GI Physiology Flashcards
The GI tract is one long _____ digestive tube that extends from the ___ to the ____
muscular
mouth to the anus
along the GI tract, there are major sections such as the esophagus, stomach, small intestines that are all separated by ____
sphincters
what are the four layers of the GI tract wall ranging from the esophagus to the anus
muscosa, submucosa, muscularis, and serosa
describe the mucosa
the innermost layer which functions in the production of mucus, digestive enzymes, hormones, absorption of nutrients, and protection against infectious diseases
what type of cells are present in the intestinal lumen of the mucosa that contains cappilaries
simple columnar epithelial cells
what function do the capillaries have in the mucosa
nourish the cells and allow for efficient absorption of digested nutrients into the blood
where is the submucosa located
the second innermost layer
what is the function of the submucosa
contains elastic fibers that enable the GI tract to regain its shape after food moves through it.
in the submucosa, what intrinsic neuronal system is housed here
enteric nervous system
what is the function of the enteric nervous system
regulated digestive activities such as motility, secretion and blood flow
where is the muscularis layer located
the muscular portion, the third layer
what types of muscles are present in the muscularis layer
longitudinally and circular layered smooth muscules
what layer in the GI tract forms sphincters
muscularis layer (located throughout the GI tract)
the coordinated contractions of the muscularis layer are responsible for what function
peristalsis and other contractions which propels food forward so that it goes towards the distal end of the GI tract
when does peristalsis occur in the GI tract
as soon as food enters into an area of the GI tract
what is the function of the smooth muscle in the front muscularis layer
it relaxes
what is the function of the smooth muscle in the behind muscularis layer
contracts and essentially squeezes food forward
where is the serosa located
the protective outermost layer
what is the function of the serosa
adheres to the GI tract to support structures and secretes serous fluid that lubricates the organs reducing friction during movement
the intestines receive _______ innervation from the autonomic nervous system
extrinsic
what is the function of the parasympathetic neurons in the GI tract
rest and digest, which occurs by the release of ACETYLCNOLINE which increase the secretions and contractions of the smooth muscles
what is the function of the sympathetic neurons in the GI tract
Epinephrine and norepinephrine which will decrease the activity of the smooth muscles, reduce secretions, and cause the sphincters to contract, blocking progression of intestinal contents
_____ receives food and mixes it with saliva from the mouth
esophagus
relaxation of the upper esophageal sphincter allows for what to occur
food to enter the upper portion of the esophagus
once food is in the esophagus, what action takes place
an esophageal contraction propels food to the lower esophageal sphincter (LES)
the lower esophageal sphincter takes part in _____ activity resulting in what action to occur
TONIC (a contracted state), however it relaxes reflexively to allow for food to enter into the stomach
the lower esophageal sphincter remains _____ between swallowing which aids in ______
- closed
- prevents regurgitation of gastric contents into the esophagus
what are the three different types of muscles present in the lower esophageal sphincter
- smooth muscle and muscularis layer of the esophagus
- skeletal muscles from the diaphragm
- smooth muscles from the stomach
when the LES opens following a meal, to expel swallow air what occurs
a burp
what is the function of the stomach
a temporary storage unit where chemical digestion of food begins
ingested contents and digestive secretions are mixed by coordinated muscular contractions forming ____ in the stomach
chyme
what are the three regions of the stomach
cardia
fundus of the body (aka corpus)
antrum
the lining of the stomach is covered in _____ cells
columnar epithelial cells folded into gastric pits
in the stomach, each gastric pit which allows for____
an opening of a duct into which one or more gastric glands empty
list the 4 types of secretory gastric cell types
- mucous cells
- parietal cells
- chief cells
- endocrine cells (G cells)
where are mucous cells located and what is their primary function
cardia and antrum
-Fx: mucus secretion
where are parietal cells located and what is their primary function
fundus and body
-Fx: gastric acid secretion
where are chief cells located and what is their primary function
fundus and body
-Fx: pepsinogen and lipase secretion
where are endocrine cells located and what is their primary function
antrum
-Fx: gastrin secretion
