Gastrointestinal Flashcards
six roles of the digestive system
ingestion, secretion, motility, digestion, absorption, defecation
the gut layer that has:
-epithelium
-lamina propria
-muscularis mucosae
mucosa
the gut layer containing vessels and glands
submucosa
the 2 muscularis externa layers on the intestine
longitudinal, circular
the 2 components of the enteric nervous system
submucosal plexus, myenteric plexus
what is the role of the serosa layer?
structure
what is the control center of the short reflex?
interneuron in ENS
what are the 2 outputs of the short reflex?
submucosal plexus, myenteric plexus
___ _____ is the major digestive enzyme in saliva that conducts startch breakdown
a-amylase
what does a-amylase’s function depend on?
how well food is chewed
why is the starch breakdown important to occur in the mouth?
a-amylase is deactivated in the stomach due to the acidic environment
what does taste depend on?
ability to detect chemicals in the food
dissolved chemicals diffuse into pores in the tongue and are sensed by taste hairs that ____ the membrane and activate the nervous system
depolarize
____ produce thick mucus to protect us against chewing sharp material
mucins
what are the 3 ways that saliva protect?
mucins producing mucus, alkaline pH buffer against food and stomach, antimicrobial secretions
absorption of ____ ___ ____ _____ occurs in the mouth
low molecular weight molecules
what kind of drugs can be absorbed in the mouth?
sublingual/under the tongue
molecules absorbed in the mouth bypass what process?
the first round of liver metabolism
mucins produce ____ that coat food so they can move around the mouth
mucins
what is the muscularis externa of the top third of the esophagus made of?
skeletal longitudinal and circular muscle
what is the muscularis externa of the bottom 2/3 of the esophagus made of?
smooth longitudinal and circular muscle
where in the brain is swallowing integrated?
medulla oblongata
the swallowing reflex requires activation of what two types of nerve?
sensory afferent, somatic motor
once the food touches the ___ ____, the swallowing reflex is triggered (AKA stimulus)
soft palate
what type of receptors are found in the soft palate to initiate the swallowing relfex?
mechanoreceptors
what are the 3 responses in the swallowing reflex?
- soft palate elevates
- epiglottis lowers
- opening of the LES
once food moves into the esophagus, what 3 things occur?
- UES closes
- epiglottis lifts, opening larynx
- breathing resumes
controlled variable in the swallowing reflex
open and clear back of the throat
sensor in the swallowing reflex
mechanoreceptor
what is described as waves of smooth muscle contractions?
peristalsis
what is the barrier between the stomach acid and the esophagus?
lower esophageal sphincter
obese, pregnancy, overeaters, and anyone with elevated stomach pressure are susceptible to what?
GERD
why is it important that the LES is located outside of the thoracic cavity?
experiences normal atmospheric pressure
food contents mixed with gastric juices is called what?
chyme
digestion of ____ is initiated in the stomach
proteins
_____ nerve activation increases acid release
vagus
___ ____ is a strong acid that sterilizes and kills bacteria presents in food we eat
hydrochloric acid
acid secretion occurs in what relfexes?
both short and long
what is the main function of the stomach?
mixing
what are the 3 muscular layers of the stomach?
- oblique
- circular
- longitudinal
___ cells of the stomach secrete mucus that protects the cells from the acidic environment
mucus
____ cells produce and secrete HCl to kill bacteria and also help with vitamin B12 absorption in the stomach
parietal
____ cells secrete digestive enzymes in the stomach
chief
____ cells in the stomach secrete gastrin
G
____ is a hormone that stimulates HCl release near the blood
gastrin
what happens when actions potentials are sustained for a long time above threshold?
increase their strength
pacemaker cells lead to the contraction of what muscle layer?
longitudinal
pacemaker cells generate a spontaneous, rhythmic depolarization known as a ___ ___ ____
basic electrical rhythm (BER)
hormone released by the parasympathetics
ACl
hormone released by the sympathetics
norepinephrine
___ of the stomach increases the force of contractions and rate of emptying
distension
where are waves of contraction in the stomach initiated?
top/fundus
where does most of the mixing occur in the stomach?
bottom/antrum
the presence of fat, acid, and amino acids in the intestine ____ gastric motility
inhibit
this type of GI Activation is when one cell released a hormone into the interstitial fluid and this acts on a nearby cell that expresses the hormones receptor
paracrine
this type of GI activation is when a hormone is released into the blood and affects cells expressing the hormone’s receptor
endocrine
what is the differentiation between endocrine and paracrine?
endocrine travels in the blood to the target cell
when food enters the stomach, ____ is released into the bloodstream to stimulate acid release
gastrin
gastrin binds to receptors on what two cells?
parietal, histamine
in the paracrine function of the stomach, ____ is released from H cells and binds to receptors present on neighboring parietal cells
histamine
what hormone is the inhibitor of acid secretion in the stomach?
somatostatin
what type of cells secrete somatostatin?
delta cells
where is somatostatin released into before it reaches parietal cells?
blood
does somatostatin respond to high or low pH?
low
a ____ is an enzyme that is stored intracellularly in an inactive form
zymogen
what is the zymogen released from chief cells that is activated by the presence of acid?
pepsinogen
___ cleaves pepsinogen into pepsin
HCl
what is the enzyme that is responsible for 20% of protein digestion?
pepsin
___ play a role in maintaining mucus integrity, bicarb secretion, and mucin production
prostaglandins
mucus is 80% what?
carbohydrate chain
B12 is typically insufficiently absorbed, by when it forms a ____ in the stomach, it can be absorbed by the intestine
complex
what trait of the stomach helps prepare iron for absorption in the intestine?
acidic environment
what are 3 consequences of taking proton pump inhibitors?
