GI Exam: Lecture 1 Flashcards
1
Q
Main Functions of the GI System:
The GI system consists of _______ and the associated __________
The overall function of the GI tract is:
-
-
-
All of these processes are controlled by ______
A
Main Functions of the GI System:
The GI system consists of the alimentary tract and the associated glandular organs emptying their contents into the GI tract
The overall function of the GI tract is:
- to breakdown food into molecular monomers
- to absorb nutriends and water into circulation
- and to particupate in the excretion of waste
All these processes are controlled by complex regulatory systems
2
Q
Main Functions of the GI System:
In order to perform its main functions the GI tract partcipates in 4 major physiological processes. These are:
1.
2.
3.
4.
The GI tract also participates in __________
A
In order to perform its main functions the GI tract participates in 4 major physiological processes:
- Motility
- Secretion
- Digestion
- Absorption
The GI tract also participates in excretion of waste substances
3
Q
Motility:
- This is part of the _____ process
- It is a concequence of __________ in the GI tract
- This is required to reduce the size of food particles allowing an increased ______
A
Motility:
- This is part of the digestion process
- It is a concequence of contractions of layers of smooth muscle cells in the GI tract
- This is required to reduce the size of food particles allowing an increased surface area for chemical digestion by enzymes
4
Q
Motility:
- Is required for mixing ______ with ______
- Is required to propel ingested food from the ____ towards the ______.
The rate at which food is propelled is regulated to optimize the time for ______ and ______
A
Motility:
- Is required for mixing food particles with the enzymes in the GI lumen
- Is required to propel ingested food from mouth towards the rectum. The rate at which food is propelled is regulated to optimize the time for digestion and absorption
5
Q
Secretion:
- is the release of _____________
- by the :
These secretions further aid in ____ and ____
A
Secretion:
is the release of enzymes, biological detergents, mucus, ions, and water in the GI lumen by the
- GI epithelium
- associated glands (Salivary, Pancreas, Liver, Gall Bladder)
These secretions further aid in digestion and absorption
6
Q
Digestion:
- Most of the nutrients in our diet are taken in as _____ that cannot be absorbed into circulation
- Digestion is the process by which _____ are converted to _______
- This consists of _____ and ______ modification of food such that they are digested into smaller molcules: ____, ____, _____
A
Digestion:
- Most of the nutrients in our diet are taken in as solids (macromolecules) that cannot be absorbed into circulation
- Digestion is the process by which macromolecules are converted inito smaller, absorbable molecules
- This consists of physical and chemical modification of food such that they are digested into smaller molecules- carbohydrates, amino acids, and lipids
7
Q
Absorption:
- Process by which nutrients, electrolytes, and water are ____ from the ____ to the ____
These absorbed particles are:
- the sources of ____ production
- rapidly used as components of _____
- Part of essential _______
-necessary to regulate _____
A
Absorption:
- Process by which nutrients, electrolytes, and water are absorbed from the GI lumen into the bloodstream
These absorbed particles are:
- the sources of energy production in cells
- Rapidly used components of various biological structures
- Part of essential metabolic pathways
- Necessary to regulate ALL physiological activities
8
Q
Excretion:
- The GI tract ___ and _____ waste substances from ingested food materials
- Excretes products from the liver:
-
-
-
A
Excretion:
The GI tract stores and excretes waste substances from ingested food materials
Excretes products from the liver:
- cholesterol
- steroids
- drug metabolites
9
Q
Immunological Function:
- The GI tract is open to the _______
- It is vunerable to ______ that can enter along with food and water
- To protect, it possesses a complex defense system of ________
- The GI tract represents the largest _____
A
Immunological Function:
- The GI tract is open to the external enviornment
- It is vunerable to infectious microorganisms that can enter along with food and water
- To protect it, it possesses a complex defense system of immune cells and other non-specific defense mechanisms
- GI tract represents the largest immune organ of the body
10
Q
Functional Anatomy of the GI System:
- What are the major functional segments of the GI tract? (note there are 7)
A
Major Functional Segments:
Mouth and Pharynx
Esophagus
Stomach
Small Intestine (duodenum, jejunum, ileum)
Large Intestines
Colons
Rectum
Anus
11
Q
Functional Anatomy:
What are the associated glandular organs within the GI tract?
