GI Theme 2 Flashcards
what is involved in chemical digestion in the mouth
a-amylase
- starch digestion at pH 7
-when bolus & enzyme hit pH 2.5 gastric juices hydrolysis will cease
lingual lipase
-breakdown of triglycerides into fatty acids and glycerol
what is involved in mechanical digestion int eh mouth
breaks into pieces
mixes with saliva
what are the function of the stomach
storage
digestion
protection
how does the stomach have a protective fucntion
acids destroys bacteria and other pathogens (HCl)
outline mechanical digestion in the stomach
gentle mixing waves
more vigorous waves
intense waves near the pylorus
with each wave a small amount of chyme enters the duodenum
outline protein digestion in the stomach
HCl denatures protein molecules
HCl transforms pepsinogen into pepsin that breaks peptide bonds between certain amino acids
outline fat digestion in the stomach
gastric lipase splits the triglycerides in milk fat
most effective at pH6 to 6
what is the cytoplasmic pH of the parietal cells
7.2
which cells secrete mucus and bicarbonate
mucus cells in the neck of gastric glands
how does gastric mucous & bicarbonate provide protection
creates a barrier protecting stomach from autodigestion
mucus-physical barrier
bicarbonate- chemical barrier
how are GI secretions regulated
Long cephalic reflexes
- CNS (feeds forward & emotional reflexes)
Short reflexes
-ENS (motility & secretion: enzymes and hormones)
what is the enteric ns
subdivision of the peripheral ns controlling GI system
capable of autonomous functions
can recieve from the autonomic ns
how are gastric secretions and motility regulated
CNS & ENS
- cephalic phase
- gastric phase
- intestinal phase
what happens in the cephalic phase
“stomach getting ready”
- cerebral cortex stimulates parasympathetic ns
- vagus n increases stomach muscle and glandular activity
what happens in the gastric phase
“stomach working”
- nervous control keeps stomach active
- endocrine influences over stomach activity
what is the function of D-cells
decrease stomach acid production
what happens in the intestinal phase
“stomach emptying”
- intestinal activity increased (duodenum)
- distension, fatty acids or sugar signal medulla
- hormonal influences
what is the role of the sympathetic nervous system in the intestinal phase
slow stomach activity
what does secretin do in the intestinal phase
decerases stomach secretions
what does cholecystokinin (CCK) do in the intestinal phase
decreases stomach emptying
what does gastric inhibitory peptides(GIP) do in the intestinal phase
decrease stomach secretions, motility and emptying
what do D cells secrete, what does this do & what is its stimulus
somatostatin
inhibits acid
acid in stomach
what do G cells secrete, what does this do & what is its stimulus
gastrin
stimulates acid secretion
acetlycholine, peptides
what do chief cells secrete, what does this do & what is its stimulus
pepsinogen & gastric lipase
protein digestion
ActChl, secretin, acid
what do mucous cells secrete, what does this do & what is its stimulus
mucus & bicarbonate
physical barrier & chem protection
irritation & secreted with mucus
what do parietal cells secrete, what does this do & what is its stimulus
gastric acid & Intrinsic factor
activates pepsin, denatures protein, kills bacteria & vit B12 absorption (IF)
ActChl, gastrin, histamine
what do enterochromaffin like cells secrete, what does this do & what is its stimulus
histamine
stimulates acid secretion
ActChl, gastrin
stimulates acid secretion
what nutrients does the stomach absorb
water esp if cold
electrolytes
drugs (aspirin & alcohol)
why would the palatal and lingual tooth surfaces be at risk of erosion
patient suffering from reflux (gastric goes through oesophagus into oral cavity)
which patients may be more at risk of aspiration of stomach contents when under GA
hiatus hernia
non fasted
pregnant
which drugs can cause a dry mouth
chelates and complexes
protein pump inhibitors (omeprazole)
which drugs can cause a chalky taste
antacids
which drug can cause staining of tongue, erythema multiforme & swelling and pain of salivary gland
H2 receptor antagonists - ranitidine
what is the approx length of the SI
6 meters
what is the approx length of the duodenum and jejunum
2.5m
what is the approx length of ileum
3.5m
what is the function of the small intestine
mechanical digestion- weak peristalsis
chemical digestion
absorption of nutrients across intestinal enterocyte
how long does chyme stay in the small intestine
3 to 5 hrs
what is meant by segmentation in the SI
local mixing of chyme with intestinal juices
sloshing back and forth
what paracrine hormones are involved in the regulating the small intestine
secretin
GIP
GLP-1
CCK
what does secretin do
regulates water homeostasis & secretions in the stomach pancreas and liver
located in S cells of duodenum (intestinal glands