- bacterial infections
- decreased iron absorption
- decreased pepsinogen activation (protein digestion)
what is the name of the pacemaker cells of the intestine?
interstitial cells of cajal
depolarized smooth muscle cells open what type of channel on the plasma membrane?
voltage-gated calcium channels
___ binding to a smooth muscle cell with activate intracellular Ca2+ release and muscle contraction
Ach
what system inhibits digestive activity?
sympathetic nervous system
what system activates digestive activity?
parasympathetic nervous system
what is the most important contributor to the parasympathetic role on the digestive system?
vagus nerve
what is the purpose of segmentation in the intestines?
mix food and chyme with digestive enzymes
what is the role of peristalsis?
move chyme forward and absorb nutrients as it moves
what occurs when all myosin heads in smooth muscle are phosphyrylated?
tetanus
what two things are released from the liver?
digestive enzymes, bicarb
what is released from the gallbladder?
bile
2 main roles of the small intestine
digestion and absorption
role of the circular folds in the intestine
increase surface area to maximize absorption
what are the crpts of lieberkuhn involved in?
secretion
most absorption in the small intestine is where?
in villi
__ cells secrete a lot of mucus in the beginning of the intestine
goblet
___ cells secrete lysozyme which is able to phagocytose
paneth
precursor cells in the __ ___ ____ replace the dying epithelium in the small intestine
crypts of lieberkuhn
what is countercurrent exchange in the villi?
tip of the villi is hypoxic and this causes the top to slough off and release digestive enzymes
___ is the breakdown of macromolecules for absorption
digestion
what are the 3 reasons that chyme is neutralized before entering the small intestine?
- enzyme function
- mucosal protection
- micelle formation
____ cells sense acidity and chemical makeup of chyme
enteroendocrine
describe the mechanism of acidic chyme neutralization
enterendocrine cells secrete mucus, they also release secretin into bloodstream, this signals the release of bicarb from pancreatic duct to intestine
what does secretin do to gastric motility?
can inhibit
____ is a hormone that is released from mucosal cells in response to fasting and stimulates the migrating motor complex and increases peristalsis
motilin
the sensing of fats, peptides, and carbs activates what type of receptor?
chemoreceptor
what cells sense the chemical makeup of food?
enteroendocrine cells
what digestive enzyme is released from the acinar cells of the pancreas when enteroendocrine cells sense food chemical makeup?
CCK
what does CCK signal for?
release of digestive enzymes from the pancreas and bile from the liver
what does CCK do to the stomach?
decrease motility
how do carbohydrates get absorbed?
glucose moves up gradient at the same time that sodium moves down, secondary active transport
what is the main enzyme of the small intestine that breaks down protein?
trypsin
what are the 3 ways that proteins are absorbed?
as di and tripeptides, amino acids, or small peptides
how do di and tripeptides get absorbed?
cotransport with H+
how do amino acids get absorbed?
cotransport with sodium
how doe small peptides get absorbed?
carried intact across the cell by transcytosis (lots of ATP is needed)
what is emulsification?
bile breaks large lipid droplets into smaller droplets
___ breaks down triclycerides and both fatty acids and monoglycerides can freely diffuse
lipases
in fat absorption, _____ are reassembled in the intenstinal cell and then move into the lacteal system before entering the blood
chylomicron
the liver ____ toxins, making them less toxic so they can be stored in the gallbladder and released into the small intestine to be excreted
conjugates
conjugated toxins are produced in the ___
liver
the hepatic portal vein carries ___ rich blood
nutrient (amino acids, carbs)
the bile moves ____ from the central vein
away
the hepatic artery carries ___ rich blood
oxygen
what is the main role of the large intestine?
water and salt absorption
what two cell types are found in the large intestine crypts of lierberkuhn?
absorptive, goblet
absorption of water relies on the absorption of ____
sodium
what are the 3 majors functions of the liver?
- production of bile salts
- carb metabolism
- conjugation of billirubin and other toxins
bile salts remain in the small intestine until absorbed in the ___
ilium
how many times is the pool of bile salts recycle during a meal?
twice
the ____ of the toxin determines if it is excreted by the kidneys or by the intestines
size
excess glucose is stored in the liver as ____
glycogen
if conjugated substances are secreted by the kidneys, they are released into the ___
blood
if conjugated substances are secreted by the intestine, they are released with ___
bile
what part of the large intestine is for squeezing out water?
haustra
the internal anal sphincter is under ___ control
involuntary (smooth muscle)
the external anal sphincter is under ____ control
voluntary (skeletal muscle)
what is the integrating center of the defecation reflex?
sacral spinal cord
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