Flashcards in Sanders. Upper and lower GI motility Deck (143):
The motility patterns of gastrointestinal organs are due to contractions of (blank) in the walls of the organs
(blank) are Regions such as sphincters and the fundus of the stomach produce sustained (tonic) contractions or periods of sustained relaxation.
(blank) are – Other regions, such as the distal stomach or small intestine, produce contractions that are transient with periods of relaxation between contractions.
(blank) are Phasic contractions superimposed upon tonic contractions. In many cases enhanced phasic contractions elicited by agonists are superimposed upon a sustained increase in basal tone.
(blank) are what allow GI smooth muscles to often be spontaneously active in the absence of exogenous stimuli
(blank) regulation is when Motor neurons (both excitatory and inhibitory) innervate smooth muscle tissues and regulate the force and pattern of smooth muscle contractions.
THis is why Many circulating agents affect the contractility of GI smooth muscles.
What kind of regulation is this?
Many substance produced in the immediate environment of GI smooth muscle cells affect contractility.
humoral or paracrine
What is the basic mechanism of movement?
What provide direction to muscle?
(blank) contain myosin and actin with dense bodies
smooth muscle cells
(boank) are flask shaped invaginations in the Plasma membrane. They are arranged in rows interposed between dense bodies. They are close to cisterna and tubules of the SR. And it has The plasmalemmal Ca-pump ATPase, the transport protein that extrudes calcium from the cell and helps maintain homeostasis within it.
SM cells are connected via (blank)
The most important gap junction protein in SM cells is (blank)
Ions can move from cell-to-cell
through . Thus, they produce low electrical
resistance pathways between cells. Allow for electrical and chemical coupling between cells.
What mmakes up a gap junction?
hexameric assembly of GJ proteins
There is no troponin in smooth muscle so instead we have (blank) which binds the calcium and it activates (blank) which then activates the myosin light chain in SM> it phosphorylates this myosin light chain which activates cross bridge formation which allows for the shortening of the myosin head which pulls the actin by it and ATP displaces the ADP which makes the muscle contraction. This process stops when myosin is dephosphorylated. SM have a very slow contraction in comparison to other muscles.
myosin light chain kinase
What controls contract of smooth muscle?
phosphorylation! phosphate=conrtaction dephosphorylate=relaxation
How do you get the calcium within a cell to start a contraction?
via voltage dependent Ca channels and nonselective cation channels
Many (blank) are expressed in GI SM cells
G protein coupled receptors
Calcium can alter be released from intracellular stores when activated; how?
Ca channels in the SR activated by IP3 receptors
(blank) increases the effectiveness of Ca2+ in contractions
Ca2+ sensitization pathway
What are the two major enzymes involved in Calcium sensitization?
Protein kinase C (PKC)
What does this describe:
These mechanisms decrease the activity of myosin light chain phosphatase (MLCP), maintaining MLC20 phsophorylation and contraction.
What do you want to inhibit to get a contraction?
you want to inhibit MLCP
Mechanisms for Ca2+ desensitization are activated by (blank)
How do you increase the activity of MLCP and therefore decrease contraction and lessen Ca2+ sensitization.
Activation of AC -> cAMP-> activation of protein kinase A
Phosphorylations by this enzyme increase the activity of MLCP.
Inhibitory agonists also affect (blank)
Give an example of how inhibitory agonists affect excitation-contraction coupling.
Protein kinase G and A activate K+ channels. Increase in K+ causes hyperpolarization and decreases opening of voltage dependent calcium channels. This reduces Ca2+ entry and reduces contraction.
What are the major excitatory receptors in the GI smooth muscle?
Muscarinic receptors (M2 & M3)
Neurokinin receptors (NK1 & NK2)
What are the major inhibitory receptors in the GI smooth muscle?
Soluble guanylate cyclase (not a membrane receptor)
Purine receptors (P2Y1)
Peptide receptor (VIP1)
What are the major excitatory hormone receptors in the GI smooth muscle?
Cholecystokinin (CCK) receptors
What are the major inhibitory hormone receptors in the GI SM?
What are the major receptors for paracrine substances in GI SM?
protease-activated receptors (PAR)
Serotonin (5-HT) receptors
The behavior of (blank) cells is affected by inputs from motor neurons and by electrical connections (gap junctions) with interstitial cells and more.
