GI Flashcards
what does a typical recommended daily diet consist of?
carbs, proteins and lipids
what is the general function of the digestive system?
to break down the foods you eat, release their nutrients and absorb them
what does the gastrointestinal tract consist of?
the organs of the alimentary canal and accessory glandular tissues
what is the alimentary canal?
a muscular tube made up of different organs that coordinate to move food in one direction from mouth to anus
what are exocrine organs?
organs that lie outside the digestive tract and empty their secretions through ducts into the digestive tract lumen
what are examples of exocrine organs?
salivary glands
the exocrine pancrease
biliary system
liver
gallbladder
what are the 4 basic tissues that line the alimentary canal?
mucosa
submucosa
serosa
muscularis
what is the mucosa?
an epithelial cell layer directly in contact with food or chyme. it seperates food from the the inner environment of the body.
INNERMOST
what is chyme?
acids and partially digested foods
what is the submucosa?
a connecctive tissue layer that anchors the epithelia (mucosa) to the rest of the alimentary canal
what is the muscularis mucosae?
smooth muscle that contracts the mucosa.
consists of?
circular muscle
longitudinal muscle
what is the serosa?
another layer of connective tissue that anchors the GI tract to other organs
the GI tract forms an effective barrier to protect it from;
acidic stomach pH
digestive enzymes
gut flora
what forms the GI tract barrier?
tight junctions and mucus
what are tight junctions?
tight junctions are between epithelial cells in the mucosa. they are very tight so that bacteria and bad things cannot get through
where is mucus produced?
mucosa
how does mucus help to protect the GI tract?
it is alkaline in nature so it helps to neutralize acidity
provides a cushion for sharp foods
what are the 4 main functions of the GI tract?
secretion
motility
digestion
absorption
describe the secretion function of the GI system;
digestive juices get secreted by exocrine glands
GI hormones help control motility and the exocrine gland secretion
describe the motility function of the GI system;
muscular contractions that mix and move food forward
propulsive movements push food forward
mixing movements facilitate absorption
describe the digestion function of the GI system;
the biochemical breakdown of complex food into small units.
there is chemical and mechanical digestion
describe the absorption function of the GI system?
the samll units from digestion are transferred from the digestive tract into blood or lymph to be transported elsewhere
how is the digestive system regulated?
recieves a stimulus
activates the receptor
creates neural reflexes or hormone secretion
activates the effector cell
change in digestive function
what are the 2 types of stimuli that digestive function can be initiated by?
external (smelling food)
internal (after eating/ having a full stomach)
what are the types of sensory receptors that are activated by specific stimuli?
chemorecceptors - sensitive to specific chemicals (a fatty mean will cause a signal for lipases)
mechanoreceptors - sensitive to stretch or tension in the stomach wall (full stomach)
osmoreceptors - sensitive to the water content of the luminal contents/food
once a neural reflex or hormone has been secreted/created what types of effector cells get activated?
smooth muscle cells - modify gut motility
exocrine gland cells - secreted digestive juices
endocrine gland cells - secrete GI hormones
what are some examples of a change in digestive function?
a growling tummy, a tummy cramp, a watery mouth after smelling some yummy yummy food
within regulation of digestive function, what 4 factors regulate the feedback system?
autonomous smooth muscle
intrinsic nerve plexus
extrinsic nerves
GI hormones
what type of cells are considered pacemaker cells because they have spontaneous variations in membrane potential?
smooth muscle cells
what is the enteric nervous system?
2 major neural networks that lie entirely in the digestive tract wall and run the entire length ( considerable self regulated)
what are the 2 neural networks in the enteric nervous system?
submucosal plexus
myenteric plexus
what is the autonomic nervous system?
originates outside the digestive system and innervates the various digestive organs
what are the 2 components of the autonomic nervous system?
sympathetic and parasympathetic
what does the sympathetic system do?
slows the contraction and secretion digestive system down (fight or flight)
what does the parasympathetic system do?
increases motility and secretion (rest and digest)
what nerve plays a crucial role in GI functions?
the vagus nerve
what are GI hormones released by?
are their responses excitatory or inhibitory?
endocrine cells in response to environment changes.
both
what organ is not part of the alimentary canal?
