NDM Trefor Morgan Liver Questions

1

Which of the fo llowing statements related to the liver anatomy and morphology is not in a correct sequence?


  Splenic vein-penal vein-sinusoids-central vein.

  Superior mesenteric artery-capillaries-portal vein.

  Hepatic artery-capillaries-portal vein.

  Bile canaliculus-intrahepatic ducts-bile duct-duodenum.

  Bile duct-cystic duct-gall bladder-cystic duct-bile duct.


The liver is strategicaly situated so that it is between the blood that goes to the intestine and its return to the systemic ciculation. Thus most foodstuffs that are absorbed go through the liver before they come to the rest of the body. The superior mesenteric artery and inferior mesenteric artery go the intestine and divide into capillaries into which products of digestion are absorbed. They then unite to form veins that enter the portal vein, which comes to the liver. The splenic vein combines with the superior mesenteric vein to form the portal vein, which then divides in the liver into sinusoids, which bathe the liver cels. The blood flows into the central vein of the hepatic lobule. The hepatic artery goes directly to the livery, and the blood flows into the sinusoids and ten into the hepatic vein. The lvier cells are arranged in lobules which take up substances from the blood and secrete them into the bile canaliculi. They unite to for the intrahepatic ducts which the bile duct and enter the duodenum through the Sphincter of Oddi. If the Sphincter of Oddi is closed, the bile, instead of going into the duodenum, comes down the bile duct, goes into into the cystic dct and to he gall bladder wher it can be concentrated. Under the stimuls of cholecystokinin and vagal activity the gall bladder can contract and release bile into the cystic duct into the bile duct which then flows through a relaxed Sphincter of Oddi into the duodenum

2

Which one of the following statements about the liver is not correct?


  Hepatic artery supplies 40% of the liver blood.

  Hepatic artery provides most of the oxygen needs of the liver.

  The liver cells are arranged in lobules.

  Sinusoids allow free access of plasma content to the liver.

  The portal vein is the major source of blood flow to the liver.


The hepatic artery supples between 10% and 20% of the blood to the liver. Thus answer (A) is incorrect. While it supples only this percentage of he blood flow, it does provide most of the oxygen needs of the liver. The liver cells are arranged in lobules with a central vein. The sinusoids through which the portal vein and hepatic artery blood flows allow free access of the plasma contents to the liver cells through the Space of Disse. The major amount of blood flow to the liver comes from the portal vein, which is formed by union of the splenic vein and the superior mesenteric vein.

3

Which one of the following is not a major function of the liver?


  Storage function.

  Excretion or electrolytes.

  Detoxification of exogenous compounds.

  Protein synthesis

  Excretion of bile acid.


The liver is strategically situated and hasa number of very important metabolic functions. It detoxifies exogenous products absorbed from teh gastrointestinal tract. It has a storage function storing a large number of different compounds, in particular, glycogen vitamin B12 and copper. Storage functions can be disrupted and can cause varios diseases. It is the important synthetic organ of the body, synthesising a large number of proteins, particularly those which are carried in the plasma. It is involved in the formation of bile acids and bile acides are secreted in the bile. In the bile some electrolytes are secreted, but it is not an important site of excretion of electrolytes from the body. The secretion of electrolytes that takes place enables thebile to be in solution and these electrolytes are all absorbed by the gastrointestinal tract.

4

Which one of the fo llowing is not a major function of the liver?


  Regulation of cholesterol metabolism.

  Storage of vitamin B12.

  Regulation of carbohydrate metabolism.

  Regulation of bilirubin formation.

  Regulation or protein metabolism.


The liver is a major regulator of carbohydrate and protein metabolism, storing glucose in the form of glycogen and regulating the delivery of amino acids to the periphery. It is also an important regulator of cholesterol and lipoprotein function. It stores vitamin B12. While the liver is important inthe handling of bilirubin, the formation of bilirubin is by breakdown of haeme and this takes place in the reticuloendothelial system of the body.

