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GI 1 Flashcards

GI Lectures 1-4 (1-3 on midterm 2)

1
Q

primary function of the digestive system

A

move nutrients, water and electrolytes from external environment into body’s internal environment

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2
Q

accessory organs in digestive system

A

salivary glands, liver, gallbladder, pancreas

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3
Q

whats mastication

A

mechanical digestion

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4
Q

4 functions of salivary glands

A
  1. moisten, soften, and lubricate foods
  2. amylase partially digests polysaccharides/carbs
  3. dissolve some food molecules (taste)
  4. lysozyme kills bacteria (defense)
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5
Q

3 salivary glands

A

parotid
sublingual
submandibular

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6
Q

esophagus anatomy

A

passageway from mouth to stomach
upper and lower esophageal sphincters
wall: top 1/3 skeletal, bottom 2/3 smooth muscle
move food via peristaltic waves

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7
Q

stomach anatomy

A

digestion continues in stomach mix food with acid and enzymes to form chyme

parts: fundus (top), body, antrum, valve/sphincter

stomach has ruggae: surface folding to increase SA

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8
Q

small intestine anatomy

A

majority of digestion
duodenum
jejunum
ileum

liver and pancreas release exocrine secretions into the duodenum

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9
Q

large intestine anatomy

A

large diameter but shorter (150cm)
ascending colon, transverse colon, descending colon, sigmoid colon

1.5L of watery chyme pass into here each day
water and electrolytes removed to create semisolid feces

feces entering the terminal section of the large intestine (rectum) trigger a defecation reflex

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10
Q

GI layers

A

mucosa, submucosa, muscularis externa, serosa

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11
Q

mucosa sublayers

A

epithelium
lamina propria
muscularis mucosa

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12
Q

submucosa sublayers

A

major blood and lymph vessels
submucosal plexus

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13
Q

muscularis externa sublayers

A

circular muscle
myenteric plexus
longitudinal muscle

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14
Q

what makes up the enteric nervous system

A

submucosa plexus and myenteric plexus both layers of nerves

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15
Q

mucosa in stomach vs small intestine

A

stomach: huge mucosa (microscopic), rugae
small intestine: plicae further increase surface area, equivalent of rugae, not vili
vili are finger like
crypt gastric glands

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16
Q

mucosa epithelial

A

includes transport epithelial cells (enterocytes), endocrine cells, exocrine secretory cells
junctions very tight in stomach and colon, leaky in small intestine
short lifespan (few days) GI stem cells constantly producing new cells about 17 billion replaced daily

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17
Q

mucosa: lamina properia

A

subepithelial tissues containing nerve fibres, small blood and lymph vessels

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18
Q

mucosa: muscularis mucosae

A

thin layer of smooth muscle that can alter SA available for absorption

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19
Q

submucosa

A

has submucosa plexus

middle distenible layer containing larger vessels (lymph and blood)

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20
Q

muscularis externa

A

2 or 3 layers of smooth muscle: circular decrease diameter, longitudinal shortens tube. contains myenteric plexus

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21
Q

serosa

A

outer covering of connective tissue that is a continuation of the peritoneal membrane, sheets of mesentery hold intestines in place

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22
Q

4 digestive functions and processes

A

digestion: chemical and mechanical breakdown of food int absorbable units

secretion: movement of material from cells into lumen or ECF, also movement of water and ions from ECF to lumen

absorption: movement of material from GI to lumen to ECF

motility: movement of material through GI tract as a result of muscle contration

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23
Q

avoiding autodigestion

A

breaking food down into small enough molecules to be absorbed without digesting the cells of the GI tract (autoimmune disease)

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24
Q

GI defense

A

absorbing water and nutrients while preventing bacteria, viruses, other pathogens from entering body

mechanisms include mucus, digestive enzymes, acid, and the largest collection of lymphoid tissue
80% lymphocytes in small intestine

