digestion structures and function Flashcards
what are parietal cells stimulated by
gastrin
what are D cells inhibited by
cephalic stage
three regions of the small intestine
deudenum
jujunum
ileum
what is segmentation
slow contractions of circular muscles
drives contents back and from mixing the chyme with digestive enzymes
strength of contraction regulated by food content
what is peristalsis
rhymic propulsive movements to move chyme along small intestine
mixes chyme with digestive enzymes
where are peristalsis contractions stronger?
duodenum to keep food going in right direction
Key histological features of the small intestine
folds called pilicae circulares adding surface area
villi and brush boarder
where does most of the absorption occur
jejunum
were are there the most plicase circulares
jejunum
lowest amount in duedenum
what are columar epitheial cells used for?
nutrient and electrolyte absorption
what is the crypt of lieberkuhn
bit at the bottom of the vili
no enzymes here but used for secretion
goblet cells
stem cells at base
what is a paneth cell?
synthesis and secretion of antimicrobial peptides and proteins
what is a goblet cell
secretion of mucin, major part of mucus
what is an undifferentiated crypt cell used for
proliferates to replace lost enterocytes
what is the fuction of enteric endocrine cells
secretion of CCK, gastrin, secretin and glucose-dependent insulinotrophic
what can be secreted by the small intestine?
mucus
water
bicarbonate
immune functions
why is mucus needed in the small intestine
protection from acids and proteases
most needed in the duodenum as lots of digestion is here and chyme is acidic
why is water secreted from the crypt/ small intestine
made in th cryt
makes mucus runny for movemnt
functional envronmnt for enzymes
where does bicarbonate get secreted from
brunners glands
role of bicarbonate
protects from acids
optimal conditions for enzymes to work in
what immune function secretions are made in the small intestine
chym is ner sterile due to acid
lots of bacteria are found in large intestin howver
antibacterial enzymes are secreted to help
where ar antimicrobials secreted?
peyers patch
paneth cells
what is the peyers patch
only found in the ileum
small masses of lymphatic tissue
boarder control for intestin and microbes
what is a brunner gland
found in the duedenum
releases bicarbonate rich alkaline fluid containing mucus
they protrude the lining of the duodenum
how is the peyers patch seen in the small intestine
small circul pumps of tissues in the cell lining
diffrnce between parts of the small intetine
duedenum: plicase and brunners glands
jejunum: plicae, more folds
ilum: vili, peyers patch
where does CCK come from
I cells of the duodenum and jejunum
where does secretin come from
S cells of small intestine
where does somatostatin come from
D cells of the stomach and duodenum
where does GIP come from
gastric inhibitory peptide
K cells in duodenum and jejunum
what does secretin do>
inhibits HCL/gastric juice
stimulates bicarbonate
neutralises the acid
what is the function of CCK
stops G cells making gastrin and stops chief and parietal cells
stimulates the pancreas to release digetive enzymes and makes the gall blader contract to digest food
what is the function of scretin
stops gastrin
neutralises acid making optimal conditions for enzymes
what stimulates secretin
pH drop
where is stomatastin made?
D cells
what does stomatastin do/
stops gastrin firther
inhibits enzymes by the pancreas
stops everything at the end
what is the gall bladers function
bile storage and concentration
what controls the release of bile and pancreatic juice
sphincters
what type of organ is the pancreas
exocrine gland
acessory digestive organ
what does the pancreas do
rich in bicarbonate
neutralises the gastric contents that enter the small intestine
digests the carbohydrates, proteins and fats
where does glucagon and insulin come from
glucagon comes from alpha cells
insulin beta cell
what is an acinar
The pancreatic acinar cell is the functional unit of the exocrine pancreas. It synthesizes, stores, and secretes digestive enzymes.
