Wake Gi Alimentary Canal

Front 1

Motility

Back 1

Contractions of smooth muscle in the wall of the tube crush, mix and move contents

Front 2

Absorption

Back 2

Transport water, ions and nutrients from lumen, across epithelium and into blood

Front 3

Secretion

Back 3

Delivers enzymes, mucus and ions into the lumen (and hormones into blood)

Front 4

Organization of the gut wall

(Name the layers...starting with lumen)

Back 4

Lumen
Mucosa (epitheliuma and lamina propria)
Muscularis mucosa
Submucosa
Muscularis externa (2 -3 layers)
Serosa/adventitia

Front 5

Esophagus

(Basic Sxr, Fxn)

Back 5

passageway for rough bolus of food

(nonkeratinized) stratified squamous epithelium

glands in submucosa for lubrication

Front 6

Stomach

(Basic Fxn)

Back 6

produces secretions required to convert food into chyme;

mucosa comprises multiple types of secretory cells.

Mechanical actions require greater smooth muscle

Front 7

Small Intestine

(Basic Fxn)

Back 7

provides additional digestive enzymes (some from extramural glands) and

absorbs amino acids, sugars, fats and other molecules liberated by digestion;

mucosa includes both secretory and absorptive cells

Front 8

Large Intestine

(Basic Fxn)

Back 8

completes absorption (especially reabsorption of water and ions) and

compacts non-digestible waste for elimination;

some absorptive cells and goblet cells to produce lubricating secretions

Front 9

In contrast to the rest of the GI tract, this layer of muscle is not just smooth muscle in the esophagus...

Back 9

the Muscularis Externa contains a variable amount of striated muscle

- proximal esophagus = striated muscle

- distal esophagus = smooth muscle

Front 10

What is the outer most layer of the esophagus?

Back 10

esophagus is not free as it courses through the thoracic cavity... it is embedded in connective tissue

the outer tunic is ADVENTITIA , not serosa

Front 11

Does absorption or secretion occur in the esophagus?

Back 11

No absorption in esophagus

Secretions lubricate the luminal surface to facilitate movement of the food bolus

Secretions provided by subepithelial glands

Front 12

esophageal cardiac glands

Back 12

occur in lamina propria of lower (and sometimes upper) esophagus; produce neutral mucus that helps neutralize stomach acid

Front 13

What innervates the muscularis externa of the esophagus?

Back 13

CN X (vagus nerve) produces peristaltic movements

Front 14

What do the submucosal glands of the esophagus produce?

Back 14

acidic mucus that lubricates the luminal wall

Front 15

Esophageal Sphincters

Back 15

Esophagus bounded by two physiologic sphincters (formed from inner circular layer of muscularis externa)

Upper esophageal sphincter closely associated with larynx; during swallowing pulls larynx forward to help rout food into esophagus

Lower esophageal sphincter where esophagus joins stomach.

Normally upper and lower sphincters closed except during swallowing to prevent entry of air from the oral cavity or reflux of stomach contents

Front 16

What occurs with the sphincters in GERD?

Back 16

In heartburn and gastroesophageal reflux disease (GERD) lower sphincter does not close properly so acid refluxes into esophagus and causes a burning sensation in the chest /throat and even coughing and sensation of choking.

Front 17

What are the components of the submucosa in the esophagus?

Back 17

mucus glands

lymphoid cells

blood vessels

elastic fibers

Front 18

Esophagogastric junction

Back 18

Transition from esophagus to stomach normally more discrete in mucosa (squamous epithelium to invaginating columnar epithelium) than in deeper layers

Esophagogastric sphincter (in muscularis externa) less prominent than sphincter between stomach and small intestine

Front 19

Stomach: four basic functions that assist in early stages of digestion and prepare for further processing

Back 19

1. Short-term storage reservoir – meal consumed quickly but dealt with over extended period

2. Substantial enzymatic digestion is initiated, particularly of proteins

3. Contraction of smooth muscle grinds food and mixes with gastric secretions; liquefaction of ingesta prerequisite for delivery to small intestine