what is GIP produced by
k cells of duodenal and jejunal mucosa
what is GLP-1 produced by
intestinal enteroendodrine L-cells and some ENS and brainstem neurones
what does CCK do in the SI
stimulates release of digestive enzymes and bile from the pancreas and gall bladder
hunger suppressant
produced by enteroendocrine duodenal cells
how does chemical digestion occur in the small intestine
pancreatic juice
what cells produce pancreatic juice
acinar
how does pancreatic juice enter duodenum
pancreatic duct
what does pancreatic juice contain
proteases
lipases
amylase
sodium bicarbonate to neutralise chyme
which hormones regulate pancreatic juice secretion
CCK- enzyme rich
secretin- bicarbonate rich
what are incretins
hormones that stimulate decrease of blood glucose levels
when are incretins released
at the beginning of intestinal phase of digestion
GIP & GLP
how do incretins cause a decrease a blood glucose levels
stimulate insulin release from pancreatic b cells
inhibit glucagon release from pancreatic a-cells
what hormone regulates bile
CCK
which hormone stimulates goblet cells
VIP
which enzymes break down carbs in the small intestine
sucrase-isomaltase
- sucrose = glucose + fructose
lactase
-lactose= glucose + galactose
how may lactose intolerance occur
damage to intestinal mucosa(age, drug treatment or chemotherapy)
where are the enzymes that break down carbs located
apical membrane of SI
where are peptidases found
brush border
how & where are food proteins hydrolysed for peptidases to act upon
pepsin - stomach
pancreatic proteases- duodenum onwards
what do enterokinases do
partially hydrolyse pancreatic zygomen proteases to release the active enzyme
do brush border hyrolases act on lipids or nucleic acids
no
why are tight junctions important for the function of polarised cells
keep extracellular fluids surrounding apical and basolateral membranes separate & prevent diffusion of membrane proteins and glycolipids between fucntional domains
what are the consequences of tight junctions
prevent passage of molecules and ions between cells
must enter by active transport
peristaltic waves cause aid mechanical digestion in the large intestine, outline how
haustral churning
gastroilial reflex
gastrocolic reflex
what happens the the haustral churning part of mechanical digestion in the LI
relaxed pouches filled from below muscular contractions (elevator)
what happens the the gastroilial reflex part of mechanical digestion in the LI
when stomach full gastrin hormone relaxes ileocal sphincter so small intestine will empty and make room
what happens the the gastrocolic reflex part of mechanical digestion in the LI
when stomach fills a strong perostaltic wave moves contents if transverse colon into rectum
are enzymes involved in chemical digestion in theLI
no, only mucus is secreted
what do bacteria ferment in the LI during chemical digestion
undigested carbs into CO2 and CH4
undigested proteins into simpler substances
bilirubin into simpler substances that produce colour
what vitamins do bacteria produce in the colon
K and B
what are faeces
dead epithelial cells, undigested foods, bacteria
what occurs during defecation in the LI
gastrolic reflex moves faeces into rectum
stretch receptors signal
parasympathetic nerves contract muscles of rectum and relax int anal sphincter
external sphincter is voluntarily controlled
What is the blood supply of the liver ?
hepatic artery from the abdominal aorta
portal vein - nutrient rich blood from the GI tract
How are hepatocytes arrnaged ?
hexagonally
What are the hepatocytes in contact with ?
bile canaliculi on one side and the blood stream on the other
What are between hepatocytes ?
vascular spaces called sinusoids
What are kupffer cells ?
phagocytic macrophages which attach to sinusoids and play a protective roole
What does a portal triad conssit of ?
hepatic artery
portal vein
bile duct
What are the functions of the liver ?
filtering of blood protein synthesis carb metabolsim lipid metabolsim secretion of bile
How can the liver remove hormones , drugs and active molecules from the blood ?
excretion into the bile
phagocytosis by kupfer cells
chemical alteration
How is ammonia produced in the liver ?
deamiantion by amino acids
What does the liver do with ammonia ?
convert it intp urea to be excreted into the urine
How is ammonia released from glutamate ?
deamination of glutamate into alpha ketoglutarate produced ammonium ions
glutamate dehydrogenase
How is ammonia turned into urea ?
in the urea cycle
What is the route for the production and release of bile ?
bile is made in the liver
secreted into the hepatic duct
joins the cystic duct from the gall baldder
enters the duodenum through the common bile duct which goes through the pancreas
What does bile act for fats ?
emulsifier
What hormone regulates bile production ?