(hint there are 5)
A
Associated Glandular Organs:
- Salivary
- Pancreas
- Liver
- Gall Bladder
- Endocrine glands or cells
12
Q
Define the term sphincter
What are the six sphincters within the GI System?
A
Sphincter: specialized circular muscle structures controlling the flow of GI contents between distinct structures
- Upper Esophogeal (between pharnyx and esophagus)
- Lower Esophogeal (between esophagus and stomach)
- Pyloric (between stomach and duodenum)
- Sphincter of Oddi: btwn pancreas and duodenum
- Illeocecal (between ileum and colon)
- Internal and External Anal Sphincters
13
Q
The gut wall is made up of several layers:
A
The gut wall is made up of several layers:
- Mucosa
- Submucosa
- Muscularis Extrerna
- Serosa
14
Q
Mucosa:
Mucosa is the _______ layer, and it is made up of ______, ______, and ________
A
Mucosa:
Mucosa is the innermost layer
Made up of epithelium, the lamina propria, and the muscularis mucosae
15
Q
Explain the epithelial layer of the mucosa:
What kind of cells make up the epithelium (note there are 4 of them)
A
(mucosa is the innermost layer of the gut wall, it is made up of epithelium, lamina propria, and muscularis mucosae)
The Epithelium is a single continous layer of specialized cells lining the lumen of the entire GI tract and innterconnected via tight junctions
Cells that make up the Epithelium:
- Absorptive Enterocytes: most abundant, plays role in digestion and absorption
- Enteroendocrine cells: releases regulatory peptides, amines - regulates GI function
- Other specialized cells are gastric mucosal cells (produce protons) and mucin producing cells that produce mucin (glycoprotein)
16
Q
The nature of the epithelium varies according to function:
- Esophageal epithelium: helps in transportation of swallowed food (________ type)
- Intestinal epithelium: helps in absorption (____ type)
- The surface area of small intestinal epithelium consists of ____
- The epithelial lining of the GI tract is continuosly renewed. The cells at the villus tip are eventually shed via cell death- lifespan about _______
- The proliferative cells are localized in the crypts: zone of ________ cells
A
The nature of the epithelium varies according to function:
1. Esophageal epithelium: helps in transportation of swallowed food (no absorption, squamous type)
- Intestinal epithelium: helps in absorption (columnar type)
- The surface area of the small intestinal epithelium consists of villi and crypts
- The epithelial lining of the GI tract is continously renewed. The cells at the villus tip are eventually shed via cell death - lifespan 3-5 days.
- The proliferative cells are localized in the crypts: zone of intestinal stem cells.
17
Q
Structural Features of Villi:
- Villi are _______ and crypts are _______
- A villus is called the __________
- Epithelial cell on the surface of a villus have numerous cytoplasmic extensions at the luminal surface - _____ or _______
- The mucosal folds, villi, and microvilli increase the surface area of the small intestine by 600 fold
- Reduced surface area causes malabsorption: example is ______
A
Structural Features of Villi:
- Villi are finger like projections and crypts are invaginations or folds
- The villus is called the unit of absorption
- Epithelial cell on the surface of a villus have numerous cytoplasmic extensions at the luminal surface- microvilli or brush border
- The mucosal folds, villi, and microvilli increase the surface area of the small intestine by 600 fold
- Reduced surface area causes malabsorption: example is Celiac Disease (flattened villi causes reduced surface area, causing malabsorption and malnutrition)
18
Q
Mucosa:
What are the two parts of the mucosa?
