GI Motility Flashcards
1
Q
What is motility?
A
Motility is the movement of food down our GI track. The walls and sphincters of the GI tract will contract and relax.
2
Q
Contraction of the ___________ mix and circulate the food inside the lumen and propels them through the GI tract.
A
Muscularis propria (inner circular muscle and outer longitudinal muscles, with the myenteric plexus in between)
3
Q
What is the purpose of the muscularis mucosae?
A
Has SM. When it contracts, it changes the shape and SA of the epithelium.
4
Q
The inner circular muscles and the outer longitudinal muscles have DIFFERENT functions.
What are they?
A
During contraction:
- Inner circular muscles: decrease the diameter of the tract
- Outer longitudinal muscles: decrease the length of the tract
5
Q
What is a unique feature of GI smooth muscle?
A
Slow waves: depolarizations and repolarization of the membrane potential, but they are NOT an AP.
6
Q
When do action potentials occur in the GI smooth muscle?
A
when the depolarization caused by slow waves moves the membrane potential above the threshold.
7
Q
In GI smooth muscle, do mechanical responses (tension) and electrical responses occur at the same time?
A
No. Mechanical responses (tension) occur AFTER the electrical response.
8
Q
What type of contractions of smooth muscle are KEY for motility in the GI tract?
A
- Phasic contractions- periods of contraction, followed by relaxation. Thus, they are resp for mixing and propelling food.
- Tonic contractions- constant levels of contraction, without regular times of relaxation.
9
Q
Mechanical responses (contraction) follows the electrical response. What is in charge of the frequency of contraction and what is in charge of the strength of the contraction?
A
Frequency is controlled by slow waves,
while the strength of contraction is controlled by how many action potentials/spike potentials are on each wave.
10
Q
Phasic and tonic are contraction of smooth muscle that are key for motility along the GI tract. What are phasic contractions and where do they occur? (4)
A
phasic is periodic contractions WITH relaxation
occurs in
- esophagus,
- stomach (antrum),
- SI and ALL tissues involved in mixing
11
Q
What are tonic contractions and where do they occur? (4)
A
Tonic maintain a constant level of contraction without relaxation
Eg:
- Stomach (orad),
- LES,
- ileocecal valve,
- internal anal sphincter
12
Q
How do stretch, ACh, and parasympathetics affect slow waves?
A
- Increase the amplitude of the slow wave
- Increase the number of AP on the slow wave, creating a larger contraction.
- RESULT: increase motility.
13
Q
How does NE ( sympathetics) affect slow waves?
A
- Decrease the amplitude of the slow wave, causing HYPERPOLARIZATION.
–> decrease AP–> decrease motility and digestion
14
Q
While the frequency of the slow waves is usually set, we can change the magnitude of the __________ in order to change the significance of the action potentials.
A
slow waves
15
Q
G.I. movement is primarily controlled by the ____________
A
myenteric plexus (Auerbach).
bc it has ICC cells
16
Q
G.I. movement is primarily controlled by the myenteric plexus (Auerbach). What does the submucosal plexus mainly do?
A
controls GI gland secretions and blood flow
17
Q
Generally speaking, in the enteric nervous system, sensory information from the ______________ starts a signal, which passes to a _______ neuron, then an __________, then a ________ neuron, creating the output.
A
Generally speaking, in the enteric nervous system, sensory information from the wall of the gut starts a signal, which passes to a sensory neuron, then an interneuron, then a motor neuron.
18
Q
Pacemaker cells in the ________ plexus create the spontaneous slow wave activity. What are these cells and what plexus are they located in?
A
Insterstitial cells of cajal (ICC), located in the myenteric plexus are the pacemaker cells for the GI smooth muscle.
19
Q
Electrical activity in the ICC drives the frequency of slow waves–> frequency of contractions.
How do the slow waves of the ICC spread rabidly to smooth muscle?
A
Gap junctions
20
Q
Mastication, or chewing, is controlled by muscles that are innervated by the?
A
5th CN (trigeminal)
21
Q
Mastication is caused by a chewing reflex which is controlled by?
A
Nuclei in the brain stem. Thus, we mastication is BOTH voluntary and involuntary.
22
Q
Is swallowing voluntary or involuntary?
A
Swallowing is a process with both voluntary and involuntary components. It begins voluntary in the mouth at the end of chewing and after that, is involuntary.
23
Q
What are the 3 phases of the swallowing process and list if they are voluntary or involtary.
