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ZOOL463 > Gastrointestinal Physiology > Flashcards

Gastrointestinal Physiology Flashcards

1
Q

digestion

A

breakdown of food into simpler molecules for absorption and transportation in bloodstream

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2
Q

what are 4 basic processes of the digestive system?

A
  1. motility
  2. secretion
  3. digestion
  4. absorption
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3
Q

what defence mechanisms exist to repel foreign invaders?

A

mucus, enzymes, acid, lymphoid tissue (GALT - gut-associated lymphoid tissue)

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4
Q

function of mouth, pharynx, esophagus

A

mechanical breakdown of food

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5
Q

function of stomach

A

acidic compartments, main role is to break down complex protein molecules

  • reservoir (storage)
  • partial protein digestion
  • disinfection
  • formation of chyme = bolus + gastric juices
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6
Q

function of upper or small intestines

A

digestion and absorption

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7
Q

function of lower or large intestines (colon + rectum)

A

absorption of water to prevent dehydration, watery chyme is converted to semisolid feces, distention of rectal wall triggers defecation reflex

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8
Q

function of anus

A

release of indigestible material

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9
Q

major regions of the stomach

A
  • fundus (predigestion storage)
  • body (where most digestion takes place)
  • antrum
  • two sphincters
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10
Q

what are the 3 sections that comprise the small intestine?

A
  1. duodenum (where all enzymes are released from)
  2. jejunum
  3. ileum
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11
Q

what modifications exist to increase lumen surface area?

A
  • rugae in the stomach
  • plicae in the small intestine
  • microvilli in small intestine
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12
Q

what are the 4 layers of the GI tract wall?

A
  1. mucosa (closest to the lumen/outside of the body)
  2. submucosa
  3. muscularis - smooth muscle
  4. serosa - connective tissue
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13
Q

mucosa

A

consists of a single layer of epithelial cells, lamina propria (capillaries + vasculature), muscularis mucosae (smooth muscle whose function is to open up epithelial cells to increase surface area)

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14
Q

what are 4 types of epithelial cells in the stomach?

A
  1. mucus cells
  2. parietal cells
  3. chief cells
  4. G cells
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15
Q

mucus cells

A

secrete mucus (these cells are replaced often)

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16
Q

parietal cells

A

secrete HCl

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17
Q

chief cells

A

secrete pepsinogen

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18
Q

G cells

A

secrete gastrin (a hormone which is released into the circulation/lamina propria layer)

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19
Q

what are the dominant epithelial cells in the small intestine?

A
  1. absorptive cells (brush-border membrane)
  2. endocrine cells
  3. goblet cells
  4. other secretory cells (e.g. mast cells which secrete histamine)
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20
Q

absorptive cells

A

move nutrients to the extracellular fluid

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21
Q

goblet cells

A

small intestine version of mucus-secreting cells

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22
Q

lamina propria

A
  • subepithelial connective tissue
  • contains nerve fibers
  • contains blood and lymphatic vessels
  • wandering immune cells
  • macrophages and lymphocytes
  • Peyer’s patches
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23
Q

Peyer’s patches

A

collection of lymphoid tissue in the mucosa layer of the stomach

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24
Q

muscularis mucosa

A
  • separates mucosa from submucosa

- contraction of this smooth muscle alters effective surface area

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25
Q

submucosa

A

a thick connective tissue layer

  • contains nerves, glands, blood vessels
  • contains the submucosal plexus
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26
Q

enteric plexus is comprised of:

A

the submucosal plexus (submucosa layer) and myenteric plexus (muscularis layer)

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27
Q

muscularis

A
  • two layers of smooth muscle
  • inner layer is circulation (constriction/dilation)
  • outer layer is longitudinal (shorten/length)
  • stomach also has a third layer (oblique for sideways contraction/movement)
  • contains the myenteric plexus (neuronal network that regulates muscles of muscularis)
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28
Q

serosa

A
  • the visceral peritoneum, holds GI tract in place
  • connective tissue and simple squamous epithelium
  • continuous with the mesenteries in some areas
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29
Q

interocytes

A

single epithelial cells in small intestine that are important for nutrient absorption

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30
Q

smooth muscle

A

contracts spontaneously and regulated by enteric nervous system and hormones, dictated by the type of food you eat

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31
Q

single unit smooth muscle

A

responsible for pacemaker/spontaneous contractions, generates basal electrical rhythm