A
Mucosa:
Lamina Propria:
- Immediately below epithelium
- Consists of connective tissue
- Rich in glands, contains lymph vessels and nodes, capillaries, nerve fibers
Muscularis Mucosa
- Thin layer of smooth muscle cells in a folding configuration caused by contractions
19
Q
Submucosa:
- The layer after mucosa, consists of ____ tissue:
- _____ are present in some regions
- Large ______ and large ____ are present
- This consists of a dense network of nerve cells called the _______ of the enteric nervous system
- Helps in the integration of motor and secretory activities
A
Submucosa:
- The layer after mucosa, consists of connective tissue- collagen and elastin fibrils
- Glands are present in some regions
- Large nerve trunks and large blood and lymph vessels are present
- This consists of a dense network of nerve cells called the submucosal plexus of the enteric nervous system (also called the Messiner’s Plexus)
- Helps in the integration of motor and secretory activities
20
Q
Muscularis Externa/Muscularis Propria:
- Contractions of this layer helps in ____
- Consists of two layers of smooth muscle cells:
* * - Between these two layers lies the _____ plexus
A
Muscularis Externa/Propria
- Contractions in this layer helps in mixing and propelling contents of the GI tract
- Consists of two layers of smooth muscle cells:
- inner circular muscle layer
- outer longitudinal muscle layer
- Between these two layers lies the myenteric plexus (Auerbach’s Plexus)
21
Q
Serosa:
This is the ______ layer of the GI tract
Consists of a layer of ______ mesothelial cells
It is part of the mesentary that lines the surface of the abdominal wall and keeps the organs suspended in the cavity
Secretion is ____, lubricates the abdominal organs to ______ between the organs during contraction/relaxation of the GI tract
A
Serosa:
This is the outermost layer of the GI tract
Consists of a layer of squamous epithelial cells
It is part of the mesentary that lines the surface of the abdominal wall and keeps the organs suspended in the cavity
Secretion is viscous, lubricates the abdominal organs to reduce friction between the abdominal organs during contraction/relaxation of the GI tract
22
Q
Portal Circulation:
- The venous blood arising from the abdominal orgams flows into the ___ first via the ___ vein (___circulation)
- Blood from the liver is transported via hepatic veins to the _______
- Heart supplies tissues
A
Portal Circulation:
- The venous blood arising from the abdominal organs flows to the liver first via the portal vein (portal circulation)
- Blood from the liver is transported via hepatic veins to the inferior vena cava
- Heart supplies tissues
23
Q
- The blood vessels that supply the GI comprise the _______ circulation
- The ______ circulation has three comprising features:
* * *
A
The blood vessels that supply the GI comprise the Splanchnic circulation
The splanchnic circulation has three striking features:
- large blood flow (receives 25% of total CO)
- large reservoir function
- The diversity of organs that it perfuses
24
Q
Splanchnic Circulation:
List the three major arteries that supply the abominal organs, and name which organs they supply
A
Three major arteries that supply the abdominal organs:
- Celiac Artery: supplies the liver, spleen, and stomach
- Superior Mesenteric Artery: supplies the pancreas, small intestine, and proximal colon
- Inferior Mesenteric Artery: supplies the distal colon
25
Lymphatic Circulation:
Lymphatic Circulation is important for the absorption of _______ and transport of them to the heart
It is also important for immune function or filtering
Removes interstitial liquids in tissues
Lymphatic Circulation:
Lymphatic Circulation is important for the absorption of **lipids and lipid soluble molecules**
It is also important for immune function of filtering
Removes interstitial liquid in tissues
26
Regulation of GI Function:
The regulation of GI has distinct features:
GI tract undergoes periods of _______ (intermeal period) or _______ after food intake (postprandial period)
Varies with meal composition
Being a long GI tube there is intercommunication between its distant segments.
Three principle regulatory mechanisms are involved:
1.
2.
3
Regulation of GI Function:
The regulation of GI has distinct features
The GI tract undergoes periods of **relative quinescence** (intermeal period) or intense activity after food intake (postprandial period)
Varies with meal composition
Being a long GI tube there is intercommunication between its distant segments
Three principle regulatory mechanisms are involved:
1. **Endocrine**
2. **Paracrine**
3. **Neural**
27
Endocrine Regulation:
Sensor cells of the GI system are called _______ cells
They respond to a stimulus by secreting a \_\_\_\_\_\_\_\_, which travels via circulation to a target cell at distant location
Explain open vs closed types
The target cells express specific _____ for the GI hormone
Endocrine Regulation:
Sensor cells of the GI system are called **enteroendocrine cells (EECs)**
They respond to a stimulus by secreting a **regulatory peptide or hormone**, which travels via circulation to a target cell at a distant location
A typical EEC cell is "**open type**", meaning the apex of the cell is in contact w/ GI lumen (for sensing) and its base releases the hormone that diffuses into capillaries
"**Closed type**" do not have contact with GI lumen surface
The target cells express specific **receptors** for the GI hormone
28
Endocrine Regulation:
EEC hormones or peptides (released from the basolateral membrane) bind to a membrane receptor in a target cell and trigger a ________ cascade
The target cells can be located in other parts of the GI tract or in the associated grandular structures (examle: \_\_\_\_)
Target cells can also be in other tissues outside of the GI
Some EEC can be directly stimulated by neuronal input not associated with a meal
Example: _______ is released by G cells in the distal part of the stomach--- stimulates acid secretion by the ____ and \_\_\_\_\_
Endocrine Regulation:
EEC hormones or peptides (released from the basolateral membrane) bind to a membrane receptor in a target cell and trigger a **signal transduction cascade**
The target cells can be located in other parts of the GI tract or in the associated grandular structures (example: pancreas)
Target cells can also be in other tissues outside of the GI tract
Some EEc can be directly stimulated by neuronal input not associated by a meal
Example: **Gastin** is released by **G cells** in the distal part of the stomach--- _stimulates acid secretion by the ECL and parietal cells_ (gastric corpus or body)
29
Gastrin is released by _____ cells
located in the \_\_\_\_\_
Gastrin stimulates _____ secretion by the ___ and \_\_\_
Gastrin is released by G cells located in the distal part of the stomach
stimulates acid secretion by the ECL and parietal cells
30
Explain paracrine regulation
How is it different from endocrine regulation?