A: pharynx
B: stomach
C: anus
D: bile duct
E: mouth
the bile duct. it is actually a part the exocrine organs that secrete things to help movement and digestion
what cell type in the alimentayr canal forms a barrier to protect thr body from the external environment?
A: mucosa epithelial cells
B: circular smooth muscle cells
C: endocrine gland cells
D: myenteric plexus
E: submucosa connective tissue
mucosa epithelial cells and protects via a mucus layer and tight junctions in a barrier
GI tract effector cells recieve numerous different inputs that regulate their function. what are the main types of signals that stimulate GI tract effector cells?
A: hormone secretion
B: extrinsic stimulation from the CNS
C: intrinsic stimulation from local nerves
D: all of the above
E: none of the above
all of the above
what role does the mouth and salivary glands have in gut motility?
chewing to break it up, mix it and propel it forward
what role does the pharynx and esophagus have in gut motility?
swallowing, primary peristalsis and secondary peristalsis
what role does the stomach have in gut motility?
gastric mixing and gastric emptying
what role does the small intestine have in gut motility?
segmentation; migrating motility complex
what role does the large intestine have in gut motility?
haustral contractions; mass movements
is the rate of propulsion consistant throughout the digestive tract?
no, food can be propelled rapidly or slowly
i.e. food rapidly transits down the esophagus ( you need to breath so the food has got to go quickly) but moves very slowly through the small intestine because evey last nutrient wants to be squeezed from the food
the muscularis is lined with 2 types of muscle;
what are they?
what are their distinguishing factors?
longitudinal: muscle fibers that run parallel to the long axis of the tract
circular: muscle fibers that run around the circumference of the tract
what role do longitudinal muscle fibers have in GI motility?
they push food forward by shortening and elongating the length of the canal.
it has a worm like movement - inchining its head forward and its body straightens out, the tail follows after and it shortens back up
what role do circular muscle fibers play in GI motility?
pushes food forward by contracting (squeezing) the circumferance of the alimentary canal.
this causes pressure to build up and it pushes the food forward
muscularis smooth muscles are a type of __________ cells.
effector
how are muscualris smooth muscle cells stimulated?
by neural reflexes or hormones
although the muscularis smooth muscle is stimulated by neural reflexes ir hormones, they also exhibit_____
autonomous contraction ability or self regulation
what are slow waves?
slow, spontaneous rhythmic changes in resting membrane potential of inner circular smooth muscle
slow waves with action potentials cause _____
muscle contractions
is the frequency of slow waves constant all over the GI tract?
no, the frequency of slow wave varies from region to region.
i.e. the frequency is faster in the stomach compared to the intestine
what are the regulators of slow wave amplitudes and the triggering of action potential?
neural activity and hormonal signals
what is peristalsis?
a series of wave-like muscle contractions that propel food and chyme along the tract. it is caused by the coordinated activity of circular and longitudinal muscle layers
what type of digestion does the salivary glands engage in?
chemical digestion
what is the role of the lips and cheeks?
to confine food between the teeth so that food is chewed evenly
what is the role of the salivary glands?
to secrete saliva to moisten and lubricatethe mouth, pharynx and food, clean the mouth after eating and manipulate food to be swallowed
what is the role of the tongue muscles?
move the tongue sideways, in and out to manipulate the food for chewing, shape the food into a bolus and push it backward for swallowing
what is the role of the taste buds?
sense food and taste in the mouth. the taste buds are sensory receptors so once food is sensed the impulses are sent to the salivary nuclei in the brain stem then to the salivary glands to secrete saliva
what is the role of the lingual glands?
secrete lingual lipase (activated in the stomach) to break down TAG into fatty acids and diglycerides
what is the role of the teeth?
shred and crush food so that the solids can be broken down into smaller pieces
what is the pharynx?
a short tube of skeletal muscle lined with a mucus membrane
what is the esophagus?
a thin-walled and pliant (flexible) muscular tube that moves food from the pharynx to the stomach
what type of muscles does the esophagus contain?
