Excretion 15.4 Flashcards
What is excretion?
The removal of waste products of metabolism from the body
What are the main waste products of metabolism in mammals?
- Carbon dioxide from respiration which is removed by lungs
- Bile pigments which are break down of haemoglobin from old blood cells in the liver which are excreted in bile and colour faeces
- Urea which is formed by the breakdown of excess amino acids by the liver. It is nitrogenous waste and it is extracted by the kidneys in the urine.
What is the largest internal organ in the body?
The liver, it takes up 5% of body mass
What is a fact about the liver?
It can regenerate and regrow quickly to repair damaged areas
How does the liver receive and deliver blood?
It has a rich blood supply of oxygenated blood from the hepatic artery and then it delivers deoxygenated blood to the heart by the hepatic vein. It is also supplied by a second blood vessel called the hepatic portal vein which carries blood from the intestines to the liver and is how many metabolic reactions take place. 75% of the blood that flows through the liver comes from the hepatic portal vein
What are liver cells called and what are their characteristics?
They are called hepatocytes.
- They have a large nuclei
- They have a prominent golgi apparatus
- They have many mitochondria which shows they are active
- They divide and replicate quickly
What are sinusoids?
Small spaces surrounded by hepatocytes where blood from the hepatic artery and hepatic portal vein are mixed
Why does the blood from the hepatic artery and hepatic portal vein need to be mixed?
It needs to be mixed to increase the oxygen content in the blood from the hepatic portal vein so that the hepatocytes can be supplied with enough oxygen to carry out their metabolic activities
What kind of cells do sinusoids contain and what is their function?
Sinusoids contain Kupffer cells which act as the macrophages of the liver. They ingest foreign particles and help to protect against disease
What do hepatocytes secrete and what does this do?
Hepatocytes secrete bile from the breakdown of blood in spaces called canaliculi and the bile will then drain into bile ductules which is then taken to the gall bladder
What is the livers’ role in carbohydrate metabolism?
The liver is closely involved in the homeostatic control of glucose levels in the blood. it interacts with both insulin and glucagon. When blood glucose levels rise, insulin levels rise and this stimulates hepatocytes into converting glucose into glycogen which can then be stored in the liver. When blood glucose levels decrease, glucagon levels increase and this stimulates hepatocytes into converting glycogen back into glucose
What is the livers’ role in the deamination of amino acids?
The hepatocytes synthesise most plasma proteins.
They also take part in deamination and transamination
Describe transamination
This is when hepatocytes convert one amino acid into another and this is important because you might not get the correct amino acids from your diet, but using transamination, you can obtain the correct balance
Describe deamination
Deamination is the removal of the amine group from amino acids which allows the rest of the amino acid to be used as a respiratory substrate or converted into lipids. The reason this has to happen is that proteins cannot be stored in the body, so any excess protein would be excreted and lost. The hepatocytes first remove the amine group and convert the amino acid into ammonia and then into urea using the ornithine cycle. Urea is then excreted by the kidneys.
What is the ornithine cycle?
- Ammonia is added to ornithine to make citruline
- Ammonia is added to citruline to make arginine
- Water is added to arginine to make urea