Paracrine Regulation:
Where a chemical messenger or regulatory peptide is released from a sensing cell and acts on nearby target cell by **diffusion** through the interstitual space
NOT transported via circulation (does not go into blood stream therefore is not endocrine)
Target cells include smooth muscle, absorptive enterocytes, etc
31
Explain the two paracine regulation examples:
Histamine
Cholecystokinin
Paracrine Examples
**Histamine** is released by ECL in stomach, it then diffuses through the interstitial space and binds to neighboring parietal cells that then secrete HCl
**Cholecystokinin (CCK)**: can be **both paracine and endocrine**, it is released in duodenum in response to protein and lipids- acts locally on nerve terminals (paracine) and on pancreas (endocrine)
32
Paracrine Regulation:
- Half of the mass of the immune system is present in the \_\_\_\_
- Immune cells in the GI system defend body from bacteria, antigens, etc
- These cells also release paracine factors
- There are serious diseases of the GI immune system linked to its hyperactivity
Half of mass of immune system is present in GI tract
Note: immune cells use paracine regulation in GI tract
33
Paracine Regulation (related pathology):
Celiac Disease:
- Due to an allergic response to a component in ______ called "\_\_\_\_\_\_"
- This causes an inflammatory response in the \_\_\_\_\_
- This results in reduction in ___ and ___ of microvilli
- Causes reduced _____ of nutrients
- The only known effective treatment is \_\_\_\_
Celiac Disease:
- Due to an allergic reaction to a component in gluten of wheat flour, rye, and barley- **gliadin**
- This causes an inflammatory response in the small intestine
- Resulting in reduction of density and length of microvilli
- Causes reduced absorption of nutriens
- Only known effective treatment is gluten free diet
34
Explain the secretion site and the stimuli for secretion of the following hormones:
Gastrin
CCK
Gastrin (endocrine) is secreted by G cells in response to small peptides and amino acids
CCK (endocrine and paracrine) is secreted by 'I' cells of the duodenum in response to fatty acids and hyrdolyzed proteins
35
Explain the secretion site and the stimuli for secretion for the following hormones:
Secretin
GIP (Glucoinsulinotropic Peptide)
Secretin (paracrine and endocrine) is released by "S" cells of the duodenum in response to H+ (protons) in the duodenum
GIP (endocrine) is released by "K" cells of the duodenum and jejunum in response to Fatty acids and glucose
36
Neural Regulation:
Neuronal regulation occurs when a _____ is released from a nerve terminal in the GI tract
This _____ then effects the cell that is innervated
Neural regulation is important within an organ and between distant parts of the GI tract
The gut is innervated by 2 sets of nerves:
\_\_\_\_\_\_ and _____ nervous systems
Neural Regulation:
- Neuronal regulation occurs when a **neurotransmitter** is released from a nerve terminal in the GI tract
- This NT then effects the cell that is innervated
- Neural regulation is important within and organ and between distant parts of the GI tract
The gut is innervated by 2 sets of nerves:
* **Extrinsic** and **intrinic** (ENS) nervous systems
37
Extrinsic NS:
- Nerves that innervate the gut with cell bodies located \_\_\_\_\_\_
- These extrinsic nerves are part of the \_\_\_\_\_\_
Intrinsic/ENS:
- has cell bodies contained within \_\_\_\_\_
- Organs of the GI can be regulated directly by extrinsic
- The extrinsic can regulate intrinsic
- The intrinsic can be independent of the extrinsic and regulates organs of the GI or muscle of the GI (motility)
Extrinsic NS:
- Nerves that innervate the gut with cell bodies located outside of the gut wall
- These extrinsic nerves are part of the **Autonomic Nervous System (ANS)**
Intrinsic/ENS:
- has cell bodies that are contained within the wall of the gut (submucosal plexus and myenteric plexus)
- Organs of the GI can be directly regulated by extrinsic
- Extrinsic can regulate intrinsic
- Intrinsic can be independent
38
Extrinsic NS:
Extrinsic neural innervation - via two major subdivisions of the ANS
Parasympathetic Innervation is mainly through which two nerves? What do those nerves innervate?
