Excretion

Question 1

Define Excretion

Answer 1

process by which toxic waste products of metabolism and substances in excess of requirement are removed from the body

Question 2

what are the main waste products

Answer 2

1- Carbon Dioxide
- waste product 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
- excreted in the bile from the liver into the small intestines via the gall bladder and bile duct, they colour the faeces.
3- Nitrogenous waste products (urea)
- formed from the breakdown of excess amino acids in the liver. All mammals produce ammonia. Fish produce ammonia while birds and insects produce uric acid. urea is secreted by the kidneys in the urine

Question 3

Outline the liver

Answer 3

• major body organ
• reddish-brown organ
• makes up about 5% of the total body mass, largest internal organ of the body

Question 4

Describe the liver’s rich blood supply

Answer 4

Blood is supplied to liver by the hepatic artery
Also supplied with blood by the **hepatic portal veins ** = carries blood loaded with products of digestion straight from intestine to the liver
Blood is returned to heart by the hepatic vein

Question 5

Structure of the liver

Answer 5

Hepatocytes (liver cells) - have large nuclei, prominent Golgi apparatus and many mitochondria. Also contain glycogen granules
- these cells manufacture bile and secrete it into spaces called canaliculi, where it is then drained into gall bladder to be stored

Blood supplied from hepatic artery and portal vein is mixed in spaces called sinusoids, which are surrounded by hepatocytes.
- the sinusoids also contain kupffer cells, act as resident macrophages of the liver, ingesting foreign particles and protect against disease.
- mixing the blood in sinusoids increases the oxygen content of the blood, supplying the hepatocytes with sufficeint oxygen for their metabolic needs

Question 6

Name three functions of the liver

Answer 6

1- Carbohydrate metabolism
2- Deamination of excess amino acids
3- Detoxification

Question 6

Outline the liver’s role in carbohydrate metabolism

Answer 6

When blood glucose conc rise, insulin levels rise and stimulate hepatocytes to convert glucose into the storage carbohydrate glycogen.
Similary wehn blood glucose conc fall, hepatocytes convert the glyocgen back to glucose under the influence of the hormone glucagon

Question 7

Outline role in protein metabolism

Answer 7

Liver plays vital role in protein metabolism, hepatocytes synthesise most of the plasma proteins, hepatocytes also carry out transamination = the conversion of one amino acid into another.
- this is important because the diet does not always contain the required balance of amino acids, but transamination can overcome this problem

Question 8

Outline role in deamination

Answer 8

Most important role is deamination = the removal of an amine group from a molecule. this first converts into ammonia, which is toxic and then into urea. urea is then excreted by the kidneys. the remainder of the amino acid can be fed into cellular respiration and converted to lipids for storage
- the ammonia produced in the deamination of proteins is converted into urea in a set of enzyme controlled reactions known as the ornithine cycle

Question 9

Describe the liver’s role in detoxification

Answer 9

ingested drugs/toxins or naturally occuring hydrogen peroxide produced in the body can damage cells
- the liver is the site where these toxins are detoxified and made harmless
Eg.
1. Breakdown of hydrogen peroxide
* hepatocytes contain enzyme catalase, which splits hydrogen peroxide into oxygen and water

2- Detoxification of ethanol (drug in alcohol)
* hepatocyres contain enzyme alcohol dehydrogenase, that breaks down ethanol into ethanal. ethanal is then converted to ethanoate which may be used to build up fatty acids used is cellular respiration

Question 10

define cirrhosis of the liver

Answer 10

Disease when normal liver tissue is replaced by fibrous scar tissue

Question 11

Describe the three stages of alcoholic liver disease

Answer 11

1- Alcoholic fatty liver
- big fat filledvesicles displace the nuclei of the hepatocytes and the liver gets larger
2- **Alcoholic hepatitis **
- patient has fatty liver along with damaged hepatocytes
- the sinusoids and hepatic veins become narrowed
3- Liver cirrhosis
- the liver is irreversibly damaged
- many hepatoyctes die and are replaced with fibrous tissue
- hepatocytes can no longer divide and replace themselves so the liver shrinls and its ability to deal with toxins in the body decreases.