____ and ____ is where most chemical digestion occurs
body and fundus
typically, how much volume is released from gastric muscosa throughout the day
3L
gastric juice consists of what types of enzymes
electrolytes
hydrochloric acid (the enzyme pepsinogen)
mucus
intrinsic factor
the primary secretion of the stomach is ________ ions produced by _____
hydrogen ions
parietal cells
what are the two types of mechanisms that control gastric secretions
neural and hormonal
what are the three enzymes regulating gastric secretion
acetylcholine, gastrin, histamine
Gastrin can directly stimulate _____ and ______
proton potassium APTase pump and parietal cells
gastrin can additionally stimulate enterochromaffin like cells (ECL) causing______
histamine
what are the two specific PGE 2 and their function
somatostatin and prostaglandins— inhibit acid secretion
the gastric juices that the stomach is exposed to, has a pH of ____
1.5-3.5 and contains digestive enzymes
the acidic environment in the stomach produced by the digestive enzymes aid in
digestion and absorption of ingested contents as well as destroys ingested bacteria and microorganisms
due to the extreme pH that the stomach is exposed to, a protective mucosal barrier is composed of
bicarbonate rich mucus
the mucosal barrier protects the stomach lining and protects the epithelial cells in the mucosa by
maintaining a thin layer of pH which is 6-7
in addition to the mucosal barrier, the stomach contains ________ ______ preventing gastric juice from leaking into underlying tissue between epithelial cells and the mucosa
thin junction
____ and ____ increase the frequency and magnitude of stomach contractions augmenting gastric mixing
gastrin and acetylcholine
gastric contents are mixed and formed into a semi solid state known as _____ typically within ___ hrs after the meal is injested
chyme
4 hours
in order for chyme to enter into the small intestine, ____ acts as a filter only allowing ___ cc in at a time
pyloric sphincter
3 cc or less
the rate of emptying is dependent on what two factors
chemical and physical contents
Carbohydrate rich meals empty ____ while fats empty ____
carbs-rapidly
fats- slows
fats empty slower due to
fat forming an oily layer at the top of the chyme and move through the stomach slower
what are the three sections of the small intestines
duodenum
jejunum
ileum
____ is made of food and digestive enzymes, passing from the stomach through the pyloric sphincter and enters the duodenum in small parts containing tiny suspended particles
chyme
______ is the primary site for the mixing of chyme with additional secretions from the common bile duct and the pancreatic ducts which aid in ____
small intestines
digestion and absorption
the small intestines provide _____ which digestion and absorption occur
substantial surface area
what are the 4 factors contributing to the large surface area of the small intestines
- length of small intestines (5 Meters)
- mini folds of mucosa and submucosa layer
- villi (finger like projections that increase absorptive surface area)
- microvillin on apical surface increase surface area (600 fold, allow for rapid mvnt of nutrients into BLOOD)
there is ___ layers of epithelial cells between the intestinal lumen and systemic blood
1
cells that are located at the base of the villi _______ as they migrate toward the tip of the villi which causes shedding every _____
differentiate
2-6 days
what is the primary physiological function of the small intestine
digestion and absorption of ingested nutrients such as (carbs, proteins, lipids)
humans shed ____ cells per day
17 billion
what are dietary carbohydrates primarily comprised of
polysaccharides (starch) and disaccharides (sucrose and lactose)
enterocytes are only capable of absorbing
monosaccharides
for enterocytes, carbohydrates must be digested as what two things
monosaccharides or simple sugars (glucose, galactose, and fructose)
describe stage 1 that occurs for carbohydrate digestion
- amylase cleaves the internal bonds of polysaccharides to form fragments such as disaccharides, trisaccharides, and oligosaccharides. If hydrolase is present at the brush border, then digest disaccharides and oligosaccharides into monosaccharides. Monosaccharides are water soluble they have to be assisted across the plasma membrane of the enterocytes by action of transport protients
_____ are water soluble, needing transport proteins to aid across plasma membrane
water soluble
describe stage 2 that occurs for carbohydrate digestion
- lipid digestion/absorption are ENTIRELY soluble in water, making lipids aggregate together. First, emulsification must occur producing a suspension of fine lipid droplets. Bile sats are then triggered to be released from the liver aiding in emulsification of lipids. Next lipids are chemically digested by LIPASE, which occurs by the brush border on the intestines.