Extrinsic Nervous System:
Extrinsic neural innervation - via two major subdivisions of the ANS: Parasympathetic (most involved) and sympathetic
**Parasympathetic Innervation**: via vagal and pelvic nerves
**Vagal Nerve**: innervates the esophagus, stomach, gallbladder, pancreas, 1st part of intestine, cecum, proximal colon
**Pelvic Nerve**: innervates distal part of colon and anorectal region
39
Parasympathetic Innervation:
- In general _____ GI function
- Nerve cell bodies are located where?
- \_\_\_\_\_ fibers synpase in ganglia in the walls of the organs and/or within ENS
- Neurons are either ______ or \_\_\_\_
What do they release?
Parasympathetic Innervaton:
- In general, the parasympathetic NS **activates** GI function
- **Long** fibers synpase in ganglia in the walls of organs and/or within the ENS
- Neurons are either:
- **cholinergic** (release ACh)
- **Peptidergic** (release peptides, like substance P or VIP)
40
Parasympathetic Innervation:
- Vagus nerve is mixed (75% are afferent/sensory and 25% are efferent/motor)
- The afferent fibers deliver _____ information from ____ to \_\_\_\_
- The vagal afferents can send _____ to the ______ then drives activity to other neutons
- Vasovagal reflexes: both ___ and \_\_\_
Parasympathetic Innervation:
- Vagus nerve is mixed (75% afferent/sensory and 25% efferent/motor)
- The afferent fibers deliver sensory information from the gut (e.g. from the mechanoreceptors and chemoreceptors of gut wall) to the CNS
- The vagal afferents can send **sensory** info to the CNS then drives activity to other neurons
- **Vasovagal reflexes**: both afferent and efferent in the vagus nerve
41
Sympathetic Innervation:
- In general _____ GI Function
- What is the exception?
- Explain the preganglionic and postganglionic fibers
- What are the sympathetic ganglia that serve the GI tract?
Sympathetic Innervation:
- In general, **inhibit** GI function
- Exception: _GI sphincter muscles are activated by sympathetic innervation_
- **Preganglionic** fibers are **shorter** and synpase in galgnlia outside GI tract
- Sympathetic ganglia that serve GI tract: **celiac, superior mesenteric and inferior mesenteric**
- Post ganglionic fibers are **adrenergic** (release NE)
42
Sympathetic Innervation:
- Post ganglionic fibers leave the sympathetic ganglia - synpase on ganglia in ___ or \_\_\_\_\_\_\_\_
- About ____ are afferent and ____ are efferent in SNS
- Thus, sensory and motor info is relayed back and forth between GI tract and CNS, coordinated by the _____ and \_\_\_\_\_
Sympathetic Innervation:
-Post ganglionic fibers leave the sympathetic ganglia - synpase on ganglia in the ENS or directly innervate smooth muscle, endocrine, or secretory cells
- About 50% of sympathetic nerve fibers are afferent and 50% are efferent
- Thus, sensory and motor information is relayed back and forth between the GI tract and the CNS, coordinated by the submucosal and myenteric plexuses
43
Enteric Nervous System has two major plexuses:
Name them, explain where they are
ENS has two major plexuses:
**Myenteric** (between the longitudinal and circular muscle layers)
**Submucosal** (in the submucosa)
Neurons are afferent, interneurons or efferent. Thus the ENS can act autonomously
These neurons also receive input from extrinsic (PSNS and SNS) neurons that modulate their activity
Many **neurochemicals** are released by ENS (NTs and neuromodulators)
44
Myenteric Plexus is important for \_\_\_\_\_
Explain how
Myenteric Plexus is important for **motility**
involving circular muscle that contracts, and longitudinal muscle that relaxes
Myenteric plexus nerves activate (ACh) or inhibit (VIP or NO) these muscles to create motility
45
Explain Long Neural Reflex vs Short Reflex
**Long Neural Reflex**: sensory afference (to medullar (eg vagal) then efference motor to GI
**Short Reflex:** ENS/GI cells communication (ex: stretch receptor)
Short Reflex always involves Enteric NS