4. Ingesta slowly released into the small intestine for further processing

Front 20

Absorption in the stomach

Back 20

Stomach absorbs few substances
- Small amounts certain lipid-soluble compounds (including aspirin and other NSAIDs)
- Ethanol

These substances recognized causes of gastric irritation; use/overuse commonly associated with development of gastritis

Front 21

Muscle layers of the stomach

(inner to outer)

Back 21

Oblique muscle layer (overlying mucosa)

Cicular muscle layer

Longitudinal muscle layer

Front 22

Four major secretory products of gastric epithelium

Back 22

1. acid

2. mucus

3. proteases

4. hormones

Other enzymes secreted by gastric epithelial cells include a lipase and gelatinase

Intrinsic factor (glycoprotein secreted by parietal cells) necessary for intestinal absorption of vitamin B12

Front 23

Mucus

Stomach Secretion

Back 23

Mucous cells cover lumenal surface and extend into the glands (mucous neck cells)

Secrete bicarbonate-rich mucus; coats/lubricates surface, protects epithelium from acid

Front 24

Acid

Stomach Secretion

Back 24

HCl secreted by parietal cells into the lumen

Acidic environment important for activation of pepsinogen and killing microorganisms

Front 25

Proteases

Stomach Secretion

Back 25

Pepsinogen (inactive) secreted by chief cells; activated by acid into protease pepsin, initiates digestion proteins

In young animals chief cells also secrete chymosin (rennin), protease that coagulates milk proteins so retained longer in the stomach

Front 26

Hormones

Stomach Secretion

Back 26

Principal hormone from the gastric epithelium is gastrin, influences acid secretion and gastric motility

secreted from enteroendocrine cells

Front 27

Six cell types in the gastric epithelium

Back 27

- Non-secretory
Stem cells (throughout GI tract)

- Secretory
Mucus:
2. Surface mucous cells
3. Mucous neck cells
Acid and Intrinsic Factor:
4. Parietal cells (oxyntic cells)
Enzymes:
5. Chief cells (peptic cells)
Peptides (endocrine/paracrine factors):
6. Enteroendocrine cells (found throughout GI tract)

Front 28

Stem cells in the Stomach

Back 28

Epithelial Renewal

Dividing stem cells primarily in isthmus region of gastric glands

Most new cells become surface cells (live 3-5 days)

Other cell types have longer lifespans (up to 150-200 days for parietal cells) but all are replaced from the stem cells

Front 29

Surface mucous cells in Stomach

Back 29

Each contains mucinogen granules forming “mucous cup” apically; when released the mucinogen forms viscous coat that adheres to epithelial surface

Provides mechanical protection and, because of high bicarbonate concentration, protects epithelium from acidic gastric juice

Front 30

Mucous neck cells in Stomach

Back 30

Shorter than surface cells, located among groups of parietal cells in neck region of gastric glands

Contain less mucinogen and no prominent mucous cup

Produce more soluble mucous, under the control of vagal stimulation

Front 31

Chief Cells in Stomach

Back 31

Protein secreting cells

Abundant rER basally, so basophilic

Eosinophilic apically due to presence of secretory (zymogen) granules containing enzyme precursors

Secrete pepsinogen (converted to pepsin on contact with gastric juice) and a weak lipase

Front 32

Parietal Cells in Stomach

Back 32

oval shape

eosinophilic cytoplasm

“fried egg” appearance with prominent central nucleus

“secrete” HCL

Front 33

Acid Production by parietal cells

Back 33

Hydrogen ion concentration in parietal cell secretions is 3,000,000-fold higher than in blood

Chloride is secreted into lumen against both a concentration and electric gradient

Ability parietal cells to secrete acid dependent on active transport and ATP

Key player is H+/K+ ATPase ("proton pump“) in cannalicular membrane

Acid production controlled in part by rapid regulation of the extent of plasma membrane over which ions can be moved between cytoplasm of parietal cells and lumenal fluid

