liver Flashcards
secretion definition
examples
release of substances from cells
e.g. beta cells secrete insulin
chromatin cells secrete adrenaline and noradrenaline
egestion definiton
example
removal of undigested food from the body
e.g. cellulose (fibre) not digested
excretion definition
removal of metabolic waste from the body
examples of 2 excreted substances
carbon dioxide
nitrogenous waste (urea)
how is CO2 formed
how and where is it excreted
aerobic respiration
excreted form gas exchange surfaces e.g. lungs (by diffusion then expired) or from surface of unicellular organisms
how is urea formed
deamination (amine group removed) and ornithine cycle converts excess amino acids into urea
how and where is urea excreted
kidneys remove it from the blood (ultrafiltration) then removed from body in urination
removed in sweat
why must CO2 be removed from body
excess CO2 is toxic
can cause respiratory acidosis
how is CO2 carried in blood
as H2CO3 ions
bound directly to haemoglobin
Effect of CO2 being carried in blood as H2CO3 ions
H+ is formed when H2CO3 dissociates into H+ and HCO3-
H+ binds to Hb (buffer) to form HHb (haemoglobin acid) which changes the shape of Hb so O2 unloading at low pO2 and high pCO2
how is CO2 carried in blood directly bound to Hb
forms carbaminohaemoglobin
(not competitively w O2)
at high pCO2 and low pO2, CO2 binding reduces Hb’s affinity for O2, aiding oxygen unloading
list functions of the liver
1.carbohydrate metabolism
2.target organ for insulin, glucagon and cortisol
3. target organ for adrenaline
4.enables interconversion of other substances with carbohydrate
5.urea formation
6.RBC synthesis (in foetus)
7.RBC destruction
8.bile, plasma protein and cholesterol synthesis
9.hormone breakdown
10. vitamin A,D B12, iron and glycogen storage
11. detoxification of alcohol/drugs
describe the role of the liver in carbohydrate metabolism
carbs carried as glucose in the blood (main respiratory substrate)
glucose not suitable for storage bc small and soluble
glucose converted to glycogen to be stored in LIVER and muscles
role of liver when blood sugar level is low
alpha cells in pancreas secrete glucagon into blood
glucagon= non-steroid hormone which binds to glycoprotein, g-protein coupled receptors on hepatocytes plasma membrane
activation of enzymes causes hydrolysis of glycogen to glucose (glycogenolysis)
also causes lipolysis (lipid hydrolysis)
gluconeogenesis forms new glucose
glucose passes into blood
BSL increases and glucagon no longer released (-ve feedback)
glucagon inhibits insulin
role of liver when blood sugar level too high
beta cells in pancreas secrete insulin into blood
insulin is a non-steroid hormone and globular protein which binds to tyrosine kinase receptors on plasma membrane of hepatocytes, causing glucose transporters to be inserted into membrane
hepatocytes take up glucose and respire it in glycolysis, convert it to glycogen (glycogenesis), or convert it to glycerol to produce fats (lipogenesis)
lowers BSL so no more insulin secreted (-ve feedback)
insulin inhibits glucagon
effect of adrenaline on liver cells
adrenaline released from adrenal medulla in times of stress
causes glycogenolysis to increase blood sugar level
what is the process by which new glucose is formed form non-carb sources
gluconeogenesis
when does gluconeogenesis take place
when supplies of glycogen are exhausted e.g. after fasting
describe gluconeogenesis using lactate/lactic acid
produced during anaerobic respiration
taken up by hepatocytes and converted to pyruvate then glucose
describe gluconeogenesis using lipids
glycerol from triglycerides can be broken down and converted into glucose
describe gluconeogenesis using amino acids
amino acids are deaminated
the nitrogen containing amine group is converted to ammonia and then urea which is excreted
the rest of the molecule is a keto acid and is converted to pyruvate then glucose
what triggers gluconeogenesis
cortisol
why can the body not store excess amino acids
the amine groups are potentially toxic
why would it be wasteful to excrete excess amino acids
they contain almost as much energy as carbohydrates
what happens to excess amino acids
transported in the blood plasma to the liver
some of them are converted to other amino acids (TRANSAMINATION)
the rest are deaminated
why is transamination useful
the diet cannot provide all the amino acids needed
what is deamination
the removal of the amine group (NH2)
deamination reaction
amino acid + Oxygen -> keto acids + ammonia
in what cycle is urea formed
ornithine cycle
what happens to the ammonia formed in deamination
why
converted to urea (less soluble and less toxic than ammonia so needs less water for removal)
what animal excretes ammonia
fish
what does ornithine act as
a carrier molecule on which urea is assembled
ornithine recycling?