skeletal (upper third) and smooth (lower 2 thirds)
because the upper thrid of the esophagus is mostly skeletal muscle, this means swallowing is a ____ reflex
voluntary
the esophagus is divided into 2 sections called;
the upper and lower esophageal sphincter
what are the 3 stages of the swallowing reflex?
the voluntary/buccal phase
the pharyngeal phase
the esophageal phase
what is the secondary name for swallowing?
deglutination
once the food enters the esophagus, what motility method takes over?
peristalsis
swallow induced peristalsis is called;
primary peristalsis
if the bolus/food gets stuck the stretch receptors are activated which causes ____ peristalsis to push food down the esophagus
secondary
how does heartburn occur?
if the lower esophageal sphincter does not remain closed, stomach contents can be expelled up into the esophagus.
over time this can cause erosion of the mucosa and submucosa
what is the fundus?
a thin wall that easily expands in the stomach
what is the rugae?
flattens as stomach expands
what is the antrum?
the thickest muscle layer that produces the strong contractions for gastric mixing and emptying
what are the 2 forms of motility in the stomach?
gastric emptying and gastric mixing
what is gastric emptying?
rhythmic mixing waves force small amounts of chyme through the pyloric sphincter and into the duodenum. full emptying happens approximately 2-4 hours after eating a meal
describe the steps of gastric emptying;
1: a peristaltic contraction starts in the fundus and sweeps down toward the pyloric sphincter
2: the contraction gets more vigirous as it reaches the antrum because of the thick muscles
3: this new strong contraction propels the chyme forward
4: the chyme begins getting pushed through the pyloric sphincter into the duodenum. the harder the contraction the more chyme goes through
what is a mixing wave?
a unique type of peristalsis.
mixes and softens food with gastric juices to make chyme.
become more intense as they reach the pylorus
describe the steps of gastric mixing;
5: when the peristaltic contraction reaches the sphincter it is tightly closed and no more chyme enters
6: when that chyme that was propelled forward hits that closed sphincter it gets tosses back into the antrum. this mixes the chyme with each contraction.
what factors regulate gastric motility and emptying?
volume of chyme (more volume = more movement and more to empty)
degree of fluidity/food water content (more fluid = more rapid)
chyme already in the duodenum (a full duodenum = no motility or emptying until the duodenum emptys)
hormone secretion (different horomes increase or decreases motility and emptying)
intense emotion or pain (i.e. fight or flight0
where is the vomiting reflex coordinated?
in the medulla in a little place called the vomiting center
how does vomiting occur?
the ab muscles strongly contract which causes the ab wall to move inward and deep breaths move the diaphragm down. this increases abdominal pressure and squeezes the stomach. the lower esophageal sphincter relaxes which allows for stomach contents to invade the esophagus. the strong abdominal contraction propels the materal through the esophagus and out through the mouth
what is the method of motility in the intestines called?
segmentation
what is segmentation?
mixing of chyme in the small intestine that slowly propels food forward
What are the benefits of the mixing movements in the small intestine?
Promote digestion by mixing food with digestive juices and facilitate absorption by exposure to surfaces of the digestive tract
What movement sweeps the intestine clean in preparation for a new meal?
Migrating motility complexes
How are migrating motility complexes triggered?
By motilin that targets gastric and intestinal smooth muscle
How is motilin inhibited?
By eating food
what is haustration?
very slow segmentation where segments (haustra) are delineated by permanent forlds in the intestinal wall.
so much slower than segmentation
where does haustration occur?
large intestine
what are mass movements?
like a peristaltic wave, exccept that a portion of the intestine contracts for a longer time before relaxing. these waves of contraction propel the luminal contents forward rapidly and sweep the colon.
happens 3-4 times a day
where are mass movements the lowest and highest in activity?
highest - before a meal
lowest - during sleep
how is the defeccation reflex triggered?
by distension of the rectum from the colon
what events does distension initiate?
1 - smooth muscle in the wall of the rectum contracts. peristaltic contractions of the sigmoid colon propels fecal matter into the rectum, further raising the pressure
2 - the internal anal sphincter relaxes while the external anal sphincter contracts, preventing exit
3 - when the pressure in the rectum reaches a certain level, the external anal sphincter relaxes allowing defecation to continue
is defecation under voluntary or involuntary control?
volunatry
what does gastric mixing do?
pulverizes food in the stomach creating chyme
what tissue layer of the alimentary canal is mainly responsible for motility?