5

Bile contains all of the following except for:


  Triglycerides.

  Cholesterol.

  Bile acids.

  Electrolytes.

  Phospholipids.


The bile contains a large number of susbtances. It contains bile acids, cholesterol, electrolytes, phospholipids and other lipid substances. HOwever, there is no significant amount of triglycerides present in the bile.

6

The following are all important functions of the liver except for:


  Synthesis of albumin.

  Release of glucose.

  Breakdown of glycogen.

  Formation of glycogen.

  Synthesis of bilirubin.


The liver is involved in the synthesis of albumin and in the formation and breakdown of glycogen, depending on the body's requirements for glucose. The breakdown of glycogen releases glucose to the rest of the body. The lier is not involved inthe synthesis of bilirubin. It is involved in teh synthesis of bile acids and the conjugation of bilirubin.

7

The following are all important functions of the liver except for:


  Synthesis of blood clotting factors.

  Synthesis of fibrinogen.

  Synthesis of albumin.

  Synthesis of globulins.

  Synthesis of blood clotting factoris is vitamin K-dependent.


The liver is an important site of synthesis of plasma proteins. Thus it synthesises albumin, fibrinogen and the blood clotting factors. Te systhesis of blood clotting factors is vitamin K-dependent. However, the syntehsis of globulins is predominantly done by the lymphoid tissue rather than the liver.

8

The following are all important functions of the liver except for:


  Synthesis of glucose from fatty acid.

  Synthesis of glucose from proteins.

  Breakdown of glucose.

  Release of glucose.

  Regulation of blood sugar level.


The liver is an important site in regulating glucose metabolism. It can synthesis glucose from proteins. It can break down glucose by the glycolytic pathway and the Krebs cycle. It can release glucose from glycogen and thereby regulate the blood sugar level. While the liver can synthesis glucose from proteins it is unable to synthesis glucose from fatty acid breakdown products, which is predominantly acetyl Co-A. It can metabolise these provided there are carbohydrates present to drive the citric acid cycle. If carbohydrates are used up fatty acid breakdown leads to keton body formation.

9

The following are all important functions of the liver except for:


  Synthesis of urea.

  Formation of the essential amino acids.

  Transamination of amino acids.

  Release of glucose.

  Detoxification of endogenous toxins.


The liver is important in synthesising urea from the amine of amino acids. It can also transaminate amino acids, thereby making certain that the amino acids are presented in appropriate proportions. It is unable to synthesis the essential amino acids. The word 'essential' means that they have to be suppled from the outside. This is because it cannot synthesis the carbon skeleton of these amino acids. It releases glucose from glycogen, as mentioned previously, and is also important in detoxification of endogenous toxins, which are produced by the body.

10

All the statements related to bilirubin are correct except for:


  Bilirubin undergoes enterohepatic circulation.

  Secretion of bilirubin into the canaliculus is the rate-limiting step in bilirubin handling by the liver.

  Bilirubin is conjugated with glucuronide.

  Unconjugated bilirubin is carried in plasma bound to albumin.

  Unconjugated bilirubin is water-insoluble.


Bilirubin is formed by the reticuloendothelial system and unconjugated bilirubin formed is carried in plasma bound to albumin. This unconjugated bilirubin is water-insoluble but lipid-soluble. Thus it can accumulated in the brain but is not able to be excreted by the kidney. In the liver the bilirubin is taken into the liver cells and is conjugated with glucuronide. The rate-limiting step for bilrubin to get into the canaliculus is secretion across the basolateral membrane. Bilirubin, once it is in the gastrointestinal tract, undergoes a series of metabolic changes, but it is not reabsorbed to any significant extent. Bile salts, not bilirubin, are reabsorbed and undergo enterhepatic circulation.

11

All of the following statements related to bile are correct except for:


  Approximately 1 litre/day is formed.

  Is always supersaturated with cholesterol.

