Digestive System 1 Flashcards
main functions of digestive system
- take materials into body
- tube mouth to anus
- take stuff from tubes, bring into body, break down
alimentary canal
continuous, muscular tube of digestive system
organs (in order) of alimentary canal
mouth pharynx esophagus stomach small intestine large intestine anus
accessory organs of digestive system
teeth, tongue, salivary glands
6 actions of digestive system
ingestion propulsion chemical digestion absorption mechanical digestion defecation
ingestion
bringing food into system
propulsion
moving food through system
2 types: deglutition and peristalsis
deglutition
swallowing
a voluntary, initial process
peristalsis
wave-like smooth muscle contractions
involuntary
chemical digestion
enzymatic breakdown of stuff brought into digestive system
begins in mouth, ends in small intestine
absorption
absorbing building blocks (monomers) of foods we eat
occurs in distal parts of small intestine out of lumen
reclaim H2O in large intestine
from what do we reclaim water in the large intestine?
mucus, gastric juice, and enzymes
mechanical digestion
physical breakdown; making food smaller increases its surface area
includes mastication, mixing, and segmentation
mastication
chewing
mixing
mixing bolus/chyme with saliva
like when stomach is churning
segmentation
kneading tube of alimentary canal
mixing and propulsion
back and forth movement
defecation
elimination of wastes from large intestine
wastes formed in large intestine exit body through anus
3 ways we control digestive system
sensors
nerve plexuses
hormones
how do hormones control digestive system
whatever sensors were stimulated can cause release/inhibition of certain hormones
how do sensors control digestive system
sensory receptors are deigned to detect stimuli
stimuli include osmolarity, pH, specific nutrients, and stretch
sensory receptors then send nervous impulses through nerve plexuses
stimuli for sensory receptors of digestive system
osmolarity
pH
specific nutrients (carbs, proteins, lipids)
stretch (can be on or off switch)
short/intrinsic nerve plexus
nervous impulse exchange that occurs entirely within GI tract
long/extrinsic nerve plexus
nervous impulse exchange that involves CNS
sensors in GI tract sending signal to brain to activate something other than GI tract is which type of nerve plexus?
long/extrinsic
stimulus in part of body other than GI tract that changes activity of GI tract is which type of nerve plexus?
long/extrinsic
mesentary
specialized peritoneal component in digestive tract
2 sided serous membrane that anchors abdominopelvic organs to back wall of abdominopelvic cavity
peritoneum
abdominopelvic serous membrane
“retroperitoneal” means
this organ is not anchored by mesentery
because its behind peritoneum
tunics of alimentary canal
mucosa
submucosa
muscular externa
serosa
mucosa
superficial layer
epithelial tissue
submucosa
deep to mucosa
dense irregular connective tissue
where all blood vessels and nerves go
where we get nutrients into circulatory system
muscular externa
deep to submucosa muscular layer (smooth muscle; involuntary) 2 layers: circular layer, longitudinal layer ^ their combined interaction moves things through digestive system
circular layer of muscular externa
fibers run sideways in a ring around lumen
more superficial than longitudinal layer
when it contracts, it changes the diameter (constricts) of lumen
longitudinal layer of muscularis externa
fibers run vertically in tube
when it contracts, the tube shortens
serosa
deepest layer of alimentary canal
visceral peritoneum
what type of tissue is pharynx made of
squamous epithelium
what type of tissue is the organs at esophagus and beyond made of?
columnar epithelium
this includes goblet cells
tunics for organs above diaphragm
mucosa
submucosa
adventitia (replaces muscular and serosa)
tunics for below diaphragm
mucosa
submucosa
muscularis
serosa
goblet cells secrete ____
mucus
functions of mucus
secretes enzymes
secretes hormones
protects alimentary canal and its blood vessels from abrasive food
where are enzymes usually produced in alimentary canal?
produced by glands in submucosa
needs to get into lumen to digest, so it passes through mucosa
where are hormones produced in alimentary canal?