Front 34

HCl Secretion by parietal cells

(the steps)

Back 34

- Dissociation water yields hydrogen ions
- Hydroxyl ions formed and rapidly combine with carbon dioxide to form bicarbonate (catalyzed by carbonic anhydrase)
- Bicarbonate transported out of the basolateral membrane in exchange for chloride
- Chloride and potassium ions transported from cytoplasm into the lumen of the cannaliculi by passive conductance channels.
- Hydrogen ions pumped out of the cell and into the lumen in exchange for potassium through the action of the proton pump (ATPase); potassium is thus recycled back into the cytoplasm
- Accumulation of osmotically-active hydrogen ions in the cannaliculus generates osmotic gradient across membrane; get outward diffusion H2O
- Acid production dependent on ATP; large numbers mitochondria account for eosinophilia of parietal cells

Front 35

Regulation of acid production

Back 35

Parietal cells bear receptors for three stimulators of acid secretion, reflecting three-way neural, paracrine and endocrine control:
- Acetylcholine (muscarinic type receptor)
- Gastrin
- Histamine (H2 type receptor)

Histamine from enteroendocrine cells primary modulator but get additive interaction of multiple signals

Low amounts histamine, gastrin or ACh released constantly from cells in the gastric mucosa

Individually only weakly stimulate acid secretion but when all are present acid secretion is strongly activated

Front 36

What is the extent of canaliculli and microvilli in parietal cells?

Back 36

Extent of canaliculli and microvilli is not constant

membrane from tubulovesicular system is inserted into plasma membrane and proton pumps are inserted under appropriate physiological stimulation; histamine influences movement of H+/K+ ATPase from cytoplasm into plasma membrane

Front 37

Enteroendocrine Cells in the Stomach

Back 37

Present throughout gland but most prominent at base

Apex often does not reach lumen (although some processes may)

Secrete basally

Granules small; usually poorly preserved and palely stained

Appears each cell specialized for one type of secretion

Front 38

Stomach Glands by region

(cardiac, fundic/corpus, pyloric)

Back 38

Glands in cardiac and pyloric regions contain a larger proportion of mucus producing cells and fewer parietal cells

Cardiac: moderately deep pits; tortuous, loosely packed tubular glands

Fundic/corpus: shallow pits; long, straight tubular glands

Pyloric: deep pits; coiled and branched glands

Front 39

Submucosa of Stomach

Back 39

No glands in submucosa, just connective tissue with lymphoid cells, blood vessels

Front 40

Epithelium of Stomach

Back 40

simple columnar epithelium covers luminal surface and invaginates into lamina propria to form gastric glands

Front 41

Outer most layer of stomach

Back 41

Serosa: connective tissue covered by simple squamous epithelial cells

Front 42

Gastroduodenal Junction

Back 42

Mucosa: change from gastric pits and glands to intestinal villi (V)

Submucosa: appearance of Brunner’s glands (B)

Muscularis externa: thicker in pyloric stomach (MEP), particularly where it forms the pyloric sphincter (PS); muscularis externa much thinner in the duodenum (MED)

Front 43

Function of Small Intestine

Back 43

Small intestine site of absorption virtually all nutrients

In small intestine macromolecular aggregates exposed to pancreatic enzymes and bile, enables digestion to molecules that are ready (or almost ready) to be absorbed

Final stages of digestion occur on the surface of the small intestinal epithelium.

Net effect of passage through small intestine is absorption of most water and electrolytes (sodium, chloride, potassium) and essentially all dietary organic molecules (e.g., glucose, amino acids and fatty acids)

Small intestine provides nutrients to the body and helps regulate water and acid-base balance

Front 44

What does the duodenum have that the ileum and jejunum lack?

Back 44

Brunner's glands

Front 45

What is the pH of the Brunner's Glands secretions in the duodenum?