  Cholesterol is kept in solution by bile salts and phospholipids.

  Approximately 98% of bile salts are reabsorbed and undergo enterohepatic circulation.

  Gall bladder concentrates bile 10-20 times.


The liver forms approximately 1 litre/day of bile. THis may be concentrated in the gall bladder 10-20 times. Cholesterol is relatively insoluble in awter but is maintained in solution because of interations with bile salts and phospholipids. Thus more cholesterol is carried than would occur in water. Bile is thus not a supersaturated solution of cholesterol, particularly when there is rapidbile formation. It may possibly become 'supersaturated' in the gall bladder. Bile salts are reabsorbed and undergo enterohepatic circulation (i.e. they are re-excreted by the liver from the portal blood). THe reabsorption is very efficient and about 98% are reabsorbed.

12

All of the following statements related to bile and bile salts are correct except for:


  Bilirubin is the excretion product of haemoglobin.

  The total pool of bile salts is about 4g.

  Bile salts undergo enterohepatic circulation.

  Retention of bile salts causes itch.

  Approximately 5g of bile salts are synthesised each data and lost in the faeces.


Bilirubin is the extretion product of haemoglobin. Bile salts aer formed by the liver and the total pool of bile salts in the body is about 5g. Bile salts, which are secreted into teh gastrointestinal tract are absorbed in the terminal ileum, enter the portal vein and are re-excreted by the liver. If bile salts accumulate in the body they cause itch; accumulation will occur when the bile duct is blocked. However, the wrong answer is the amount of bile salts synthesised each day. It is probably closer to 0.5g rather than 5g owing to the extensive recycling that takes place.

13

All Lhe statements related to cholesterol are correct except for:


  LDL is formed in the liver.

  VLDL is formed in the liver.

  Apoproteins are formed in the liver.

  Elevated HDL reduces the risk of vascular disease.

  Cholesterol is an essential component of membranes.


Very low density lipoproteins (VLDL) are formed in the liver. In the circulation and peripher VLDL has triglycerides removed and LDL is formed via an intermediate step (IDL). High density lipoproteins (HDL) are formed in the liver, and a high level of HDL apears to reduce the risk of vascular disease. While excess cholesterol causes problems to humans, it is an essential component of membranes.

14

All the statements related to cholesterol are correct except for:


  Elevated triglycerides are associated with heart disease.

  Elevated LDL is associated with heart disease.

  Cholesterol is transported in lipoprotein complex.

  Extra cholesterol in the diet increases liver cholesterol synthesis.

  Cholesterol production is increased by low liver cell cholesterol.


ELevated triglycerides are associated with heart disease. Elevated LDL is also directly asociated wth eart disease. Cholesterol, which is insoluble to water, is transported around th ciculation in a lipoprotein complex. Cholesterol may be transported to the tissues and transported back to the liver for metabolism. The has good homeostatic control of cholesterol and, when the liver cell cholesterol is low, production of cholesterol by the liver is stimulated. Cholesteron in the diet does not increase the synthesis of cholesterol in the liver. It probably decreases it because the cholesterol which is presented to the liver after absorption is taken up, so that the liver does not synthesise as much cholesterol as before. However, excessive cholesterol in the diet can elevate blood cholesterol levels.

15

All Lhe statements related to cholesterol are correct except for:


  Bile salts are formed from cholesterol

  Poor bile salts absorption reduces liver cholesterol production.

  Poor absorption of bile salts reduces plasma cholesterol.

  Cholesterol is a precursor of steroid hormone.

  Exercise increases HDL.


Bile salts are formed from cholesterol and are an important mechanism of cholesterol excretion. If bile salts are not absorbed from the gastrointestinal tract more cholesterol is converted into ile salts, ad thus the liver cell and plasma cholesterol will fall. The fall in cholesterol in the liver cell increases the production rate and uptake of cholesterol by the liver. Cholesterol is a precursor of many of the steroid hormones which are formed, particularly in the adrenal and sex glands. Exercise increases the high density lipoprotein content of the body, and this is one mechanism bywhich exercise may be beneficial in protecting the body from atherosclerosis.