A
1. Oral phase (voluntary)
2. Pharyngeal phase (involuntary)
3. Esophageal phase (involuntary)
24
Q
Describe the swallowing process.
A
- Oral phase (voluntary) occurs after we finish chewing.
2 Pharyngeal phase (involuntary): the soft pallate moves upward, moving the epiglottis. This allows the UES to relax. The pharynx initiates peristalsis and the food moves through the UES.
- Esophageal phase (involuntary): now that the food is inside the ESO, the swallowing reflex will initiate [primary peristaltic waves]. If those do not clear it, then it wil move via [secondary peristaltic waves] initate by th ENS caused by distention of the ESO.
25
The **pharynx** and the **first 1/3 of the esophagus** is comprised of what type of muscle?
How about the **later 2/3 of the esophagus**?
1. skeletal muscle
2. smooth muscle
26
During what stage are there two types of peristaltic contraction?
**Esophageal**
27
After the oral and pharyn phase, the last phase is the esphageal phase, which is involuntary. What is this phase controlled by? (2)
1. Swallowing reflex (primary peristaltic contractions)
2. ENS (secondary peristaltic contractions)
28
**_Primary peristaltic wave:_** what is it, what is it controlled by, cannot it occur after a vagotomy. Why or why not?
* The primary peristaltic wave is a **continuation of the pharyngeal peristalsis.**
* Controlled by: **medulla**
* **Cannot occur after a vagotomy** because afferent sensory information from the Vagus nerve is needed for the swallowing reflex to occur.
29
**_Secondary peristaltic wave_**: what is it, what is it controlled by, when does it occur and can it occur after a vagotomy?
* Secondary peristalitic wave will occur if the primary peristaltic wave fails.
* Controlled by: medulla and ENS
* Can occur with or without the oral and pharyngeal phases
* CAN occur after a vagotomy, because controlled by ENS.
30
The **_involuntary swallowing reflex_** is controlled by the \_\_\_\_\_\_\_
**medulla**
31
**The involuntary swallowing reflex is controlled by the _medulla_.**
What are the steps in the reflex: Starting with food in the pharynx and ending with efferent input to pharynx?
1. Food in pharynx
2. Somatosensory receptors located near the pharynx, detect the afferent sensory informttion (food in mouth)
3. Vagus/glosspharyngeal N. both send sensory information --\> swallowing center.
4. Swallowing center--\> sends efferent info to pharynx to initiate swalling reflex :)
32
. We can see as the food bolus passes down the esophagus the pressure at that level markedly \_\_\_\_\_\_\_\_.
**increases**
33
Here we can see various pressures in the esophagus at different levels. We can see as the food bolus passes down the esophagus the pressure at that level markedly increases.
Interestingly, the pressure of the **LES** _________ (why) before the food bolus arrives in the segment above it.
* Pressure of the LES will **decrease**, indicating that the **sphincter is relaxing**: **Vasoactive intestinal peptide (VIP)** is released by the vagus n, causing the smooth muscle in the LES to relax.
34
**What is "receptive relaxation"?**
At the same time that the LES relaxes, the top **(orad) portion of the stomach relaxes** as well to accommodate food.
35
During swallowing there are changes in pressure along the esophagus as the food bolus passes through it.
## Footnote
**What is the main difference between throacic pressure and sphincter pressure?**
* The thoracic pressure would be sub-atmospheric (below 0), cause they are normally relaxed. When food passes, pressure increases d/t constriction.
* The sphincter pressure **(UES, LES, fundus)** would be above 0 because they are normally constricted (closed). When food passes, pressure decreases d/t relaxation.
36
draw the mono whatever for the UES, 1 part of the pharynx, LES and fundus of the stomach.
37
Two problems with the location of the intrathoracic esophagus:
* 1. keeping air out of the upper end of the esophagus.
* 2. keeping acid out of the lower end.
How are these problems solved?
UES/LES are closed except when food is passing through :)
38
What is **achalasia**?
What happens?
**Achalasia**- When you swallow, the LES does not fully relax.
What happens:
* Peristalsis is impaired
* LES says closed during swallowing, causing food to back up.
* Increases LES resting pressure (V tight)
39
**Why does achalasia happen?**
1. Lack of VIP
2. ENS was KO'd
3. Damage to nerves in the ESO, preventing it from squeezing food into stomach.
40
**achalasia** can result in
1. Regurgitation
2. Dysphagia- difficulty swallowing liquids and solids
3. chest pain
41
**Draw mono with achalasia and GERD**
Achalasia (orange): LES pressure is set higher; when bolus reaches, it does not go to 0 bc does not relax
42
How do **GERD** and achalasia differ?
