digestion post midterm Flashcards
the enterogastric reflex involves the activation of what?
receptors in the duodenum via the ENS and ANS to inhibit signal
what can inhibit ENS neurons in the enterogastric reflex?
Parasympathetic input from vago-vagal input
what will the sympathetic input inhibit in the enterogastric reflex?
inhibit excitatory neurons
what is the purpose of the enterogastric reflex?
Purpose is to slow down the rates of peristalsis
what are some factors that contribute to enterogastric reflex?
o Distension as the meal enters the duodenum
o Ph < 3.5 signals to slow down peristalsis
o Chemical composition
o High osmolarity
o Fats» proteins > carbs
what does the enterogastrone hormone complex contribute to?
antral peristalsis
what is the gastric emptying due to?
due to a balance between gastric and duodenal conditions
what happens do the duodenal and gastric factors in gastric emptying?
Duodenual factors will decrease motility
Gastric factors increase motility
what causes vomiting?
• Results from an increase in intrabdominal pressure due to the concerted action of the diaphragm and abdominal muscles
what happens to the abdomen and diaphragm during vomiting?
The diaphragm will lower
Abdominal muscles contract
is the GIT active or passive during vomiting?
passive process
is their resistance to flow at the level of the LES?
no
what happens to the force of vomiting if the pressure increases?
greater force
what are some factors that may stimulate/trigger vomiting?
- pharygeal stimulation
- GIT or urogenital distention
- pain, cardiac ischemia
- biomechanical disequlibrium
- vestibular signals
- psychogenic factos
is the chemoreceptor trigger zone the same as the vomiting center?
they are distinct but both part of the medulla.
what is the function of the chemoreceptor trigger zone
it signals the vomiting center
what happens if the CTZ is removed?
vomiting can persist
where is the CTZ located?
Sits at the forth ventricle, outside the blood brain barrier
what happens when the vomiting center is activated?
- widespread autonomic discharge
- nausea
- retching
- emesis
how does the widespread autonomic discharge affect the para/sympathetic System?
Leads to imbalances between the parasympathetic and sympathetic system which a continuously activated and disactivating leading to accompanying symptoms
what are some symptoms that will accompany the widespread autonomic discharge in vomiting?
- Sweating
- Vasoconstriction
- Salivation
- Alternating bradycardia & tachycardia
what causes nausea?
unknown cause
what is retching?
incomplete contraction of muscles which leads to Abrupt, uncoordinated respiratory movements with glottis closed
how are the teeth protected during vomiting?
increase salivation to protect teeth from the high acidity
what type of experience is nausea described as?
A psychic experience
what is emesis?
Actual expulsion of contents of the upper GIT
what is the function of the SI?
site where all digestion and absorption of the nutrients occurs
what is the SI divided up into?
o duodenum
o jejunum
o ileum
what does the Upper SI neutralize?
the chyme comming from the stomach due to its high acidity
will the chybe be isotonic or isomostic as it leaves the duodenum?
isotonic (process known as osmotic equilibration)
what motor activities take place in the SI?
Effective mixing
Slow propulsion
what governs intestinal contractions?
electrical characteristics of the smooth muscles
what controls the frequency of intestinal contractions?
the BER
what are the ERA spikes initiated by?
by stretch or increased release of ACh
what is the amplitude of contraction of the SI related to?
Related to the number of spikes/bursts of the ERA
how does the frequency of the BER differ in the SI compared to the somach?
in duodenum ~ 12/minutes and in ileum ~ 8/minute (declines as we move trhough the SI) vs 3/minutes in the stomach
what caused for the frequency of the cells of SI to change?
Changes along the length due to groups of pacemaker cells which drive ~1000 cells
excitability of the smooth muscle cells of the SI is greater in the proximal or distal SI?
proximal
what part of the SI has the thickest smooth muscle?
greater in the proximal stomach
what does the greater thickness of the smooth muscle in the proximal SI caused?
oth the Frequency and the amplitude of contractions will be greater in the proximal portion of the small intestine
what is the most common type of contractile in the SI after a meal?
segmentation and peristalsis
what is segmentation?
circular muscles which contract at different points
what is the use of segmentation?
Effective at mixing the contents within the intestine
aids in absorption due to greater contact with luminal contentes
what is segmentation caused by?
myogenic response to distention
what coordinates and organizes contraction over the length of the SI?
