WEEK 11 Flashcards
fill in.
The enteric nervous system contains ~100 million ______, ______, and ______ and innervates the alimentary canal from the ________ to the anus.
motor; sensory; interneurons ; esophagus
fill in.
The enteric nervous system is considered the _________ innervation of the alimentary canal
intrinsic
What are the two plexuses of the enteric nervous system?
- myenteric plexus (plexus of Auerbach)
- submucosal plexus (plexus of Meissner)
Myenteric plexus (plexus of Auerbach) is located between which two layers of the muscularis layer?
circular and longitudinal layer
Describe the myenteric plexus of the enteric nervous system?
- between the circular and longitudinal layers of the muscularis layer
- regulates motility, especially the specific rhythm of each region (pacemaker)
- controls force of contractions
Where is the submucosal plexus located?
- the submucosal layer
The submucosal plexus is also known as what?
the plexus of meissner
describe the submucosal plexus?
- lies in the submucosal layer
- regulates secretions
- sensory neurons in this plexus are sensitive to changes in the environment caused by the presence of food
- the chemoreceptors are sensitive to acid, glucose, and amino tasting luminal contents
- the mechanoreceptors respond to stretch and tension
Fill in.
The digestive system provides the body with a continuous supply of _______, ________, _______ and nutrients
water; electrolytes ; vitamins
True or false.
Ingested food is broken down mechanically and chemically to release energy.
True.
True or false.
Ingested food that is broken down into mechanically and chemically needs to be absorbed into either the blood or lymph for distribution
True.
Describe the alimentary canal.
- essentially a long hollow tube
- oral cavity (mouth) > pharynx > esophagus > stomach > small intestine > large intestine > anus
- each region of the canal is specialized to perform specific functions
What are the accessory structures or organs connected to the alimentary canal by ducts?
- salivary glands (lubricate food)
- gallbladder
- liver
- exocrine pancreas
the Gallbladder, liver and exocrine pancreas lead to what of the alimentary canal?
- the duodenum
How does mechanical digestion assist chemical digestion?
- mechanical expands the surface area of the food
Fill in.
_________ are important structures that regulate the movement of the contents of the alimentary canal from one segment to another
sphincters
True or false.
In order for food to be released for swallowing to proceed the upper esophageal sphincter does not need to be released.
False. the upper esophageal sphincter does
True or false.
The lower esophageal sphincter is a regular sphincter.
False. The lower esophageal sphincter is a physiological sphincter. It is not made of skeletal muscle, but smooth muscle.
the upper esophageal sphincter is made of skeletal muscle
What sphincter regulates movement of food from the stomach to the duodenum?
Pyloric sphincter
Where does the sphincter of Oddi connect?
- the bile duct and pancreatic duct to the duodenum
- does not regulate food
Describe the internal and external sphincter
- the internal sphincter is made of smooth muscle and is under involuntary control
- the external sphincter is made of skeletal muscle and is under voluntary control
Describe the illeocecal valve?
Found between the ileum and colon
- allows for food to pass from the small intestine to the colon ( large intestine)
Fill in.
The diaphragm helps regulate movement of food from the ___________ to the stomach
esophagus
List the tissue layers of the alimentary canal from internal to external
- mucosa
- submucosa
- muscularis
- serosa
What makes up the mucosa? Describe each layer from internal to outermost.
- epithelium:
- this is in direct contact with the contents of the alimentary canal
- surrounds the lumen
- this layer is non-keratinized, stratified squamous epithelium in the mouth, pharynx, esophagus, and anal canal
- in the stomach its a simple columnar epithelium
- contains goblet cells that secrete mucus
- contains enteroendocrine cells that secrete hormones
- lamina propria:
- contains loose connective tissue, blood, and lymphatic vessels
- mucosa- associated lymphoid tissue (MALT). MALT in the distal ileum is called peyer’s patches - muscularis mucosa
describe the submucosa
- immediately external to the mucosa
- it’s a layer of dense connective tissue
- includes blood and lymphatic vessels
- submucosal glands. the necks of this gland perforate the mucosa
- submucosal plexus runs through this layer
Describe the muscularis
- in the small intestine, it is made up of double layer of smooth muscle
- an inner circular layer
- an outer longitudinal layer
- contractions of these layers are responsible for:
1. organ motility (movement)
2. promoting mechanical digestion
3. exposing food to more digestive chemicals
4. move the food along the canal
what exceptions apply to the muscularis of the alimentary canal?
- in the mouth, pharynx, anterior part of the esophagus, and external anal sphincter the muscularis is made of skeletal muscle
- the two-layer structure is modified in the stomach and colon
describe the serosa
- superficial to the muscularis
- only in the region of the alimentary canal w/in the abdominal cavity
- consists of a layer of visceral peritoneum and a layer of loose connective tissue underneath
- mouth, pharynx, and esophagus have a dense sheath of collagen fibers called the adventitia
The serosa of the mouth, pharynx and esophagus is called what? What is it made of?
the adventitia; made of collagen
If the ANS could no longer innervate the alimentary canal would there still be function?
Yes, because the enteric nervous system still has the components (sensory, motor and interneurons) necessary to innervate the canal
What nerves are associated with parasympathetic innervation of the alimentary canal?
- vagus nerve
- pelvic nerve
True or false.
The vagus nerve is not a mixed nerve
False.
It is mixed. it has both sensory and motor components
Fill in.
