GI Physiology Flashcards
(107 cards)
1
Q
Bolus
A
rounded mass of food ready to swallow
2
Q
Borborygmi
A
abdominal rumblings sounds (gas)
3
Q
Chyme
A
semifluid mass of partly digested food passed from stomach to duodenum
4
Q
Diverticulum
A
outpouching of GI wall
5
Q
Eructation
A
belching
6
Q
Peristalsis
A
propulsion of food through esophagus and intestines
7
Q
Postprandial
A
after feeding
8
Q
Sitophobia
A
fear of eating
9
Q
Steatorrhea
A
fatty stools
10
Q
Upper GI Structures
A
oral cavity, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum)
11
Q
Lower GI Structures
A
large intestine (cecum, colon, rectum, anus)
12
Q
Accessory Organs
A
All secrete substances into GI tract Salivary Glands Exocrine Pancreas Liver Gallbladder
13
Q
Sphincters purpose?
A
regulate movement into GI tract and allow some compartments to act as reservoirs
- proximal pressure –> relaxation
- distal pressure –> contraction
14
Q
GI epithelial cells undergo constant renewal….
A
stem cells at base of crypts divide, differentiate, and migrate toward tips of microvilli –> apoptosis occurs 3-6 days –> cell is shed into lumen
*loss of APC –> colorectal cancer risk
15
Q
Diverticulum
A
single pouch protruding from alimentary tract (usually false)
- individuals with diverticulosis have multiple diverticula due to lack of fiber in diet –> can progress to diverticulitis
16
Q
Mucus
A
viscous, hydroscopic gel secreted by goblet cells
Mucin protein monomers combined into complexes by disulfide bonds
- glycosylation protects protein core from proteases
- Enterocytes are coated with transmembrane mucins
17
Q
Digestion
A
mechanical and chemical reduction of food into nutrients
- Teeth –> masticate food, saliva provides lubrication
- Stomach –> movements and pepsin digest food creating chyme
- Duodenum contains brush border enzymes and additional enzymes from pancreas
18
Q
Absorption
A
transport of nutrients across epithelium into blood
Dependent on splanchnic circulation –> all blood entering intestines leaves through portal vein to liver for detox
- AA, monosaccharides, and lipids are absorbed in duodenum and jejunum
- Bile salts/acids absorbed in ileum
- small intestines and colon absorb water and electrolytes
19
Q
Enterohepatic circulation
A
recycling of bile salts/acids (95% of bile salts are recycled)
-return to liver via the hepatic portal vein
20
Q
Chylomicrons absorption
A
chylomicrons are too large to pass through capillaries –> therefore they are absorbed through lacteals which empty into blood stream via thoracic duct
21
Q
Mesenteric Ischemia
A
occlusive mechanism –> thrombi
nonocclusive mechanism –> prolonged reflexive vasoconstriction
*causes postprandial pain and sitophobia
22
Q
Water secretion and absorption
A
Majority of fluids absorbed in small intestine
- fluids help uptake of nutrients and minimize damage to epithelium
- fluid is supplied by many GI organs
Water moves across epithelium by pressure gradients and AQP channels that follow gradients set up by ions and nutrients
23
Q
Diarrhea
A
Osmotic diarrhea –> overgrowth of bactera –> increased production of organic acids –> pull water from blood stream into lumen by osmosis
Secretory diarrhea –> infection leads to excess secretion of chloride –> drawing water into lumen
24
Q
Antidiarrheals
A
some work by slowing transit time –> increase absorption
25
Motility
```
controls length of time for digestion and absorption
Esophagus --> 10 seconds
Stomach --> 4-5 hrs
Small Intestine --> 2-3 hrs
Large Intestine --> 30-40 hrs
```
26
Muscle in GI tract
most is smooth muscle
| long slender cells separated into branching bundles --> gap junctions/nexuses enable contraction wave
27
GI Smooth Muscle
phasic contraction --> seconds
tonic contraction --> minutes/hours --> sphincters
can shorten considerably
initiate depolarization in response to stretch
28
Contraction/Relaxation of Smooth Muscle Pathway
ACH binds to muscarinic --> influx of Ca --> activation of calmodulin dependent MLC kinase --> phosphorylation of myosin --> increased myosin-ATPase --> binding of myosin to actin --> contraction --> dephosphorylation of myosin by MLC phosphatase --> relaxation
29
Peristaltic contractions
propel intestinal contents forward
30
Segmenting contractions
contractions of circular muscles --> mixing contents, no propulsion
31
Migrating Motor Complex
relaxation of sphincters and contraction of smooth muscle in stomach and intestines occurs during fasting by MOTILIN
32
Submucosal Nerve Plexus
within small and large intestines --> within submucosa
33
Myenteric Nerve Plexus
between circular and longitudinal muscle layers --> from esophagus to anus