produced in submucosal layers
enteric neurons
intrinsic nerve plexus nerves found in wall of alimentary canal
submucosal or myenteric
submucosal nerve plexuses
sensory receptors in submucosa that detect stretch, chemical composition, or pH
once activated, they send signals to whatever part of digestive system to make that work
function in secretion
why do submucosal nerve plexuses exist
because theres no nerve fibers in mucosa
myenteric nerve plexuses
enteric neurons located between 2 layers of muscle in muscular externa function in motility
motility action of enteric neurons
activation of myenteric nerve plexus causes muscle contraction
secretion action of enteric neurons
activation of submucosal nerve plexus causes things like secretions of enzymes/hormones (glandular action)
t/f motility and secretion actions of enteric neurons cannot happen at the same time
false
they can both happen at same time
oral/buccal cavity
entry to alimentary canal
connected to pharynx so we can breathe and eat
involved with ingestion, propulsion, mechanical, and chemical digestion
only part of digestive system involved with ingestion
oral/buccal cavity
components (accessory organs) of oral/buccal cavity
palate
tongue (papillae)
salivary glands
teeth
palate
roof of buccal cavity and floor of nasal cavity
includes uvula
uvula
extension off back of soft palate
blocks nasopharynx when swallowing
tongue
functions in swallowing (deglutition)
moves food around oral cavity- causes mixing
creates bolus
includes diff types of papillae
bolus
foodstuff ball that we swallow
types papillae
fungiform
circumvallate
filiform
fungiform papillae
contain taste buds
sensory component
circumvallate papillae
make V in back of tongue
have some taste buds and chemoceptors
filiform papillae
bumps on top
give tongue grip
salivary glands
parotid
sublingual
submandibular
parotid salivary gland
far back in oral cavity
made of serous cells, which produce enzymes
enzyme-producing salivary gland
parotid
sublingual salivary gland
under tongue
made of mucous cells (make mucus)
help lubricate
submandibular salivary glands
somewhere between parotid and sublingual glands
made of both mucus and serous cells- produces both secretions
how much saliva do we produce per day
1-1.5L
actions of saliva
cleans mouth
dissolves food to make it biologically active
moistens food- helps form bolus
enzyme in saliva (amylase) starts starch digestion in mouth
pH of saliva
slightly acidic (6.75-7)
components of saliva
water electrolytes amylase mucin lysosome IgA metabolic wastes
salivary amylase
enzyme that starts starch breakdown in mouth
mucin
protein that gives mucus its slipperiness to help move food
immune components of saliva
IgA and lysosome
metabolic wastes in saliva
we produce things like urea/uric acid when breaking down proteins
get rid of these wastes through defacation
control of salivation
parasympathetic nervous stimulation controls saliva production
chemoreceptors and pressure receptors send signal to ANS to produce saliva
why do we get cottonmouth when nervous
sympathetic nervous system shuts off saliva production
teeth are involved in which digestion process?
mastication
2 sets of teeth in humans
primary teeth
permanent teeth
primary teeth
aka vesiduous/baby teeth
20 total- don’t all appear at same time
we have all by 2 years old
they will fall out
we have all primary teeth by how old?
2
permanent teeth
32 total
replace primary teeth
dont necessarily last whole life- but will not be replaced
types of teeth
incisors
cuspid
bicuspid
molars (incl 18 yr molar)
incisors
front 4 teeth
“shearing teeth”- allow us to cut/pull things
cuspid
one on each side of incisors
“canine/fang tooth”- for piercing/grabbing hold of things
bicuspids/premolars
2 on each side of cuspids
for shearing/cutting
molars
last 3 teeth on each side
flat teeth
for grinding and breaking up seeds/plants
3rd molar/wisdom tooth/18 yr molar
last tooth to come in
in evolution, human jaw has shrunk
often doesn’t emerge at all or emerges not in line with other teeth
often removed
“carnivorous teeth”
cuspids and bicuspids
components of tooth structure
crown root neck enamel dentine pulp root canal cementum
crown of tooth
part of tooth above gumline
gingiva
gumline
root of tooth
part of tooth below gumline
embedded in bone in jaw
neck of tooth
transition part between crown and root
enamel
hard substance covering crown of tooth
strengthens tooth; only on crown
pulp of tooth
soft tissue deep to dentine
contains blood vessels and nerves
root canal
pulp that extends into root
dentine
substance deep to enamel
in root and crown
cementum
connective tissue
glues tooth into socket
digestive function of pharynx
propulsion
which parts of pharynx are pathways for food?