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32
Q

interstitial cells of Cajal (ICCs)

A

network of cells that produce the slow waves in circular muscle of musculars (spontaneous slow waves of graded depolarization)

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33
Q

basic electric rhythm (BER)

A

frequency of slow waves generated by ICCs, varies in different areas of the GI tract, propagation because of electrical coupling via gap junctions, affected by neural and hormonal input

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34
Q

tonic contractions

A

sustained, occur in smooth muscle sphincters and stomach, keep bolus from moving backwards

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35
Q

phasic contractions

A

last a few seconds, peristalsis moves bolus forward, segmentation mixes (mixes food in both directions)

36
Q

peristaltic reflex

A

waves triggered by distention of wall

37
Q

peristalsis

A
  • progressive wave of contraction that promotes forward movement
  • mediated through the enteric nervous system
  • influenced by hormones, paracrines, autonomic nervous system
38
Q

segmental contractions

A
  • mixing contractions
  • circular muscle contracts while the longitudinal muscle relaxes while the opposite pattern occurs in the receiving segment
  • mixes food while keeping them in contact with absorptive epithelium
39
Q

zymogens

A 
inactive proenzymes:
chymotrypsinogen - chymotrypsin
procarboxypeptidase - carboxypeptidase
procolipase - colipase
prophospholipase - phospholipase
trypsinogen - trypsin
pepsinogen - pepsin
40
Q

trypsinogen is converted to trypsin by:

A

enteropeptidase (which is stored in the brush border membrane of the small intestine)

41
Q

what enzyme is necessary for cells that secrete acid/bicarbonate?

A

carbonic anhydrase

42
Q

where does bicarbonate secretion occur?

A

pancreatic duct cell or duodenal cell

43
Q

where does chloride secretion occur?

A

intestinal and colonic crypt cells

(chloride ions enter lumen through CFTR channel), also causes sodium secretion by paracellular pathway

44
Q

amylase

A

found in the mouth, breaks down glucose polymers to disaccharides

45
Q

disaccharidases

A

found in the intestinal epithelium (on the brush border membrane), breaks down disaccharides into monosaccharides

46
Q

how does glucose enter the body?

A
  • enters interocytes via SGLT (sodium-glucose transporter)

- enters bloodstream via GLUT (glucose transporters)

47
Q

proteases

A

breaks down proteins into smaller peptides, usually secreted as inactive proenzymes, secreted by stomach, intestine, pancreas

48
Q

endopeptidases

A

targets inside of protein for cleavage, produces smaller peptides

49
Q

exopeptidases

A

cleaves from the ends of protein, produces single amino acids
-can be further subdivided into amino- and carboxy-peptidases

50
Q

how do amino acids enter the body

A
  • enter interocytes via sodium-coupled transporters on the apical membrane (symport)
  • facilitated diffusion into ECF and circulation
51
Q

transcytosis

A

formation of vesicles (endocytosis) that allows proteins to enter interocytes and then circulation via exocytosis (basis of food allergies, proteins aren’t supposed to enter circulation, otherwise it may activate the immune system)

52
Q

fat digestion is aided by 2 types of secretions:

A
  1. bile

2. colipase

53
Q

fat digestion

A
  1. mouth: lingual lipase breaks down triglycerides into monoglyceride and free fatty acids (released by serous glands in the tongue)
  2. stomach: lingual and gastric lipases
  3. small intestine/pancreas: bile salts break up large globules of lipids into tiny droplets called micelles, pancreatic lipase breaks down triglycerides into monoglycerides and free fatty acids stored in micelles
    absorption via simple diffusion of monoglycerides and micelles
54
Q

bile

A
  • assist in fat breakdown for digestion and absorption
  • contains salts, pigments, cholesterol
  • stored in the gallblader
55
Q

bile salts

A

bile acid combines with amino acids

this is what coats fat droplets

56
Q

chylomicrons

A

formed in intestinal cells/interocytes by combination of absorbed fat with cholesterol and proteins, chylomicrons are then released into the lymphatic system via lacteals

