GI I Flashcards
The smooth muscles of the intestine are connected __ and form an ___.
The smooth muscles of the intestine are connected by gap junctions and form an electrical syncytium (an action potential anywhere will travel in all directions.)
Smooth muscle in GI tract: experiences continuous ‘slow waves’- ____believed to act as pacemakers.
Resting membrane potential?
___form gap junctions with ___& act as pacemakers. Slow waves spread via?
How is Ca++ involved?
Interstitial cells of Cajal believed to act as pacemakers.
-resting membrane potential (-40 to -80mV), Na+K+-ATPase significantly electrogenic
-membrane potential oscillation (slow waves), 3/min in stomach-12/min in intestine
-Interstitial cells (Interstitial cells of Cajal) form gap junctions with longitudinal & circular smooth muscles, act as pacemakers. Slow waves spread via gap junctions.
No Ca++ entry, only Na+, so no contraction during slow wave.
GI Smooth Muscles:
How do APs of SM differ from APs of skeletal muscle?
Rising phase ions?
Contraction intensity a function of ?
Sympa. Stim. vs parasymp stim. do what do the amplitude?
Depolarization from? (4)
Hyperpolarization from? (2)s
Action potentials in smooth muscle cells are prolonged (compared to skeletal muscle) and show little ‘overshoot’. Rising phase combination of Na and Ca currents, with Ca helping to initial contraction.
Contraction intensity a function of the number of action potentials riding along the depolarization.
-tone maintained between contractions
Sympa. Stim. decreases wave amplitude, parasympa. stim. increases amplitude.
Depolarization from: 1) stretch, 2) acetycholine, 3) parasympathetic stimulation 4) GI hormones.
Hyperpolarization from: 1) norepinephrine and epinephrine, 2) sympathetic stimulation.
Two major components of enteric NS:
1) Myenteric plexus: what is it, where, what doe its stim. cause? What transmitters does it release?
2)Submucosal plexus: what does it control?
Note autonomic system projections to enteric system, and sensory projections to prevetebral ganglia, spinal cord, and brain stem.
Parasympathetic system control via what nerves? Its stimulation does what?
Sympathetic system, endings release mostly?
Two major components:
1) Myenteric plexus. Outer plexus between longitudinal and circular muscles. Runs length of the tract, controls mostly GI movements. Stimulation increases 1) overall tone, 2) rate & intensity of rhythmical contractions 3) increase in velocity of ‘waves’ of excitation. Mostly releases Ach, usually excitatory but does have some inhibitory functions, releases vasoactive intestinal polypeptide (VIP) to inhibit some muscles, as at sphincters
2)Submucosal plexus. Inner plexus, works ‘segment by segment’, controls GI secretions and local blood flow.
Parasympathetic system: via vegus nerve and sacral parasympathetics, stimulation increases activity of enteric system, enhances GI functions
Sympathetic system: endings release mostly norepinephrine, inhibits activity in GI tract.
Enteric Nervous System: -myenteric (used for?) & submucosal (used for?) ganglion.
- interneurons connect ____with ___ & secretory cells to form reflex arcs.
- chemoreceptors and mechanoreceptors in wall of GI tract, note these cells will synapse _____, and will project up to the CNS.
Enteric Nervous System: -myenteric (motility) & submucosal (secretion & absorption) ganglion
- interneurons connect sensory fibers with smooth muscle & secretory cells to form reflex arcs.
- chemoreceptors and mechanoreceptors in wall of GI tract, note these cells will synapse locally for local reflexes, and will project up to the CNS.
GI Innervation: Sympathetic: -What fibers and where do they project? What does it cause/which organs does it interact with?
Parasympathetic: -which nerves? Where do they terminate? Function?
Sympathetic: -post ganglion fibers project mostly to intramural plexus.
-inhibits motor activity of muscularis externa (indirectly via enteric system).
-vasoconstriction.
-reduces motility and secretion.
Parasympathetic: -comes from vegas and pelvic nerves.
-terminate on ganglion in intramural plexus.
-increases motility & secretory activity.
Gastrin: where? why released? functions? etc. Chlecystokinin (CCK); explain. Secretin; ? Gastric Inhibitory Peptide (GIP)? Motilin; ?
Gastrin: from ”G” cells in antrium of stomach, in response to stomach distention, proteins in the stomach, gastrin releasing peptide from gastric mucosa during vagal stim., actions include stimulation of gastric acid secretion, stimulation of growth of gastric mucosa.