1SMC + xSMCs=?
smooth muscle tissue (interactions via electrical and mechanical connections)
xSMCs + ICs =?
integrated SIP syncytium (interactions via electrical connections)
xSMCs + ICs + motor neurons =?
controlled smooth muscle tissue (interactions via neurotransmitters)
xSMCs + ICs + motor neurons + hormones + paracrine substances = ?
controlled smooth muscle tissue (interaction via circulating and local chemicals)
xSMCs + ICs + motor neurons + hormones + paracrine substances + inflammatory mediators = ?
pathological smooth muscle tissue
SMooth muscle cells are excitable. THey express a variety of (Blank) in the PM and organellar membranes that set and regulate what three things?
1) set and regulate membrane potential
2) generate excitable events
3) facilitate calcium entry into and removal from cytoplasm
How does Cl- move with a cell?
HOw does K+ move with a cell?
Cl- channels, while mediating outward movement of Cl- ions in most instances, still generate net inward current (defined as the inward flux of positive charge).
Many species of K+ channels are present and these channels produce outward currents due to the ionic gradients of smooth muscle cells.
What makes the plasma membrane negative?
Greater resting permeability of K+ channels makes the plasma membrane negative
Two types of Ca2+ channels are responsible for releasing Ca2+ from internal stores in sarcoplasmic reticulum. What are they?
These are IP3 receptor-operated channels (IP3) and ryanodine-sensitive (RYR) channels
Several exchangers and pumps help to maintain gradients. The (blank) helps remove Na+ that leaks into cells and exchanges 3 Na+ for 2 K+ ions. The plasma membrane (blank) removes Ca2+ that enters cells during excitable events. A (blank) retrieves Ca2+ into Ca2+ stores. Energy from ATP is used for these ATPases to pump the ions up electro-chemical gradients. The (blank) removes Ca2+ from cells and utilizes the downward gradient of Na+ for this task.
Na+/K+ ATPase (“Na+ pump”)
sarcoplasmic reticulum Ca2+ ATPase (SERCA) Na+/Ca2+ exchanger (NCX)
How is resting membrane potential set in GI smooth muscle cells?
In GI muscle cells resting membrane potentials are typically between (blank)
Ionic gradients to sustain resting potentials are maintained by ion pumps using (blank) for energy.
permeability of PM to ions especially K+ channels\ -50 and -80 mV
What does the AP look like in the gastric antrum?
single peaks equally spaced
What does the AP look like in small intestine?
2-3 superimposed spikes followed by brief moments of recovery
What does the AP look like in colon?
numerous superimposed spikes followed by brief moments of recovery
(blank) increases open probability of Ca2+ channels
slow wave depolarization
What do Interstitial cells of Cajal (ICC) do?
generate constant slow wave activity in phasic regions of the gastrointestinal tract. (which increase prob of open Ca2+ channels)
Inward current or suppression of outward current=?
hyperpolarization= tiny contraction
Do all parts of the GI tract have the same frequency of electrical activity?
What generate the pacemaker activities of the GI tract and form networks throughout GI tract?
What are the 3 types of ICC and where do you find them?
ICC-MY next to myenteric plexus
ICC-IM in muscle bundles (near processes of enteric neurons)
ICC-SEP in septa of SM cell bundles
The response at the motor neuron is not just a muscle response it is also a response to the (blank) within it.
Which ICC are primary pacemaker (i.e generate slow wave)?
What will you find in the taenia coli?
Loss of (blank) results in reduced responses to motor nerve activation. Thus these cells are innervated and mediate part of the response to neural regulation.
What 2 cell types of interstitial cell are involved in regulation of motility? What does these cells form?
PDGFR alpha cell
a SIP synctium with SM cells
What cells are in myenteric plexu?
Myenteric ganglia (MG)
What cells have fusiform bodies and multiple processes both primary and secondary from the central cell body?
SIP syncytium is the syncytium formed by (blank x 3) (blank) is likely to activate receptors in all of these cells. Thus, neural responses in the GI tract are integrated responses occurring within the SIP syncytium.
Smooth muscle cells, Interstitial cells of Cajal and PDGFRa+ cells.
Activation of (blank) causes hyperpolarization which can inhibit phasic contraction for a few cycles.
inihbitory nerves (application of NO)
Stimulation of intrinisc motor neurons can induce (blank) and inhibit contraction
(blank) the ring of contraction that moves in the aborad (toward anal) direction.
(blank) is the ring of contraction that is stationary
Regions of the GI tract undergo (blank) contraction to adjust organ volume and compliance and to maintain sphincter function.
The basic propulsive motor activity of the GI tract is (blank), a band of contraction which moves in
an aboral direction.
There are also (blank) contractions in which a ring of contraction pinches off a region, separating the compartment into two areas.