The vagus nerve innervates _____ ____ of the esophagus. The _______ , _____ intestine , _______ and ________ transverse colon
upper 1/3 ; stomach ; small ; ascending ; proximal
True or false.
The vagus nerve is mostly sensory
True. The vagus nerve is 75% afferent and 25% efferent
What are vagovagal reflexes?
- reflexes in which both the sensory and motor components are controlled by the vagus nerve
Fill in.
The pelvic nerve innervates the ________ transverse colon. The _____ colon and the ______ colon
distal ; descending ; sigmoid
True or false.
The vagus and pelvic nerve both innervate the descending colon
False. The vagus nerve innervates the ascending and proximal colon , while the pelvic colon innervates the distal, descending and sigmoid colon
Fill in.
Parasympathetic ganglia pre and postganglionic neurons are in the _______ and _______ plexuses
- myenteric ; submucosal
Fill in.
Parasympathetic preganglionic and postganglionic neurons use ____ and ____ as neurotransmitters
acetylcholine ; peptides
Substance P and vasoactive intestinal peptide are peptides used by _________ and _________ parasympathetic neurons
preganglionic ; postganglionic
Where do sympathetic preganglionic neurons synapse vs. sympathetic postganglionic neurons
- sympathetic preganglionic neurons synapse in the sympathetic ganglia located outside of the alimentary canal
- sympathetic postganglionic neurons synapse on neurons in the myenteric plexus, the submucosal plexus or target cells
fill in.
The interstitial cells of cajal are the ________ of the gut
pacemakers
what are the two types of ICC
- pacemaker: ICC-Myenteric and ICC-Submucosa
- mediator ICC
True or false.
ICC (interstitial cells of cajal) occur at different locations and densities throughout the alimentary canal.
True.
Where are ICC-myenteric cells found?
Between the longitudinal and circular layers of the muscularis externa
Where are ICC-submucosa cells found?
between the submucosa layer and the circular layer of the muscularis externa
where are the mediator ICC cells found?
in the circular and longitudinal layer of the muscularis externa
What are the sympathetic prevertebral ganglion that innervate the alimentary canal? What part of the alimentary canal do they innervate?
- celiac ganglion: stomach
- superior mesenteric ganglion: small intestine
- Inferior mesenteric ganglion: descending colon
- hypogastric ganglion: rectum
Fill in.
Sympathetic preganglionic neurons use _________ as their neurotransmitter. Sympathetic postganglionic _____________ neurons use as their neurotransmitter
acetylcholine; norepinephrine
Fill In.
The _________ and _______ divisions of the autonomic nervous system provide extrinsic innervation
Sympathetic ; parasympathetic
Fill in.
Sympathetic postganglionic fibers release ________. Sympathetic Postganglionic fibers synapse either on neurons in the _______ and _____ plexuses, ________ muscle, _______ and________ cells. They ________ the activity of enteric neurons. They decrease GI _________ and __________ (motility/inmotility). They ________ the tone of GI sphincters. They _________ tone of GI blood vessels, often diverting or redistributing blood away from the gut.
NE; myenteric; submucosal; smooth; Endocrine; secretory; reduce; secretion; motility; increase; increase
Parasympathetic activation utilizes _________ neurotransmitter
Acetylcholine (Ach)
Fill in.
Parasympathetic activation.
The ______ nerve innervates the upper GI tract. The _______ nerve innervates the Lower GI tract, from the ________ colon to the _________
anal canal. The parasympathetic ________ enteric activity. The parasympathetic also ________ GI secretion and motility, but _________ GI sphincter tone.
Vagus ; Pelvic; transverse; external; increases; increases; decreases
Fill in.
Parasympathetic postganglions synapse in _________ of the alimentary canal. they release ______ or _______
muscle ; Ach; peptides
Fill in.
The mucosa holds _______ _______, endocrine cells, and secretory cells
muscularis mucosae;
True or false.
Sympathetic preganglion synapse on sympathetic ganglia inside the alimentary canal.
False. They do not. They synapse on ganglion outside the alimentary canal
Fill in.
Sympathetic ganglia synapse on postganglia in the _______ plexus, _______ plexus, and target cells. which includes cells in the circular muscle of the muscularis externa
myenteric ; submucosal;
describe local reflexes.
- Integrated entirely within the gut wall
- Control GI secretion, peristalsis and mixing contractions, and Local inhibitory reflexes
_________ _____ are integrated entirely within the gut wall. They control GI secretion, _________ and mixing contractions, and _______ inhibitory reflexes
Local reflexes; peristalsis ; local
Describe short reflexes.
- include reflexes from the gut wall to the prevertebral sympathetic ganglia that then project back to the GI tract
- Gastrocolonic reflex
- Enterogastric reflex
- Colonoileal reflex
Short reflexes include _________ reflex , ________ reflex, and _________ reflex
gastrocolonic, enterogastric , colonileal
describe long reflexes.
- Reflexes from the gut to the spinal cord or brain stem and then project back to the gut
- Vagovagal reflexes
- Pain reflexes (inhibitory)
- Defecation reflexes
long reflexes include _______ reflexes, ________ reflexes which are inhibitory , ________ reflexes
vagovagal ; pain ; defecation
Fill in.