34
Afferent neurons of enteric nervous system
- excited by fast distention of gut wall or chemical signals
| - many sensory neurons stimulated by 5-HT from enterochromaffin cells
35
Efferent neurons of enteric nervous system
- found primarily in myenteric plexus (unipolar)
| - excited by EPSPs, respond with sustained trains of APs
36
Parasympathetic activity
mostly cholinergic of vagus
| - stimulates activity of enteric plexuses --> increased motility and secretory activity
37
Sympathetic acitivity
mostly adrenergic
| - inhibits activity of enteric plexuses --> decreased motility and secretory activity
38
Neurotransmitters of Enteric
1. ACh --> primary excitatory transmitter --> increases intracellular Ca --> relaxation
2. Gastrin Releasing Peptide --> released from vagus to stimulate G cell secretion of gastrin
3. Substance P --> excitatory transmitter generally released with ACh
4. Vasoactive Intestinal Peptide --> promotes motility, relaxes smooth muscle, stimulates fluid secretion
5. Nitric Oxide --> inhibitory NT co-released with VIP from inhibitory neurons --> relaxation
39
GI Hormones
1. Gastrin --> released by G cells of stomach in response to detection of AA --> pepsinogen and H+ release
2. CCK --> released by I cells in D/J in response to detection of fat and AA --> secretion of pancreatic enzymes and bile salts
3. Secretin --> released by S cells in D/J in response to acid detection --> release bicarb and inhibit gastric motility
4. Gastric Inhibitory Peptide --> released by K cells in D/J in response to detection of carbs and fat --> inhibits gastric acid secretion and stimulate insulin
5. Motilin --> secreted by endocrine cells --> released cyclically during fasting to initiate MMC
40
Microbiota
greatly outnumber us in cell number
| reside in outer mucus layer of large intestine --> constitue 60% of fecal mass
41
Achalasia
failure of LES to relax
42
Aspiration
inhalation of oropharyngeal or gastric contents into respiratory tract
43
GERD
heartburn due to inappropriate closure of LES --> acid in esophagus
44
Deglutition
swallowing
45
Dysgeusia
distorted ability to taste
46
Halitosis
bad breath
47
Manometry
test to measure pressure in GI tract
48
Mastication
chewing
49
Xerostermia
dry mouth
50
Saliva contents
```
Generally an exocrine secretion
Water --> majority
Digestive enzymes
Mucins --> lubricate
Defense Molecules
Growth factors
Bicarbonate
Sex Steroids
```
51
Salivary glands
Parotid --> entirely serous (25% volume)
Submandibular --> mixed (70% volume)
Sublingual --> mucous (5% volume)
52
Flow rate affecting saliva [ ]
fast flow rate = hypertonic and basic
| slow flow rate = hypotonic
53
Parasympathetic Nervous system affecting saliva
acts through VIP and ACh on muscarinic receptors --> increased watery saliva
54
Sympathetic Nervous system affecting saliva
acts through NE on beta-1 and alpha-1 to increase viscous saliva
55
Oral Cavity Digestion
Mastication
Salivary amylase --> hydrolyzes alpha-1,4 glycosidic linkages
Lingual lipase --> breaks down TG
56
Physiology of Taste
Taste ligands bind to GPCR --> secondary messengers --> release NTs --> taste signals to nucleus tractus solitarius --> gastric acid secretion
57
Causes of Xerostomia
Sjogren, Meds, Head/Neck radiation, Dehydration, Sialothiasis, Nerve damge, Postmenopause
58
Consequences of Xerostomia
- Increased risk of opportunistic infections
- Halithosis --> production of hydrogen sulfide
- Decrease in oral pH --> tooth decay
- Decrease in taste
- Problems with speech
- Dysphagia
59
Central Input for Swallowing
mucosal mechanoreceptors transmit messages through glossopharyngeal and vagus --> medullary swallowing center
- somatic nerves --> contract top 1/3
- autonomic nerves --> regulates smooth muscle in bottom 2/3
60
Swallowing a bolus
1. tongue contacts hard palate pushing bolus against and closing soft palate
2. Breathing inhibited as bolus passes airway (epiglottis is closed to prevent aspiration)
3. Food moves down into esophagus by perastalsis
61
Mechanoreceptors sense distention or pH
contractions (ACh) above and relaxation (NO/VIP) below
62
Secondary Peristalsis
restricted to smooth muscle --> elicited by distension of esophagus or acid in esophagus`
63
Retrograde movements
eructation, vomitting, regurgitation
| - don't require additional movements except relaxation of sphincters
64
Diffuse esophageal spasms
uncoordinated contractions --> regurg
65
Control of LES
depends on enteric plexus neurons
- closed between swallows --> cholinergic
- relaxed during swallows --> NO/VIP
66
Functions of stomach???