A: mucosa
B: muscularis
C: submucosa
D: serosa
E: plexus
muscularis
My grandfather has terrible heartburn. This may be caused, in part, due to a specific sphincter that connects the esophagus to the stomach. When the sphincter opens inappropriately, stomach acid can enter and damage the esophagus, causing pain. what is the name of this sphincter?
A: upper esophageal sphincter
B: lower esophageal sphincter
C: pyloric sphincter
D: sphincter of boyden
E: sphincter of oddi
lower esophageal sphincter
what aspects of GI motility do we have some concious control over?
A: secondary peristalsis
B: swallowing
C: gastric emptying
D: defecation
E: b and d
both the defecation and swallowing reflexes are under coluntary control
where do exocrine gland cells secrete substances?
into the lumen of the GI tract
where do endocrine gland cells secrete substances?
directly into the blood stream
what do duct cells secrete? (exocrine)
aqueous sodium bicarbonate solution
what do acinar cells secrete? (exocrine)
digestive enzymes
what are the cells of the endocrine portion of the pancreas?
islets of langerhans
where are digestive juices secreted?
lumen by exocrine gland cells
where are GI hormones secreted?
blood by endocrine cells
what are the 5 digestive juices that are secreted into the alimentary canal?
saliva
gastric juice
pancreatic juice
intestinal juice
bile
where is saliva produced?
salivary glands
where is gastric juice produced?
gastric mucosa
where is pancreatic juice produced?
exocrine pancreas
where is intestinal juices produced?
intestinal mucosa
where is bile produced?
hepatic gland
what are the functions of saliva?
begins digestion of carbs via saliva amylase
facilitates swallowing and speech
lysozyme is antibacterial
rinses out the mouth after eating
serves as a solvent
what are the parotid glands?
secrete 20% of saliva. contains amylase to begin starch digestion
waht are submandibular glands?
secrete a mixture of serous fluid and mucus. 65-70% of saliva produced here
what are sublingual glands?
mainly produce mucus and about 5% saliva
what are the 3 salivary glands?
parotid
submandibular
sublingual
what secretion is the only digestive secretion under neural control?
salivary secretion
what does the parasympathetic system stimulate in the salivary glands?
watery saliva rich in enzymes
what does the sympathetic system stimulate in the salivary glands?
thick saliva rich in mucus
where is the salivary center?
medulla
what are the contents of gastric juices?
water, HCl, electrolytes, mucus, pepsins, and protein
is gastric juice acidic or basic?
highly acidic
what are the functions of gastric juices?
activates pepsinogen to become pepsin
aids in breakdown of connective tissue and muscle fibers
denatures protein
kills microorganisms ingested with food
what are the 3 phases of gastric secretion?
cephalic phase
gastric phase
intestinal phase
what is the cephalic phase?
- vagus nerve stimulates gastric secretion even before food is swallowed
- thinking, tasting, smelling, chewing, swallowing
- increases gastric secretion by vagal nerve activity
what is the gastric phase?
- food stretches the stomach and activates myenteric and vagovagal reflexes. These reflexes stimulate gastric secretion. Histamine and gastrin also stimulate acid and enzyme secretion
- begins when food actually reaches the stomach
- presence of protein, stomach distension, ceffeine and alcohol increase gastric secretion
what is the intestinal phase?
- intestinal gastrin breifly stimulates the stomach, but then secretin, CCK and the enterogastric reflex inhibit gastric secretion and motility while the duodenum process the chyme already in it. sympathetic nerve fibers suppresses gastric activity, while vagal stimulation of the stomach
- fat, acid, hypertonicity or distension in the duodenum inhibit gastric secretions
- the intestinal phase shuts off the flow of gastric juices when chyme begins to be emptied into the small intestine
the gastric mucosa is arranged into invaginated ________
gastric pits
what do mucous cells produce?
what are their purpose?