46
GI Motility:
- Define Motility
- Explain the muscles in the different parts of the GI tract
GI Motility: is the contraction and relaxation of the walls and sphincters of the GI tract
Almost all contractile tissues of GI tract are smooth muscles
**Those in pharynx, upper 1/3rd of esophagus, the external anal sphincter are striated muscle**
Smooth muscle forms gap functions with intersitial cells of Cajal (ICCs)
47
GI Motility:
GI smooth muscle contraction can be phasic or tonic
Explain phasic contractions vs tonic contractions
GI smooth muscle contraction can be phasic or tonic
**Phasic contractions** - periodic contractions followed by relaxation- found in esophagus, gastric antrum, small intestine - involved in mixing and propulsion
**Tonic contractions**: a constant level of contraction or tone without relaxation periods - found in upper region of stomach and lower esophageal, ileocecal, and internal anal sphincters
48
GI Motility:
Slow waves are unique feature of smooth muscle electrical activity:
They are slow electrical waves that are _____ to elicit an AP and or contractions
If at the peak of the slow wave, the membrane potential is depolarized up to threshold, then an AP occurs \_\_\_\_\_\_\_
GI Motility:
**slow waves** are unique features of smooth muscle electrical activity
They are slow electrical waves that are not large enough to elicit AP and or contractions
If at the plateau or peak of the slow wave, the membrane potential is depolarized up to threshold, then **AP occurs on top of the slow wave** ---\> stronger contraction
49
When AP occurs on top of the slow waves, it is followed by ________ contractions
The amplitude and to a lesser extent the frequency of slow wave are under \_\_\_, \_\_\_\_, and ____ influences
When AP occurs on top of the slow waves, it is followed by strong contractions-**phasic contractions**
The amplitude and to a lesser extent the frequency of slow waves are under neural, hormonal, and paracrine influences
50
The slow waves only originate in the \_\_\_\_\_\_\_\_\_, located between the longitudinal and circular layers of muscularis externa
They are called the ______ cells for GI smooth muscle
Slow waves only originate in **interstitial cells of Cajal** (ICCs) located between longitudinal and circular layers of muscularis externa
They are called the **pacemaker cells** for GI smooth muscle
51
Segmentation Contractions:
- Segmentation contractions occur in the ____ and \_\_\_\_
- Goal of segmentation contractions:
Segmentation Contractions:
- **Segmentation contractions** occur predominately in the small and large intestine
- These allow **MIXING** of luminal contents with Gi tract secretions and increase exposure to mucosal surfaces where absorption occurs
- A small section contracts, splitting chyme, sending it in both orad and caudad directions
- Section then relaxes to allow chyme to merge- allowing it to mix but producing no forward movement
52
Peristaltic Contractions:
-Peristaltic contractions occur in the \_\_\_\_, \_\_\_, \_\_\_\_, ____ and \_\_\_\_\_\_
These contractions help \_\_\_\_\_\_\_
Here a contraction occurs at a point ___ to the bolus, simultaneously, the portion ____ to the bolus \_\_\_, the chyme is thus propelled in the ___ direction
Neurotransmitters:
\_\_\_\_\_ and ____ are involved in contraction
\_\_\_\_ and ____ are involved in relaxation
Peristaltic Contractions:
Peristaltic contractions occur in the pharynx, esophagus, gastric antrum, small and large intestine
These contractions help **propel the chyme** along the GI tract
Here a contraction occurs at a point orad to the bolus, simultaneously, the portion caudad to the bolus relaxes; the chyme is thus propelled in the caudad direction
-NTs:
**ACh** and **Substance P** are involved in contraction
**VIP** and **NO** are involved in relaxation