1. highly acidic environment (defense against germs)
2. reservoir for food storage
3. fragments bolus into chyme --> maximal absorption
4. protein digestion --> acid hydrolysis and pepsin
5. empty contents into small intestine controllably
67
Bezoar
ball of foreign material trapped in stomach
68
Emesis
vomiting
69
dyspepsia
indigestion (pain in upper abdomen)
70
Gastroparesis
delayed emptying
71
Migrating Motor Complex
clears undigested material from GI tract
72
Regurgitation
flow of material that has not reached stomach back up esophagus
73
Rugae
stomach folds which expand as stomach fills
74
Scintigraphy
dual-radiolabeled solid and nutrient meal to measure gastric emptying
75
Trituration
grinding of food into small molecules
76
Gastrin
- polypeptide with variable length that binds CCK2 receptors
| - secreted by G cells in antrum --> activates parietal cells in fundus/body to secrete acid
77
Triggers for Gastrin
1. Seeing food or stomach distension --> vagal stimulation of gastrin
2. aromatic AA in lumen
78
Substances that activate parietal cells to secrete acid??
Gastrin, histamine, and ACh
| - all activate the H/K ATPase which pumps H into gastric lumen which is followed by Cl- to make HCl
79
ACh stimulating acid release
1. Binds muscarinic receptors on parietal cells
2. Activates ECL cells to release histamine
3. Acitvates enteric neurons to release GRP --> release gastrin
80
Gastrin stimulating acid release
1. Bind to parietal cells
| 2. Activates ECL cells to release histamine
81
Histamine stimulating acid release
1. released from ECL cells --> activates parietal cells via cAMP pathway
82
Parietal cell stimulation secretes acid how?
Upon stimulation, tubulovesicular membranes fuse with luminal membrane --> increases # of H/K ATPase channels in apical membrane
- protons are generated via carbonic anhydrase
- Na/K ATPase maintains K gradient
- HCO3 exported basolaterally --> alkaline tide
83
Inhibitor of gastrin release?
Somatostatin --> secreted from D cells in antrum when pH<3
- a rise in pH decreases Somatostatin secretion
- it prevents G cells from releasing gastrin by inhibiting formation of cAMP and prevents ECL cells secretion of histamine
84
Interdigestive phase
low acid secretion, D cells secrete somatostatin to maintain low levels of gastrin
85
Cephalic phase
dorsal vagal complex integrates input from higher centers to activate vagus. GRP activates gastrin and ACh activates ECL and parietal cells
86
Gastric phase
distension of stomach activates vagal afferents --> AA activate gastrin secretion and food raises pH --> decreasing somatostatin
87
Intestinal phase
introduction of gastric contents into small intestine --> activates duodenal G cell secretion of gastrin --> activation of secretin and other enterogastrones
88
Intrinsic factor
- required for B12 absorption in ileum
- glycoprotein secreted by parietal cells
- PPI inhibit parietal cells but not intrinsic factor part
- Lack of B12 caused by autoimmune destruction of parietal cells --> pernicious anemia
89
Pepsinogen secretion
- inactive proenzyme protease
- secreted by chief cells is gastric glands in response to ACh and gastrin.....inhibited by secretin
- activated in acidic envrionment --> pepsin (proteolytic enzyme)
90
Mucous gel layer in stomach
- surface epithelial cells secrete mucus and bicarb in response to PGE2
- NSAIDs block PGE2 --> gastric irritation
91
Trefoil factors
signal repair and regeneration of injury epithelium
92
Zollinger-Ellison Syndrome
caused by gastrin-secreting tumor
| - results in excess H secretion
93
Peptic Ulcer Disease
-hyperacidity --> deterioration of gastro-mucosal barrier
94
Achlorhydria
reduced acid secretion
| - caused by aging, gastric resection, autoimmune attack
95
Gastric motility
when food enters stomach --> very little change in pressure --> receptive relaxation
- dorsal vagal complex integrates input to alter gastric secretion and relaxation
96
Gastrocolic reflex
induces need to defecate
97
Gastroileal reflex
causes ileocecal valce to relax and transfer contents into large bowel
98
Gastric digestion
low pH denatures proteins --> parietal cells
pepsin releases peptides --> chief cells
gastric lipase produced FFA
mechanical movements emulsify
99
Gastric trituration
emptying of liquids --> tonic (body and fundus)
| emptying of solids involves antral pump --> phasic (antrum)
100
Peristalsis occurs at Basic Electrical Rhythm
- establishes max frequency of wave that is propagated over stomach
- amplitude can be altered (para (+), sympathetic (-))
- contractions speed up and strengthen as they approach pyloric sphincter
101
Gastric emptying
when food enter duodenum --> many signals feed back to slow gastric emptying time
- pure glucose --> faster emptying
- protein --> intermediate emptying
- solid meal/fat --> slow emptying
102
Gastric contractions inhibited by.....
- acid in duodenum
| - fat in duodenum (CCK)
103
Pyloric stenosis
congenital condition where pylorus fails to relax
104
Gastroparesis
reduced gastric emptying often to diabetic neuropathy --> treat with prokinetic drugs
105
Dumping syndrome
rapid gastric emptying from gastric bypass, vagotomy, high sugar meals
106
Peptic ulcer disease
scarring and ulcers near pylorus can delay emptying
107
Vomiting (emesis)
expulsion of contents of one's stomach contents through reverse peristalsis of intestine
- lots of stuff can cause it, all influence emetic center in CNS
- increased salivation to neutralize acidity
- preceded by retching
- glottis closes to prevent aspiration, contraction of ab muscles and diaphragm