(exocrine)
a thin, watery mucus
protect mucosa
what do epithelial cells produce?
a thick, viscous alkaline mucus over the surface of the mucosa\
what do parietal cells produce?
what are their purpose?
produce both HCl and intrinsic factor
activates pepsinogen, breaks down connective tissue, denatures proteins, kills microorganisms
what do cheif cells produce?
what are their purpose?
pepsinogen
when activated begins protein digestion
what can compromise the protective mucus in the stomac?
H. pylori and overuse of NSAIDs
what happens when the mucous layer in the stomach is compromised?
pepsin and HCl causes extensive damage to the stomach wall and creates a stomach ulcer
the pancreas is a mixed gland, it contains both ____ and ____ glands
exocrine and endocrine
what do islet cells in the pancreas secrete?
insulin and glucagon
what are the components of the pancreatic juices secreted by the exocrine pancreas?
- the pancreatic enzymes secreted by the acinar cells ( trypsinogen, amylase, lipase)
- aqueous alkaline solution secreted by duct cells
what does the biliary system include?
the liver, gallbladded and associated ducts
what is the secretion of the small intestine?
an aquesous salt and mucus solution (succus entericus)
increases in response to presence of chyme
what is the secretion of the large intestine?
colonic secretion of an alkaline mucus solution to protect the large intestine from injury, facilitate feces passage and neutralize irritating acids
what does cystic fibrosis impair?
digestive secretions
what does CFTR mutation impair?
chloride transport
what is CFTR involved in?
exocrine gland secretions
what do G cells secrete?
where are G cells found?
gastrin
found only in the PGA gastric pits
what do enterochromaffin-like cells secrete?
histamine
what do D cells secrete?
somatostatin in response to acid
what is gastrin?
- stimulated by protein in the stomach
- increases HCl and pepsinogen secretion
- enhances gastric motility, stimulates ileal motility, relaxes the ileocecal sphincter and induces mass movements in the colon
- gastrin secretion is inhibited by an accumulation of acid in the stomach and duodenal lumen
what is ghrelin?
- produced by endocrine cells of stomach
- “hunger hormone”
- increases food intaake
- increases gastric motility and gastric acid secretion in preparation for food intake
what is secretin?
- stimulated by acid in the duodenum
- inhibits gastric emptying to prevent further acid from entering the duodenum
- inhibits gastric secretion to reduce the amount of acid being produced
- stimulates pancreatic and liver sodium bicarb secretion which neutralizes duodenum acid
what is CCK?
stimulated by fat and other nutrients in the duodenum
- inhibits gastric motility and secretion
- stimulates pancreatic acinar cells to secrete pancreatic enzymes
- causes contraction of the gallbladder to empty bile into the duodenum
- important regulator of food intake
what is motilin?
- secreted by endocrine M cells within crypts of the small intestine
- motilin released into the general circulation during fasting period or in between meals
- inhibited by feeding
- increases motility
what is GLP-1?
- secreted by L cells in response to nutrients in the lumen of the small intesine
- promotes insulin sensitivity and insulin secretion from the pancrease
- inhibits gastric secretion and gastric emptying in the stomach
- increases satiety. thereby reducing food intake
digestive juices are secreted into the lumen of the digestive tract by;
A: myenteric plexus gland cells
B: endocrine gland cells
C: exocrine gland cells
D: parathyroid gland cells
E: hormonal gland cells
exocrine
what is not a function of saliva?
A: serves as a solvent for molecules
B: begins digestion of proteins via salivary lipase
C: facilitates swallowing and aids speech
D: antibacterial actions via lysozyme
E: rinses out mount after eating
B
which of the following GI hormones exter stimulatory effects of digestive tract effector cells?
A: secretin
B: aldosterone
C: GLP-1
D: all of the baove
E: none of the above
none
what is absorption?
the process by which the products of digestion are absorbed by the blood to be supplied to the rest of the body
where does most absorption take place?
small intestine
what part of the GI absorbs nonpolar substances such as asprin and alcohol?
the stomach
does every type of food take the same amount of time to digest?
no
carbs empty the fastest
next is high protein foods
high TAG content foods take the longest
what are villi?
small finger-like projections that protrude from the mucosal lining to increase nutrient absorption surface area
what are microvilli?
hair-like projections that aid in absorption of nutrients
where are villi and microvilli located?