what are found in acinar cells
lots of RER and ribosomes
lots of proteins that are made and packages for ecretion
what prevents autodigestion in the acinar cells
granules are acidic so not yet activated and require alkali for this
they are transported in acidic capsule then released and they can work
what is a zymogen
digestive enzyme in the inactive form
prevents autodigetion
what is trypsinogen
the inactive form of trypsin
cleaves peptide bonds
what is elastase
also cleaves internal peptide bonds
how do zymogens get activatd
for trypsin it gets activated by something in the brush boarder
once this is activated it can then go on and activate all the other zymogens of proteases
what inceases the secretion of the pancreas
CCK and secretin
vagal nerve
contraction
describe the process of activating the pancreas
food arives contains polypeptides to stimulate CCK pH drops stimulates secretin secretin released into blood CCK acts on pancreas to make zymogens moves to intestines and are ativated CCk causes gall blader to contract releasing bile secretin acts on liver making more bile more bicarbonate made too
what action do CCK, gastrin and acetylcholine have on the pancreas
increassed secretion of pancreatic enzymes and chloride right fluid by acinar cells
what action do secretin, histodine and vasoactive intestinal polypeptide have on the pancreas
increased secretion of bicarbonate rich fluid from the duct cells
what action do insulin and insulin like growth factors have on the pancreas
increased enzyme synthesis and secretion
what action does stomatastatin have on the pancreas
inhibited secretion from acinar and duct cells
where is the most digestion
duodenum
brush boarder specifically
most absorption
jejunum and ileum
what role does the borush boarder have on digesion
enzymes are localise here and they digest the macromolecules
what is sodium key for in digestion
osmolarity and transport of molecules from lumen to the blood
where does Na need to be
less Na in lumen
follows a concentration gradient of diffusion
but polar so needs some help to move
what allows Na to move
facillitatied diffusion
then active transport
describe the process of sodium absorption
sodium channels allows facillitative diffusion of Na acros from the lumen of intestine into epithelial cell
from here, activate transport is used to pump it from the epithelial cell to the blood where it can enter the vessel
whats the balance of amino acids like?
more in cells that in the lumen
how are amino acids transported
active transport along with na
allos them to get in, glucose too
secondary active transport
once in epithelia cells can diffuse into the blood
what does exopeptidase do
cut ends of proteins into oligopeptides
what does endopeptidase so
cut middles of proteins into oligopeptides
describe the process of protein digestion
enzymes break them down into oligopeptides then into dipeptides or tripeptides or single amino acids
they are transported across the membrane along with Na in co- transport
Na is moved back out again to maintain a gradient
cytosolic peptidases then complete the digestion
what completes protein digestion
cytosolic peptidases
where do proteins go once in the cells
hydrophobic amino acids move into the blood by diffusion
hydrophilic amino acids need co-transport with Na+
how do amino acids get to the liver
portal vein
describe the proecss of breaking down carbohydrates
saliva in mouth, amylase breaking down to maltose
then brush boarder
what happens at the brush boarder to carbohydrtes
enzymes at the boarder are needed to separate the parts down further
competes the digestion of it
how are carohydrates transported after being broken down
Na gradient i key
activive transport moves glucose/galactose into cell, the go with Na
now diffuse into blood
Na pumped back out for gradient maintene
what is the GLUT2 transporter
carrier to move glucose into the cell
works when there is more glucose in the lumen than then cell after eating
rising glucose in lumn activates the GLUT2 into apical membrane
where is fructose moving
higher conc in lumen than cell
diffuses through a carrier
independent of Na
diffuses into blood
what carrier out lipid hydroloysis
lipase
describe the proces of lipid digestion
bile salts from liver coat fat droplets
pancreatic lipase and colipase breaks down fats inot monoglycerides and fatty acids
stored in micelles
monoglycerides and fatty acids move into cels by diffusion
at same time cholesterol transported into cells
cholesterol combined with aborbed fats and protens in intestinal cells forming chylomicrons
these are then removed by the lymphatic system
what is a chylomicron
fats combining with cholesterol and proteins in the intestinal cells form these structures
what substances are found in the lumen?
glucose proteins oligopeptides sucrose fructose peptides tryglycerols
what is found in the interstitial space
glucose
amino acids
fructose
triglcerols
main function of the large intestine
absorbing left over water
sorts and concntrates faecal matter
name the parts of the large intesine
caecum appendix colon: ascending, transverse, desending, sigmoid rectum anal canal
what are taeniae coli
longitudinal muscles thickened to form bands
what are haustra
circular mucles contracting at intervals to make sacks
where are the least numbers of bacteria found
duodenum
why are bacteria needed in the large intesine
ferment indigestiable carbohydrates and proteins
make vitamins B and K
describe the process of defecation
gastroileal refex increases ileal contractions after a meal
chyme enters caecum through the sphincter
slow mixing and propulsive movements
defecating refex initiated by distension of rectal wall
relaxation of external anal sphincter
explusion of faeces
