Havering Sixth Form College
Biology A2 Optional unit
Mammalian Physiology and Behaviour.
Liver.
1
(a) Describe the gross structure of the liver, including its associated blood vessels. p.17-19.
Blood supply:
double blood supply(receives twice as much blood);
hepatic artery supplies oxygenated blood;
hepatic portal vein supplies blood rich in products of digestion (amino acids, fatty acids, glucose etc) / coming
from digestive system;
blood leaves by the hepatic vein;
(liver has high metabolic rate – high oxygen requirement)
blood leaving the liver via hepatic vein has:
more urea;
less oxygen;
more carbon dioxide;
less amino acids;
less bile salts;
less vitamins;
less fatty acids;
less glucose;
2
(b) Describe the histology of the liver and recognise this using the light microscope.
liver consists of lobules;
branch of hepatic vein at centre of each lobule;
branches of hepatic artery and hepatic portal vein and bile duct;
run between lobules;
made up of hepatocytes;
arranged in rows / plates;
sinusoids run between these rows / parallel to canaliculi;
bile canaliculi run between rows / parallel to sinusoids;
hepatocytes / canaliculi lined with microvilli;
each hepatocyte in contact with sinusoid and canaliculus;
endothelial cells line sinusoids;
pores present in lining;
Kupffer cells present;
Look at this website and use to revise the structure of the GI tract and explain how each organ differs and is
adapted for it’s function. http://www.mednote.co.kr/11CYTOHISTO.htm
CV represents the central vein label the other parts of the lobule on this section
3
(c) Explain the roles of the liver in carbohydrate metabolism and the production of glucose from amino
acids. p.19-20.
liver maintains / controls blood glucose level;
fall in blood glucose causes secretion of glucagon;
causes glycogenolysis / conversion / breakdown of glycogen to glucose;
also causes release of adrenaline;
gluconeogenesis / glucose synthesis;
from lactate / amino acids / glycerol / fatty acids;
via pyruvate;
rise in blood glucose causes secretion of insulin;
causes liver (cells) to increase uptake of glucose;
causes glycogenesis / conversion of glucose to glycogen;
glycogen stored in the liver;
glucose respired by liver cells;
excess glucose converted to fat ;
4
(d) Explain the roles of the liver in fat metabolism, including the use of fats in respiration, the
synthesis of triglycerides from excess carbohydrate and protein, the synthesis and
regulation of cholesterol, and the transport of lipids to and from the liver as lipoproteins.
(No biochemical details are required.) p.20-22.
(fat) used as a respiratory substrate / energy source / for respiration;
(fat) used for ATP production;
(liver) converts fatty acids to ketones;
which are then taken from liver to other areas of the body;
excess carbohydrate converted to lipid;
triglyceride synthesis;
stored as adipose tissue;
lipoprotein formation;
cholesterol synthesis;
for cell membranes / steroid hormones;
reduced synthesis of cholesterol when present in diet;
saturated dietary fats cause increase in liver synthesis of cholesterol;
removes excess cholesterol from blood;
removes excess phospholipids from blood ;
Use this metabolic pathway to follow some of the liver functions
Try this website to investigate some of the other liver metabolic pathways
http://www.humboldt.edu/~rap1/BiochSupp/PathwayDiagrams/PathIndex.html
5
(e) Explain the roles of the liver in deamination, transamination and urea formation. (An
outline of the ornithine cycle is all that is expected.) p.22-24.
breakdown of excess amino acids;
deamination / removal of amino group / from amino acid;
in hepatocytes;
production of ammonia;
which is toxic;
ammonia combined with carbon dioxide;
to form urea;
which is less toxic;
via ornithine cycle;
remainder of amino acid molecule converted/metabolised/changed to fat/glucose/carbohydrate/stored;
(or) used in respiration;
plasma protein production;
named example of plasma protein;
lipoprotein production;
reference to transamination;
to produce new amino acids;
breakdown of haemoglobin;
6
(f) Describe the production and use of bile.
p.24-25.