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25
mass balance of GI tract
we secrete a lot more than we ingest ingestion = 2L, secretions total = 7L
26
3 fluid secretions from GI
water, digestive enzymes, mucus
27
water secretions in GI
saline ions transported from ECF into lumen, creates osmotic gradient for water movement
28
digestive enzyme secretion in GI
exocrine glands (salivary and pancreas) epithelial cells in stomach and small intestine - proteins synthesized on rough ER and packaged into secretary vessels until needed - once released some remain bound to apical membrane by lipid anchors - some released in an inactive form (zymogen) will stockpile without damage
29
mucus secretion in GI
viscous glycoproteins (mucins) secretions that protect GI cells and lubricate contents - mucus cells in stomach and salivary glands, goblet cells in intestine
30
fluid secretions role in digestion
most fluids facilitate digestion, have enzymes acidic conditions= stomach, HCl alkaline conditions = intestine, HCO3
31
motility purposes
1. move food from mouth to anus 2. mechanically mixing food breaks it into uniformly small particles skeletal muscle in mouth and throat, smooth muscle in esophagus down
32
what determines GI motility
properties of smooth muscles and modified by chemical/mechanical input from nerves, hormones, and paracrine signals single unit smooth muscle, connected by gap junctions, contract together ECF Ca, sarcoplasmic reticulum Ca, CaCalmodulin, activates Myosin light chain kinase, mysosin and actin crossbridges
33
slow wave AP
spontaneous depolarizations, likely orignate from networl of cells called inerstitial calls of cajal (ICC)
34
what do ICC do
modified smooth muscle cells serving as pacemaker for slow wave activity, AP spread to adjacent smooth muscle through gap junctions diff regions controlled by diff ICC groups 3-12 waves/min
35
migrating motor complex (motilin) contractions
between meals begin in stomach and passes from section to section terminating in the ileum 90-120 mins, first 45-60 mins inactive 20-30 min period of infrequent peristaltic contractions 5-15 min cycle of rapid forceful contractions sweeps out food remnants and bacteria out of the upper GI and into large intestine
36
peristaltic contractions
during or after a meal progressive wave of contraction of circular muscle behind a bolus of food (2-25cm/s)
37
segmental contractions
during or after a meal small segments alternatively contract and relax circular and longitudinal (churn and mixes)
38
what functions of GI are regulated
motility and secretion are the primary regulated functions
39
neural regulation in GI
submucosal and myenteric plexuses form ENS neurons synapse with each other, smooth muscles, glands, and epithelial
40
short reflex
integrated entirely within the ENS
41
long reflex
integrated within CNS
42
GI Peptide regulation
hormones, neuropeptides, cytokines
43
5 similarities between ENS and CNS
1. intrinsic neurons 2. neurotransmitters and neuromodulators 3. glial support cells, similar to astrocytes 4. diffusion barrier, like BBB 5. integrating center, can function autonomously
44
myenteric plexus short reflex controls
motility
45
submucosa plexus short reflex controls
secretion from GI secretory cells
46
cephalic reflex
long reflex that starts in the brain, feedforward and emotion
47
ENS receives input from CNS via
autonomic system
48
parasympathetic input __ GI, symp?
parasympathetic= enhance/stim (vagus) sympathetic= inhibits
49
GI peptide function
act as hormone or paracrine signals excite or inhibit motility and secretion can be secreted into lumen to act on apical membrane receptors or ECF to acto on neighbouring cells some act outside the GI (in brain) like: cholecystokinin- satiety, ghrelin-hunger
50
GIP
Glucose dependent insulinotropic peptide glucose, fa, aa in small intestine stimulate release onto beta cells in pancreas, stimulate insulin release (feedforward), inhibits gastric emptying and acid secretion
51
GLP-1
glucagon-like peptide-1 mixed meal that includes carbs or fats to stimulate release onto endocrine pancreas, stimulates insulin release, inhibits glucagon release and gastric function, promotes satiety
52
VIP
vasoactive intestinal peptide stimulates ENS neurons to release on small intestine and pancreas, smooth muscle relaxation , increase secretions from small intestine and pancreas
53
CCK
cholecystokinin fa and aa stimulate release onto gallbladder, pancreas, stomach, stimulates gallbladder contraction and pancreatic enzyme secretion, inhibits gastric emptying and acid secretion, promotes satiety
54
3 hormone families (structure)
gastrin: - gastrin - cholecystokinin secretin: -secretin -VIP -GIP GLP-1 other: -motilin
55
3 phases of integrated function in GI
1. cephalic/oral: digestive processes occurring before food enters the stomach 2. gastric phase: digestive processes in the stomach 3. intestinal phase: digestive processes in the intestines (small and large)
56
cephalic phase- neuro details
long reflex beginning in the brain increase parasymp from medulla to salivary glands via facial glossopharyngeal and to ENS via vagus nerve: vagus reflex
57
what kind of secretion is saliva
exocrine
58
how much saliva is secreted
1.5L/day
59
what is in saliva
99.5% water, 0.5% solutes Na, Cl, K, HCO3, PO3 amylase, lysozyme, mucus, immunoglobulin A (antibodies)
60
secretory cells are called
acini (in clusters) mucous cells and serous cells
61
parotid gland solution
watery with amylase
62
submandibular secretion
watery with amylase and some mucus
63
sublingual secretion
mainly mucus