oropharynx and laryngopharynx
when swallowing, epiglottis is _____
down!
covers trachea so food only goes through esophagus
esophagus
muscular tube involved in propulsion; sits just behind trachea
includes upper esophageal sphincter and gastroesophageal sphincter
upper esophageal sphincter and gastroesophageal sphincter
prevent food from going wrong way
not true sphincters
main steps of deglutition
- food compacted into bolus
- buccal phase (voluntary)
- pharyngeal-esophageal phase (involuntary)
buccal phase of deglutition
voluntary part
- tip of tongue placed against hard palate
- tongue contracts to force bolus into oropharynx
- bolus stimulates tactile receptors
t/f you cannot swallow with your tongue against roof of mouth, you need something in between
true
that is usually bolus
pharyngeal-esophageal phase of deglutition
involuntary part
1. tactile receptors stimulate medulla and pons
2. motor impulses (parasympathetic) sent to muscles in pharynx and esophagus
3. peristalsis moves bolus to stomach
(in stomach, bolus is liquified and turned into chyme)
digestion events that occur in stomach
propulsion
mechanical digestion
chemical digestion of proteins
2 types of action that stomach can engage in
secreting gastric juice
muscular contraction
cardia
part of stomach that’s connected to esophagus
fundus
part of stomach above direct path from esophagus to body
pylorus
portion where stomach constricts again
cardiac sphincter
kink in cardia created from distention/bending of stomach when it fills
prevents stuff from going back up
not true valve
pyloric sphincter
regulates emptying of stomach
true valve
connects to duodenum
muscular layers of stomach
circular
longitudinal
oblique
rugae
folds all over lining of stomach to increase surface area
flatten to increase volume of stomach
volume of empty/relaxed stomach
50 mL
volume of stretched stomach
~4L
stomach cells
goblet cells mucous neck cells parietal cells chief cells enteroendocrine cells
gastric glands are located __
at base of gastric pits of stomach
goblet cells
found in mucosa, which lines gastric pits and stomach wall
produce mucus
mucous neck cells
first cells of gastric glands
produce slightly acidic mucus
parietal cells
embedded within mucus neck cells
produce HCl and Intrinsic factor
HCl
digestive component secretion of parietal cells
pH= 2
activates pepsinogen to become pepsin
intrinsic factor
glycoprotein required by small intestine to absorb B12
B12 needed to make RBCs and carry O2
chief cells
cells in stomach that produce pepsinogen (inactive form of pepsin)
enteroendocrine cells
cells in stomach that release gastrin
gastrin regulates activity of others parts of digestive tract
at way bottom of gastric gland
aka G cells
G cells are also known as
enteroendocrine cells
phases of gastric secretion
cephalic (reflex) phase
gastric phase
intestinal phase
cephalic (reflex) phase of gastric secretion
first thing that can cause stomach to activate
acquired/learned
if we THINK about eating foods we like, stomach starts to activate and secrete
before food arrives to stomach
long reflex arc
t/f cephalic reflex phase occurs for any foods, whether we like them or not
false
it only happens with foods we like
gastric phase of gastric secretion
begins once food starts arriving in stomach
several different stimuli occur once food is in stomach
these stimuli stimulate enteroendocrine cells to start producing gastrin
gastrin activates cells in gastric gland to start secreting things
stimuli in stomach during gastric phase of secretion
stretch, change (elevation) in pH, or presence of proteins
stretch stimulus in gastric phase of secretion
- food causes stretch in wall of stomach
- sends signal to ANS
- ANS sends parasympathetic impulses back
- causes release of acetylcholine
- acetylcholine stimulates gastric gland to start secreting
pH stimulus in gastric phase of secretion
stomach pH is very low (2), saliva pH is closer to 7
body senses this change once saliva reaches stomach
feedback loop of gastric phase of gastric secretion
increased pH activates gastrin secretion gastrin activates gastric gland cells (like parietal cells) parietal cells produce HCl HCl makes pH go down low pH shuts off gastrin secretion
intestinal phase of gastric secretion
stomach is still active as food leaves stomach entering small intestine
2 parts: excitatory then inhibitory
excitatory intestinal phase
arrival of some material in small intestine continues to activate stomach
basically stomach “finishing up” its job
inhibitory intestinal phase
after excitatory part has gone for a while, small intestine says it is time to start slowing down
bc stomach is probably getting pretty empty, so we don’t want to digest the stomach itself
contents from stomach trickle into small intestine _____ (vol) at a time
3 mL
enterogastric reflex
small intestine shutting off stomach by inhibiting nervous stimulation
continued stretch on small intestine inhibits parasympathetic activity and activated sympathetic activity
causes pyloric sphincter to squeeze shut
what prevents us from digesting our own stomach by HCl and pepsinogen?
