Disorders affecting the GI system Flashcards
What is Hirschprung disease?
megacolon
- colon doesn’t move
- congenital absence of intrinsic ganglion cells in the myenteric and submucosal plexuses of the GI tract
What was the main gene discussed in Hirschprung disease?
RET
What is RET?
- protooncogene… helps regulate cell growth
- responsible for MEN
What are MEN syndromes?
multiple endocrine neoplasia
-GOF mutations: gene product gets a new function or pattern of gene expression
-
What is the case with Hirschprung disease and the RET gene?
its a loss of function mutation that results in reduced or abolished protein function
What does the RET gene normally do?
makes a protein involved in signaling within cells.
-without it, we cannot transmit signals within cells
What does not develop porperly if RET isn’t working?
the enteric nervous system
What is Iron controlled by?
the need for hemoglobin
What transports iron in the body?
transferrin
what is iron stored in?
ferritin molecules (liver and heart)
How do we excrete iron?
trick question, we can’t physiologically
-blood loss….
What happens when too much iron is absorbed (iron in excess of transferrin binding capacity) ?
gets deposited in the liver, heart, and some endocrine tissues
-tissue damage and fibrosis
What happens when too many erythrocytes are destroyed?
iron accumulates in the reticuloendothelial macs first
-then tissue parenchyma after macs
What is secondary hemochromatosis?
a buildup of iron due to anemia, chronic liver diseases,
-usually a result ofhep C or alcoholism. Frequent blood transfusions
What gene is pretty important for iron absortion regulation?
HFE
What gene is responsible for most common form of iron overload: hemochromatosis?
HFE
What gene is responsible for most cases of jevenile hemochromatosis?
HJV
What gene is less common but with similar clinical presentation to HFE mutations?
TFR2
Which gene is responsible for hepcidin, and iron-regulating hormone critical for absorption?
HAMP
are there more things that increase Iron absorption or decrease it?
increase it
What are the 3 things that decrease iron absorption?
- regular blood transfusions
- high iron diet
- iron loading vitamins
How does HFE work?
it regulates circulating iron uptake by regulation the interaction of TFR1/2 with transferrin
What is hepcidin?
a key regulator of the entry of iron into the circulation
What is transferrrin?
and iron binding blood plasma glycoprotein that controls the level of free iron in biological fluids
What is TFR1?
protein required for iron import form transferrin into cells by endocytosis
What is TFR2?
a protein involved in the uptake of transferrin-bound iron into cells by endocytosis, although its role is minor compared to TFR1
What is Ferroportin?
a transmembrane protien that transports iron fromthe inside of a cell to the outside of the cell, inhibited by hepcidin, and results in the retention of iron
In states of iron deficiency, how are the levels of hepcidin?
low… we want to take in iron
What does hepcidin do to stop iron intake?
it blocks ferroportin on the enterocyes and macrophages in duodenum
If we have high iron levels and there is inappropriate contiued transport of iron into the plasma, what protein is there a mutation in?
HRE, HJV, or TFR2…. all resulin in low hepcidin levels
What two molecules compete for a binding site at the TFR1 receptor?
Transferin and HFE
Which molecule binds transferrin better? HFE or transferrin?
Transferrin
What is the significance of unboune HFE on the cell surface?
stimulates expression of hepcidin
What is the result of too much Fe2+?
more TFR2 will be made than TFR1
What is the significance of TFR2?
transferrins bind it more than TFR1 becuase more TFR2 is expressed
- TFR2 binding stimulates hepcidin expression
- also, more HFE is free
How many molecules does transferrin bind?
2 of them
What is the result of decrease unbound HFE?
decreased TFR2
- resulting in decrease HAMP expression
- leading to increased Fe transfer out of enterocytes
What are some characteristics of hemochromatosis?
late onset
- nonspecific symptoms
- progresses to hepatosplenomegaly
- increased incidence of infections with decreased hepcidin
What is the iron fist a sign of?
hemochromatosis
-but not everyone has it
What is the problem with intracellular iron?
it leads to increased fre radical production and perosidation of P-lipids of organelles
- cells di e
- liver enzymes increase
What does Serum ferritin measure?
the amount of iron contained or stored int he body
What is total iron binding capacity?
tells us how well our body can bind to iron
-Siron/this is important for transferrin iron saturation percentage
What is the treatment for reducing iron?
blood removal
What is the Hereditary Hemochromatosis?
C282Y
-cysteine to Tyrosine at residue 282
In wilson disease and MEnkes syndrome, what element are we worried about?
copper
Where is copper absorbed?
in the stomach and duodenum
-bound to albumin and transported to the liver
What 2 genes are involved in copper homeostasis?
ATP7A - expressed in most cells
ATP7B - in liver, brain, kidney, and placenta
What is the major copper-carrying protein in the blood?
ceruloplasmin
-ATP7B is needed with copper as a co factor in order to make it from apoceruloplasmin
What is ceruloplasmin?
an iron oxidoreductase important in iron absorption
-each ceruloplasmin carries 6 copper atoms
What does ceruloplasmin promote?
iron loading onton transferrin which only binds Fe2+
What does reduced copper lead to?
reduced Fe2+ transport that leads to an increased attempt to increase Fe2+ absorption
Where are DMT1 and CRT1 located?
on both sides of the enterocyte
- they let copper in
- when copper’s in, it binds to proteins with a high affinity for it
What is Menke’s syndrome?
ATP7A mutation
- it’s normal function is to move Cu2+ from intestinal mucosa into blood
- so, now uptake is impairs and Copper deficiency occurs
- reactions can’t happen without it
What is the sign of Menke’s syndrome?
twisted short light hair
- temperature instability
- failure to thrive
- steel wool cleaning pad hair
What does the vasculature in Menkes syndrome look like
Markedly toruous intracranial and extracranial vessels, which are characteristics of Menkes disease
What are the skin and the occipital bone like in Menke’s disease?
skin is lax
and there are occipital horns
What is Wilson Disease?
ATP7B mutation
- prevents copper release from hepatocytes
- apoceruloplasmin is degraded and ceruloplasmin levels decrease
- iron levels affected
- now, the only way to get rid of copper is to shed it through enterocytes which is not going to cut it
What are the 2 ways to excrete copper?
metallothionein (MT) on enterocytes which get shed
-Ceruloplasmin binds excess copper in the liver which gets excreted with bile
What is the clinical presentation of the Wilson disease?
progressive lenticular degeneration
- bilateral softening of the lenticular nucleus
- liver cirrhosis
- depression
What is the giveaway sign of wilson’s disease?
Kayser-Fleischer rings
- copper deposited in descemet’s membrane of the cornea
- reflects a high degree of copper storage in the body
What is the defect in Menkes syndrome?
the intestinal absorption of copper
- we can’t get it in
- *decreased liver copper
- but increased intestinal/kidney copper
- we need to GIVE THEM COPPER
What is the defect in wilson disease?
the biliary excretion of copper
- we can absorb copper but we can’t get it out of the damn liver!
- we need to CHELATE THE COPPER