GERD is much the **opposite** of achalasia in that it is a **RELAXATION** of the LES (barrier between the esophagus and stomach).
43
**GERD is d/t?**
1. low pressure in the LES
2. intragastric pressure increases (commonly after a big meal)
44
GERD is when there are changes in the barrier between the esophagus and the stomach (LES weak/relaxes). This occurs due to low pressure in the LES or if intragastric pressure increases.
**What are the results from GERD?**
Acid, pepsin, bile in the esophagus= heartburn
If this continues for a while, **barrett's esophagus** can occur where there is a transition of the cells
45
The stomach can be divided according to its differences in motility and its anatomtical divisions. What are the anatomical divisions and the motility regions?
**Anatomical**: fundus, body, antrum
**Motility**: orad and caudad
46
What is interesting about the muscles in the stomach?!?!
**3 different layers: _OBLIQUE_, _CIRCULAR_ and _LONGITUDINAL_!**
47
The stomach has an orad (closer to mouth) and caudad part, with 3 layers of muscles! (Oblique layer between longitudinal and circular in muscularis). What are the extrinsic and intrinsic innervations?
* Extrinsic: para/sympathetic
* Intrinsic: myenteric and submucosa plexuses (ENS)
48
**What is receptive relaxation?**
A **vagal-vago reflex** where the **orad region** of the stomach **relaxes** (decrease pressure and increase volume) when the LES relaxes to accommodate food, rather than contracting (mixing and ingesting).
*Recall that this is all due to vasoactive intestinal peptide relaxing the muscle of the lower esophageal sphincter.*
49
The orad exhibits minimal contractile activity and minimal mixing of food occurs here. How does **CCK** affect this area?
**CCK wants to _DECREASE gastric emptying:_**
* **Decrease contractions**
* **increase gastric distension.**
50
How will a vagotomy affect the receptive reflex?
**inhibit**
51
What occurs in the **caudad region of the stomach?**
**mix and digestion**
52
How does food move in the stomach?
**Primary peristaltic contractions** of the stomach moves food from the caudad region of the stomach--\> antrum--\> pylorus.
53
**How do the contractions change as they get closer to the pylorus?**
**Force and velocity of contractions increase.**
**Max frequency is 3-5 waves a minute.**
54
how do contractions change as you get to the pylorus of the stomach on the monocyte graph
55
Primary Peristalsis occurs here, what is the difference between the distal body and pylorus regarding peristalsis?
**phase lag decreases as the force and velocity of the contractions increase**
56
What is **_retropulsion_**?
When contents in the **caudad region of stomach** are propelled back into stomach for further mixing and to reduce particle size.
57
The more violent contractions of the distal portion of the stomach and the antrum, along with the closing of the pyloric valve, causes \_\_\_\_\_\_\_. This allows for further mixing and reduction of particle size by the stomach.
**retropulsion**
58
**_Regulation of gastric contractions_**
What increases the AP and force of contraction?
1. **Parasympathetic NS**
2. **Gastrin**
3. **Motilin**
59
**_Regulation of gastric contractions_**
What decreases the AP and force of contraction?
1. **Sympathetic NS**
2. **Secretin**
3. **GIP**
60
**_Gastric emptying_** takes about **3 hours to complete**.
**What 4 things in the stomach and duodenum INCREASES the rate of gastric emptying?**
1. -Decrease in distensibility (stretchability) of the orad, increasing pressure in stomach.
2. -Increase in force of peristaltic contraction in caudad
3. -decrease in the tone (strength) of the pyloric sphincter
4. -increase in diameter and inhibition of segmenting contraction in the proximal duodenum
61
In general, how is **gastric emptying** accomplished?
**Coordinated contractile activity between the stomach, pylorus and the proximal small intestine**
62
Why is gastric emptying closely regulated?
* 1. Allow time for digestion and absorption
* 2.Allow time for neutralization of gastric H+ in the duodenum.
63
What inhibits gastric emptying?
1. Relaxation of the orad of the stomach, decreasing pressure in stomach.
2. Decrease in peristaltic contractions in the stomach.
3. Incerase in tone of the pyloric sphincter
4. Increase the segmental contractions in the duodenum.
64
What is the **entero-gastric reflex**?
When the duodenum is full, negative feedback will prevent the stomach from emptying.
65
There are 3 different ways that negative feedback from the duodenum slow dow the rate of gastric emptying. What are they?