mucosal barrier
mucosal barrier components
bicarbonate-rich mucus
tight junctions in mucosal epithelium
HCl-impermeable plasma membranes in gastric gland cells
undifferentiated stem cells at junction of gastric pits and gastric glands
bicarbonate-rich mucus of mucosal barrier
produced by goblet cells
buffers pH at lining of stomach (not secreting into stomach)
how do tight junctions in mucosal epithelium contribute to mucosal barrier
impermeable junctions mean no acid can slip in between cells to get into underlying tissue
how do HCl-impermeable plasma membranes in gastric gland cells contribute to mucosal barrier
so that the acid that gastric gland cells are producing can only go into gastric pit; cannot go to other side
how do undifferentiated stem cells at junction of gastric pits/glands contribute to mucosal barrier
gastric pits and glands in lining of stomach need to constantly replace cells
entire wall of stomach is replaced every 3-6 days
2 types of gastric filling
receptive relaxation
adaptive relaxation
t/f stomach has ability to change shape when it’s filling
true
receptive relaxation
thinking about food can make stomach start secreting and make it change shape even before food has gotten there
no stretch has occurred yet! increased size is due to rug flattening out
adaptive relaxation
after food has started arriving in stomach
rug continue to flatten out
stretch starts to occur only after we have ~ 1 L of food in stomach
^ this stretch causes signals to brain to stomach to start secreting
gastric contractions are mostly what kind?
longitudinal contractions for propulsion
interstitial cells of Cajal
autorhythmic cells of stomach (pacemaker of stomach)
within longitudinal layer
t/f anything that increases production of HCl also increases rate of muscular contractions in stomach
true
includes stretch, proteins, and increased pH
basic electrical rhythm of gastric contraction
longitudinal cells of stomach contain some autorhythmic cells (interstitial cells of Cajal)
creates basic rhythm of contraction, which happens about 3x per minute
autorhythmic cells
cells that can depolarize because of leaky membranes
reasons for slow release of chyme from stomach
increases efficiency of digestion
prevents giant wave of low pH from getting into stomach
stomach starts to empty about ___ after you’ve had your meal
4 hours
process of gastric emptying
- chyme enters duodenum
- stretch and chemoreceptors of small intestine activated
- enterogastric or enterogastrone reflexes initiated
- gastric activity reduced
- pyloric contractions reduced
- duodenal filling stopped
enterogastrone
hormone of small intestine that inhibits gastric secretion
what happens during gastric emptying? like how is this chyme actually leaving stomach?
every time we get contraction, pressure pushing against pyloric sphincter increases
with each contraction, 30 mL of chyme leaves stomach and goes to duodenum
BUT as “squeeze” relaxes, 27 mL goes back into stomach
only 3 mL escape stomach with each muscular contraction
t/f vomiting/emesis is reverse peristalsis
false!
