One of the liver's most important overall functions is maintaining nutrient homeostasis. It controls the blood level of a number of macro- and micronutrients, and attempts to keep them all at optimal levels.
Here's a list of some of the liver's functions I'm aware of:
- Buffers blood glucose by taking it up or releasing it when needed
- A major storage site for glycogen (a glucose polymer)
- Clears insulin from the blood
- Synthesizes triglycerides
- Secretes and absorbs lipoprotein particles ("cholesterol")
- Stores important vitamins: B12, folate, A, D, E, K (that's why it's so nutritious to eat!)
- Stores minerals: copper and iron
- Detoxifies the blood
- Produces ketone bodies when glucose is running low
- Secretes blood proteins
- Secretes bile
- Converts thyroid hormones
- Converts vitamin D (D3 --> 25(OH)D3)