Chemoreceptors and Mechanoreceptors in the gut wall send signals via _________ and _______ afferents to the CNS while ______ afferents stimulate the myenteric and submucosal plexus
splanchnic ; vagal ; local
Chemoreceptors and mechanoreceptors in the gut wall send signals via the splanchnic and vagal afferents to the CNS. Which then travel through the parasympathetic and sympathetic efferents to the gut (smooth muscle, endocrine cells, secretory cells, blood vessels). This describes what kind of reflex?
Long reflexes because they start from the gut, go to the brain/CNS, then back to the gut
What type of reflex does the following describe?
Chemoreceptors/mechanoreceptors in gut > local afferents > myenteric & submucosal plexuses > local efferents > Gut
local reflexes
What type of reflex does the following describe?
chemoreceptors/mechanoreceptors in gut > splanchnic & vagal afferents > CNS > Parasympathetic & sympathetic efferents > myenteric & submucosal plexuses > local efferents > gut
short reflexes because it travels from the gut wall to the pre-vertebral sympathetic ganglion then back to the gut
What are the six types of nutrients found in food?
1.carbohydrates
2. fats
3. proteins
4. vitamins
5. minerals
6. water
True or false.
Glucose is a disaccharide.
False. Glucose is a monosaccharide
Examples of monomers of carbs are? of disaccharides? Examples of polymers of carbs?
monomers: glucose, fructose, galactose
disaccharides: maltose, lactose , sucrose
polymer: starch, cellulose (fiber), glycogen
Fiber is also known as what?
cellulose
What purpose do carbohydrates serve
carbon skeleton for building other organic molecules; primary metabolic energy source
True or false.
Triglycerides are fats
true
What is the purpose of fats ?
building blocks for membranes
used for energy storage
provide insulation
What is the monomer of protein? polymer of proteins
amino acids; peptides
What is the purpose of proteins?
create diversity
fuel source
Fill in.
_______ are small organic molecules
Vitamins
what is the purpose of vitamins?
diversity
Cofactors for enzymes
Minerals are _____ ions
inorganic
true of false.
Food processing is a single stage process
false. it is a Muti-stage process
Fill in.
Humans are _______
heterotrophs- an organism that eats plants or animals for nutrients b/c it cannot produce its own food.
Fill in.
Nutrients are raw materials needed for _________ and _________ ________ (ATP synthesis)
anabolism; energy production
What are the four stages of food processing
- ingestion (eating)
- digestion :
mechanical digestion (requires physical force)
chemical digestion (enzymes for hydrolysis) - absorption
- elimination
Fill in.
_________ refers to contraction and relaxation of the walls and sphincters of the GI tract
Motility
What are the general functions of motility
- grind and fragment
- mix
- propel
- storage
fill in.
Contractions of gastrointestinal smooth muscle can be either _______ or _______.
phasic; tonic
Fill in.
Phasic contractions are ______ contractions followed by _______
periodic ; relaxation
Phasic contractions include mixing also known as ________ and propulsion known as _________
segmentation ; peristalsis
Describe tonic contractions.
Tonic contractions maintain a constant level of contraction or tone without regular periods of relaxation.
True or false.
GI Tract is an electrically excitable, paced tissue
True.
The GI tract is like the _____ in that it is electrically excitable, paced tissue
heart
Fill in
Normal mechanical function depends on _____ _________ activity. Disruptions leads to _________ .
high coordinated; arrhythmias
Name the seven things GI arrhythmias are responsible for.
- GERD
- Achalasia (impaired esophageal peristalsis)
- Gastroparesis (impaired gastric motility)
- Rapid gastric emptying
- Nausea, vomiting
- Diarrhea
- Constipation
What are the gastric pacemaker cells? Where are they found generally?
- Interstitial cells of cajal
- found in the myenteric plexus in the stomach, SI, and colon
Fill in.
Interstitial cells of cajal generate ______ wave activity. These wave propagate _______ and _____
slow; radially ; longitudinally
Fill in.
Slow waves are a _______ electrical feature of the GI tract. They are characterized by periodic oscillations of the ________ muscle membrane potential. However, _________ stimulation does not change the _________ of slow waves.
Sub-threshold slow waves produce _______ contractions. Slow waves do not require _____ _____ to produce contractions.
Slow waves can cause _________ if above threshold to activate L-type calcium channels. This results in ________ -based action potentials.
Interstitial cells (ICCs) set the frequency of the slow wave in the different regions of the GI tract. Each region of the alimentary canal has a
characteristic frequency. In the Stomach it’s ______ min. In the duodenum it’s ____ min. In the Colon it’s ______ min. The slow wave of that particular region of the GI tract entrain to the fastest frequency.
Slow waves are transmitted to adjacent muscle via ______ junctions.
unique; smooth; Excitatory; frequency; weak; action potentials;
depolarization; calcium
3-5 ; 12-20 ; 6-8
gap
Describe primary peristalsis and secondary peristalsis.
Peristalsis is the basic propulsive movement of the
GI tract.
- Primary peristalsis propels food forward.
- Secondary peristalsis is initiated if the primary peristaltic wave does not clear the tube.
what do the circular and longitudinal muscles do behind and in front of the bolus?
behind:
- Circular muscles cause constriction
- Longitudinal muscles lengthen
in front:
- Circular muscles relax
- Longitudinal muscles
shorten
Fill in.
Excitatory neurotransmitters cause ________.
