GI Flashcards
(35 cards)
1
Q
lamina propria
A
layer of CT that contains glands, hormone-containing cells, LN and capillaries
2
Q
submucosa
A
- layer of CT that contains glands, large bv, and lymphatics
- outermost region has nerve net called meissner’s plexus
- Meissner’s plexus = part of enteric nervous system; involved in secretory activity
3
Q
an increase in sympathetic activity has what effects on the GI tract
A
- decrease motility, decrease secretion (through NE)
- increase constriction of sphincters (through NE)
4
Q
an increase in parasympathetic activity has what effects on the GI tract
A
- promotes digestive and absorptive processes:
- incresaed motility and secretions (through ACh)
- increased gastrin (GRP stimulates G cells)
- decreased constriction of sphincters (through VIP = inhibitory parasympathetic transmitter)
5
Q
nerve gas has what effect on GI tract
A
nerve gas increases GI and bronchial secretions
6
Q
Electrical activity in GI Smooth muscle
A
- resting membrane potential = close to depolarization (-45 to -60)
- oscillation of membrane potential generated by interstitial cells of Cajal that act as pacemakers (creates the intrinsic motor activity)
- this is called slow waves or basic electrical rhythm (always some basal motor activity in the GI tract)
- slow waves create low-level contractions
- if threshold is reached, generates AP
- AP are generated by opening of slow channels that allow entry of BOTH Na and Ca
- AP strengthen the contractions
- duodenum contracts the most often
7
Q
Response to stretch in the GI tract
A
- stretch produces a contractile response
- ex) stomach distention stimulates ACh and increased parasympathetic activity (increases stomach motility)
- overload of the duodenum decreases stomach motility
8
Q
Secretin
- source
- stimulus
- effect
A
- source: S cells lining duodenum
- stimulus: acid entering duodenum
- inhibits stomach motility and secretion
- stimulates fluid secretion (HCO3-) from the pancreas
(neutralizes stomach acid entering duodenum) - stimulates insulin release (pancreas)
- no effect on gallbladder
9
Q
anticholinergic medications have what effect on GI motility
A
slow GI motility
- ex) atropine or TCA
- however, atropine alone cannot slow the stomach, bc GRP bypasses ACh
10
Q
Cholecystokinin (CCK)
- source
- stimulus
- effect
A
- source: cells lining duodenum
- stimulus: fat and AA entering duodenum
- inhibits stomach emptying (increase the degree of pyloric constriction)
- stimulates enzyme secretion from pancreas
- stimulates insulin release (from pancreas)
- stimulates Gallbladder contraction and relaxation of sphincter of Oddi for bile into the duodenum
11
Q
Gastrin
- source
- stimulus
- effect
A
- source: G cells of stomach, stimulate stomach distention
- Source: Pyloric Antrum, stimulate parasym peptides (GRP)
- source: duodenum, stomach acid inhibits (negative feedback)
12
Q
Gastric Inhibitory Peptide (GIP); Glucagon-like peptide (GLP)
- source
- stimulus
- effect
A
- source: duodenum
- stimulus: fat, carb, AA
- inhibits stomach motility and secretion
- effect on gallbladder:
1. GIP increases insulin
2. GLP decreases glucagon
13
Q
In swallowing, how is relaxation of the LES triggered?
