Quick GI/ Liver flashcards
oral phase of swallowing
tongue presses against hard palate
bolus passes into oropharynx
soft palate lifts to close nasopharynx
voluntary
pharyngeal phase of swallowing
tongue seals off oropharynx
nasopharynx closed
epiglottis prevents aspiration by swinging down
pharynx widens and shortens - longitudinal muscles
oesophageal phase of swallowing
LES relaxes
what do mucous cells produce?
mucin
where is vitamin B12 absorbed?
terminal ileum
what do chief cells produce?
PEPSINOGEN!
what do these cells produce, and what is the result?:
ECL cells
G cells
D cells
ECL
- histamine
- stimulates HCl secretion
G
- gastrin
- stimulates HCl and histamine
D
- inhibits HCl secretion
mucosal protective mechanisms
alkaline mucus on luminal surface
tight junctions between epithelial cells
rapid replacement of damaged cells by stem cells in base of gastric pits
feedback loops regulate HCl secretion
causes of peptic ulcers
NSAIDS
H Pylori
gastrinoma
chemical irritants e.g alcohol, bile salts
which nerve mediates cephalic phase of digestion?
vagus
what mediates gastric phase of digestion
vagus
gastrin
volume of empty and full stomach
50 ml
1500ml
what increases strength of gastric contractions?
gastrin
stomach distension
what decreases strength of gastric contractions?
duodenal distension
low duodenal pH
increase in duodenal fat/ osmolarity
an increase in sympathetic stimulation
decrease in parasympathetic stimulation
where are entrogastrones released?
duodenum
BMI measurement
weight / height2
kg/m2
BMI ranges
under 18.5 = underweight
18.5 - 25 = normal
25 - 30 = overweight
30 - 40 = obese
over 40 = morbidly obese
normal BMR
24kcal/kg/day
increase BMR
male
pregnangy
hyperthyroidism
exercise
decrease BMR
female
malnutrition/ starvation
hypothyroidism
how are fat soluble vitamins absorbed?
with fat in micelles
ileum
where are water soluble vitamins absorbed?
B and C
but not B12
where and how is B12 absorbed?
with intrinsic factor in terminal ileum
function of vitamin A
cellular growth and differentiation
vision
lymphocyte production
sources of vitamin A
liver
dairy
oily fish
function of B12
erythrocyte formation
DNA synthesis
source of B12
eggs
milk
meat
fish
consequence of B12 deficiency
pernicious anaemia
function of vitamin C
collagen synthesis
antioxidant
source of vitamin D
UV light
fish oils
egg yolk
sources of vitamin E
nuts
seeds
symptoms of vitamin E deficiency
muscle weakness
retinal degeneration
source of vitamin K
bef
liver
leafy green veg
protein digestion
small intestines
- protein to polypeptides
SI
- polypeptides to endopeptidases (trypsin, chymotrypsin, elastase) by pancreatic endopeptidases
final digestion
- endopeptidases to amino acids by exopeptidases
- aminopeptidases on luminal membranee of epithelial cells
- also intracellular peptidases
how much water passes through GI tract per day?
9L
water from
food and drink
saliva
gastric secretions
bile
pancreatic secretions
intestinal secretions
colonic mucous secretions
2L
1.5L
1.5L
0.8L
0.8L
2L
0.2L
where does most water absorption occur?
small intestine - 80%
only 1.5L enters large intestine
what percentage of fluid is reabsorbed?