16

All the statements related to cholesterol are correct except for:


  Cholesterol production is increased by low liver cell cholesterol.

  Cholesterol is an essential component of membranes.

  Cholesterol in the diet is the most important cause or high blood cholesterol.

  Saturated fatty acids control the synthetic rate of cholesterol.

  Absence of LDL receptors results in a high plasma cholesterol.


Cholesterol production rate by the liver cells is increased if the liver cel cholesterol is low. The cholesterol produced is an essential component of membranes. If there are no LDL receptors present, as occurs in certain genetic diseases, the liver cells see a low cholesterol internally, thus producing more cholesterol, which results in a high plsama cholesterol level. The factors that control the level of cholesterol are not absolutely understood, but a diet high in saturated fatty acids increases the synthetic rate of cholesterol, and a high saturated fatty acid iet elevates blood cholesterol level. This appears to be more important than cholesterol in the diet. Cholesterol in the diet, if in excessive amounts, can levate blood cholesterol, but i general it has nowhere near the same effect as a high saturated fatty acid intake.

17

All the statements related to cholesterol are correct except for:


  Apoproteins are produced in he liver.

  Chylomicrons are formed in the liver.

  HDL is formed inthe liver.

  VLDL is formed in the liver.

  Cholesterol is a precursor of steroid hormone.


The liver forms teh apoproteins which are important for the protein struture of the lipoproteins involved in both HDL and VLDL formation. The liver also packages cholesterol and other lipids in VLDL and HDL. Cholesterol, as mentioned above, is a precursor of the steroid hormones. Chylomicrons are important in carry cholesterol around the body, but the chylomirons are formed in the intestinal cells, go into the lacteals and enter the bloodstream through the thoracic duct. They come to the liver where they are rboken down adn the other components of lipid transports are formed.

18

All the statements related to cholesterol are correct except for:


  Absence of ileum decreases cholesterol level.

  Absence of LDL cholesterol increases cholesterol synthesis.

  Cholesterol in the diet increases LDL production.

  Absence of LDL cholesterol results in a high plasma cholesterol.

  Saturated fatty acids control the synthetic rate of cholesterol.


See Questions 14, 15 and 16. If the ileum is not present bile acids will not be reabsorbed. As bile acids are not reabsorbed more cholesterol will be broken down into bile acids. This will result in a decrease in the cholesterol level. This is used therapeutically by ingesting bile acid binding resins that prevent the bile acids being reabsorbed, thus lowering cholesterol. owever, lowering of cholesterol is not as great as would b expected because the level of cohlesterol inside te lvier cell falls and this decrease in cholesterol lvel increases the synthetic rate. If cholesterol from the plasma cannot be taken up into the liver cells, which occurs when there are no LDL receptors, cholesterol synthesis increases, and this results in a high plasma cholesterol level. Cholesterol in the diet does not directly increase LDL production. LDL is not produced by the liver and it is not stimulated by cholesterol intake.

19

All the statements related to cholesterol are correct except for:


  Alcohol decreases HDL.

  Smoking reduces HDL.

  Exercise increases HDL.

  Decreased fat intake decreases HDL.

  Elevated HDL reduces the risk of vascular disease.


A high HDL level reduces the risk of vascular disease. The HDL level is modified by a number of factors. A reduced fat diet reduces the total cholesterol level and the CLDL and LDL level, but also causes a fal in HDL. Exercise will increase the HDL level. Smoking reduces the HDL level, and is one reason why smoking is associated with atherosclerosis. Alcohol increases the HDL level and this may be one of the mechanisms to explain why people who drink one or two alcoholic drinks a dayhave a better cardiovascular prognosis than teetotallers.

20

If the bile duct is obstructed, which one of the following processes will be predominantly affected?


  Formation of glycogen.