64
what neuro system controls salivary glands
parasymp
65
what is deglutition
reflex that pushes bolus into esophagus - pressure against soft palate and back of mouth (voluntary) activate sensory neurons going to medulla - medulla swallowing center - soft palate closes off nasopharynx, peristaltic contractions in pharynx - contraction moves larynx up and forward, epiglottis closes trachea - upper esophageal sphincter relaxes and opens
66
medulla swallowing center
somatic motor outputs to pharynx and upper esophagus and autonomic outputs to lower esophagus
67
GERD
churning action of stomach contraction can cause backflow negative intrapleural pressure during inspiration can cause esophagus to expand drawing gastric acid and pepsin from stomach Lower esophageal sphincter not a true anatomical sphincter
68
what type of function is gastric phase
integrated
69
3 general functions of stomach
1. Storage: stores food and regulates its passage into the small intestine 2. Digestion: chemical and mechanical digestion into chyme 3. Defense: Destroys bacteria and other pathogens in food and pathogens trapped in airway mucus (mucociliary escalator)
70
how is Motility and secretion initiated during cephalic phase now reinforced in gastric phase
short reflexes initiated by distension or peptides and aa -> sensory input (mucosa) -> enteric plexus SHORT REFLEX -> post ganglionic parasymp and intrinsic enteric neurons-> target cells -> secretion and motility
71
what's receptive relaxation
Upon swallowing food, parasympathetic neurons to the ENS cause the fundus of the stomach to relax
72
distension of the stomach enhances...
motility
73
what is propulsion
weak peristaltic waves 15-20secs increase in force proceeding down to antrum moves chyme toward pylorus
74
what is retropulsion
larger particles are moved back to the body of the stomach
75
function of stomach motility
mix food w acid and digestive enzymes, small amounts of chyme squeeze through pylorus
76
G cells release
gastrin
77
why do G cells release this hormone
in response to aa, peptides, distension (short reflex-GRP) parasymp neurons to ENS, stims gastrin production during cephalic phase (long reflex) stim gastric acid secretion DIRECTLY from parietal cells
78
indirect stim of parietal cells by
histamine release from enterochromaffin like cells (ECL)
79
what stimulates gastrin secretion from G cells
histamine from enterochromaffin like cells (ELC) or ACh from ENS neurons via long and short reflexes
80
parietal cells stimulated by
gastrin from G cells
81
parietal cells produce
1-3L of gastric acid (HCl), produced daily with pH as low as 1
82
5 functions of gastric acid
1) stim release of pepsinogen from chief cells, cleaves pepsinogen to pepsin (digest proteins) 2) denatures proteins making it easier for pepsin to function 3) kills bacteria and other ingesting microorganisms 4) inactivates amylase from saliva 5) stim D cells to release somatostatin
83
mechanism of acid secretion
- free H+ actively transported across apical w K+ - water dissociates to H+ and OH-, frees up more H to be actively transported - OH- combines with CO2 via Carbonic Anhydrase (CA) to generate HCO3- - HCO3- exchanges for Cl- at BLM -Cl- diffuses across apical through open channels following electrochem gradient
84
stimuli for acid secretion causes
stimuli (gastrin, histamine, ACh, (somatostatin inhibit) ) cause exocytosis and insertion of apical transporters, the apical transporters are stored in vesicles
85
how is excessive acid treated
H2 receptor antagonists or proton pump inhibitors
86
gastric acid secretion long reflex pathway
-cephalic phase stim (brain) -increase ENS activity -ENS stims G cells/gastrin secretion = parietal cells/acid -G stims ECL Cells/histamine = parietal cells/acid secretion - high HCl- stim D cells/somatostatin secretion = inhibits parietal cell/acid secretion, eventually inhibit gastrin secretion
87
gastric acid secretion short reflex pathway
- gastric phase stimuli: luminal distension aa and peptides stims gastrin secretion
88
do intestinal hormones stim or inhibit acid secretion
inhibits!
89
hormones that inhibit gastric acid secretion
CCK, secretin, VIP, GIP, somatostatin
90
gastric digestive enzyme secretion stimulated by...
acid secretion via short reflex (chief cell) pepsinogen + gastric lipase = pepsin pepsin + (parietal cell) HCl + intrinsic factor = cleave protein to peptides
91
paracrine secretion: ECL
histamine, activates H2 receptors on parietal cells to stim HCl secretion
92
paracrine secretion: parietal cell
intrinsic factor binds to vit B12 so it can be absorbed
93
paracrine secretion: d cell
somatostatin neg feedback for acid secretion (g, parietal, ECL) inhibits pepsinogen release
94
mucus cells secretes..
mucus and HCO3 secreted from mucus cells
95
mucus cells stim by..
parasympathetic input and irritation (break in mucus layer exposes it to acid) HCO3 by parasymp input and H+
96
function of mucus
mucus layer is a physical barrier for acid and cells, bicarbonate is a chemical barrier that neutralizes acid so pH is 7 at cell surface
97
what is a peptic ulcer
- a sore or break in the lining of the stomach or duodenum - excessive acid production - gastrin secreting tumors - nonsteriodal anti-inflammatory drugs (NSAIDS) - Helicobacter pylori
98
H pylori
used to think it was stress, spicy foods, and over production of acid causing peptic ulcers hypothesized bacteria caused majority of peptic ulcers, tested on themselves bacteria buries through mucus layer and infects cell

BMSC 208 (8 decks)

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