Back 45

8.1 - 9.3

(a mixture of glycoproteins and bicarbonate ions that neutralize chyme as it is delivered from the stomach, making it close to the optimal pH for pancreatic enzymes)

Front 46

Layers of the Small Intestine

Plicae Circularis

Back 46

involve both submucosa and overlying mucosa

Front 47

Layers of the Small Intestine

Villi

Back 47

represent evaginations of the mucosa

Front 48

Layers of the Small Intestine

Crypts (glands)

Back 48

represent invaginations of the epithelium into the underlying lamina propria

Front 49

Layers of the Small Intestine

Glycocalyx

Back 49

formed by glycoproteins projecting from apical plasma membrane of absorptive cells provides additional surface for absorption and includes enzymes needed for the final digestion of proteins and sugars

Front 50

Layers of the Small Intestine

Microvilli

Back 50

Absorptive cells (enterocytes) bear microvilli on their apical surface that increase the area of the apical cell membrane

Front 51

Six cell types in the small intestinal epithelium

Back 51

Non-secretory
1. Stem cells (found throughout GI tract)
2. Intermediate cells (differentiating cells)
3. Enterocytes (aka absorptive cells)
Secretory
3. Enterocytes (produce digestive enzymes)
4. Goblet cells – produce mucus
5. Paneth cells – produce lysozyme
6. Enteroendocrine cells – produce peptides (hormones, etc., found throughout GI tract)

Front 52

Paracellular

Back 52

transportation across tight junctions between epithelial cells for absorption

tight junctions are impermeable to organic molecules

Front 53

Transcellular

Back 53

transportation across the plasma membrane of the epithelial cells for absorption

organic molecules (amino acids and glucose) transported transcellularly

Front 54

Features of the Ultrastructure of Absorptive Cells

Back 54

Microvillous (brush) border: Microvilli contain actin microfilaments that extend into the apical, terminal web cytoplasm.

Extensive apical SER: Involved in packaging some nutrients for transport through cytoplasm

Cells tightly opposed apically; intercellular space is wider basally

Front 55

What is critical to enterocyte function?

Back 55

the establishment of an electrochemical sodium gradient across the epithelial cell boundary

- cells must have low intracellular [Na] to remain viable

Front 56

How mcuh sodium is tranported out of each small intestinal enterocyte per minute?

Back 56

About 150,000 sodium pumps per small intestinal enterocyte allow each cell to transport about 4.5 billion sodium ions out of each cell per minute

This flow and accumulation of sodium is ultimately responsible for absorption of water, amino acids and carbohydrates.

Front 57

Absorption of Fatty Acids

Back 57

Most products of lipid digestion (fatty acids and monoglycerides) enter enterocyte by diffusion across plasma membrane (fraction enters via specific fatty acid transporter )

Once inside enterocyte fatty acids and monoglycerides transported into ER, used to synthesize triglyceride

Beginning in ER and continuing in the Golgi, triglyceride packaged with cholesterol, lipoproteins and other lipids into chylomicrons.

Chylomicrons extruded from Golgi into exocytotic vesicles, which are transported to the basolateral aspect of the enterocyte; vesicles fuse with plasma membrane and undergo exocytosis, dumping chylomicrons into extracellular space

Front 58

How does the structure of enterocytes vary?

Back 58

Structure of enterocytes varies with functional state (may not be apparent light microscopic level

In “active” enterocyte on there is extensive sER in apical region, large membrane-bound vesicles in middle portion cell, and chylomicrons discharged in extracellular space basalaterally

Front 59

How is transportation of lipids into circulation different rom transportation of sugars and amino acids?

Back 59

Lipids enter the lymphatic capillary in the core of the villi as chylomicrons

Chylomicron-rich lymph drains into the lymphatic system and then ultimately into the blood

Sugars and AAs drain into the blood capillaries

Front 60

What is the function of goblet cells in the intesetinal epithelium?