98%
how is sodium absorbed?
active transport
cotransport with glucose, amino acids
water follows with sodium
how is potassium absorbed?
passive diffusion
how is Cl- absorbed
exchanged with bicarbonate - active transport
liver embryology
foregut
begins forming week 3
hepatocytes derived from endoderm (like all foregut derivatives)
start processing bile at week 12
mesenchymal tissue and Kuppfer cells arise from mesoderm
function of foetal liver
haematopoeisis
cells migrate to bone marrow
hepatic diverticulum
liver cranially
gallbladder caudally
functional unit of liver
lobule
hexagonal
- central vein
- portal triad branches at each corner
is the sinusoid fenestrated?
sinusoid is fenestrated
what separates sinusoid and hepatocytes
space of Diesse
sinusoid lining
specialised endothelial cells
Kupffer cells
junctions in bile canaliculi
tight junctions, gap junctions, desmosomes
how is bile pumped towards bile duct?
actin filament
what does liver store?
vitamins
- fat soluble ones
- 3-5 year supply of non-fat soluble B12
minerals
- iron
- copper
glycogen
- 100g
- 12h supply
function of copper
RBC formation
copper transport
in plasma bound to ceruloplasmin
how much glycogen stored?
100g
12 hours supply
which types of protein does liver produce?
plasma proteins
clotting proteins
complement proteins
plasma protein examples
albumin, fibrinogen, globulin
which clotting factors are not made in liver?
3,4,8
function of complement proteins
innate immunity
albumin functions
oncotic pressure
transport large hydrophobic molecules
xenobiotic
foreign chemicals not normally found or produced in the body and cannot be used to produce energy
phase 1 reactions
transformation of substance from one type to another
oxidation/ hydrolysis reaction
adds -SH or -OH
.g cytochrome p450
phase 2 reactions
glucuronidation - adds glucuronic acid
conjugation - adds chemical group to substance
excretion (often in bile/urine)
UDPGT
glucuronyl transferase
- liver enzyme. It changes bilirubin into a form that can be removed from the body through the bile.
aim of phase 1 and 2 reactions
transform substance to be less toxic
more water soluble so it can be excreted
2 different ways of doing this
glucose alanine cycle purpose
move proteins from muscles to liver when glycogen is low
what can be used to measure liver health?
ALT
alanine aminotransferase
glucose alanine cycle
excess alanine transferred to liver and converted to pyruvate (transamination)
pyruvate is used to produce glucose in gluconeogenesis
glucose enters blood and is used by muscles (glycolysis)
- also removes excess ammonia
glutamate to ammonium by oxidative deamination
dissociates to ammonia
converted to urea for urea cycle
urea cycle function
remove excess nitrogen
ammonia converted to less toxic urea
urea cycle
arginine (from diet or protein breakdown) + arginase –> ornithine + urea
ornithine + CO2 + ammonia –> citrulline
citrulline + ammonia –> arginine
only product of urea cycle
urea
why must ammonia be excreted?
neurotoxic - crosses bbb
would require lots of water to excrete - dehydration
very water soluble
lipid metabolism
lipids + bile salts –> micelles
micelles constantly break and reform
lipids + pancreatic lipase –> glycerol and fatty acids
fatty acids absorbed by enterocytes and link to form triglycerides
triglycerides combine with proteins to form chylomicrons in Golgi
chylomicrons enter lacteal and are transported away from intestine to liver
VLDL transport lipids from liver into blood to adipose tissue
triglycerides diffuse into adipocytes for storage
where are LDLs made?
plasma
cholesterol delivery to all body cells
where are HDLs made?
liver
removes excess cholesterol from blood and tissues via excretion in bile
where are VLDLs made?
hepatocytes
triglyceride delivery from liver to adipocytes
fatty acid beta oxidation
catabolism of fatty acids to produce energy
in mitochondria of hepatocytes
each cycle shortens fatty acid chains by 2 carbons, continues until only 2 carbons remain
if odd number of chains, e.g 3C, cannot be oxidised further
leads to production of CO2 and ATP via Krebs
2 carbons removed as acetyl CoA is 2C
dduring every round, 2 carbons are cleaved to form acetyl CoA
what is in bile
bile salts
phospholipids
bicarbonate
cholesterol
bile pigments e.g bilirubin
how is bile concentrated in gallbladder?
microvillous epithelial cells
rugae
bilirubin metabolism
haem converted to biliverdin and Fe2+ by haem oxygenase
biliverdin to unconjugated bilirubin by biliverdin reductase
unconjugated bilirubin transported to liver by albumin
in the liver, unconjugated bilirubin is converted to conjugated bilirubin by glucuronyl transferase (glucuronidation by UDPGT)
conjugated bilirubin enters duodenum in bile
conjugated bilirubin is converted to urobilinogen by colonic bacteria
some urobilinogen is reabsorbed into blood, to liver, to urobilin
urobilin is recycles to bile or excreted by kidneys - yellow urine
most is oxidised to stercobilin by bacteria for excretion - brown faeces
what carries out glucuronidation?