1. **Acid in the duodenum**--\> stimulates the release of secretin, which inhibits gastrin
2. **Fats**--\> stimulate CCK and GIP--\> directly inhibit stomach motility.
3. **Hypertonicity** in the duodenum
66
What is the most common problem assx with disorders of gastric motility?
**Slow gastric emptying**
67
Slow gastric emptying is the most common problem with disorders of gastric motility. Present with **fullness**, **loss appetit**, **nausea caused by ulcer**s, **cancer**, **vagotomy**. What is the treatment? (2)
pyloroplasty/balloon dilation
68
What is **gastroparesis** and what is a common cause?
Gastroparesis is a **_slow emptying of the stomach WITHOUT mechanical obstruction._**
* a common cause of gastroparesis diabetic neuropathy (type 1) of the vagus N.
69
Gastroparesis is slow emptying of the stomach/paralysis of stomach in the absence of mechanical obstruction. 20% type 1 diabetes patients are affected due to neuropathy. What are the symptoms?
nausea, vomitting, early feeling fullness when eating, weight loss, bloating \*also caused by injury to vagus nerve
70
During fasting, you have large particles of undigested residue in your tum. How do you get rid of this?
* **Motilin**--\> activate the **migrating myoelectric complex --\>** initiate periodic bursts of contractions throughout the stomach (even in the ORAD region!) every 90 minutes during fasting.
71
if you were to inject motilin into the smooth muscle of the stomach, what would it do?
Induce the **migrating myoelectric complex.**
72
The small intestine is important for digestion and absorption of nutrients.
## Footnote
**What is KEY for these functions to occur?**
**Motility in the SI will**
1. Mix chyme with digestive enzymes and pancreatic secretions
2. Exposure the nutrients to intestinal mucosa so they can get absorbed
3. Push unabsorbed chyme from SI--\> LI
73
There are 2 main motility patterns.
## Footnote
**What are they?**
1. Segmentation contractions
2. Peristaltic contractions
74
What are **segmentation contractions**?
Segmentation contractions occur in the SI and are responsible for **mixing food** by creating back and forth movements. Thus, they do NOT propel it forward.
75
**Peristaltic contractions** in the SI do move the bolus forward.
The circular and longitudinal muscles work in opposition to complement each other. What do they do?
First, _behind the bolus_, **_circular M contracts_** and _longitudinal relaxes_
Second, _in front of the bolus_, **circular relaxes** and **longitudinal contracts**
76
How do we ensure that both the circular m and longitudinal m work in opposition to compliment each other?
**THEY ARE RECIPROCOLLY INNERVATED**
77
How are the slow waves, initiated by the ICCs, different in the **SI** than the **stomach**?
**Slow waves are always present, but the slow waves in the SI cannot cause contraction. They only set the maximum frequency.**
**In order for contraction to occur, _spike AP are necessary._**
78
Slow wave frequency (ICC electrical activity) in the small intestines sets how frequent contraction may occur.
What is the gradient from the **duodenum --\> jejunum --\> ileum**?
**Contraction rate slows.**
**12** cycles/min --\> **10** cycles/min --\> **8** cycles/min
79
How is peristalsis regulated in the SI?
80
Regulation of peristaltic contractions in the small intestine is started by serotonin (5-HT) from enterochromaffin cells binding to receptors in the \_\_\_\_\_\_\_\_?
intrinsic primary afferent neuron (IPAN) (sensory)
81
IPANs bound by serotonin signal to interneurons which synpase either inhibitory or excitatory motor neurons, which are what, respectively?
Acetylcholine and Substance P (contraction) VIP or Nitric Oxide (relaxation)
82
What controls the contractions of the intestines?
1. ICCs
2. Smooth muscle
3. **Neural input**
4. **Hormones**
83
What plexus would detect distention of muscle in the intestinal wall and which would detect chemical/mechanical stimulation of the mucosa?
**Myenteric for contraction/relaxation of intestinal wall**
**Submuscosal (meissner) sense lumen environment**
84
Contractions of intestines is controlled by ICCs, Smooth muscle, neural and hormonal responses. What are the neural inputs? (2)
1. **Peristaltic reflex** mediated by ENS
2. **PNS stimulates** and **SNS inhibits** contractions
85
**How are contractions controlled by hormones? (9)**
* Serotonin, Prostaglandins, Gastrin, CCK, Motilin, and insulin --\> **stimulate contractions**
* Secretin, glucagon and EPI--\> **inhibit contractions**
86
The **vomiting center of the brain** is located in the \_\_\_\_\_\_\_\_.