peristalsis only moves in one direction (down)
vomiting/regurgitation/emesis
something enters stomach that causes too much stretch or irritation
excessive stress/irritation stimulates abdominal muscles and diaphragm to contract
this contraction puts lots of pressure on stomach- contents are forced up through esophagus
continues as long as there is stretch/irritation
projectile vomiting
when the pressure on stomach from contraction of abdominal muscles and diaphragm is very intense
why do we have dry heaving
emesis continues as long as there is stretch/irritation
even with no food left, there may still be irritation
as this continues, contractions can be so hard you pull up bile from small intestine
major digestive organ of body
small intestine
functions of small intestine
chemical digestion of every class of macromolecule
absorption once everything is digested
propulsion through alimentary canal
length of small intestine
8-13 ft
runs from pyloric sphincter to ileocecal valve
when we die how long is out small intestine
like 20 ft
how much intestinal juice does small intestine produce per day
1 to 2 liters
production of intestinal juice in small intestine stimulated by _______
arrival of acidic chyme
function of intestinal juice
slightly alkaline, so it neutralizes pH and shuts off/denatures pepsin
digestion occurs mostly in _____
duodenum
absorption of nutrients happens mostly in _____
jejunum
subdivisions of small intestine
duodenum
jejunum
ileum
duodenum
first 10 inches of small intestine
contains hepatopancreatic ampulla
jejunum
middle 8 ft of small intestine
ileum
last part of small intestine
ends with ileocecal valve
structural modifications of small intestine
length
plicae circulares
villi
microvilli
structural modification of small intestine: length
long length gives small intestine increased surface area
surface area ~ 200 m^2
plicae circulares
aka spiral valve
folds in mucosa and submucosa of lining of small intestine
make incoming chyme spiral while going through small intestine
–slows liquid down
–increases contact of liquid with wall to increase efficiency
villi of small intestine
fingerlike projections of mucosa that increase surface area
help increase contact with chyme to break down its contents
microvilli of small intestine
within modified plasma membrane of epithelial cells of villi
increases surface area further
why lining of small intestine is called brush border
brush border
lining of small intestine
because of the villi and microvilli
chyme leaving small intestine to go into large intestine is ______; what would happen if we let it all go at once?
hypertonic; significant water loss
factors of small intestine emptying
gastroileal reflex
gastrin
pressure
gastroileal reflex
linkage between activity (action/motility) of stomach and ileocecal valve
signal from stomach tells small intestine to start releasing contents
causes segmentation-like contractions within small intestine
contractions caused by gastroileal reflex trigger ____ in small intestine
segmentation
how does gastrin affect small intestine emptying
activates stomach and small intestine
relaxes (opens) ileocecal valve
how does pressure affect emptying of small intestine
as chyme from small intestine is released into cecum, it starts to accumulate
this causes stretch and back pressure on ileocecal valve to close it
largest internal organ in body
liver
major function of liver
process blood (recycle RBCs and turn hemoglobin into bilirubin and amino acids)
byproduct of major function of liver
bile production!
functions of bile
acts as emulsifier
breaks big fat globs into smaller fat globs –> increases surface area
basically causes mechanical digestion of fats to occur
t/f bile is an enzyme
false!
it does not chemically break anything down
bile composition
water bile salts bile pigments- bilirubin, urobilinogen cholesterol neutral fats phospholipids electrolytes
lobes of liver
4: right, left, caudate, quadrate
falciform ligament
attaches liver to muscular diaphragm and separates R/L lobes
bile salts
made of salts from breakdown of blood cells and bilirubin/biliverdin
what’s actually doing the emulsifying
urobilinogen
when bile is secreted into digestive tract, bilirubin is converted into urobilinogen
brown color
common hepatic duct
from liver to bile duct
right and left hepatic ducts merge to form common hepatic duct
cystic duct
brings bile from gallbladder to common hepatic duct
bile duct
from common hepatic duct to hepatopancreatic ampulla
takes bile from liver and gallbladder to small intestine
hepatopancreatic ampulla is also known as
ampulla of vater
pancreatic duct
connects to bile duct
brings secretions from pancreas
hepatopancreatic duct is only open when?
at mealtime
functions of gallbladder
store bile
concentrate bile
how does the gallbladder concentrate bile?
