is obtained via bacterial conversion of bilirubin at the colon

62
Q

How do you form bile salt?

A

Bile acids are conjugated with glycine/taurine to form bile salts

63
Q

What is the feature of bile salt?

A

Amphipathic

64
Q

Where does bile reabsorption occur?

A

Terminal ileum

65
Q

How is bile recycled?

A

From the small intestine to the liver and back (pool of bile salt is limited!)

66
Q

What occurs in the luminal digestive phase of lipid absorption?

A

Digestion of fats via lipase activity

67
Q

What occurs in the mucosal absorptive phase of lipid absorption?

A

Emulsification of fat globules into micelles via bile salt

Micelle absorption via contact with the microvilli

68
Q

What occurs in the post-absorptive phase of lipid absorption?

A

Fatty acids are re-esterified and packaged with dietary cholesterol into chylomicrons, transported to other parts of the body

69
Q

What is the function of phospholipids in bile?

A

AKA lecithin, functions to increase the detergent power of bile salts as it stabilises triglyceride emulsion

70
Q

Do all fatty acids require re-esterification?

A

No, medium and short chained fatty acids (i.e. length < 12) do not!

71
Q

Why does the large intestine secrete HCO3-?

A

To neutralise the acidity released by bacteria fermentation in the colon

72
Q

What hormone does pancreatic acinar cells react to?

A

CCK - to secrete enzymes

lsm3214 (5 decks)

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