Excretion and liver

Question 1

Define the term excretion

Answer 1

The removal of metabolic waste products from the body

Question 2

Explain the importance of excretion in maintaining metabolism and homeostasis.

Answer 2

1. Waste products are toxic if they are allowed to build up

2. Maintains the water balance and pH

Question 3

Name the 3 main metabolic waste products in mammals, describe where they come from and where they are excreted

Answer 3

1. Carbon dioxide- One of the waste products of cellular respiration which is excreted from the lungs
2. Bile pigments- Formed from the breakdown of haemoglobin from old red blood cells in the liver. They are excreted in the bile from the liver into the small intestine via the gall bladder and bile duct. They colour faeces.
3. Nitrogenous waste products (urea)- formed form the breakdown of excess amino acids by the liver. Urea is excreted by the kidneys in the urine.

Question 4

Name the nitrogenous waste products in mammals, fish, birds and insects.

Answer 4

1. All mammals produce urea as their nitrogenous waste.
2. Fish produce ammonia
3. Birds and insects produce uric acid.

Question 5

Describe the location of the liver in mammals and draw and label a diagram to show the blood vessels going to and from the liver.

Answer 5

1. It lies just below the diaphragm and is made up of several lobes
2. Oxygenated blood goes to the liver via the hepatic artery (branched off from the aorta)
3. Deoxygenated blood is removed from the liver via the hepatic vein (which joins to the inferior vena cava)
4. The liver is also supplied with blood by the hepatic portal vein. This carries blood loaded with the products of digestion straight from the intestines to the liver.

Question 6

Name the type of cell which makes up the liver and describe the adaptations they have for their functions.

Answer 6

1. Hepatocytes have a large nuclei
2. prominent Golgi apparatus
3. lots of mitochondria, indicating they are very metabolically active cells

Question 7

Draw and label a diagram to show the arrangement of tissues within the liver.

Answer 7

p416 Difficult to explain

1. Venule from hepatic portal vein and arteriole from hepatic artery mix in the sinusoids
2. The sinusoids are surrounded by hepatocytes
3. There is a big white space in the middle which is the bile canaliculli.
4. There are Kupffer cells on the hepatocytes

Question 8

Label and annotate a photomicrograph of liver tissue at low and high power to show key histological features

Answer 8

1. Low power- Central vein is big white circle type thing
   - Sinusoids are white lines in the pink
   - The cells are pink parts with nuclei in
2. High power- Can see red blood cells in white sinusoids
   - Kupffer cells can be seen around the edge of sinusoids
   - Hepatocytes are big pink areas- can see nucleus and little dots which are mitochondria

Question 9

Describe the role of Kupffer cells in the liver.

Answer 9

1. Act as resident macrophages of the liver, ingesting foreign particles and helping to protect them from disease.
2. They are in the sinusoids

Question 10

What are the sinusoids

Answer 10

1. Blood from hepatic artery and hepatic portal vein is mixed in spaces called sinusoids which are surrounded by hepatocytes.
2. This mixing increases the oxygen content of the blood from the hepatic portal vein, supplying the hepatocytes with enough oxygen for their needs.
3. They contain Kupffer cells

Question 11

Describe how bile is formed and how it travels to where it is stored.

Answer 11

1. Hepatocytes secrete bile from the breakdown of the blood into spaces called the canaliculi
2. From these, the bile drains into the bile ductiles which take it to the Gall bladder.

Question 12

Describe 6 roles of the liver.

Answer 12

1. Carbohydrate metabolism
2. Deamination of excess amino acids
3. Synthesis plasma proteins
4. (Transamination)
5. Production of urea (ornithine cycle)
6. Detoxification
7. Production of bile

Question 13

Describe the role hepatocytes play in the control of blood glucose concentration.

Answer 13

1. Carbohydrate metabolism
2. When blood glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose to the storage carbohydrate glycogen.
3. When blood glucose levels start to fall, the hepatocytes convert the glycogen back to glucose under the influence of the hormone glucagon

Question 14

Define the term transamination

Answer 14

1. The conversion of one amino acid into another.
2. This is important because the diet does not always contain the right balance of amino acids but transamination can over come the problems this might cause.

Question 15

Define deamination

Answer 15

1. The removal of the amino group from amino acids

Question 16

Describe the process of deamination.

Answer 16

1. The body cannot store either proteins or amino acids.
2. Any excess ingested protein would be excreted and therefore wasted if it were not for hepatocytes
3. They deaminate the amino acids removing the amino group, and converting it first into ammonia which is very toxic and then into urea
4. Urea is toxic in high concentrations but not in concentrations normally found in the blood.
5. Urea is excreted by the kidney.
6. The remainder of the amino acid can then be fed into cellular respiration or converted into lipids for storage

Question 17

Draw a diagram to show how urea is produced from excess amino acids via the ornithine cycle.

Answer 17

1. Ornithine + NH3 + CO2 → H2O + Citruline
2. Citruline + NH3 → H2O + Arginine
3. Arginine + H2O → Urea + ornithine
   Overall: 2NH3 + CO2 → H2O + Urea

Question 18

Define the term detoxification

Answer 18

1. Removal or breakdown of toxins.

Question 19

Give two examples of detoxification by the liver.

Answer 19

Hydrogen peroxide
1. Breakdown of hydrogen peroxide (a by-product of various metabolic pathways in the body)
2. Hepatocytes contain the enzyme catalase, one of the most active known enzymes that splits the hydrogen peroxide into oxygen and water
Ethanol
1. Hepatocytes contain the enzyme alcohol dehydrogenase that breaks down the ethanol to ethanal.
2. Ethanal is then converted to ethanoate which may be used to build up fatty acids or used in cellular respiration