ENS
what happens to the para/sympathetic systems in response to hormones during segmentation?
parasympathetic signal will increase,
sympathetic decreases
what does segmentation also contribute to?
slow propulasion; Forward movement of the contents in the aboral direction
how are peristaltic contractions in the SI defined as?
infrequent and irregular, weak and shallow
do peristaltic contractions travel over large distances in the SI?
no, short distances
what is peristalsis mediated by in the SI?
a series of local reflexes
what gastric motility involves the interaction of longitudinal and circular muscles
peristalsis
the max frequency of peristalsis cannot exceed the max frequency of what?
the max frequency of the BER
integrity of what is needed in SI peristalsis?
integrity of the ENS
what is peristalsis modulated by?
by the ANS and hormones
following the law of the intestines; what happens to the muscle contraction ahead of the bolus?
contraction of longitudinal muscles and relaxation of circular muscles AHEAD of the bolus [path becomes shorter]
following the law of the intestines; what happens to the muscle contraction behind of the bolus?
contraction of the circular muscle and relaxation of the longitudinal muscles BEHIND the bolus [increase pressure behind bolus, while decreasing pressure and length ahead of the bolus]
contents from the SI move into the colon through what?
the ileocecal valve
is the the ileocecal valve generally open or closed?
closed
how does the action of the colon differ from the SI
• The muscular activity in the colon is similar to that of the SI, but slower, more sluggish and irregular.
what is the main fucntion of the colon?
absorb water and ions
how many L of water chyme leaves the SI and enters the colon daily?
1.5L/day
how much of the water chyme that enters the colon is excreted as fecal matter?
200 mL
what is the function of the colon?
mixing to promote absorption of water and ions
propulsion
storage
what rate does propulasion in the colon take place?
slow, takes about 50-60H for chyme to be converted to feces in the colon
what motor activity occurs in the colon?
Segmentation & peristalsis
what controls the motor activity in the colon?
BER
how often does emptying of the large intestine occur daily?
2-3x daily
what does small intestine emptying increase?
- increase gastoileal reflex (ileum)
- opening of the ilocecal valve to push contents into the colon
- increases gastrocolic reflex
what does the emptying of the intestine allow?
room to accomodate new meals
what does an increased gastrocolic reflex
leads to defecation reflex
due to increased activity in the distal part of the colon
what is GI motility organized into?
organized into intense pattern of cyclic myoelectric (motor) activity
what intervals does the cyclic pattern of GI motility occur?
~90 minutes
at what speed does the interdigestive period sequential motility occur?
2-10cm/minute
where does the migrating myoelectric complex take place?
begins at the distal part of the stomach & moves down sequentially until the distal ileum
what initiates the MMC ?
unknown cause most probably the ENS
how does the propagation of the MMC occur?
• via the ENS with modulation via ANS & Gut peptides
when is the MMC disrupted?
the intake of a meal
how long does the 1st phase of MMC last?
60 minutes
what happens during the first phase of MMC?
not much;
• no spike potentials
• no contractions of the muscles
how long does the 2nd phase of MMC last?
~20 minutes
what occurs during the 2nd phase of MMC?
• irregular spike potentials and contractions
how long does the 3rd phase of MMC last?
~10 minutes
what happens during the 3rd phase of MMC?
• Regular spike potentials and contractions at max frequency
how does the MMC progress through out the MMC?
it gets delayed as it moves through the GIT
what are the main functions of the MMC
-housekeeping function
constant cell turnover
gastric emptying of large, non-digestible particles
what is found in the colon in exponential amounts?
bacteria
what is the bacteria’s role?
its favorable for digestion
how does the MMC function in bacterial control?
The MMC allows to push bacteria back into the colon if it ever reaches the SI.
where do endocrine secretions travel?
into the blood stream
where do exocrine secretions travel?
into the GIT
how does digestion occur?
in a sequence of interdependent steps
what are enzymes?
proteins
what happens to enzymes in digestion?
they also need to be broken down
what is digestion?
• chemical breakdown of food to progressively smaller molecules
what causes for digestion to occur?