57
Q

nucleic acid

A
  • not a significant part of most diets
  • digested by pancreatic and intestinal enzymes
  • breaks down into nucleotides, then bases + monosaccharides
  • absorption of bases via active transport, monosaccharides enter via the same mechanisms as glucose uptake
58
Q

absorption of vitamins A, D, E, K

A

(fat soluble), absorbed with fats

59
Q

absorption of water soluble vitamins

A

mediated transport

60
Q

absorption of vitamin B12

A

absorption depends on intrinsic factor secreted by stomach, if deficiency of B12 absorption = pernicious anemia

61
Q

absorption of minerals

A

active transport (linked to their concentrations in the body because they can contribute to the electrical gradient)

62
Q

CNS integrates:

A

long reflexes

63
Q

ENS integrates

A

short reflexes (motility, secretion, growth)

64
Q

cephalic phase of digestion

A

reflex outside of ENS, i.e. CNS-mediated reflexes

65
Q

gastric pits

A

invaginations in the stomach that increase surface area

66
Q

gastrin family of GI hormones

A
  • gastrin and cholecystokinin (CKK)
  • gastrin is synthesized by G cells in the stomach
  • CCK is synthesized in intestinal mucosa
67
Q

secretin family of GI hormones

A
  • secretin
  • vasoactive intestinal peptide (VIP)
  • glucose-dependent insulinotropic peptide (GIP)
  • glucagon-like peptide 1 (GLP-1)
68
Q

secretin

A
  • synthesized in intestinal mucosa
  • released in response to acidic chyme in small intestine
  • causes release of pancreatic buffers (bicarbonate ions) to neutralize small intestine environment
69
Q

vasoactive intestinal peptide (VIP)

A
  • synthesized in the ENS

- contracts/relaxes muscle

70
Q

glucose-dependent insulinotropic peptide (GIP)

A
  • released in resopnse to carbohydrates
  • synthesized in intestinal mucosa (epithelium interocytes of duodenum)
  • in the presence of glucose, it stimulates insulin release (a trophic hormone, acts on pancreas)
71
Q

glucagon-like peptide-1 (GLP-1)

A
  • functions similarly to GIP

- stimulates insulin-release by pancreas

72
Q

motilin

A

regulates motility, peristalsis, segmentation contractions

73
Q

cholecystokinin

A
  • released in response to fatty food
  • synthesized in intestinal mucosa
  • stimulates gallbladder contractions for bile release
  • delay of gastric emptying (helps fat digestion)
  • enhance satiety
74
Q

gastrin

A
  • synthesized in the stomach
  • released following parasympathetic activity after a meal or by stimulation from enteric nervous system
  • stimulates acid secretion by direct action on parietal cells in stomach or indirectly through histamine
75
Q

procolipase

A

split into colipase (signals to act on fat) and enterostatin (released into duodenum)

76
Q

enterostatin

A

satiety signal for fat ingestion

77
Q

histamines

A

secreted into ECF on the basolateral side, effects acid secretion
- secreted by enterochromaffin cells in gastric-mucosal lumen

78
Q

serotonin

A

increased luminal pressure, stimulates reflex

79
Q

what are the gastric events following a meal?

A

cephalic phase (brain involvement, long reflex), gastric phase (short reflex), intestinal phase

80
Q

reflux esophagitis

A

heartburn

81
Q

what is the negative feedback signal that modulates acid and pepsin release?

A

somatostatin release by D-cells (triggered by increased H+) - causes inhibition of cells that stimulate digestion

82
Q

stomach ulcers

A

erosion of stomach lining by gastric juices

83
Q

peritonitis

A

inflammation of the peritoneum caused by perforating ulcers (perforation of mucus layer), can be fatal

84
Q

effect of aspirin and other non-steroidal anti-inflammatory drugs

A

inhibit mucus and bicarbonate secretion

85
Q

helicobacter pylori

A

stomach bacteria that can precipitate an immune response that destroys the stomach lining making it more vulnerable

86
Q

solutions for stomach ulcers

A
  • buffer stomach acid (milk, antacids)

- proton pump inhibitors (omeprazole)

87
Q

what comprises the intestinal phase?

A

reflexes that direct digestion action

  • limit chyme entrance rate and motility (chyme in the small intestine inhibits gastric motility and secretion)
  • neutralize HCl, add bile and enzymes
  • most of digestion/absorption occurs in the small intestine
  • large intestine concentrates waste for excretion
  • mass movement triggers defection
  • absorption of bile salts, water, and some nutrients
  • microbe-mediated digestion of complex carbohydrates

ZOOL463 (7 decks)

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