Back 60

Produce mucus that contributes to barrier functions:

- Carbohydrates on mucin molecules bind bacteria; helps prevent colonization and causes aggregation, accelerating clearance

- Reduced diffusion hydrophilic molecules in mucus (compared aqueous solution) retards access of many damaging chemicals, including gastric acid, to epithelial surface

Front 61

Paneth Cells

Back 61

- Provide defense against microbes (functionally similar neutrophils)

- Produce alpha-defensins

- Secrete defensins when exposed to bacteria or bacterial products
secrete lysozyme and phospholipase A2 (antimicrobial activity)

- In intestinal crypts identified by basophilic basal cytoplasm and intensely acidophilic apical secretory vesicles

Front 62

Alpha-defensins

Back 62

interact with phospholipids in cell membranes and form pores to disrupt membrane function and kill cells - bacterial membranes have higher concentrations of negatively-charged phospholipids than vertebrate membranes so intestinal cells are protected

Front 63

Which part of the small intestine has the greatest development of lymphoid tissue?

Back 63

Ileum (peyer's patches)

Front 64

What is the main site of absorption?

Back 64

Jejunum (most extensive development of plicae and most complex villi)

Front 65

Are there glands in the submucosa of the small intestine?

Back 65

only in the duodenum

Front 66

Small Intestine Mucosa

Back 66

Simple columnar epithelium covers luminal surface and invaginates into lamina propria to form glands (crypts of Lieberkuhn)

Front 67

Recovery water and electrolytes in LI

Back 67

by time ingesta reaches terminal ileum 90% of water absorbed but some water and electrolytes like sodium and chloride remain and must be recovered by absorption in large intestine

Front 68

Formation/storage of feces in LI

Back 68

as ingesta moved through large intestine is dehydrated, mixed with bacteria and mucus, and formed into feces

Front 69

Microbial fermentation in LI

Back 69

large intestine all species filled with microbes; produce enzymes capable of digesting many molecules that to vertebrate cells are indigestible (e.g., cellulose) - extent and nutritional benefit of fermentation varies among species

Front 70

Cecum

Back 70

is a blind-ended pouch, in humans terminates in worm-like extension called vermiform appendix

Front 71

Colon

Back 71

constitutes majority of the length of the large intestine

Front 72

Rectum

Back 72

is short, terminal segment of the digestive tube, continuous with anal canal

Front 73

Histology of Large Intestine

Back 73

Mucosa has smooth surface (no villi) although crypts are present and extend down to the muscularis mucosa.

No submucosal glands are present.

The outer longitudinal layer of the muscularis externa is thinner than the inner circular layer except where the outer layer forms the tenia coli

Front 74

Teniae coli

Back 74

Outer longitudinal layer muscularis externa exhibits three equally-spaced bands called teniae coli (TC, in rectum outer band uniformly thick, as in small intestine)

Front 75

What cell is in the epithelial intestinal glands of the small intestine, but not the large intestine?

What cells are there in spades?

Back 75

Paneth cells

Large bowel contains higher percentage goblet cells than small intestine but absorptive cells still predominate over goblet cells except in the distal colon near the rectum

Absorptive cells absorb water and electrolytes as waste is compacted

Front 76

Mucosa of the Large Intestine

Back 76

Crypts (glands) in large intestine straight and unbranched with regularly-spaced openings to surface epithelium

Absorptive cells most common apically, goblet cells predominate deeper in glands (where enteroendocrine cells (E) may be present)

Plasma cells (P, antibody-producing cells) often present in lamina propria

In contrast to small intestine lymphatic capillaries generally absent from lamina propria large intestine

Front 77

When do the goblet cells secrete mucus in the colon?