• results from the secretory activity of a large number of exocrine gland found within and in association with the GIT
the digestive secretions are released into what?
into the lumen of the digestive tract
what is amylase?
enzyme that breaks down CHO
what is proteases?
enzyme that breaks down proteins
what are lipases?
enzymes that break down fats
what are secretion dependent on?
energy and blood flow
what is the pattern of regulation throughout the GIT
it will vary along the GIT
nervous system inputs are more important in the proximal or distal part of the GIT?
proximal
what type of mechanism is responsible for secretion regulation at the distal part of the GIT?
hormonal mechanisms
in the stomachs, more than half the inputs for secretory regulation are obtained from?
nervous and hormonal inputs
what are the 3 large glands that produce saliva in the mouth?
paratoid gland
sublingual
submandibular
what is secreted by the parotid gland?
mainly serous fluid
what is secreted by the submandibular gland?
mixed fluid
what is secreted by the sublingual gland?
• Mucin-rich fluid (thick-viscous secretion)
the secretion by which salivary gland is essential to move the bolus via the GIT
subliginual
what is the role of saliva?
aids in chemical digestion
what is salivary amylase
it initiates the digestion of CHO
what enzyme is produced in the mouth?
lingual lipase
salivary amylase
how much saliva is produced daily?
0.5-1.5L/day
what ions are present in saliva?
Na+, K+, Cl-, HCO3-
what is the function of the ions in saliva
helps neutralize the food
what is the pH of saliva?
6.5-7
what is the function of mucin?
protects the mouth and lubricates food
under what pH does lipase operate?
operates at a lower pH and continues to function bettwe in the stomach and duodenum as the pH is more acidic
what is the function of lysozymes?
they break down bacterial cell wall
what regulates the salivary gland
both parasympathetic and sympathetic NS
what do the preganglionic parasympathetic fibers activate?
excitatory ENS neurons
the activation of excitatory ENS neurons releases what and causes what
releases ACh on muscarinic receptors
causes an increase of secretions & leads to vasodilation
what is the most important system for salivary activation
parasympathetic NS
what can atropine block in the salivary glands
its activation as it blocks parasympathetic NS
do the para/sympathetic NS have opposing functions in salivary gland regulation?
no
what is the main function of the sympathetic NS in salivary regulation?
causes vasoconstriction without however preventing saliva production and release
can salivation be a conditionned reflex?
yes
what is the cephalic phase of secretion?
- psychic due to a conditionned reflex
- gustatory after tasting
what is one of the functions of saliva related to taste?
saliva allows to bring the food in contact with the taste receptors of the tongue
in what cases will the gastric and intestinal phases of secretion be activated?
in cases where very spicy food are eaten
what type of secretion occurs in the stomach?
mixed gastric juices
what volume of secretions is released in the stomach daily?
1.5-2L/day
what ions are contained in gastric secretion?
Na+, K+, Cl-, H+
what is the pH of gastric secretions?
1-2
What is pepsinogen broken down to and what is its function?
o Broken down into pepsin which is needed to break down proteins
where is pepsinogen released?
in the stomach
what is the utility of intrinsic factor
allows to absorb B12
what is the function of mucin in the stomach?
protects the gastric mucosa
how are proteins broken down
broken down from proteins to polypeptides to peptides to AA
what secretes mucous through out the GIT
• Surface epithelial cells
What type of fluid is mucous
alkaline fluid
what increases the amount of secretory cells in the stomach
the amount of tubular glands in the stomach which cause increase in surface area
what do the Cardiac and Pyloric tubular glands secrete
an Alkaline, Mucin rich fluid
what is released in the fondus of the stomach?
Acid, enzymes and intrinsic factors
what are the 3 gastric glands found in the fondus and corpus of the stomach?
parietal cells
chief cells
mucous neck cells
what is released by parietal cells
HCL
what is a given ability of the parietal cells
Have the ability to increase their own surface area on its apical surface i
what are the addition invaginations of the parietal cells known as?
intracellular canaliculus
what is the function of the canaliculus?
• Each canaliculus is a pathways for acidic secretions to pass through the lumen of the stomach
what is contained in the parietal cells that gives them energy
mitochondria
why are mitochondria found in the stomach?
they require lots of energy to produce the HCl and pump it against concentration gradient
what is the base of parietal cells in contact with?
capillaries
what is the concentration of HCl pumped into the lumen vs in capillaries
The concentration of HCl pumped into the lumen is much greater than what is present in the capillary [4x10^-5 mEQ] vs 150 mEq H+ & 150 mEq Cl-] in the parietal cells (7M increase)
what happens to HCO3- for every HCL pumped into the lumen?