UDPGT
pancreatic embryology
originates as 2 buds
dorsal bud
- neck, body, tail, part of head
ventral bud
- ucinate process, part of head
dorsal and ventral buds undergo clockwise rotation
pancreas sits in C shape of duodenum
exocrine and endocrine cells - endoderm, foregut derivative
mesenchymal tissue - mesoderm
insulin secretion at week 20
pancreatic histology
lobulated connective tissue that stains dark
lighter stained circular cells that lack lumen are islets of langerhans (endocrine)
how are beta cells stained?
blue by aldehyde fuchsin
where are delta cells and what do they produce?
in pancreas
somatostatin
other hormones produced by pancreas
pancreatic polypeptide
vasoactive intestinal polypeptide
substance p
serotonin
function of islets
endocrine
function of tissues surrounding islets
exocrine
terminal secretory units
acini
pyramidal cells arranged in a circle without visibe lumen
pancreatic secretion pathway
acini, interlobular ducts, pancreatic ducts, pancreatic sphincter, sphincter of Oddi
lining oof pancreatic ducts
simple columnar epithelia
exocrine pancreas
acini of pancreas –> digestive enzymes as zymogens
released via pancreatic duct to duodenum
acini are exocrine to duodenum (enzymes)
endocrine pancreas
islets of langerhans produce insulin, glucagon, somatostatin
to regulate glucose
islets are endocrine to blood (hormones)
is most pancreas endocrine or exocrine?
exocrine
what activates zymogens?
enterokinase on brush border
pancreatic juice
amylase - starch to maltose
lipase - triglycerides to fatty acids
endopeptidase - peptides to amino acids
nuclease - DNA to nucleosides
bicarbonate ions neutralise stomach acid
what stimulates bicarbonate release from pancreas?
stimulated by secretin
bicarbonate secreted into duct lumen via Cl-/ HCO3- exchanger on cells lining ducts
Cl- recycled back into lumen by CFTR channel
cells in endocrine pancreas
alpha, beta and delta
delta = somatostatin
- inhibit exocrine secretions of pancreas
- reduce gastric emptying
main enzyme required in phase 1 detoxification reactions
cytochrome P450
urea cycle
in cytosol and mitochondria
which mesenteries does the foregut have?
midgut
hindgut
dorsal and ventral
dorsal
ventral
gag reflex
afferent ticking - glossopharyngeal
efferent response - motor vagus
what passes through parotid gland?
facial
external carotid
retromandibular vein
submandibular secretions
mixed serous and mucus
wharton’s duct
serous acini form crescents around mucous acini
facial
parotid gland
serous
stensens duct
sublingual
mucus
whatrons duct
anterior to submandibular
cells in cardia
foveolar - mucus
cells in fundus
parietal
chief
ECL
cells in body of stomach
G cells
duodenal cells
D - somatostatin
I - choleocystokinin
S - secretin
action of gastrin and histamine
more H+/K+ ATPase pumps
enterogastrones
secretin and CCK
effect of secretin
stimulate somatostatin
inhibit gastrin
gastric embryology
week 4
trilaminar disc folds medially and horizontally
endoderm fuses to form primitive gut tube
end of week 4
- oropharyngeal membrane ruptures
week 7
- cloatal membrane ruptures
midgut and hindgut development
longation
herniation
rotation
retraction
fixation
foregut development
week 4 - fusiform dilation in primitive gut tube
week 7 - 90 degree clockwise longitudinal rotation creates lesser sac
week 8 - ventrodorsal rotation - curves up