Production of bile:
Complete:
Look at this website for more details of how Bile is produced.
http://www.studentbmj.com/back_issues/1098/data/1098ed3.htm
Content of bile:
bile pigments / biliverdin;
bilirubin;
bile salts / Na glycocholate;
Na taurocholate;
cholesterol;
(inorganic) salts / NaHCO3;
Use of Bile:
allows lipids to form an emulsion;
decreases surface tension of, fats / oil droplets;
increases surface area of droplets;
allows more efficient breakdown by lipase;
neutralises the acidic, chyme / stomach contents;
method of excretion;
and detail, e.g. products of haemoglobin breakdown;
(bile salts ‘activate’ lipase).
7
Use this website for liver structure and function
http://www.biologymad.com/master.html?http://www.biologymad.com/A2Biology.htm
8
(g) Describe the production, and explain the roles, of the plasma proteins fibrinogen, globulins and
albumin.
p.23-24.
fibrinogen / prothrombin important in blood clotting;
fibrinogen converted into fibrin;
soluble into insoluble;
prothrombin converted into thrombin;
inactive to active;
globulins / globular proteins transport substances;
e.g.
thyroxine/insulin/phospholipids/lipids/cholesterol/iron/vitamins A/E/B12/D/K;
albumen transports substances;
e.g.
hormones/thyroxine/drugs/aspirin/penicillin/vitamins A and/or
C/acetylcholine/bilirubin/calcium/copper/zinc;
exert a solute potential / maintain osmotic pressure / maintain concentration of blood;
reference to role of plasma proteins in regulating viscosity / density of blood (and importance in determining
pattern of blood flow in vessels );
reference to buffering effect of plasma proteins (combine with hydrogen ions);
Breakdown of haemoglobin:
haemoglobin broken down to haem and globin;
globin broken down to its constituent amino acids;
iron removed from haem (not haemoglobin);
inside Kupffer cells / phagocytes;
iron combined with transferrin / plasma protein;
(transferrin iron complex) released into blood;
iron used to make new haemoglobin ;
in bone marrow;
or stored as ferritin;
in hepatocytes / liver;
(remainder of haem – not haemoglobin) is converted to biliverdin / bilirubin / bile pigment;
Jaundice is frequently an indication of liver damage. In this condition, the skin takes on an abnormal yellow
coloration because the bile pigments are circulating in the blood as they are not excreted because hepatocytes
are unable to remove them from the blood.
Use this website for liver function
http://www.biologymad.com/master.html?http://www.biologymad.com/A2Biology.htm
9
(h) Outline the roles of the liver in detoxification.
p.25-26.
produced by deamination / breakdown of excess amino acids / nitrogenous bases;
converted to urea;
which is less toxic / poisonous / harmful ( R dangerous);
by ornithine / urea cycles ;
breakdown of alcohol / antibiotics / other named type of drug / bacterial toxins / lactic acid;
taken up by hepatocytes / liver cells;
combined with other substances / oxidised / reduced / methylated;
on smooth E.R.;
breakdown of steroid hormones / oestrogen / progesterone;
(liver dealing with) heavy metals / copper / lead;
10
(i) Describe the metabolism of alcohol in the liver, and the long term consequences of
excessive alcohol consumption.
p.25-26.
Metabolism of alcohol:
alcohol is metabolised instead of fat / carbohydrate (alcohol is used as a source of energy, it has a high calorific
value;
alcohol is metabolised to ethanal;
using the enzyme alcohol dehydrogenase;
with NAD used as the hydrogen carrier;
ethanal is converted to ethanoic acid / ethanoate / (active) acetate;
using the enzyme ethanal dehydrogenase;
acetyl CoA / enters Krebs cycle / is oxidised / is respired to CO2 and H2O;
synthesis of fatty acids;
Look at this website for details of the role of alcohol dehydrogenase
http://tutor.lscf.ucsb.edu/instdev/sears/biochemistry/presentations/f00_student_presentations/suhair/buttons.htm
Long term consequences of excessive alcohol consumption:
Hepatitis:
fatty deposits develop inside cells / ‘fatty liver’;
inflammation;
Cirrhosis:
cells die;
fibrous tissue begins to develop;
collagen;
nodules develop;
cells grow within nodules;
(and) do not receive a good blood supply;
11
Look at this website for more details on cirrhosis http://www.bnaiyer.com/health/liver-2.html
tumours develop /cancer;
Look at this website for more details on liver cancer http://www.livercancer.com/liver_upclose.html
And liver diseases use http://www.biologymad.com/master.html?http://www.biologymad.com/A2Biology.htm
Social consequences:
Family: violence; family breakdown / divorce; child abuse; poverty as a result of cost of drink / parental neglect;
teenage drinking; unwanted pregnancies; family disputes (between parents and children); unemployment;
homelessness; children of alcohol-dependent parents often become dependent themselves;
Crime: drunk and disorderly; vandalism; accidents at home / at work; road accidents involving drunk drivers;
drunken pedestrians; murder; crime; sexual crimes; high proportion of alcoholics in prison population.
