The Liver

Question 1

What is excretion?

Answer 1

-the removal of waste products of metabolism from the body (waste products from chemical reactions in the cells)

Question 2

Why is it important that substances are removed from the body and don’t build up?

Answer 2

They may be toxic if they build up, causing damage to cells and affecting other metabolic reactions

Question 3

Explain what the 3 main excretory products are in mammals

Answer 3

1) carbon dioxide = waste product of cellular respiration, excreted via the lungs

2) nitrogenous waste = all mammals produce urea in the liver which is then passed to the kidneys to be excreted as urine. Other animals produce different forms of nitrogenous waste

3) bile pigment =produced from the breakdown of haemoglobin in old red blood cells in the liver. These pigments pass to the gall bladder for temporary storage before leaving the body as bile via the intestines

Question 4

What is the difference between egestion and excretion?

Answer 4

-egestion, the release of faeces, is substances that have never been involved in metabolic reactions in cells. It is simply undigested food which never entered the bloodstream

Question 5

List the 4 main structures of the liver

Answer 5

-hepatic artery
-hepatic vein
-hepatic portal vein
-bile duct

Question 6

What is the function of the hepatic artery?

Answer 6

-it supplies the liver with oxygenated blood from the heart, so the liver has a good supply of oxygen for respiration, providing plenty of energy

Question 7

What is the function of the hepatic vein?

Answer 7

-takes deoxygenated blood away from the liver

Question 8

What is the function of the hepatic portal vein?

Answer 8

-brings blood from parts of the small intestine, so it’s rich in products of digestion. This means any ingested harmful substances are filtered out and broken down straight away

Question 9

What is the function of the bile duct?

Answer 9

-takes bile (a substance produced by the liver to emulsify fats) to the gall bladder to be stored

Question 10

Why is it important that blood flows from the stomach and intestines to the liver before it enters general circulation?

Answer 10

So that any toxins can be dealt with which entered the blood from the digestive system can be removed from the blood before it enters general circulation, preventing potential harm to body cells

Question 11

Explain what a hepatocyte and a lobule is?

Answer 11

-a hepatocyte is an individual liver cells
-a lobule is a cylindrical structure made up of rows of hepatocyte, which radiate outwards from the centre

Question 12

What is a liver sinusoid?

Answer 12

-specialised capillaries/ blood channels that flow past the liver cells

Question 13

What is the central vein of a hepatic lobule?

Answer 13

-connects the sinusoids to the centre, which then carries blood away to join the hepatic vein, leaving the liver

Question 14

What are the portal triads?

Answer 14

-made up of a hepatic artery branch, which brings oxygenated blood to the liver cells
-a bile duct, which collects bile and passes it down to the gall bladder
-and a hepatic portal vein which brings digested food to the liver cells from the small intestine

Question 15

What are kupffer cells?

Answer 15

-specialised phagocytic cells which can deal with any pathogens entering the liver
-they are important as prevent infection in the liver, which would be fatal

Question 16

From a diagram how can you tell the difference between the hepatic artery and the hepatic portal vein?

Answer 16

-hepatic portal vein is much bigger in diameter of lumen compared to artery

Question 17

What are canaliculi?

Answer 17

-little channels where the bile produced by the hepatocytes flow
-they flow in the opposite direction to the sinusoids and they drain into branches of the bile duct
-from here the bile passes to the gall bladder for temporary storage, until it is needed and released onto digested food

Question 18

How does bile help with digestion?

Answer 18

-bile emulsifies lipids (fats) = it breaks them down into smaller droplets which have a larger surface area, this can be acted upon more efficiently by lipase enzymes which digest the lipid droplets further

Question 19

What organelles are found in large quantities in a hepatocyte cell and why?

Answer 19

-very large nucleus= carry out lots of protein synthesis (making enzymes for detoxification)
-many Golgi apparatus = modifies and packages the proteins
-many mitochondria = requires lots of energy in the form of ATP for respiration

Question 20

What are some amino acids used for that are released from digested proteins?

Answer 20

-protein synthesis
-repair in our cells

Question 21

What does the body do with left over amino acids?

Answer 21

-can’t be stored
-they are passed to the liver to be converted to urea for excretion
-as they are broken down useful components are kept and are used in the respiration pathway, so the whole amino acid is not excreted

Question 22

Explain the first stage in the formation of urea in the liver

Answer 22

Deamination
-amino acid + oxygen = keto acid + ammonia

Question 23

Explain the second stage in the formation of urea in the liver

Answer 23

The ornithine cycle
-the toxic ammonia from deamination is now converted to urea in a sequence of enzyme-controlled reactions

Question 24

Why do we convert ammonia into urea for excretion, rather then just excreting the ammonia?

Answer 24

-urea is less toxic and less soluble than ammonia
-less water is needed to excrete it from the body, reducing water loss

Question 25

How does the liver deal with alcohol?

Answer 25

-hepatocytes contain the enzyme Alcohol dehydrogenase which is used to convert ETHANOL to ETHANAL -the ETHANAL is then converted to ETHANOATE -this can be converted into FATTY ACIDS then into ACETYL-CO-A (beta oxidation pathway) which then enters RESPIRATION (fed into Krebs cycle)

Question 26

How does the liver deal with too much alcohol?

Answer 26

-the fatty acids produced can’t all enter respiration -instead some of them will accumulate as fat-filled cells inside liver tissue, which gradually replace the functioning hepatocytes -the sinusoids become narrowed, and blood flow is inhibited and irreversible damage occurs to the liver cells -hepatocytes stop functioning, stop dividing and are replaced by fibrous tissues (cirrhosis) -toxins are no longer dearth with and accumulate in the blood, eventually leading to death if the person does not stop drinking

Question 27

Explain how the liver is involved in carbohydrate metabolism

Answer 27

-hepatocytes are closely involved in the homeostatic control of glucose levels in the blood by their interaction with insulin and glucagon -when blood glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose to the storage carbohydrate glycogen -when blood levels start to fall the hepatocytes convert the glycogen back to glucose under the influence of the hormone glucagon

Question 28

Explain the role of the liver in transamination

Answer 28

=the conversion of one amino acid into another. This us important because the diet doesn’t always contain the required balance of amino acids, but transamination can overcome the problems this might cause

Question 29

Explain the role of the liver in detoxification

Answer 29

-levels of toxins in the body increase through metabolic pathways producing potentially poisonous substances, and through choice by alcohol and drugs. The liver is the site where most of these substances are detoxified and made harmless E.g the break down of ethanol into ethanal using alcohol dehydrogenase