intestines
what 4 cells are housed in the epithelial cell layer?
enterocytes
brush border
goblet cells
crypt cells
what are enterocytes?
absorptive cells
what is brush border?
microvilli-covered cells expressing digestive enzymes
what are goblet cells?
mucus secretory cells
what are crypt cells?
epithelial stem cell whoch replenish dead cells (approx. every 4 days)
what are the 4 different ways nutrients are absorbed?
co-transport
facilitated diffusion
osmosis
simple diffusion
most carbs in diets are ____
polysaccharides
where do starch and cellulose come from?
plant products
where does glycogen come from?
animal products
can cellulose be digested?
no
what are disaccharide examples?
sucrose and lactose
what are monosaccharide examples?
glucose and fructose
what is the absorbable form of carbs?
monosaccharides
what do polysaccharides get digested by?
salivary and pancreatic amylase
where does salivary amylase get inactivated?
in the stomach by acids
amylases reduce polysaccharides to ___
maltose or limit dextrins
what enzymes complete digestions of carbs to monosaccharides?
brush border enzymes bound to apical membranes of absorptive cells lining the small intestine
what enzymes break down limit dextrins and straight chain glucose polymers?
dextrinase and glucoamylase
what breaks down sucrose into glucose and frutose?
sucrase
what breaks down lactose into glucose and galactose?
lactase
what breaks down maltose into glucose molecules?
maltase
how is fructose absorbed?
facilitated diffusion
how does glucose and galactose enter epithelial cells?
active cotransport with sodium
what transporter is utilized in sports drinks to provide energy to high performance athletes?
Na+ linked glucose transporter
how do monosaccharides enter the blood stream?
through facillitated diffusion across the basolateral membrane
the in active/ storage form of digestive enzymes are called ___
zymogens
how are zymogens activated?
proteolytic activation
where is pepsinogen secreted and how is it activated?
pepsin - active form
secreted by cheif cells
activated by hydrogen ions from parietal cells
the pancreas secretes more zymogens such as…
trypsin and chymotripsin
the brush borded houses the enzyme _____ which converts trypsinogen to trypsin which activates other zymogens.
enterokinase
what do exopeptidases do?
digest small peptides into amino acids
which enzymes are endopeptidases?
pepsin, trypsin, chymotrypsin and enterokinase
which enzymes are exopeptidases?
carboxypeptidase and aminopeptidase
are small peptides and mino acids transported via active or simple transport?
active - requires energy
most dietary lipids are ___
TAG
lipids are ___ so they do not mix with the rest of the stomachs contents
hydrophobic
what is the purpose of bile salts?
facilitates the action of digestive enzymes by emulsifying fat globules into smaller droplets
where are bile salts secreted?
bile
lingual lipase, gastric lipase and pancreatic lipase digest ___
lipids
when monoglycerides and fatty acids are liberated they associate with bile acids and other lipids to form___
micelles
what form are vitamins consumed in?
the absorptive form thus do not undergo digestion
what vitamins are absorbed with lipids and thus bile salts help in their absorption?
hydrophobic or fat soluble
how are water soluble vitamins absorbed?
active transport ot facilitated diffusion
how does mineral absorption usually occur?
active transport
how much sodium is usually secreted vs consumed?
S: 80%
C: 20%
how is calcium absorption regulated?
based on bodily need
enhanced by 1, 25 Vitamin D3 which increases calcium-binding portein
which 2 ways can iron be absorbed?
reduced inorganic (2+)
and bound to heme (3+)
water absorption is ___ and is driven by ___
passive
osmotic gradient
2L of water a day come from _____
7L of water a day come from ___
consumption
secretions from stomach, intestine and accesory glands
which organ is responsible for absorbing most of the nutrients in our diet?
A: pancreas
B: large intestine
C: stomach
D: small intestine
E: liver
small intestine
what type of nutrient gets packaged into chylomicrons?
A: Vitamin A
B: calcium
C: monosaccharides
D: lipids
E: a and d
a and d
what type of enzyme would cleave in the middle of a polypeptide chain?
A: zymogen
B: amylase
C: endopeptidases
D: aminopeptidases
E: carboxypeptidases
endopeptidases