_________ is released by enterochromaffin cells, activating ________ neurons following distention.
__________ and GI _______ (substance P and
neuropeptide Y) stimulate contraction of circular and longitudinal muscle behind the bolus
contraction; Serotonin (5-hydroxytryptamine); sensory
Acetylcholine ; peptides
Fill in.
Inhibitory neurotransmitters cause ________. The relaxation of circular muscle in front of the bolus is due to inhibitory motor neurons to _____ muscle layers.
relaxation ; both (circular and longitudinal)
Describe the MMC
- Migrating motor complex (MMC) is a pattern of electromechanical activity that occurs in GI smooth muscle ~every 90 minutes between meals.
- The MMC cycle consists of 4 phases
1. smooth muscle quiescence (45 to 60 min); rare action potentials and contractions.
2. peristaltic contractions (~30 min) progressively increase in frequency originating in the stomach and propagating through the small intestine.
3. rapid, evenly spaced peristaltic contractions (5 to 15 min). In contrast to the digestive period, the pylorus remains open during these peristaltic contractions, allowing many indigestible materials to pass into the small intestine.
4. A short period of transition between the barrage of contractions in phase 3 and the quiescence of phase 1.
true or false.
An increase in gastric, biliary and pancreatic secretion is also seen in conjunction with MMC.
true.
gastric, biliary and pancreatic secretion assist the MMC in what way?
- aid in the cleansing activity of the migrating motor complex
- help preventing a buildup of bacterial populations in the proximal segments of the digestive tube.
Segmented contractions occur when ______ is in the alimentary canal. This slows the propulsion of the luminal contents and allows for adequate mixing of chyme to occur.
chyme
Describe the mechanism for mixing
- rings of contraction form at periodic intervals along the alimentary canal
- A second ring of contraction then forms at the center of each segment.
- Unlike peristalsis, the rings of contraction force the chyme a short distance in both directions. Thus, there is no net forward movement of the luminal contents
- this continue for as long as material remains in the lumen.
What are the stimulus for the following GI hormones:
- Motilin
- cholecystokinin
- secretin
- Gastric Inhibitory Peptide
- Motilin:
Fat, Acid, and Nerve stimulus - cholecystokinin
Fat, Acid and Protein stimulus - secretin
Fat, Acid and Protein Stimulus - Gastric Inhibitory Peptide
Fat, Acid and Protein stimulus
What is the site of secretion for the following GI hormones?
- Motilin
- cholecystokinin
- secretin
- Gastric Inhibitory Peptide
- Motilin
M Cells of the duodenum and Jejunum - cholecystokinin
cells of the duodenum and jejunum - secretin
cells of the duodenum and jejunum - Gastric Inhibitory Peptide
cells of the duodenum and jejunum
What are the actions of the following GI hormones
1. Motilin
2. cholecystokinin
3. secretin
4. Gastric Inhibitory Peptide
- Motilin
stimulates: gastric and intestinal motility - cholecystokinin
Inhibits: Gastric emptying - secretin
Inhibits: Gastric emptying - Gastric Inhibitory Peptide
Inhibits: Gastric emptying
True or false.
Gastrointestinal secretions occur throughout the entire GI tract.
True.
True or false.
All the fluid secreted by the alimentary canal is not reabsorbed.
True. Most of the fluid secreted by the alimentary canal (about 7 liters) is reabsorbed in addition to 2 liters that are ingested
What would happen if we were not able to reabsorb the majority of the alimentary secretions?
- rapid dehydration and electrolyte imbalance
Which gland/organ secretes the largest volume within the GI tract? which secretes the smallest volume?
Small intestine (about 1800 ml) ; Large intestine and Brunner’s glands
which Glands of the GI tract has the highest pH and the lowest pH?
Highest pH: Brunner’s glands (8-9)
Lowest pH: stomach (1-3)
What are the basic mechanisms for stimulation of the alimentary tract glands?
Local effects:
* Direct contact with food
* Tactile, chemical, distention
Enteric nervous system:
- Mucus
- glands
Autonomic stimulation of secretion
* Hormones
Fill in.
Mucous cells are found in the ______ & Goblet cells are found in the _______ ______
stomach ; small intestine
what are the properties of Mucous cells (stomach) & Goblet cells (small intestine)
- sticky/supportive (adherent) properties
- there’s enough to prevent contact of most food particles with tissue
- lubricates the food well
- very resistant to digestive enzymes
- have neutralizing properties
True or false.
The mucus that covers the GI tract varies in its properties in different regions of the alimentary canal.
True.
Fill in.
Mucus is secreted by _____ cells and contains several components. The major of the components is _______.
goblet cells (SI) ; water (98%)
Mucins in goblet cells make up about ____ %.
1-2%
Describe Mucins
- a single pass transmembrane proteins with a cytoplasmic tail and an large, densely glycosylated extracellular mucin domain
- a mucin monomer has an N-terminus and C-terminus
- a mucin monomer contains oligosaccharides, cysteine residues, and repeating structures.
- mucins give mucus its gel-like consistency and properties
- mucin domains are rich in O-glycosylated Serine, Threonine, Proline
- MUC2 forms the bulk of intestinal mucus
- MUC5AC forms most of the mucus on the stomach
surface - Other classic mucins include MUC6 (stomach glands)
and MUC5B (salivary glands) - MUC1, MUC3, MUC4, MUC12, MUC13, and MUC17 are also found in the gastrointestinal tract
______ forms the bulk of intestinal mucus. _______ forms most of the mucus on the stomach surface. Other classic mucins include ______ found in stomach glands and ______ found in salivary glands. Other forms of mucin domains are found in the _____ tract
MUC2; MUC5AC ; MUC6 ; MUC5B ; GI
Describe the two types of mucus organization in the GI tract.