Chlecystokinin (CCK); from “I” cells in mucosa of duodenum, jujenum in response to fat, fatty acids. monoglycerides. Induces strong contractions of the gall bladder to push bile into the small intestine for emulsifying fats. Also slows emptying of stomach but inhibiting stomach contractions- inhibits appetite (somewhat).
Secretin; from “S” cells in mucosa of duodenum in response to gastric juice coming into the duodenum through the stomach pylorus, promotes secretion of bicarb from pancrease.
Gastric Inhibitory Peptide (GIP) from mucosa of upper small intestine in response to fatty acids, amino acids, partly carbs, slows stomach emptying, stimulates insulin release
Motilin; from upper duodenum, released during fasting, increases gastric motility. Poorly understood.
The small intestine is generally divided into the __ then the ___(the next 45%), and ends with the ___ (last 50%). It runs 3 to5 meters long, and takes 2-4 hours for material to travel the length.
Movement in the GI tract is exemplified by the movement in the small intestine. Material moved by ___,which means? The usual stimulus is ?
“Law of Intestine”; (Law of the Gut) is what?
Intestinointestinal reflex?
Segmentation: movement by closely spaced contractions, this mainly serves to do what?
Slow waves work as before- depolarizations whose contraction force is a function of?
The small intestine is generally divided into the duodeum (the first 5 to 10%), then the jejunum (the next 45%), and ends with the ileum (last 50%).
Material moved by peristalisis-
progressive contraction wave. usual stimulus is distention, function of myenteric plexus.
“Law of Intestine”; (Law of the Gut) intestine will contract behind and relax in front of a bolus, myenteric reflex.
Intestinointestinal reflex: over distention of one segment induces relaxation in the next
Segmentation: movement by closely spaced contractions, mixes chyme.
Depolarizations whose contraction force is a function of how many action potentials were evoked.
___ is the blood system that circulates through the gut, spleen, and pancreas, all of which then goes to the liver through the portal vein. The blood in the liver passes through ___ and finally leaves through the __. In the liver, the blood is cleansed of bacteria that may have entered from the gut. Liver also absorbs many nutrients picked up by the circulation through the gut.
Arterial blood supply here is what? Explain.
The circulation in the villi operates much like a smaller version of the countercurrent mechanism in kidney. How so? Normally this works well but in conditions of poor circulation or hypoxia, the tips can become ischemic.
Splanchnic circulation. The blood in the liver passes through liver sinusoids and leaves through the hepatic veins into the vena cava.
Arterial blood supply; superior and inferior mesenteric arteries supply the walls of the small and large intestine with an “arching arterial system”. As they inter the wall of the gut, arteries branch into smaller arteries which circle around and meet on the other side of the gut. From these even smaller arteries spread along the muscles and into the intestinal villi.
Blood flow through an intestinal villi: Note the looping capillaries. The circulation in the villi operates much like a smaller version of the countercurrent mechanism we saw in the kidney. Much of the O2 flows from arterioles to venules without getting to the end of the villi. Normally this works well but in conditions of poor circulation or hypoxia, the tips can become ischemic.
Digestive enzymes only work on?Swallowing: there is a pharyngeal stage and an esophageal stage.
1) the pharyngeal?
2) Esophageal phase?
Esophagus; upper part has striated muscle, lower has smooth muscle. As peristaltic waves approaches stomach, it is proceeded by waves of relaxation. Upper and lower esophageal sphincters are usually __, lower is the gastroesophageal sphincter, which___ when peristaltic waves arrive.
Digestive enzymes only work on exposed surfaces
1) In pharyngeal, once decision to swallow is made, it follows a largely invariant reflex; trachea is closed, esophagus opened, fast peristaltic waves forces food into upper esophagus, peristaltic wave then forces food through upper sphincter- takes
GERD Treatment: Foods/ eating habits? smoking does what to the sphincter? Drugs for GERD are among the most prescribed, -\_\_\_\_ (Prevacid, Prilosec) -antacids -alginic acid (seaweed) -\_\_\_\_blockerss -Surgery \_\_\_\_.
GERD Treatment;
Foods; -avoid coffee, alcohol, excessive vitamin C, fatty foods
- Avoid eating 2-3 hours before bed, avoid overeating
-avoid acidic foods (oranges, tomatoes) and cruciferous veggies (onions, broccoli)
- smoking reduces sphincter competence.
Drugs for GERD:
-proton pump inhibitors (Prevacid, Prilosec)
-antacids
-alginic acid (seaweed)
-H2 receptor blockers
Surgery- vagotomy.
Stomach 1) stores food until processed, 2) mixes food with gastric juices, forming chyme (semifluid), and 3) emptying of chyme into___ at rate suitable for digestion and absorption.