Back 77

Goblet cells abundant in the colonic epithelium and secrete mucus in response to tactile stimuli from lumenal contents, as well as parasympathetic stimuli - mucus as lubricant protects epithelium and helps bind dehydrated ingesta to form feces

Front 78

Absorption and secretion in the Colon

Back 78

Water absorbed in response to osmotic gradient ; mechanism essentially identical to that in small intestine – Na+ transported from lumen across epithelium to basolateral extracellular space by virtue of active sodium pumps on basolateral membranes and means of absorbing sodium through lumenal membrane

Chloride absorbed by exchange with bicarbonate at apical surface; resulting secretion of bicarbonate ions into lumen aids in neutralization of acids generated by microbial fermentation

mucus secretion

Front 79

Key cell types in the epithelium of the large intestin

Back 79

Absorptive cells in surface epithelium (absorb mostly water and ions)

Many goblet cells (mucus secreting)

Stem cells (deep in crypts)

Enteroendocrine cells

Front 80

Key cell types in the Lamina Propria of the large intestine

Back 80

Fibroblasts

Many scattered lymphocytes (mostly T cells); often small lymphoid nodules containing (mostly) B lymphocytes

Eosinophils

Muciphages

Front 81

Could the appendix have a purpose?

Back 81

recent evidence suggests that the appendix is a sanctuary for beneficial gut bacteria

Front 82

How does the appendix change as we age?

Back 82

greatly increased lymphoid tissue in children

greater connective tissue in aubmucosa in adult

Front 83

Vermiform Appendix

Back 83

- Blind-ending tubular extension of cecum
- Structure similar to that of colon but smaller diameter and taeniae absent
- Mucosa similar to colon - straight glands with absorptive cells, goblet cells and some enteroendocrine cells
- Lamina propria and submucosa may contain abundant lymphoid tissue (even confluent nodules); lymphoid tissue accumulates during childhood then progressively disappears so only traces evident in adults
- As the lymphoid tissue atrophies is replaced by fibrous connective tissue

Front 84

What are the 3 zones of the anal canal?

Back 84

colorectal zone

anal transitional zone

squamous zone

Front 85

colorectal zone of anal canal

Back 85

upper 1/3

simple columnar epithelium (as in rectum)

Front 86

anal transitional zone of anal canal

Back 86

middle 1/3

transition from simple columnar to stratified squamous epithelium (which continues to the cutaneous zone)

muscularis mucosa ends here

Front 87

squamous zone of anal canal

Back 87

lower 1/3

stratified squamous epithelium that is continuous with perineal skin

Front 88

Peyer's Patches

Back 88

lymphoid follicles located in mucosa and extending into submucosa small intestine (especially ileum).

In adults, B lymphocytes predominate but T cells also present.

maller lymphoid nodules found throughout intestinal tract

Front 89

Lamina propria lymphocytes

Back 89

lymphocytes scattered in lamina propria of mucosa

most are IgA-secreting B cells

Front 90

Intraepithelial lymphocytes

Back 90

Lymphocytes positioned in basolateral spaces between lumenal epithelial cells (beneath tight junctions)

Front 91

Immune function in the GI system –GALT

Back 91

Lumen of GI tract populated with potentially pathogenic microorganisms

Immune system maintains strong presence at mucosal boundary with lymphocytes, macrophages and other immune cells

Lymphoid tissue in gut collectively referred to as gut-associated lymphoid tissue or GALT, represented by three primary populations:
- peyer's patches
-lamina propria lymphocytes
- intraepithelial lymphocytes

In addition to GALT the lymph nodes that receive lymph draining from gut (mesenteric nodes) and Kupffer cells (phagocytic cells in liver) help protect against invasion

Front 92

Lymphoid follicles

Back 92

Lymphoid follicles contain both B- and T-cells, generally in discrete zones

Germinal centers of secondary follicles contain replicating and maturing B-cells

Lymphoid follicles do not have afferent lymphatic vessels but have efferent lymphatics.