**medulla**
87
**What are the events in the vommiting reflex?**
1. Vagus and sympathetic afferents carry nerve impulses--\> brainstem nuclei
2. Reverse peristalsis in SI
3. Stomach/pylorus relax
4. Forced inspiration to increase abdominal pressure
5. Movement of larynx
6. LES relaxation
7. Glottis closes
8. Forceful expulsion of gastric contents
88
**How do gut contents go from the SI--\> LI?**
Ileocecal junction regulates the flow of contents from the SI--\> LI.
* 1. Ileum is distended--\> ileocecal sphincter is relaxed--\> contents go into colon
* -----as food goes into colon----
* 2. Colon is distended--\> ileocecal sphincter contracts--\> contents do NOT go back to the ileym
89
In the LI, there are two muscular layers again (longitudinal and circular).
The **longitudinal layer** has taeniae coli which are?
**3 flat bands of longitudinal fibers that run from cecum to rectum**
90
What are the sphincters of the LI?
**1. Internal anal sphincter--\> smooth muscle**
**2. External anal sphincter--\> skeletal m**
91
What N the external anal sphincter?
**Pudendal nerve**- remember; it is skeletal muscle.
92
What N the internal anal spincter?
**Pelvic splanchnic N**- under autonomic control (smooth muscle)
93
**Parasympathetic innervation to the LI includes:**
\_\_\_\_\_\_\_\_\_\_ to the cecum, ascending and transverse colon.
\_\_\_\_\_\_\_\_\_ descending colon, sigmoid colon, rectum.
**Vagus nerve**--\> cecum, ascending colon and transverse colon
**Pelvic splanchnic nerve**--\> descending colon, sigmoid colon, rectum.
94
What is the sympathetic innervation to the **proximal region of the LI**?
**Superior mesenteric ganglion**
95
What is the sympathetic innervation to the **distal regions of the LI**?
**Inferior mesenteric ganglion**
96
What is the sympathetic innervation to the **distal rectum and anal canal**?
**Hypogastric plexus**
97
**Motility in the large intestine** is described as what? (two words)
**MASS MOVEMENTS**
98
**Describe the MASS MOVEMENT that occurs in the colon.**
Main job of the LI is absorption of water. Thus, most of the shit that gets there does not need to be absorbed. Thus, mass movement occurs to move contents over large distances. This happens 1-3 times a day and causes us to poop. A final movement moves it to the RECTUM, where it is stored until we poop.
99
Why is motility in the LI important?
**1. Absorption of water and vitamins**
**2. Convert digest food--\> poop**
100
What happens when motility is poor in the LI?
Greater absorption--\> hard feces in the transverce colon--\> CONSTIPATION
101
What happens when there is too much motility in the LI?
**Less absorption--\> diarrhea and loose feces**
102
What is the **rectosphincteric reflex (defication reflex**?
Rectum and anal canal fills with feces--\> SM wall of the rectum contracts--\> internal anal sphincter relaxes
103
As the rectum fills with feces, the smooth muscle wall of the rectum contracts and the internal anal sphincter relaxes in the rectosphincteric reflex.
**Will we poop now?**
NO. the external anal sphincter is still **_tonically contracted._**
104
As the rectum fills with feces, the smooth muscle wall of the rectum contracts and the internal anal sphincter relaxes in the rectosphincteric reflex. Defecation will not occur at this time, however, because the external anal sphincter (composed of striated muscle and under voluntary control) is still tonically contracted. However, once the rectum fills to 25% of its capacity, there is an urge to defecate
**how do we poop**
When appropriate, the external anal spincter will relax voluntarly--\> smooth muscle of the rectum contracts and creates pressure--\> feces are forced through anal canal.
105
**What controls the rectosphincteric reflex?**
* Under neural control (ENS)
* The reflex is reinforced by neurons in the spinal cord
106
What controls the sensation of rectal distension and voluntary control of the anal sphincter ?
**Pathways in the SC --\> cerebral CTX**
107
What is a result of Hirschsprungs Dz?
**VIP levels are low**--\> SM constriction--\> contents of colon increase
108
What is the **intestino-intestinal reflex**?
**If an area of the bowl is grossly distended, contraction in the rest of the bowl is INHIBITED**
109
What is the **gastroileal reflex (gastroenteric)**?
**Gastric distension relaxes the ileocecal sphincter**
110
What are the gastro-