ornithine is reformed at the end of the cycle and can be reused in the next cycle
what is used to form urea in the ornithine cycle
ornithine
CO2
ammonia
what binds to ornithine in ornithine cycle
CO2
role of liver synthesising RBC
in foetus
bone marrow not fully developed so RBC made in liver from mitosis of stem cells, which then differentiate (lose mitochondria, nucleus etc)
role of liver in destruction of RBC
RBC destruction involves white blood cells nd hepatocytes
haemoglobin broken down:
Globin broken down into amino acids
Haem groups converted into bilirubin (used to make bile or is an excretory waste product)
role of liver in bile synthesis
bile is made from the breakdown for haemoglobin
stored in gall bladder
bile emulsifies fats to increase SA for lipase enzymes
neutralises stomach acid so optimum pH for digestive enzymes
examples of plasma proteins synthesised in liver
e.g. fibrinogen converted to fibrin in blood clotting
albumin causes oncotic pressure of the blood and transports steroid hormones e.g. oestrogen, cortisol
roles of cholesterol
major components of cell membranes (regulates and maintains fluidity of phospholipid bilayer)
used to make steroid hormones
used to make vitamin D
transported as a lipoprotein
role of liver in breakdown of hormones
liver breaks down fat soluble substances into water soluble substances that can be excreted in the urine e.g. steroid hormones (testosterone etc)
what is vitamin B12 needed for
manufacturing coenzymes (cofactors) like NAD and FAD
Haemoglobin synthesis
how does the liver render dangerous substances/molecules as less toxic
oxidation
reduction
methylation
combination with other molecules
(kidneys eliminate breakdown products)
how does the liver break down hydrogen peroxide
uses catalase enzyme
2H2O2 -> 2H2O + O2
examples of drugs the liver breaks down
antibiotics
paracetamol
cocaine
steps of ethanol metabolism in liver
1: ethanol to ethanal
uses ethanol dehydrogenase enzyme
NAD converted to reduced NAD
2: ethanal to ethanoate
uses ethanal dehydrogenase enzyme
NAD converted to reduced NAD
3: ethanoate to acetyl coA
(oxidation so lots of NAD in)
ethanol properties
C2H5OH
small
lipid-soluble
toxic an damages cells
oxidation of ethanol releases 30kJ/g of energy
broken down into harmless products
use of acetyl-coA produced in ethanol metabolism
to Krebs cycle to be used to make energy as ATP
used for fatty acids synthesis (this pathway favoured if lots of NADH)
effects of alcohol consumption
reduced NAD accumulates
therefore reactions oxidised by NAD are less likely to occur
therefore fatty acids accumulate bc not oxidised
therefore fats deposited in the liver -> fatty liver -> cirrhosis
describe how exchange pathways function to maintain relatively constant concentrations of biochemicals in the liver cell
blood acts as transport fluid and has a high HP
tissue fluid created as fluid leaves capillaries, and bathes liver cells
blood transports glucose/a.a’s/glycerol/FAs from gut to liver cell by FD/AT
blood transports O2 from alveoli to liver cells for aerobic respiration
CO2 released by liver cell into blood by diffusion
CO2 transported as HCO3- or carbaminohaemoglobin
CO2 excreted by alveoli
liver cell deaminates excess amino acids & passes ammonia to ornithine cycle
urea diffuses into blood
liver releases glucose due to action of glucagon/glycogenolysis
liver makes steroid hormones & releases into blood by endocytosis
where is the liver located
below the diaphragm
overlaps the stomach towards the RHS of the body
liver weight
1.5kg
how much of body mass does liver make up
3-5%
where does bile leave the liver
via the hepatic duct to the gall bladder
describe blood flow into the liver
hepatic artery carries oxygen blood from aorta to liver
hepatic portal vein carries deoxy blood from small intestine to liver (rich in nutrients)
describe blood flow out of the liver
hepatic vein carries deoxy blood containing amino acids, glucose, plasma proteins, lipids, cholesterol, CO2, urea to the vena cava to the heart
how many lobules does the liver contain
up to 100,000
lobule diameter
look like hexagons
1mm in diameter each
what are individual liver cells called
hepatocytes
what are lobules made up of
hepatocytes
what are hepatocytes arrange in to make up lobules
cords
where do lobules radiate from and to
from centre towards periphery
thickness of lobules
2 cells thick
in close contact w blood
what runs alongside each lobule (at the corners)
interlobular blood vessels (between the lobules)
what are interlobular blood vessels branches of
the hepatic artery and hepatic portal vein
what’s at the centre of each lobule
branch of the hepatic vein (interlobular vessel)
what connects the interlobular and intralobular vessels
sinusoids
what are sinusoids lined by
endothelial cells
what are the pores in endothelial cells of sinusoids called
fenestrations
do sinusoids endothelial cells have a basement membrane
no
why do sinusoids endothelial cells not have a basement membrane
allows hepatocytes to get easy access to nutrients
where are kupffer cells
along the walls of the sinusoids
what are kupffer cells
large macrophages which remove bacteria
destroy old RBCs and WBCs (produces bilirubin to form bile)
where do hepatocytes shed bile
into bile canaliculi
what do bile canaliculi connect up with
a bile ductile
these eventually reach the main bile duct (hepatic duct)
what do hepatocytes contain
prominent nuclei
Golgi aparatus
many mitochondria
glycogen granules
fat droplets
lysosomes
peroxisomes
rough and smooth ER
can hepatocytes replicate
yes
past what point can the liver not regenerate
if 65% of liver lost it can regenerate
past this it cannot