___: secrete digestive juices, found all along wall of body of stomach
__Waves (mixing waves): mid & upper portions move toward __, occur every 15 to 20 sec- get progressively stronger as contents pushed to ___, mixes food
What does the pyloric pump do? Pyloric sphincter? (its rate is controlled by what?).
Stomach- increased food volume in stomach promotes emptying; 1) & 2) ?
Duodenum- as food enters, reflexes inhibit stomach emptying through 1), 2) 3) ?
Stomach 1) stores food until processed, 2) mixes food with gastric juices, forming chyme (semifluid), and 3) emptying of chyme into smaller intestine at rate suitable for digestion and absorption.
Gastric glands: secrete digestive juices, found all along wall of body of stomach.
Constrictor Waves: mid & upper portions move toward antrum, occur every 15 to 20 sec- get progressively stronger as contents pushed to pylorus, mixes food.
Pyloric Pump: for stomach emptying, contractions of peristaltic waves stronger than mixing waves, known as “pyloric pump”. Each pushes several mls of chyme at a time through the pylorus. Pyloric sphincter keeps out food particles which are still too large, need to be further mixed into chyme Rate is controlled by stomach and duodenum;
Stomach- increased food volume in stomach promotes emptying; 1) stretching evokes myenteric reflex, 2) contents evoke release of gastrin which enhances stomach emptying.
Duodenum- as food enters, reflexes inhibit stomach emptying through 1) duodenum to stomach through enteric system, 2) nerves going to prevertebral sympathetic ganglia, then through inhibitory sympathetic nerves to stomach, and 3) through vegus to brain stem, then back through the vegus to inhibit pyloric pump.
Stomasch behavior is influenced by- degrees of __, irritation of __, acidity of ___(explain), presence of___.
Fats evoke hormonal response of ?
Influenced by- degrees of distention, irritation of duodenum, acidity of chyme (if pH falls below 3.5 to 4 then negative feedback is evoked), presence of breakdown products, especially fats.
Fats evoke hormonal response of cholecystokinin (CCK), gastric inhibitory peptide (GIP)
Movement in the Small Intestine:
Mixing is also called “segmentation”, a ring of contraction happens in one place, then another.
Chyme moves by __, .5 to 2 cm/sec, goes 3 to 5 cm at a time, so 3 to 5 hr to move the length of SI
1) gastroenteric reflex: initiated by ?, goes through ?, increases ?after a meal.
2) gastrin, CCK, insulin, motilin, serotonin: there are alll hormones which do what?
Secretin, glucagon, gastric inhibitory peptide (GIP): hormones do what?
Ileocecal Valve
Protrudes slightly into cecum, prevents what via what?
Just upstream is the ileocecal sphincter. Resistance at ileocecal valves and sphincter serves what function?
Movement in the Small Intestine
As described, there are mixing and propulsion contractions. Mixing is also called “segmentation”, a ring of contraction happens in one place, then another..
Chyme moves by peristaltic waves, .5 to 2 cm/sec, goes 3 to 5 cm at a time, so 3 to 5 hr to move the length of SI.
1) gastroenteric reflex: initiated by distention in stomach, goes through myenteric reflex, increases peristaltic waves after a meal.
2) gastrin, CCK, insulin, motilin, serotonin: hormones which enhance motility.
Secretin, glucagon, gastric inhibitory peptide (GIP): hormones which inhibit motility.
Ileocecal Valve -protrudes slightly into cecum, prevents backflow of fecal matter into small intestine, forced closed with pressure in cecum (beginning of colon).
Just upstream is the ileocecal sphincter, resistance at ileocecal valves and sphincter keeps chyme in Ileum longer, allows for maximal reabsorption.
Movement and Function of Colon:
Functions of colon: 1)2) ?
Movement:
Mixing: as in SI, mixing occurs by “segmentation”, produces buldges called “____”.
During mixing, a constriction occurs by the circular muscles along the colon. At the same time, longitudinal muscles contract. These circular and longitudinal contractions cause bulges in large intestine called haustrations. This goes on for 30 seconds or so, then dissipates. After a few minutes, another contraction occurs- and the result is?
Functions of colon: 1) water & electrolyte absorption, especially in proximal colon, and 2) storage of fecal material, especially in distal colon
Mixing: as in SI, mixing occurs by “segmentation”, produces buldges called “haustrations”
After a few minutes, another contraction occurs- the result is the material is mixed and ‘rolled over’, exposing material to the mucosal surface for maximal reabsorption.