Costs: police; court costs; fire service / ambulance service for road accidents etc.; cost to NHS for treatment of
alcoholism and related diseases;
NB/ Links to nervous system chapter / Effects of alcohol on the nervous system:
inhibitory / integrating activity of cerebral cortex / higher centres is lost;
loss of speech control / impaired vision;
respiratory / cardiovascular centres depressed;
enlargement of (brain) ventricles;
shrinkage of brain cells;
loss of cells in cortex;
short term memory loss;
poor (motor) co-ordination / balance;
impaired judgement;
dementia;
sleep disturbance / reduced REM sleep;
confusion / disorientation / anxiety / hallucinations;
damage to brain due to hypoxia / hypoglycaemia;
12
The liver 1
The liver synthesises almost all of the plasma proteins in the body. One of these is albumin.
(a)
Describe
(i)
how plasma proteins, such as albumin, act as buffers;
[2]
(ii)
the other functions of albumin in the blood.
[3]
Thromboplastin, fibrin, prothrombin, fibrinogen and thrombin are all molecules involved in the blood clotting
process.
(b)
(i)
(ii)
State which two of these are plasma proteins synthesised by the
liver.
[2]
Describe the role of thrombin in the blood clotting process.
[2]
Lipoproteins are another class of proteins synthesised by the liver. They transport lipids to and from the liver. The
liver produces mainly very low density lipoproteins (VLDLs) which transport triglycerides also synthesised by the
liver.
(c)
Suggest what could happen if VLDL synthesis could not keep pace with triglyceride synthesis.
[1]
Small losses of fat from the body occur daily, for example, in the faeces.
(d)
State three ways in which these losses can be replaced.
[3]
[Total: 13
ESSAY Q
Explain the role of the liver in the maintenance of nutrient levels in the body.
(11)
13
Drugs 1
Alcohol is mainly eliminated from the body by being metabolised in the liver.
(a)
Describe briefly how alcohol is metabolised in the liver.
[4]
Fig. 1 is a micrograph of a section, as seen through a light microscope, of the liver of a young person who was
heavily dependent on alcohol.
Fig. 1
(b)
(i)
Suggest why many of the liver cells shown in Fig. 1 are enlarged and appear white.[1]
(ii)
Explain how alcohol dependence in a young person may lead to this condition.
[3]
(c)
Describe how a section through the liver of someone suffering from cirrhosis would differ from that
shown in Fig. 1.
[3]
(d)
State two ways in which drinking alcohol reduces the ability of a person to drive a car.
[2]
Total: 13
14
Student Self-Assessment Checklist: Liver
Now that you have done the Key Assessment for this unit assess yourself on the following
learning outcomes:
Do you
Do you
Learning Outcome
understand it?
know it?
YES/NO
YES/NO
(a) Describe the gross structure of the liver, including its
associated blood vessels. p.17-19.
b) Describe the histology of the liver and recognise this
using the light microscope
c) Explain the roles of the liver in carbohydrate
metabolism and the production of glucose from amino
acids. p.19-20.
(d) Explain the roles of the liver in fat metabolism,
including the use of fats in respiration, the
synthesis of triglycerides from excess carbohydrate and
protein, the synthesis and
regulation of cholesterol, and the transport of lipids to
and from the liver as lipoproteins.
(No biochemical details are required.) p.20-22.
(e) Explain the roles of the liver in deamination,
transamination and urea formation. (An outline of the
ornithine cycle is all that is expected.) p.22-24.
(f) Describe the production
and use of bile.
p.24-25.
(g) Describe the production, and explain the roles, of the
plasma proteins fibrinogen, globulins and albumin.
p.23-24.