  Synthesis of coagulation factors.

  Synthesis of albumin.

  Conjugation of bilirubin.

  Detoxification of exogenous and endogenous products.


Obstruction othe bile duct will not have any major effect on the metabolic functions of the liver. The liver will still be able to form glycogen, synthesis albumin, conjugate bilirubin and detoxify exogenous and endogenous products. The prblem will occur with the synthesis of coagulation factors. This is not because the liver cannot synthesis coagulation factors but, in the absence of bile salts inthe gastrointestinal tract, vitamin K wil not be absorbed, so that a precursor required for the synthesis o coagulation factors by the liver is not present. The administration of vitamin K parenterally will supply vitamin K to the liver, which can then synthesis coagulation factors in a normal way.

21

Which one of the following is the rate limiting step for the excretion of bilirubin.


  Diffusion of bilirubin through the Space of Disse.

  Binding of bilirubin to the membrane at the blood surface.

  Transport of bilirubin across membranes at the blood surface.

  Conjugation of bilirubin with gucuronide.

  Secretion of conjugated bilirubin across basolateral membrane.


Unconjugated bilirubin, which is formed by the reticuloendothelial system, is carried through the circulation bound to albumin. The Space of Disse is between the sinusoids and the liver cells. Albumin readily goes though the sinusoid fenestrae and bilirubin is presented to the surface membrane of the liver cell. The bilirubin binds to receptors on the surface membrane and is taken up across the blood surface membrances. It is conjugated glucuronide in the liver cells. The rate-limiting step is the secretion of conujgated bilirubin across the basolateral membrane. Even in people who have disease of the liver cells conjugation of bilirubin still occurs. In liver disease, wheter it is due to obstruction ofthe bile duct or to hepatocellular disease, conjugated bilrubin increases in the circulation. This conjugated bilirubin is able to be excreted by the kidey and is the reason that people withjaundice have a yellow urine. Unconjugated bilirubin is not excreted by the kidney.

22

Questions 22 to 30 refer to the diagram below which represents part of a liver lobule. Points are labelled A, B, C, D, E. Select the answer which matches the location or process given. Space of Disse


  A

  B

  C

  D

  E


The sinusoid is separated from the liver cell by the Space of Disse (A). The sinusoid has fenestrae, and bilirubin bound to albumen enters the Space of Disse. The bilrubin is taken up and crosses the mebrane (B) into the cell where it is conjugated with glucuronide (C). It is then excreted across the basolateral membrane (D) and this is the rate-limiting step in bilirubin secretion. Kupfer cells, part of the reticuloendothelial stem, are present in the Space of Disse (A). Insulin acts on the membrane (B) to promote the uptake of glucose, which is synthesised into glycogen (C). Electrolytes are secreted into the bile canaliculs to allow bile flow (E).

23

This question refers to the diagram in Question 22. Rate-limiting step for bilirubin secretion.


  A

  B

  C

  D

  E


See the explanation for Question 22.

24

This question refers to the diagram in Question 22. Bilirubin bound to albumin.


  A

  B

  C

  D

  E


See the explanation for Question 22.

25

This question refers to the diagram in Question 22. Bilirubin glucuronide formed.


  A

  B

  C

  D

  E


See the explanation for Question 22.

26

This question refers to the diagram in Question 22. Kupfer cells.


  A

  B

  C

  D

  E


See the explanation for Question 22.

27

This question refers to the diagram in Question 22. Site of bile acid formation.


  A

  B

  C

  D

  E


See the explanation for Question 22.

28

This question refers to the diagram in Question 22. Site of electrolyte secretion.


  A

  B

  C

  D

  E


See the explanation for Question 22.

29

This question refers to the diagram in Question 22. Principal site of action of insulin.


  A

  B

  C

  D

  E


See the explanation for Question 22.

30

This question refers to the diagram in Question 22. Glycogen synthesis.


  A

  B

  C

  D

  E


See the explanation for Question 22.