What do these do:
Manometry (measures pressures in hollow organs)
Strain guages (measure contractions of muscle tissues)
Fluid propulsion (measures propulsive forces developed by organs)
Extracellular electrodes (measures level of electrical excitability)
Video imaging (measures movements and contractile patterns)
Ca2+ fluorescence (measures activating Ca2+ transients in groups of smooth muscle cells)
study electrical and contractile behaviors of SM
What makes propulsion efficient?
propulsive force and receptive relaxation
What does swallowing induce?
receptive relaxation in the LES and proximal stomach
With each swallow the (blank) stomach relaxes to receive the bolus. The swallow-induced relaxation is mediated through the same mechanism as LES relaxation (vagal inhibitory fibers activating intrinsic enteric inhibitory neurons). The neurotransmitter for these enteric inhibitory nerves is (blank).
What are the components of the stomach?
fundus, corpus, antrum, pylorus
Bottom half distal portion
upper half proximal portion
What does the proximal stomach do?
What does the distal stomach do?
grinding of solids
What does the pyloric sphincter do?
sieving of particles
Why does the proximal stomach actively relax?
to accomodate meals
What is gastric accomodation dependent on
What three mechanisms regulate gastric resevoir function?
adaptive relaxation,, feedback relaxation, and receptive relaxation
Feedback, receptive and adaptive relaxation all (blank) gastric motility and increase the fundic storage capacity.
(blank) involves: Sensory stimuli (mechanical or chemical) stimulation of vagal and/or enteric nerves in the duodenum or distal gastric regions.
(blank) relaxation involves: sensory stimuli, which include mechanical stimulation of pharynx and esophagus, and efferent motor vagal pathways, which activate inhibitory enteric nerve pathways (myenteric muscle motor neurones release NO + VIP).
(blank) relaxation involves sensory stimuli which include mechanical or chemical activation of vagal and/or enteric nerves.
Motor pathways involve local vago-vagal or enteric reflexes, which activate inhibitory myenteric muscle motor neurones (releasing NO + VIP)
Sensory motor neurons recognize you are eating and tell the vagal nerve to make gastric accomodation occur.
(blank) responses: vago-vagal or enteric reflexes activate inhibitory motor neurones with cell bodies in myenteric ganglia (which release NO + VIP as transmitters)
How do you get gastric emptying?
restoration of fundic tone and volume via Ach dependent contraction
What parts of the stomach of phasic contractions?
The dominant pacemaker in the stomach resides in the (blank) and is located where?
greater curvature of stomach (spreads contraction like a ring toward pyloric sphincter)
slow waves propagate rapidly (blank) the stomach and more slowly (blank) the stomach
How do slow waves propogate through the stomach?
as a band toward the pylorus, activating contractions as SM cells depolarize
THe antrum has a very low intrinsic pacemaker activity so instead what does it do?
follows the activity of the dominant pacemaker (ALL parts of stomach follow dominant pacemaker)
(blank) determine the amplitude and duration of propagating slow waves
local neural inputs
Coordinated motility of gastric antrum happens in hat three steps?
WHat is retropulsion?
the rebound of food against the pyloric sphincter allowing for mixing and breakdown of larger food particles
Changes in duodenal nutrients, osmolarity or pH alter gastric motility via (blank)
via vagal reflex pathway
Emptying of liquids starts (blank) and is exponential. Emptying of large solid particles only begins after sufficient grinding (lag phase). Afterwards the viscous chyme is emptied in a nearly (blank) fashion.
Gastric emptying of liquids is very fast, solids as slow.
Put in order of gastric emptying from fastest to slowest:
isotonic, hypertonic, hypotonic
isotonic, hypotonic, hypertonic
The rate of gastric emptying is dependent upon to the (blank) content of isotonic meals
THe more calories, the faster or slower the food is emptied?
(blank) in the distal small intestine delay gastric emptying.
What are the major functions of the small intestine?
-digest macromolecular nutrients
-absorb digestion products
-retain nutrients in small bowel until maximal digestion and absorption can be accomplished
How do you get phasic contraction in smooth muscle?
Activate L-type Ca2+ receptors by depolarization of slow wave at across the mechanical threshold (-40mV)
A slow wave not crossing the mechanical threshold is usually in a state of (blank). Thus, the intestine can regulate its response to slow wave activity by “conditioning” the response of the smooth muscle cells to the slow wave depolarization.
(blank) are characteristic of digestive motility patterns in the small intestine
Segmentation (mixing) movements
(blank) consist of propulsive and receiving segments where there are net excitatory neural inputs and inhibitory neural inputs, respectively.