- mucus is released by mucous cell and goblet cells (SI)
- there is tethered mucus, that remains as a protective barrier to the epithelial cells, and there is free mucus (gel-like)
- mucus thickness increases is highest in the duodenum and jejunum
- there is bacteria in mucus in the SI and colon
True or false.
Mucus moves with the peristaltic waves
True.
Fill in.
Mucus contains a number of _________ secretions, such as antibacterial peptides and ______, and tumor suppressor proteins.
The antibacterial secretions create an antibacterial _______ within the mucus layer. The mucus layer acts as a _______ ______ to pathogens.
antibacterial; lysozymes; gradient ; diffusion barrier
Fill in.
The way ______ is arranged in layers, it acts as a __________ barrier.
This inner mucus layer is not penetrable to bacteria or beads with sizes down to _____ μm although smaller objects, e.g. 50 kDa proteins, are
able to pass through. The outer mucus layer in the large intestine is a habitat for ________ bacteria
MUC2 ; size-exclusion; 0.5; commensal
What purpose does the rapid turn over of the inner mucus layer serve?
the rapid turn over keeps the bacteria away from the epithelial surface.
What happens when there are mutations in the CFTR channel, such as cystic fibrosis.
- there’s a lack of bicarbonate secreted from CFTR channels.
After mucus is secreted from the goblet cell where does it go? specifically MUC2
- it remains anchored to the goblet cell
- specifically MUC2 mucin remains anchored to the goblet cell after secretion. it requires a specific enterocyte protease to cleave the protein core of MUC2 in order to release the mucin and mucus.
Describe how digestive enzymes work. As well as H20 and electrolytes release
- the nerve stimulates the cell on the basal side of the cell adjacent the capillary.
- the stimulus triggers release of digestive enzymes which are secreted
for H2O and electrolytes:
- the nerve innervates the cell on the basal side
- the resting membrane potential is -30 to -40 mV
- neural stimulation causes influx of Cl- ions making the membrane potential more negative
- Na+ ions follow and H2O follows via osmosis. thereby increasing intracellular pressure and making the membrane potential less negative
- the increased hydrostatic pressure opens the apical ports allowing water and electrolytes out. thus bringing the membrane potential back down.
What are the salivary glands digestive enzymes? and what do they do
Amylase: breaks down starch
lingual lipase: has limited actions, but breaks down triglycerides
What are the stomach digestive enzymes? and what do they do?
Pepsin (inactive form is pepsinogen) : breaks down proteins
gastric lipase: breaks down triglycerides
What are the pancreas digestive enzymes? and what do they do?
Amylase: breaks down peptides
Lipase and co-lipase: break down triglycerides
Phospholipase: breaks down phospholipids
Trypsin (inactive form trypsinogen): breaks down peptides
Chymotrypsin (inactive form chymotrysinogen) : breaks down peptides.
What are the digestive enzymes in the intestinal epithelium (apical surface)? and what do they do?
Enterokinase: activates trypsin
Disaccharidases: breaks down disaccharidases
1. sucrase: breaks down sucrose
2. Maltase: breaks down maltose
3. Lactase: breaks down lactose
Peptidases: breaks down peptides
1. endopeptidases: breaks down interior peptide bones
2. exopeptidase: break down terminal peptide bonds
a. amino-peptidases: break down the amide end of the peptide
b. carboxypeptidases: break down the carboxyl end of the peptide
What is the source, stimulus, target, and action of Gastrin?
Source: G cells ( in stomach)
Stimulus: peptides in lumen
Target: histamine secreting cells and parietal cells (in stomach)
Action: increase acid secretion in stomach and increase gastric motility
What is the source, stimulus, target, and action of CCK?
Source: endocrine cells in the SI
Stimulus: partially digested proteins and fatty acids in duodenum
Target: gallbladder, pancreas (gastric muscle)
Action: increase contraction in gallbladder, inhibit gastric emptying, stimulate secretion of pancreatic enzymes
What is the source, stimulus, target, and action of Secretin?
Source: endocrine cells (SI)
Stimulus: acid and partially digested proteins and fatty acids in the duodenum and SI
Target: Pancreas and stomach
Action: stimulates bicarbonate secretion and pepsin release, inhibits gastric emptying, inhibits gastric acid secretion, stimulates bile ejection
What is the source, stimulus, target, and action of Motilin?
Source: endocrine cells (SI)
Stimulus: fasting
Target: smooth muscles of gastric antrum and duodenum
Action: increases gastric and intestinal motility, stimulates gastric contractions (aka hunger pangs)
What are the salivary glands?
- parotid,
- submandibular
- sublingual
Fill in
A. Salivary glands (the parotid, submandibular, and sublingual glands) consist of hollow clusters , aka ______ of ______ cells continuous with ducts that communicate with the oral cavity.
B. Parasympathetic activation (ACh) increases ______
secretions. Sympathetic activation (NE) increases ________ and ______ secretions.
acini ; acinar
watery ; mucous ; viscous
Fill in.
The formation of saliva is a ________ process
two-stage
Fill in.