what is another lipase
phospholipase (which hydrolyzes phospholipids and cholesterol esterase which break down esters in cholesterol… ex soap and water in an oiled pan (soap is the emulsifier and washes away the oil)
proteins must be able to digests to _____, _____, and ____ for transport into enterocytes
tripeptides
dipeptides
amino acids
where do digestion of proteins being
in the stomach, where the acidic environmentw can hydrolyze peptide bonds
what do the chief cells in the stomach release and
pepsinogen
Pepsinogen causes a cascade of events which is activated by
the low pH to an ACTIVE form called pepsin
premature activation of digestive enzymes can lead to
damage of the intestinal lining or stomach lining
when does pepsin function the best
in an acidic environment
pepsin is preferentially hydrolyzes the peptide bond following the aromatic amino acids such as
phenylalanine, tryptophan, and tyrosine
since pepsin only constitutes a few of the amino acids, a more complete digestion of proteins require additional _____
proteases released by the pancrease
in the stomach, the pancreatic proteases are released as _______ precursors which are converted into ___ enzymes
inactive and active
EX: trypsinogen inactive is converted into trypsin active
when trypsin is converted to the active form, it activates
all other pancreatic proteases
digestion of oligopeptides occurs ______ which produced what three peptides
brush boader proteases
tripeptides, dipeptides, or individual amino acids
the converted oligopeptides are transported into the cells via _________ containing ____ or coupled with ____ symporters
secondary active transport
sodium or coupled with proton symporters
____ and _____ and further digested by systolic peptidase to individual amino acids
dipeptides and tripeptides
The small intestines is the major site for what type of absorption.
water and electrolyte
water absorption is _______ and most occurs by what type of route
passive
transcellular route via water channels (aka aquaporins)
small amounts of water can still move through a _______route, even though epithelial cells are interconnected by tight junctions
paracellular route
in the duodenum and jejunum tight junctions are ____ and become _______ in the ileum or colon
leaky
progressively tighter
how does water move in the small intestines
both directions across the mucosa depending on the osmotic gradient
depending upon the intestinal contents, osmolarity of the duodenal contents may be ____ or ______ to that of the plasma
hypertonic or hypotonic
once contents enter the jejunum, the osmolarity is _________
similar to plasma and maintained throughout the rest of the small intestine
sodium absorption in the small intestines is mainly _______traveling through the cells passing through both ____ and _____ membranes
transcellular
apical and basolateral membranes
the Sodium potassium ATPase, maintains what in the small intestines
low intracellular concentrations of sodium allowing for the luminal sodium to enter the enterocyte
sodium transport is primarily coupled with ______
glucose and some amino acids
glucose is also important in driving what
sodium reabsorption
since ______ can drive sodium reabsorption, what is important to remember for individuals with HTN
GLUCOSE—we need this patient population to avoid glucose
______ are reabsorbed through a antiporter exchanger
quadions (which bicarb ions are secreted into the lumen)
______ acts on the protected epithelial cells in the most proximal section of the duodenum, where acid and pepsin are in high levels
bicarbonate
the movement of electrolytes and nutrients form the intestinal lumen into the blood creates the _____ driving what process to occur
osmotic gradient
drive water absorption
the net movement of water and electrolytes int eh small intestines is primary
absorptive, allowing electrolytes secretion to occur
what ions are secretes through channels in the small intestines
potassium
chloride
where is potassium secreted in the SI
through K channels into the intestinal lumen
where are chloride ions secreted in the SI
the intestinal lumen via chloride channels located in apical membrane
the movement of negatively charged ions, create a
electrical gradient
the result of increased ions in the intestinal lumen causes an increase in the
osmotic concentration
water will move from _____ into the _____ to maintain equal solid concentrations
plasma into the lumen
what is the target drug therapy for patients struggling with constipation
by increasing the amount of ions in the intestinal lumen, this results in higher water contents in the intestines allowing for more intestinal contents to pass freely
how do fluid and electrolyte secretions act to protect the mucosal layer
they flush bacterial products and toxins away from epithelial cells
what two signaling molecules stimulate fluid and electrolyte secretions in healthy and sick individuals
neural and paracrine signaling
what are the two ways that smooth muscle contractions can occur in the small intestines
segmentation contractions and peristaltic waves
what occurs during segmentation contractions
nonadjacent segments of the intestines, rhythmically contract and relax moving food in both directions, mixing intestinal contents with cell secretions
what occurs during peristaltic waves
these waves propel the chyme forward through SI towards the large intestines, allowing for adjacent segments to alternatively contract and relax propelling food forward.