Breakdown of haemoglobin:
(i) Describe the metabolism of alcohol in the liver,
Describe the long term consequences of
excessive alcohol consumption. p.25-26.
TOTAL YES
NO
YES
NO
Overall:
How well do you understand this unit (see total)?
How well do you know this unit (see total)?
Which methods suit your style of learning?
Have you completed the background reading and extention activities?
Have you asked for extra support and explain anything you don’t confidently understand?
Any comments to help your tutor teach this unit better next year.
15
MARK SCHEMES
The liver 1
(a)
(b)
(i)
when blood pH is acidic/low / when the H+ concentration of blood is high;
albumin/plasma proteins pick up H+;
restoring pH to normal / increasing pH / reducing H+ conc. of blood;
2 max
(the converse argument is also acceptable i.e. “when blood pH is alkaline...”)
(ii)
forms a colloid in plasma / contribute to viscosity / density of plasma;
generates osmotic potential / generates solute potential / maintains osmotic concentration;
transports molecules;
e.g. hormones / thyroxine / bilirubin / minerals /calcium / copper / zinc / drugs / aspirin / penicillin
/ vitamin A / vitamin C / acetylcholine;
3
(i)
fibrinogen;
prothrombin;
2
(ii)
acts as an enzyme;
hydrolyses / breaks down / converts fibrinogen;
into fibrin;
i.e. soluble to insoluble;
2 max
(c)
triglycerides accumulate in the liver / ‘fatty liver’ / fat droplets in cytoplasm of liver cells;
1
(d)
intake of fats in the diet;
synthesis of fats;
from glucose / carbohydrate;
from amino acids;
from ketones;
3 max
16
(b)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
1.
2.
3.
4.
5.
6.
1.
2.
3.
4.
5.
6.
7.
1.
2.
3.
4.
5.
6.
Explain the role of the liver in the maintenance of nutrient levels in the body
[11]
control of blood glucose levels
insulin increases / stimulates / causes ;
synthesis of glycogen from glucose / glycogenesis;
glucose uptake by liver;
increased respiration of glucose;
glucose stored as glycogen;
glucagon increases / stimulates / causes;
breakdown of glycogen to glucose / glycogenolysis;
adrenaline increases breakdown of glycogen;
gluconeogenesis;
ref. to amino acids / glycerol / lactate / fatty acid being converted into glucose;
control of blood amino acid levels
excess amino acids deaminated;
(amino group) converted to ammonia;
(ammonia) converted to urea;
via ornithine cycle;
remainder of molecule used in respiration;
transamination / conversion into different amino acids;
control of blood lipid levels
conversion of excess carbohydrate / protein to lipids ; for storage;
use of lipid as respiratory substrate / for energy;
cholesterol synthesis;
for use in cell membranes / steroid hormones / named hormone / waterproofing skin;
breakdown / removal from blood of (excess) cholesterol / phospholipids;
lipoprotein formation;
for lipid transport;
vitamins / minerals
storage site for vitamins;
e.g. A / D / B12 / C / E / K;
storage site for mineral elements;
e.g. Cu / Zn / Co / Mb / Fe / K;
iron stored as ferritin;
ref. to release of vitamins / minerals in time of shortage; max 5 for any nutrient
17
Drugs 1
(a)
(b)
(c)
(d)
dehydrogenase;
(ethanol) to ethanal;
enters mitochondrion;
to (‘active’) acetate;
enters Krebs cycle;
NAD to reduced NAD;
carbon dioxide and water / converted to fats;
(i)
fatty liver / liver cells contain droplets of fat / fat stores;
(ii)
alcohol is used as a source of energy;
high calorific value;
less fat / fatty acids respired;
reduced NAD accumulates;
some used in production of fat;
max 4
1
max 3
scarring / fibrous tissue / collagen fibres;
nodular;
obstructed blood vessels;
many dead liver cells;
max 3
slower reflexes / longer reaction time / slower to react;
poor co-ordination;
slower transmission of (nerve) impulses;
limited ability to see red lights / blurred vision;
overconfidence / release of inhibitions;
depression of nervous system / depressant;
poor judgement of speed / distance;
loss of concentration;
aggressive behaviour;
max 2
18