Intro To GI Tract Physio - Lec14 Flashcards
Layers of the gut track wall
out to in:
Serosa - continuous with mesentary - replaced with adventia in the esphogus and lower portion of large intestine
Longitudinal smooth muscle layer
Myenteric plexus
Circular smooth muscle later
Meissner’s plexus (or submucosal plexus)
Submucosa
Mucosa - lamina propria and muscularis mucosa (rigdes and ofld in gut tract) w/ globet cells: muscus production
Describe the components of the enteric nervous system.
Myenteric and Meissner’s Plexus
Can operate autonomously by intrinsic regulation and sensory reflexus
Supported by intrinsic glial cells
What are the differences between the myenteric plexus and meissner’s plexus?
Myenteric Plexus - btwn longtinal and circular smooth muscle layers and controls intertinal smooth muscle.
- tonic and rhythmic contractions
- mostly excitatory (Ach/NO)
- increases tonic contraction, intensity of rhythmical contractions and velocity
Meissner’s plexus
-controls GI secretion, absorption and contraction of local submucosal muscle
Compare effects of parasympathetic and sympathetic stimulation
Sympathetic system generally decreases GI tract activity
Parasympathetic system generally increases GI tract activity
What’s the difference between slow contraction waves and spike potentials?
Oscillating potentials, not action potentials
occur spontaneously
originate in interstitial cells of Cajal- pacemakers
-may be caused by complex interactions between smooth muscle cells and the interstitial cells
frequency ranges from 3-14/min and increases from stomach to duodenum
set the max freq for each part of the GI tract
slow waves excite the appearance of spike potentials
What factors cause hyperpolarization?
Norepinephrine and epinephrine - sympathetic nerves or adrenal gland (medulla?)
Stimulation by synpathetic nerves
What causes tonic contraction?
Continuous repetitive spike potentials
Hormones
Continuous entry of Ca++ ions
What are the 3 types of GI reflexes? Name examples
- Reflexes entirely within the gut wall enteric nervous system
- GI secretion, mixing contractions, peristalsis, local inhibitory effects - Reflexes from the gut to the prevertebral sympathetic ganglia and then back to the GI tract
- long distance signals to other areas of the gut tract, evactuation of the colon, inhibit stomach motility and secretion, empty ileal contents into the colon - Relfexes from the gut to spinal cord or brain stem and back to the GI tract
- relfexes from the stomach and duodenum to brain stem and back tothe stomach control gastric motor and secretory activity
- pain reflexes cause general inhibition of the entire GI tract
- detection reflexes extend from the colon to the rectum to the spinal cord and back
Spike potentials
GI action potentials
Occur automatically with GI smooth muscle becomes more positive than -40 mv
The higher the slow wave potential, the greater the frequency of spike potentials
10-40X as long as nervous AP
They open Ca2+ channels and some Na+ channels in GI smooth muscle cells
Open slowly and close rapidly
Gastrin: stimulus for secretion, site of secretion, target and actions
Secretion stimulation:
small peptides or amino acids in stomach lumen (particularly F and W), distention of stomach, vagal stimulation mediated by GRP
Secretion inhibition
-acid from stomach, somatostatin
Site of Secretion:
-G cell of ntrum, duodenim, jejunum
Actions:
- stimulation Gastric acid sectretion by parietal cells
- stimulates mucosal growth by stimulating synthesis of RNA and new protein
CCK- chelecystokinin- stimulus for secretion, site of secretion, target and actions
Secretion stimultus:
- small peptides and amino acids
- fatty acids and monoglycerides
Site of secretion
-I cells of duodenum, jejunum and ileum
Actions
- stimulates contration of gallbladder and relaxation of sphincter of Oddi for bile secretion
- inhibits gastric emptying and appetite
- stimulates pancreatic enzyme secretion, bbiocarbonate secretion (pancreatic) and growth of exocrine pancreas.
Secretin: stimulus for secretion, site of secretion, target and actions.
Stimulus for secretion:
-acid and fat in lumen of duodenum
Site of secretion:
-s cell of the duodenum, jejunum, and ileum
Actions
-stimulation of pepsin secretion, pancreatic bicarbonate secretion, niliary bicarbonate secretion, growth of exocrine pancreas and inhibits gastric secretion by parietal cells
Gastrin Inhibitory Peptide (GIP): stimulus for secretion, site of secretion, target and actions.
Stimulus for secretion:
-only GI hormone released in response to protein, fat and carbohydrate
(And orally administred glucose)
Site of secretion:
-K cells of duodenum and jejunum
Actions:
- stimulation insulin release
- inhibits gastric acid secretion oby parietal cells
Motilin: stimulus for secretion, site of secretion, target and actions.
Stimulus for secretion:
-Fat, acid and nerve action
Site:
M cell of duodenum and jejunum
Actions:
Stimulates gastric and intestinal motility
Secreted during fasting
What is the formation and destination of the portal vein, what does it transport?
Blood from the gut, spleen and pancreas go directly to the liver by portal vein before rejoining systemic circulation via the hepatic vein (then vena cava)