when does peristalsis occur in the digestive process
late, after most nutrients have been absorbed
segmentation contractions aid in _____ transit, and increase contact time which ultimately _______
slowing transit
this increases contact btw chyme and epithelial cells (increasing absorption)
what three segments compose the large intestines
ascending, transverse, descending
what are the 4 functions of the colon (large intestines)
- complete digestion
- absorb remaining water/electrolytes
- secrete mucus
- store unabsorbed material until eliminated by the body
the wall of the large intestine differs from the small intestines because
- few folds
- no villi
- no cells secreting digestive enzymes
- large number of goblet cells (increasing mucus production)
once the unabsorbed material reaches the LI, ____ nutrients remain
very few
how much digestion occurs in the LI
very little except for the small amounts of digestion by the intestinal microbial flora
similar to the SM, in the LI water absorption is coupled to _____ and _____ electrolyte movement
sodium and chloride
_____ nervous system is composed of nerve fibers from the elementary track from esophagus to the anus
enteric
how many nerve fibers are present in the enteric nervous system
100 million (which rivals the number found in the entire spinal cord)
majority of the enteric nerve fibers are found along the _____ and are within the walls of _____
alimentary track
gastrointestinal tissues
the other nerve fibers that enter and leave the ENS (enteric) maintain communication with high control centers found in what two systems
autonomic nervous system and central nervous system
the enteric nervous system is primarily localized to two
extensive plexuses (web like collection of nerves)
the enteric NS runs along the ____ tissue layer in the GI tract
inner
where is the myenteric plexus located and what is the primary function
- located btw longitudinal and circular muscle layers
- fx: responsible for control of muscular contraction and mechanical aspects of digestion
what are the two plexuses from the enteric nervous sytem
myenteric and submucosal
where is the submucosal plexus and what is its function
- lies in the submucosa
- fx: controlled digestive secretions, absorption, and local contration of submucosal muscle leading to enfolding of the mucosa
the enteric nervous system must be able to respond to control signals from the ____ & _____ nervous sytem
sympathetic and parasympathetic
why does the gut need to know how to respond to the autonomic nervous system
to permit or inhibit blood flow to our GI tract
- fight/flight: blood and nutrients shunted to skeletal muscles and brain
- rest/digest: blood/nutrients increases activity of the gut to replenish nutrients, minerals, water
the enteric nervous system must additionally respond to what two nerve fibers
efferent (carry signals to the ENS)
afferent (originate in the wall of gut/carrying signals alimentary canal into ENS plexuses allowing GI tract to respond)
some of the afferent nerve fibers lead the GI tract all together causing the relay of signals from the ___ to the _______
gut to the prevertebral sympathetic ganglion
when the afferent nerve fibers transfer signals to prevertebral sympathetic ganglion, this evokes a
reflex whereby distant portion of the GI tract can be controlled by effects else where
(EX: signals can be sent to the stomach to initiate colon motility as room is needed for the newly digested foods_
an additional afferent nerve fiber that runs into the ____ nerve allows higher level control for all aspects of digestion
vagus
over-activation or under-activation fo the enteric nervous system can lead to
excessive or diminished secretions, absorption, motility, prolonged food residents and chyme
abnormal enteric nervous system functions can also manifest as
pain and other sensations
when adding a medication to a patients stomach, it is important to remember the potential impact on the ENS as well as the
microbiome located in their system