bile is mostly water, gallbladder reclaims some of the water
gallstones
when gallbladder concentrates bile so much that it crystallizes
get stuck in ducts, cause pain and pressure
bile storage
- hepatopancreatic sphincter closed when not digesting
- liver continually produces bile
- bile backs up cystic duct into gallbladder
bile release
- fatty chyme entering duodenum stimulates intestine to produce cholescystokinin (CCK)
- CCK causes parasympathetic nervous impulses to promote gallbladder contraction to squeeze out bile
- CCK also relaxes hepatopancreatic sphincter
endocrine function of pancreas
insulin and glucagon
exocrine function of pancreas
produce pancreatic juice
goes into pancreatic duct, connects to bile duct, and released at hepatopancreatic ampulla
pancreatic juice components
water
enzymes
bicarbonate
bicarbonate component of pancreatic juice
secreted by cells of pancreatic duct
pH > 8
helps neutralize chyme so enzymes can function
enzyme component of pancreatic juice
from exocrine cells of pancreas enzymes for every class of macromolecule
protease enzymes of pancreatic juice
break down proteins
secreted into duct in inactive form; activated in duodenum
trypsin, carboxypeptidase, and chymotrypsin
other enzymes (not proteases) of pancreatic juice
secreted in active form
amylase (starches), lipase (lipids), nuclease (nucleic acids)
trypsin
protease enzyme in pancreatic juice
inactive form trypsinogen is activated by enterokinase (enteropeptase)
where is enterokinase produced
brush border of SI
carboxypeptidase
protease enzyme in pancreatic juice
inactive form procarboxypeptidase is activated by trypsin
chymotrypsin
protease enzyme in pancreatic juice
inactive form chymotrypsinogen is activated by trypsin
components of pancreatic secretion control
secretin
CCK
parasympathetic impulses
how does secretin help control pancreatic secretion
stimulates cells of pancreatic duct to start producing bicarbonate
how does CCK help control pancreatic secretion
opens hepatopancreatic ampulla
stimulates production of enzymes
activates some exocrine cells to start producing/secreting enzymes
how do parasympathetic impulses help control pancreatic secretion
stimulates exocrine cells or duct cells to start producing/secreting
acidic chyme stimulates intestine to produce _____, which stimulates production of bicarbonate and lowers acidity of chyme
secretin
presence of fats/proteins stimulates wall of intestine to produce ___, which stimulates production of enzymes to break down proteins and fats
CCK
digestive actions of large intestine
absorption (mostly water)
propulsion
elimination
length of large intestine
9 feet
segments of large intestine in order
cecum ascending colon transverse colon descending colon sigmoid colon rectum/rectal canal anus
rectal valve
“bends” in large intestine
separates solids and gases
allow gases to pass at higher rate than solids
internal anal sphincter
closest to rectum
smooth muscle; involuntary
external anal sphincter
outside of internal sphincter
skeletal muscle
voluntary
vermiform appendix
appendage that hangs off cecum
no longer any function (possibly used to function in cellulose digestion)
harbors microbiota from digestive tract
becomes trap- things we ate plug opening and cause appendicitis
appendicitis
something plugs opening of appendix
appendix becomes inflamed/swollen and loses blood supply
caused by tiny seeds, or (most common) gum, or (2nd most common) opiates
haustra
saclike puckering that divide large intestine
taenia coli
bands of smooth muscle from muscular that wrap around large intestine and create haustra
epiploic appendages
deposits of adipose tissue accumulated along large intestine
no known function
intestinal bacteria functions
ferment indigestible carbs
synthesize B vitamins
synthesize K vitamins
intestinal bacteria fermentation of indigestible carbs
produces gas rich in dimethylsulfide (smelly)
intestinal bacteria synthesis of B vitamins
we get all the B vitamins we need in diet, bacteria just add a little more
absorbed with water thats being reclaimed
intestinal bacteria synthesis of K vitamins
we get enough K vitamins from healthy diet, this just adds more
vitamin K used by liver to make clotting protein
motility of large intestine
haustral contractions
mass movements
haustral contractions
activated by stretch caused by arrival of chyme in large intestine
one haustra contracts and slowly moves contents to next haustra, etc
every 30 minutes all day
basically a form of segmentation
mass movements
arrival of food in stomach causes us to push previous meal from large intestine
happens 3-4 times per day; usually triggered by meal
defecation reflex
- mass movements cause stretch on large intestine wall
- stretch triggers parasympathetic stimulation of sigmoid colon and rectum, and inhibits anal sphincters
- external anal sphincter under voluntary control still (can ‘hold it’)
- valsalva’s maneuver assists emptying
valsalva’s maneuver
“pushing”
contracting diaphragm and intercostal muscles to help poop
what makes up feces
undigested food residue
sloughed off epithelial cells from ileum and large intestine
bacteria from digestive tract
tiny bit of water
constipation
if too much water is reclaimed
diarrhea
if not enough water is reclaimed