(blank) appear as non-propagating contractions because, unlike long propagating contractions, there is no net movement. The digestive pattern of motility consists of segmentation intermixed with short propulsive peristaltic contractions. Thus, there is net aboral movement with time.
A variety of different contractile patterns exist in the small intestine what are the three most prominent?.
(blank) contractions are spatially and temporally coordinated
In contrast, (blank) contractions are not phase locked and occur rather randomly.
(blank) contractions occur as migrating or stationary complexes.
(blank) is a mix of stationary, segmenting, stationary and migrating clusters of contraction and short perstaltic waves (all random and crazy)
Motility of the small intestine during the (blank) state enhances digestion and absorption
What are these properties of:
Short segment peristaltic contractions
Timed by slow waves
Descending frequency gradient
What are the enhancing effect of the postprandial state?
nutrient contact with mucosa
What is a cyclic motor pattern that is often called migrating myoelectric complex (MMC). how many phases does this have?
Fasting motor pattern
Where does the MMC originate?
stomach and propagates through intestine
The powerful contractions of (blank) of the MMC, sweep all undigested materials in the aboral direction and serve to clean out the GI tract. Sometimes this is called the “house keeping activity” of the GI tract. What phase is no contraction?
Phase I (phase 2 is slight contraction)
What interrupts the MMC cycle?
What does feeding activate/
the fed pattern
(blank) occurs in pathological states with diarrhea, abdominal pain, and nausea
Intestinal power propulsion
What can enteritis via bacteria, virus, parasites and radiation as well as enterotoxins and food toxins, and food allergies like shellfish and treenuts in adults and eggs, milk and peanuts in kids cause?
intestinal power propulsion
What are the major functions of the colon?
conservation of water and electrolytes and formation, storage and periodic elimination of feces
(blank) result from the anatomic arrangement of the longitudinal muscle which is concentrated in three bundles or (blank)
The wall bulges out in the large intestine where the longitudinal muscle is thin and these bulging bands are segmented by circular muscle contractions. These haustra change shape and position as the location of (blank) changes.
circular muscle contractions
In the lower sigmoid colon and rectum, there are no (blank) as the longitudinal muscle coat is continuous around the circumference of the colon. At the terminus of the rectum, the circular muscle coat thickens and becomes the (blank)
internal anal sphincter.
The right side of the colon receives dual parasympathetic and sympathetic innervation. Cranial parasympathetic innervation via the (blank) serves the right colon, whereas the sacral parasympathetic innervation, via the (blank), supplies the entire colon. Sympathetic innervation is similarly divided with the (blank) serving the right colon and the (blank) serving the entire colon.
lumbar colonic nerves
What somatic nerve controls the external anal sphincter?
pudendal somatic nerve
What controls the internal anal sphincter
parasympathetic pelvic nerve
What is the major function of the right colon?
absorption of water and electrolytes
What is the major function of the left colon?
formation and storage of feces
Is there extensive mixing of different meals in the colon? WHere does the majority of this occur?
ALl of the colon moves in a aborad direction except for what?
the right colon (moves in orad)
What are the three contractile patterns displayed by colon?
(blank) movements-These contractions segment the colon and its contents, displacing the contents in both orad and aborad directions.
(blank) move the contents for several cm. In the proximal (right) colon, the direction of these movements are generally in the orad direction. The general direction is in the aborad direction in the distal (left) colon;
(blank) are the least frequent motor pattern. These are most commonly seen after meals, and they move in the aborad direction. these movements are preceded by relaxations of haustra and they cause propulsion of colonic contents 35 cm or more. After the mass movement, haustra reappear. Mass movements can deposit feces into the rectum and initiate an urge to defecate.
(blank) allows defecation and provides continence
anal sphincter reflex
(blank) is a complex act involving the left colon, rectum, anal sphincters and the striated muscles of the pelvic floor, abdominal wall and diaphragm.
The afferent limb of the defecation reflex is activated by (blank) in the rectosigmoid. When distension reaches a threshold, afferents to the cerebral cortex provide the opportunity to determine whether to allow the reflex to continue to completion or to inhibit passage of feces.
explain how the sphincters control dephication
Distention leads to external sphincter contraction and internal sphincter relaxation; Internal then contracts and external relaxes-> defection
What does the relaxation of the internal sphincter tell us?
provides sensory information about whether the material distending the rectum is solid, liquid or gas.
The lumbar sympathetic outflow (blank) the colon and (blank) the internal anal sphincter.
The sacral parasympathetic outflow in the pelvic nerves (blank) the colon and (blank) the internal anal sphincter. (blank) fibers from the tissues surrounding the anal canal and from the wall of the colon run in the pelvic nerves.