CCK
Where are chylomicrons produced ?
in the intestinal mucosa
enoplasmic reticulum of enterocytes
Where are chylomicrons found ?
in the blood and the lymph
Where are newly formed chylomicrons secreted from ?
through the basolateral membrane
into lymphatic vessels to veins
What is the role of chylomicrons ?
transport fat from the intestine top the liver and the adipose tissue
What do chylomicrons consist of ?
95% TAG
5% cholesterol
Apo B48
What are chylomicrons recognised by ?
lipoprotein lipases on the lining of blood vessels
What happens in chylomicron breakdown ?
broken down into FFA- oxidiesed for energy
LDL
HDL - taken up by the liver
reminants - taken up by the liver
What is the bile production rate in the liver ?
250-1500 ml a day
What is bile pigment ?
bilirubin
Where is bilirubin formed ?
spleen
bone marrow
liver
What is bilirubin a derivative of ?
haem groups without iron
What does bilirubin combine with ?
glucorinic acid - conjugated bilirubin
What is conjugated bilirubin converted into ?
urobilogen
by intestinal bacteria
What is urobilogen absorbed by ?
intestine into the hepatic vein
What does bile consist of ?
bile acids and bile salts
detergents for fat ingestion
glucoronic acid
95% of bile acid is reabsorbed by?
ileum
What is the sphincter oddi ?
betwene the bile duct and thre duodenum
What is the pancreas an outgrowth from ?
duodenum
What are the 2 types of glands found in the pancreas ?
endocrine and exocrine glands
What is the arrangement of cells in the exocrine pancreas ?
arranged as raspberry like acini around a central lumen
compound acinar
Many lumens contact each other to form what ?
ductules - coalesce to form the pancreatic duct
What do acinar cells form from ?
invagination of embryonic endoderm
What do the acianr cells open into ?
pancreatic duct
What is the apical membrane orientated towards ?
lumen
What is the basolateral membrane orientated towards ?
bloodtstream
Which hydrolytic enzymes do acinar cells synthesisie ?
amylases
proteases
lipases
nucleases
What are enxymes usually sotred as in the exocrine acinar cells and how are they released ?
as zymogens
as secretory vesivles in the apical membrane
What does the basolaterla membrane contain ?
receptors which hormones bind to to regualte zymogen secretion from the secretory vesicles in the apical membrane
What is the neural control of the exocrine pancreas ?
vagus in anticipation of a meal
As chyme nters the duodenum what doe CCK do ?
circualtes to the basoalterla membrane of acinar cells and binds to a specific receptor
What is secretin released from ?
enteroendocrione cells
What is secretin reelase din repsonse to ?
acid in the duodenum
What does secretin do ?
activates the secretion of bicarbinate from the pancreas
as pH increases bicarbonate release is stopped
What is the secretin receptor on the basolaterla membrane of the acinar cells like n?
7 pass trans membrane structure
GPCR
How are proteases sotred in the exocrone pancreas ?
as zymogen sin the secretory vesicles in the apical membrane of the acianr cell s
What are tehe enzymes released from the exocrine pancreas ?
lipases
phospholipas A2
amylases
Where is bicarbiante relesed from in the oancres ?
epithelial cells in the pancreatic duct
What are the endocrine cells in the pancreas arranged as ?
isleets of langerhans
What are the hormones released from the endocrine opancreas and where from ?
alpha cells - glucagon
beta cells - insuklin
delta cells - somatostain - GHIH
What is vomiting controlled by ?
emetic centre in the chemoreceptor trigger zone in an area of the meduall oblangata
What is the process of vomiting ?
increaseed parasymapthetic acrtivity leads to increased salivation
retroperistalsis
increase in abdominal pressure and decrease in intrathoracic pressure
propel stomach contents into the oesophagus
What is the sympathetic resposne in vomiting ?
sweating and increased HR
What are the cell to cell junctions in the apical membrane ?
tight junctions
claudin and occludin
adaptor proteins which link to underlying actin- Z0-1 AND Z0-2
What are the cell0 cell junctions in the basolateral membrane ?
adherens junctions
E-cadherin
A AND BETA CATENIN
What is the gut assocaited lymphoid tissue ?