Epithelium overlying Peyer’s patches (dome epithelium) has cuboidal rather than columnar cells and also many intraepithelial lymphocytes (IEL)

Some epithelial cells are microfold cells (M cells), can transfer antigens (by endocytosis) between lumen and Peyer’s patch

Front 93

Microfold (M) cells

(sxr and location)

Back 93

are epithelial cells with apical folds instead of microvilli

Have deep recesses within which lymphocytes sit in close apposition to lumen of small intestine

Bear MHC II molecules and present antigens to T lymphocytes within their recesses (see box 16.5, p. 509 for further description)

Front 94

M cell function

Back 94

Microfold cells endocytose protein and peptide antigens; instead of digesting proteins M cells transport them into underlying tissue

Interact with dendritic cells to help coordinate immune response

Are exploited by some infectious agents to gain access

Function is altered when rest of mucosal barrier is altered by pathology (as in inflammatory conditions)

Front 95

Role of Auonomic Nervous System in GI Function

Back 95

sympathetic stimulation causes inhibition of gastrointestinal secretion and motor activity (and contraction of gastrointestinal sphincters and blood vessels)

parasympathetic activation typically stimulates digestive activities

Front 96

Lymphoid follicles

Back 96

Lymphoid follicles contain both B- and T-cells, generally in discrete zones

Germinal centers of secondary follicles contain replicating and maturing B-cells

Lymphoid follicles do not have afferent lymphatic vessels but have efferent lymphatics.

Epithelium overlying Peyer’s patches (dome epithelium) has cuboidal rather than columnar cells and also many intraepithelial lymphocytes (IEL)

Some epithelial cells are microfold cells (M cells), can transfer antigens (by endocytosis) between lumen and Peyer’s patch

Front 97

Microfold (M) cells

(sxr and location)

Back 97

are epithelial cells with apical folds instead of microvilli

Have deep recesses within which lymphocytes sit in close apposition to lumen of small intestine

Bear MHC II molecules and present antigens to T lymphocytes within their recesses (see box 16.5, p. 509 for further description)

Front 98

M cell function

Back 98

Microfold cells endocytose protein and peptide antigens; instead of digesting proteins M cells transport them into underlying tissue

Interact with dendritic cells to help coordinate immune response

Are exploited by some infectious agents to gain access

Function is altered when rest of mucosal barrier is altered by pathology (as in inflammatory conditions)

Front 99

Name the 3 types of Neurons in the enteric plexuses

Back 99

Sensory Neurons

Motor Neurons

Interneurons

Front 100

NTs secreted by enteric neurons

Back 100

Acetylcholine generally excitatory; stimulates smooth muscle contraction, intestinal secretions, release of enteric hormones and dilation blood vessels

Norepinephrine (from extrinsic sympathetic neurons) is generally inhibitory (opposes ACh)

Front 101

Interneurons

of the enteric nervous system

Back 101

integrate information from sensory neurons and relay it to motor neurons

Front 102

Motor neurons

of the enteric nervous system

Back 102

control GI motility and secretion (possibly absorption)

act on smooth muscle, secretory cells (chief, parietal, mucous, enterocytes, pancreatic exocrine cells) and enteroendocrine cells

Front 103

Sensory neurons

of the enteric nervous system

Back 103

Receive information from sensory receptors in mucosa and muscle

Respond to mechanical, thermal, osmotic and chemical stimuli;

Collectively provide information on gut contents and state of GI wall
- Chemoreceptors sensitive to acid, glucose and amino acids "taste“ lumenal content
- Sensory receptors in muscle respond to stretch and tension

Front 104

Components of the Submucosal and Myernteric plexi

Back 104

axons and postganglionic parasympathetic neurons

Front 105

What doe the nervous system influence in the GI tract

Back 105

motility,

ion transport (associated with secretion and absorption), and

gastrointestinal blood flow

Front 106

Myenteric Plexus

Back 106

located between longitudinal and circular layers of muscle in tunica muscularis; exerts control primarily over digestive tract MOTILITY

Front 107

Submucosal plexus

Back 107

within submucosa; principal roles include
1. sensing environment within lumen,
2. regulating gastrointestinal blood flow, and
3. controlling epithelial cell function (sparse in esophagus where these functions less relevant)