Acinar cells produce ______ saliva. It is ______ to plasma and rich in _______ . In this first stage, ______ lipase hydrolyzes dietary lipases. a-amylase breaks down _______ into ________ . Lysosyme is a ________ enzyme with antimicrobial and _________ functions important in clearing the _____ cavity of pathogens.
primary ; isotonic ; proteins : lingual ; starch ; maltose ; proteolytic ; anti-viral; oral
Fill in.
In the second stage of saliva formation the epithelial cells lining the ducts modify the saliva. The presence of ______ in saliva makes it _______ and helps to neutralize any gastric secretions that reflux into the esophagus. Saliva in this stage is _______ to the plasma
HCO3- (bicarbonate) ; alkaline ; hypotonic (meaning it has less solutes than plasma)
Fill in.
The esophagus is a conduit from the oral cavity to the _______ . Potential sources of injury include: __________ __________ ______ and ________ ______ _____
stomach ; incompletely masticated food ; refluxed gastric acid
What are the three mechanism used to minimize the exposure of the esophageal mucosa to gastric acid?
- lower esophageal sphincter limits the mount and frequency of reflex.
- esophageal clearance by gravity and peristalsis.
- esophageal secretions.
Where do esophageal secretions originate from? and what do they secrete?
the submucosal glands (SMG). The submucosal glands secrete protective substances such as HCO3- and mucin.
Fill in.
Pre-gastric motility beings with ______
chewing
What are the three functions of chewing?
- it reduces the size of food particles, which facilitates
swallowing - it mixes food with saliva, lubricating it to facilitate
swallowing - it mixes ingested nutrients with enzymes to begin
chemical digestion
explain the voluntary and involuntary components of chewing.
- food goes into the oral cavity
- this stimulates oral mechanoreceptors
- that signal reflex inhibition of jaw muscles allowing them to relax, to open the jaw/drop jaw
- jaw lowering activates the spindle fibers
- stretch reflex of jaw cause muscles to contract and jaw to close.
True or false.
The process of chewing is predominately voluntary
false. it is mostly involuntary
What are the three phases of swallowing?
- oral (voluntary) : has two parts 1. oral preparatory and 2. oral propulsion
- pharyngeal (reflex)
- esophageal (reflex)
Fill in.
Activation of sensory receptors in the ________ trigger the swallowing reflex.
The pharyngeal and esophageal peristalsis initiated by the swallowing reflex is _________ peristalsis.
pharynx ; primary
The pharyngeal stage of swallowing must propel the bolus of food through the _______ to the _______ and protect the airway.
pharynx; esophagus
describe the four steps of the pharyngeal stage
1.Nasopharynx closure: The soft palate is pulled upward, so food cannot reflux into the nasopharynx.
- Airway protection: The breathing cycle is briefly
interrupted. The epiglottis covers the opening to the
larynx to prevent food from entering the trachea. - Elevation of pharynx: The upper esophageal sphincter relaxes, allowing food to pass from the pharynx to the esophagus.
- Peristaltic waves: of contraction are initiated in the
pharynx and propel food to and through the open sphincter.
describe the esophageal phase of swallowing.
- The upper 1/3 of the esophagus is striated muscled innervated by the vagus (X) and glossopharyngeal (IX) cranial nerves.
- The lower 2/3 is smooth muscle controlled by the enteric nervous system and regulated by the vagus nerve.
The esophageal phase of swallowing is controlled in part by the swallowing reflex and in part by the enteric nervous system
Describe the orad region and the caudad region.
Orad:
- thinner-walled
- includes the funds and upper part of the body
Caudad:
- thicker-walled
- includes antrum and pylorus
Fill in.
The ______ and ________ layers exhibit numerous folds known as rugae, that expands the surface area of the stomach. The surface epithelium gastric mucosa is a simple ________ epithelium rich in mucous cells and gastric pits. The muscularis externa has an additional __________ innermost layer
mucosa ; submucosa; columnar; oblique
What is gastric juice in the stomach made of ?
HCl
* Pepsinogen
* Intrinsic factor (B12 absorption in ileum)
* Mucus
What is the importance of acidic pH in the stomach (ph<2)
- denatures proteins
- activates pepsin
- kills food-borne bacteria
- facilitates absorption of minerals including phosphate, calcium, and iron.
- threatens the structural integrity of the gastric mucosa.
what overrides parasympathetic controls/inhibit gastric phase of gastric secretion?
emotional upset, this activates the sympathetic nervous system
What inhibits the gastrin secretion from G cells in the gastric phase?
low ph/ excessive acidity
what inhibits the cephalic phase of gastric secretions?
- Loss of appetite
- depression
What are the three phases of gastric secretions? Describe each one.
- Cephalic phase: prepares the stomach for digestion
- it is short. lasts minutes
- stimulated by sight, smell taste, even the thought or memory of food.
- Mechanisms: Mediated entirely by the vagus nerve, no sensory involved
- Actions:
1. Mucus cells increase mucus production
2. Parietal cells increase HCl production
3. Chief cells increase pepsinogen release
secondary effect- neural stimulation of G cells to increase gastrin - gastric phase: builds on the secretions begun during the cephalic phase, homogenizes the chyme, and begins protein digestion.