A
VIP acts as an inhibitory transmitter of the myogenic smooth muscle of the LES
14
Q
Difficulty initiating swallowing
A
= oropharyngeal dysphagia, usually neural in origin
- bc swallowing is a reflex controlled from the brain stem
15
Q
Stomach emptying in order from fastest (1) to slowest (4)
A
- liquids
- carb
- protein
- fat
16
Q
ileocecal sphincter
A
- valve btw SI and LI
- distention of ileum creates a muscular wave that relaxes sphincter
- distension of colon creates a nervous reflex to constrict the sphincter
17
Q
motilin
A
- SI hormone
- stimulates the migrating myoelectric complex (propulsive movement repeated every 90-120 mins during fasting that moves from stomach to colon)
- this movement prevents the back flow of bacteria from the colon into the ileum and its subsequent overgrowth in the distal ileum
18
Q
composition of salivary secretions
A
- low in Na+ and Cl-, bc reabsorption
- high in K+, HCO3- , bc of secretion (pH = 8)
- salivary fluid is HYPOtonic bc of reabsorption of NaCl and impermeability of ducts to water
- alpha-amylase (ptyalin): secreted in the active form and begins the digestion of carbs
- mucus, glycoprotein
- immunoglobulins and lysozymes
- regulated via parasympathetic input
19
Q
Parietal cells
A
- secrete HCL
- intrinsic factor combines w Vit B12 and is reabsorbed in the distal ileum
- this is the only substance secreted by the stomach that is required for survival
- it is released by the same stimuli that release HCL
20
Q
Chief Cells
A
- pepsinogen is converted to pepsin by H+
- active pepsin continues the process
- only active in the acid pH medium of the stomach
- begins the digestion of protein but is NOT essential for life
- Pepsin is secreted by chief cells
21
Q
Mucous Neck Cells
A
- secrete the protective mucous, HCO3 combination
- the epithelial cells that cover the gastric mucosa secrete a highly viscous alkaline fluid (mucin + HCO3) that protects the stomach lining from the acid
- NSAID decrease the secretion of mucin and HCO3
22
Q
3 natural substances that stimulate parietal cells
A
- gastric acid secretion via a H/K-ATPase pump
1. ACh; release is stimulated by sight/smell of food and reflexly in response to stomach distention (vasovagal reflex)
2. locally released histamine; stimulated by ACh and gastrin
3. hormone gastrin; stimulated by release of GRP - as stomach pH falls, SOMATOSTATIN is released, and inhibits gastrin and reduces acid secretion (feedback regulation of acid secretion)
23
Q
Diarrhea
A
- a loss of isotonic fluid that is high in HCO3 and K+
- EXCEPT in infants, where it can be HYPOtonic
24
Q
pepsinogen is converted to pepsin by
A
- H+
- only active in the acid pH medium of the stomach
- begins the digestion of protein but is NOT essential for life
- Pepsin is secreted by chief cells
25
Carbonic anhydrase
- converts CO2 to H+ and HCO3
26
Compared to extracellular fluid, gastric secretions
- high in H+, K+, Cl-
- low in Na+
- the greater the secretion rate, the higher the H+ and lower the Na+
27
Trypsin inhibitor
- protein present in pancreatic secretions
| - prevents activation of the proteases within the pancreas
28
how do you get active trypsin
- trypsinogen is secreted by the pancreas and activated to trypsin by enterokinase (aka enteropeptidase)
- enterokinase = enzyme secreted by the lining of the SI. NOT A BRUSH BORDER ENZYME.
- trypsin then goes on to activate the other proteases (i.e. chymotrypsinogen and procarboxypeptidase)
29
stercobilin
- produced from metabolism of bilirubin by intestinal bacteria
- gives stool its brown color
30
how does cholera produce diarrhea
- cholera toxin binds and activates Gs, increases cAMP
| - cAMP opens luminal Cl- channels, causing massive secretory diarrhea
31
Where are bile salts reabsorbed
- distal ileum ONLY
- electrolytes and water (but not bile pigments or bile salts) can be absorbed from the gall bladder lumen
* distal ileum also absorbs intrinsic factor-Vit B12 complex
32
lipid digestion requires
- bile micelles and pancreatic lipase
| - end products absorbed include 2-monoglycerides and FA
33
digestion of carbs requires
- pancreatic amylases and the small intestinal brush border enzymes
- end products absorbed: monosaccharides
- disaccharides can't be absorbed from the SI
34
digestion of protein requires
pancreatic proteases (must be activated by enterokinase/enteropeptidase and the intestinal brush border enzymes)
35
Absorption in the colon
- net absorption of water and electrolytes
- influenced by aldosterone, but has a net secretion of HCO3 and K
- doesn't have digestive enzymes or transporters to absorb products of digestion
