Excretion, Homeostasis, and the Liver (homeostasis chapter 4)

Question 1

Main metabolic waste products in mammals

Answer 1

• Carbon dioxide - waste product of cellular respiration, excreted from the lungs
• Bile pigments - formed from the breakdown of haemoglobin from old RBCs in the liver
• Urea - formed from the breakdown of excess amino acids by the liver

Question 2

Excretion

Answer 2

The removal of the waste products of the metabolism from the body

Question 3

The liver

Answer 3

• One of the major body organs involved in homeostasis

- Lies below the diaphragm and is made up of several lobes

Question 4

Blood supply of the liver

Answer 4

• Rich blood supply - about 1 dm³ of blood flows through it every minute
• Oxygenated blood is supplied to the liver by the hepatic artery and taken away back to the heart by the hepatic vein
• The hepatic portal vein (up to 75% of blood flowing through the liver) carries blood loaded with the products of digestion straight from the intestines to the liver - starting point for many metabolic activities of the liver

Question 5

Liver structure

Answer 5

• Liver cells/hepatocytes - large nuclei, prominent Golgi apparatus, and lots of mitochondria (metabolically active cells). These can divide and replicate
• Sinusoids - surrounded by hepatocytes, the areas where blood from the hepatic artery and hepatic portal vein are mixed - the mixing increases oxygen content of the blood from the hepatic portal vein, supplying hepatocytes with enough oxygen for their needs
• Kupffer cells - found in sinusoids, act as the resident microphages of the liver; they inject foreign particles
• Canaliculi - the spaces where the hepatocytes secrete bile from the breakdown of blood to. The bile later drains into bile ductules, which take it to the gall blagger

Question 6

Functions of the liver - carbohydrate metabolism

Answer 6

• Hepatocytes are closely involved with the homeostatic control of glucose levels in the blood by their interactions with insulin and glucagon
• Blood glucose concentration rises, leading to a rise in insulin levels, stimulating the hepatocytes to convert glucose into glycogen - and vise versa, as glycogen is converted back into glucose by glucagon when blood glucose concentrations decrease

Question 7

Function of the liver - deamination of excess amino acids

Answer 7

• Transamination - the conversion of one amino acid into another, carried out by hepatocytes
• Deamination - the removal of an amino group from a molecule
  1. Amino acids deaminated
  2. Amino group is removed
  3. Conversion into ammonia
  4. Conversion into urea
• The rest of amino acids are fed into cellular respiration or converted into lipids for storage

Question 8

Ornithine cycle

Answer 8

A series of enzyme controlled reactions in the liver converting ammonia formed by deamination of amino acids into urea

Question 9

Function of the liver - detoxification

Answer 9

• Removal or breakdown of toxins
• Hydrogen peroxide - hepatocytes contain catalase, which splits hydrogen peroxide into oxygen and water
• Ethanol - hepatocytes contain dehydrogenase, which breaks down the ethanol into ethanal. Ethanal is then converted to ethanoate which may be used to build up fatty acids or used in cellular respiration

Question 10

Example of a liver disease

Answer 10

Cirrhosis