- lasts a Long time. Begins with the arrival of food in the stomach. can last 3-4 hours
- stimulus :- Neural: activation of stretch and chemical receptors by gastric wall distension and an increase in pH
- Hormonal: peptides and parasympathetic increase Gastrin release
- Local: Release of histamine by ECL cells
Actions: processes ingested food into chyme
- Mucus cells increase mucus production
- Parietal cells increase HCl production
- Chief cells increase pepsinogen release
secondary effect- neural stimulation of G cells to increase gastrin
- pancreatic/intestinal phase::
lasts Long. Lasts many hours
Stimulus: - stretching of the duodenum enhances vagal reflexes
- acid and semi-digested food in the duodenum trigger the enterogastric reflex
Neural: Enterogastric reflex reduces vagal stimulation of the stomach and stimulates sympathetic neurons that send inhibitory signals to the stomach.
Hormonal: cholecystokinin (CCK), gastric inhibitory peptide (GIP) , secretin released
Actions: Inhibits HCl and pepsinogen production. Reduces gastric motility.
where are the following cells found in the stomach and what do they secrete?
- chief cells
- parietal (aka oxyntic) cells
- mucous cells
- G cells
- chief cells:
location: body of the stomach
secrete: pepsinogen ; gastric lipase - parietal cells
location: body of the stomach
secrete: HCL, intrinsic factor - mucous cells
location: antrum of stomach
secrete: mucus - G cells
location: antrum of stomach
secrete: gastrin (circulation)
Fill in.
Gastric juice is a mixture of the secretions of _________ ________ cells and the secretions of ________ ______ .
surface epithelial ; gastric glands
Fill in.
G cells secrete _______ . They are found in ______ glands.
D cells secrete _________
gastrin; antrum ; somatostatin
where does the gastric gland being?
at the gastric pit of the rugae
the isthmus contains what type of cells that are responsible for replenishing the cells above and below?
stem cells
The base of the corpus gland compared to the base of the antral gland, contain what cells?
base of the corpus gland: chief cells
base of the antral gland: deep mucous gland cells
Enterochromaffin-like cells (ECL) secrete ________, which is a major stimulus for parietal cells to secrete HCL. ECL cells are found in the ______ of the gastric gland, along with parietal and D cells of the corpus gland
histamine ; neck
Describe the process of HCL Secretion
- Na-k ATPases and bicarbonate-chloride exhangers are found on the basal side of the parietal cell
- H-K ATPases, K+ pump and CFTR channel are found on the apical side of the parietal cell
- Carbon dioxide diffuses across the basal lateral side of the parietal cell and reacts with water in the presence of carbonic anhydrase.
- this reaction produces biocarbonate and protons
- the bicarbonate is take up by the bicarbonate-chloride channel and exported in exchange for chloride coming in.
- the proton is taken up by the H-K ATPase and exported in exchange for potassium coming in
- the chloride leaves through the apical side via the CFTR channel into the lumen of the stomach
- K+ also leaves via the potassium pump on the apical side into the lumen
- 160 mmol/L of HCL is secreted. the ph is about 0.8
define potentiation
the ability of two stimuli to produce a combined response that is greater than the sum of the individual responses
Fill in.
The M3 receptor and CCKb receptor both stimulate _______ which produces IP3/Ca2+. This _________ H-K ATPase to secrete H+
Gq ; stimulates
Fill in.
H2 receptor stimulates ______ . This stimulates ______ which stimulates H-K ATPase to secrete H+
Gs ; cAMP
Somatostatin and Prostagladins act on receptors that stimulate _______. This ________ cAMP production, in turn decreasing stimulation of H-K ATPase to secrete H+.
Gi ; inhibits
The vagus nerve releases ______ that binds with the M3 Receptor. This is also called ________ transmission. _______ is acts as an antagonist on the M3 receptors, blocking stimulus of Gq
Ach ; synaptic ; atropine
The G cells release _______ that binds with the CCKb (or CCK2) receptor. This is also called ________ communication.
gastrin ; endocrine
The ECL cells release _______ that binds with the H2 receptor. This is also called ________ communication. ________ acts as an antagonist that binds with the H2 receptor blocking stimulus of Gs.
histamine ; paracrine ; cimetidine
_________ is a proton pump inhibitor that blocks H+ secretion into the lumen of the stomach. It Inhibits the secretion by forming __________ bonds with _______ residues on the apical surface of the H-K ATPase.
This is an improvement over H2 receptor blockers because the covalent bonding of the pump results in a _______ effect.
Omeprazole ; disulfide ; cysteine ; longer
Why is atropine not effective?
It is not effective because other pathways can stimulate the H-K pump
True or false.
HCl secretion from parietal cells is regulated by neural endocrine factors, and the luminal contents of the stomach.
true.
What stimulates parietal cells to release HCL?
- histamine produced by enterochromaffin-LIKE cells (ECL).
- activation of the enteric and PNS .
- Gastrin produced by G cells
What stimulates Histamine to be released from ECL cells?
- Gastrin released from G cells that are in the antrum of the stomach
- gastrin is released in response to protein. this is the strongest stimulator of histamine/acid complex.
- gastrin is carried by the blood stream but is also carried directly into the lumen from gastric pit so it has a direct local stimulating action
The release of HCL from parietal cells decreases pH. HCL stimulates ________ released from D cells
somatostatin
Somatostatin released from _____ cells directly inhibits ______ production by G cells, ________ production by ECL cells, ______ secretion by parietal cells. However, the ________ and ANS directly _______ D cells, thus somatostatin production.