protects agaisnt antigens entering across the intestinal mucosal barrier
aggregates of lymphoid tissue
What are peyers patches ?
bumps of lymphoid tissue in mucosa of GI tract
macrophages , dendritic cells and B and T lymphocytes found within
What are M cells ?
microfold cells
What are the role of M cells ?
specialised epithelial cells that overly peyers patches
provide info about the contents of the gut lumen to the immune cells of the GALT
What does the apical surface of the M cells contain ?
clathrin coated pits with embedded receptors
What happens when antigens bind to the receptor ?
transcytosis to basolateral membrane
released to intestinal fluid macrophages and lymphocytes
trigger inflammatory response
What do M cells transport microbes by ?
endocytosis
phagocytosis
transocytosis
What do dendriticc cells do ?
convert T cells into T reg cells - release IL10
supresses unecessary immune response
Damage to the intestinal epithelium leads to what ?
epithelial cells release signalling molecules
inhibition of IL10
D and T cells produce IL and TNF
neutrophils undergo NETosis and Apoptosis
How does food poisoning occur with M cells ?
some bacteria have evolved receptors which bind to M cell receptors
bacteria transported acorss M cells
immune system react- diarrhoea and vomiting
Good intestinal bacteria ?
biotin
vitamin K
intestinal flora
Good bacteria generate which antomicrobial peptides ?
lysoxymes
lactoferrin
defensins
What are the 2 types of multicellular glands ?
acinar and tubular
What is the epithelium in the excretory duct ?
pseudostratified columnar epithelium
Which salivary duct has pseudostratified columnar epithelium ?
excretory
Which parts of the salivary duct has simple cuboidal epithelium ?
intercalated dcut
What are serous demilunes ?
mixture of mucous and serous cells
What nutrients are abosrbed by the stomach ?
water , drugs , electrolytes and alcohol
What are some proteins produced in the liver ?
lipoproteins
plasma proteins- albumin, fibrinogen, globulin,transferrin
In what form is pigment secreted int the bile ?
conjugated bilirubin
What are the gut defence mechanisms ?
taste and mouth fell vomiting gastric acid hydrolytic enzymes mucosal epithelial barrier GALT intestinal bacteria
What controls vomiting ?
the enteric centre in the chemoreceptor trigger zone in the medulla oblanagata
What initiates vomiting ?
chemoreceptors and the CNS
What is the parasympathetic contribution to vomiting ?
increased salivation
retroperistalsis
Describe the pressure changes in vomiting ?
abdominal muscles contract- increase in abdominal pressure
lowering of thoracic pressure
propels stomach contents into the oesophagus
What is the sympathetic response in vomiting ?
sweating and increased heart rate
What type of junctions are in the mucosal epithelial barrier ?
tight junctions
What is the role of the mucosal epithelial barrier ?
keeps the ECF around the apical and basolateral memebranes separate
what is Gut Associated Lymphoid Tissue (GALT)
protects against antigens entering the body across mucosal barrier
what is a component of MALT
system of nodes
where are the collection of lymph nodes of MALT
tonsils
appendix
payers patches
what are microfold (M) cells
specialised epithelial cells that overlie peyers matches
what do M cells do
provide info about lumen contents to immune cells of GALT. move particles into lymphoid vessel
what does the apical surface of m cells contrian
clathrin-coated pits with embedded receptors
what do Dendritic cells do
accept antigen and develops reaction on whether is harmful.
associate with basal membrane with epitherlial cells and hijack proecsses through tight junction
project processes into intestinal lumenn
what do T lymphocytes do
develop into regulatroy t lymphoctes which generate iL10 important for response
how do m cells transport microbes and food particels
endocytosis
phagocytosis
transcytosis
outline the pathiophysiology of gut immune function
- Damage of intestinal epithelium
- Epithelial cells release signalling molecules
- inhibition of IL10 production by TReg cells
- D cells start to produce IL6, IL12 and IL23
- T cells start to produce IL17, IFγ and TNFα
- Neutrophils undergo NETosis
- Neutrophil apoptosis, start of cell repair and regeneration
what do bacteria (salmonella etc) do to cause food poisoning
have surfaces tha bind to m cells and are transported across epithelial barriet into body
- diarrhoea nad vomiting
what are the Intestinal bacteria (good bacteria!)
biotin
vit k
intestinal flora
antomicrobal polypeptides
what are the antomicrobal polypeptides
- Lysozymes- effective against gram + species (streptococcal)
- Lactoferrin- antiviral properties
- Defensins- antiviral properties