1 HCO3- needs to be pumped out into the capillary
what does the pump in HCL/ pump out HCO3 cause in blood?
alkalinizes the blood & o Production of the postprandial (urinary) alkaline tide
when does the postprandial (urinary) alkaline tide occur?
Occurs primarily after ingestion of a protein rich meal
what enzyme favours the pump in HCL/ pump out HCO3 cause in blood?
carbonic anhydrase
what happens to the H+ produced by carbonic anhydrase
The H+ ions produces are pumped in the lumen by H+/K+/ATPase into the canalicular membrane
what is the main target of the H+/K+ATPase pump?
main target in cases of ulcers as proton pump inhibitors
what will pump sodium out and potassium into the parietal cell?
Na+/K+-ATPase
what is the pH of parietal cell secretions?
pH ~0.8
the secretions of parietal cells are independent of what?
Secretion independent of type and magnitude of stimulus
what modifies the pH of the contents of the stomach so it sits around 1-2
non-parietal alkaline gastric secretions
what dictates the pH in the stomach?
the amount of parietal cells , higher amount = lower the pH
how is Cl- entering the cell transported across what?
across the canalicular membrane
H+ available from the dissociation of intracellular water is pumped where and for what?
actively pumped into the canaliculi in exchange for K+
what do the H+ secretion leave an excess of in the cell?
leave an excess OH which increases intracellular pH
what does the increase intracellular pH cause?
This causes more CO2 to diffuse in from the plasma combines with H20 in the presence of carbonic anhydrase, to produce H2CO3
what happens to the H2CO3- produced by carbonic anhydrase?
diffuses into the circulation, thus restoring the intracellular status quo, and giving rise to an increased alkalinity in the venous blood.
what are the main functions of HCl in the stomach
precipitates soluble proteins
denatures proteins into digestible structures
activates pepsin and provides optimal pH for pepsin activity
what is the usefulness of precipitating soluble proteins?
Allows the proteins to remain longer in the stomach
what is required to activate pepsin?
a low pH
what is the only secretion of the stomach essential for life
intrinsic factor release
what is intrinsic factors and what is it secretes by?
• It’s a glycoprotein that is secreted by the parietal cells
what is released by chief cells?
pepsinogen
what does pepsinogen get converted to?
pepsin
what pH is needed to convert pepsinogen to pepsin?
low pH <6
what is a specific property of pepsin?
it can autocatalyze pepsinogen into pepsin
what pH is is needed for pepsin to break down proteins into peptides?
pH 2-3
where does IF-B12 complex get absorbed?
in the ilieum
what is IF deficency known as?
pernicious anemia
what is released by mucous neck cells?
mucin
mucin is produced by all what?
all surface epithelial cells
what is mucin secreted by other than the mucous neck cells?
cardiac and pylori tubular glands
where are mucous neck cells located?
in the fundus and corpus in the stomach
what part of the GIT has the most mucous production?
in the stomach
what is released by HCO3- and mucin
surface epithelial cells
what does mucin produce?
mucous
what is the pH of the lumen of the stomach?
pH ~2
what is the pH of the epithelial cells and mucous gel
pH ~7
what is the usefulness of mucous?
it protects the cell against acidic pH
how can mucous protect against acidic pH?
entering HCO3- to be broken down into H20 & CO2 within the mucous gel layer and thus H+ entering the gel won’t reach the epithelium cells.
what primary factor acts to protect the GIT from acidic damamge?
Gastric Mucosal Barrier (GMB)
what is the GMB?
Specialization of the epithelial cells and their apical surfaces and the tight junctions that connect them in order to make them impermeable to the H+ ions
what is rapid cell turnover important for?
in protecting the GIT from acidic content
how many cells are replaced daily in the stomach
~1 million cells
how can ulcers be formed?
weakening of barriers due to drugs (Asprin/NSAIDs) or by helicobacter pylori
how does helicobacter function in the GIT?
colonizes the GIT
burrys between mucous layer and epithelial cells and releases toxin that breaks down epithelial cell
how can the normal barrier be broken and cause for ulcers?
excessive HCl output
how are gastric secretions inhibited?
release NANC onto the secretory cells in order to inhibit secretion