D ; gastrin ; histamine ; HCL ; enteric ; inhibit
Food in the stomach ________ somatostatin secretion from _____ cells, because the _______ in pH acts as a buffer. Without the production of somatostatin, ______ production, _______ production and ______ secretion cannot be inhibited
inhibits ; D; increase ; gastrin ; histamine ; HCL
The presence of peptides stimulates ______ production
gastrin
Food in the stomach activates mechanoreceptors because of the distension of the stomach wall via ________ and ______ reflexes in the ENS and PNS. Thus, Parasympathetic activity (ACh) increases ______ secretion
long ; local ; HCl
True or false.
The intestinal phase of gastric secretion begins when chyme enters the stomach. Its excitatory and inhibitory components regulate the rate that chyme enters the duodenum
False. intestinal phase beings when chyme enters the duodenum
Gastric colonization by different strains of H. Pylori leads to __________ of acid secretions
dysregulation
True or false.
Most strains of H.pylori inhibits acids secretion.
True.
What does too much H.pylori do?
- represses H-K ATPase a-subunit transcription
- elevates/augments somatostatin release
- enhances microbial adhesion
- once attached to epithelial cells it can cause apoptosis, disrupt tight junctions, and cause gastric inflammation
- causes ulcers.
what environmental factors contribute to H.pylori? What host factors?
environmental: smoking, alcohol, NSAIDs, and PPI
Host factors: gene polymorphisms, immune responses
Fill in.
the majority of H.pylori causes result in ________ ______. Low presence of H.pylori leads to ______, with the risk of a small amount developing gastric cancer. High presence of H.pylori leads to _______ _________, with a small amount at risk for developing peptic ulcer disease.
Chronic gastritis ; pangastritis ; antral-predominant gastritis
True or false.
Digestion of proteins begins in the stomach.
True.
Fill in.
Pepsin is an _____________ that cleaves peptide bonds within ingested proteins.
Pepsinogen secretion is stimulated by ____________ directly, gastrin ________ , secretin from ____ cells in the duodenum, directly. low pH directly and _______
endopeptidase ;Acetylcholine ; indirectly ; S ; indirectly
True or false.
Pepsin can activate additional pepsinogen autocatalytically.
True
Fill in.
Pepsinogens are converted into the proteolytic enzyme pepsin. On exposure to an acidic pH, a portion of the peptide is cleaved, exposing the active site and generating _________ pepsin.
active
What is the optimal activity of pepsin in terms of pH
1.8 to 3.5
At what pH are pepsins reversibly inactivated at? what pH are they irreversibly inactivated
reversibly inactivated : ph 5
irreversibly inactivated: pH 7-8
Fill in.
Based on motor pattern.
The __________ stomach lacks slow
wave activity but has tonic contractions. The ________ stomach has slow waves and _________
activity
proximal ; distal ; peristaltic
True or false.
Gastric motility patterns depend on whether the person has eaten or is in between meals.
true.
fill ins.
Interdigestive phase motility refers to ______ meals. Muscle tone is _______ in proximal stomach. The resting membrane potential of _______ smooth muscle is at or near threshold. There is sustained ____________ stimulation from the vagus nerve. The distal stomach is engaged _______. This clears the stomach of secretions, debris, and microbes during fasting.
Inbetween ; high ; fundic ; cholinergic ; MMC
What are the postprandial phases?
- receptive relaxation
- results in gastric accommodation
- mediated by reflexes that reduce cholinergic input and trigger the release of nitric oxide (dilator)
- increases the storage capacity of the stomach
- keeps intragastric pressure low to keep you from becoming full too soon . - tonic contraction of the proximal stomach
- this pushes the food distally.
- Distension of the antrum triggers reflex peristaltic contractions. these contractions begin mid-corpus and proceed towards the pylorus. - Retropulsion of chyme
- the pyloric sphincter constricts, forcing the contents back toward the proximal stomach.
- allows only liquids through. so food gets pushed back to get grounded down more.
- contraction of the pyloric sphincter and peristaltic motion forms homogenous gastric chyme.
Fill in.
Intragastric pressure is an important determinant of _________.
satiation
True or false.
High gastric pressure is a signal of saitity (fullness)
true.
What are the three major functions that the postprandial motor pattern serves.
(i) the proximal stomach acts as a reservoir enabling the ingestion of a large volume of food without a major increase in intragastric pressure;
(ii) mechanical digestion begins by antral contractions that mix and grind food to smaller particles;
(iii) tonic and peristaltic contractions generate a steadily controlled flow of food
Fill in.
Increasing food caloric and osmotic density ______ gastric emptying.
slows
At what point in time does gastric emptying slow or almost stop
at about 40 mins
What types of food prolong gastric emptying? what amino acid is associated with prolonging gastric emptying?
- fatty food or food with a high lipid content
- tryptophan
what gastric factors enhance emptying?
Increased food volume
- via local myenteric plexus reflexes because they trigger stomach distension
- Gastrin released from the antral mucosa enhances stomach emptying
what duodenal factors inhibit gastric emptying?
The following mechanisms inhibit the propulsive movements and increase tone of pyloric sphincter.
Neural mechanisms
- Distention of the duodenum
- Irritation of the duodenum
- Acidity of the duodenal contents
- Osmolality of the chyme
- peptides
Hormonal mechanisms:
* The stimulus for these hormones is mainly fats entering the duodenum
- CCK blocks increased stomach motility caused by gastrin
- GIP inhibits gastric motility but also stimulates the release of insulin by the pancreas
