I was intending to write a summary of everything you need to know about photosynthesis for A2, having just finished the topic at school, but today one of my biology teachers set an interesting homework; “How many functions of the liver can you discover?” He currently has a list of 22, so I challenged myself to find more! Using my A2 textbook and a quick Google search I managed to create the following list; the points in italics are those that are relevant to AS/A2 biology.
1. Metabolizes proteins, fats, and carbohydrates (e.g. the break down of glycogen stores to glucose)
2. Stores vitamins, minerals, and sugars (e.g. storing glucose as glycogen)
3. Filters the blood (however this is not the same as the function of the kidney, the liver filters out things that need to be chemically broken down or altered before they can be safely excreted from the body, e.g. toxins, or filters out glucose and fats for storage.)
4. Creates bile (which breaks down lipids in the small intestine)
5. Stores fat soluble vitamins (e.g. vitamins A, E, D and K)
6. Destroys fat soluble toxins.
7. Stores extra blood that can be quickly released when needed.
8. Creates serum proteins that maintain fluid balance and act as carriers.
9. Helps maintain electrolyte and water balance.
10. Creates immune substances such as gamma globulin.
11. Breaks down and eliminates excess hormones.
12. Vascular functions (i.e. blood management).
13. Provides blood clotting factors.
14. Produces immune factors.
15. Breaks down toxins such as ammonia created in the colon by bacteria.
16. Helps to maintain blood pressure.
17. Constructs cholesterol and estrogens and reconstructs hormones.
18. Humanizes nutrients.
19. Synthesizes urea.
20. Constructs blood protein.
21. Converts amino acids.
22. Constructs 50,000 systems of enzymes to govern metabolic activity throughout the body.
23. Removes damaged red blood cells.
24. Converts the thyroid hormone thyroxine (T4) into the more active form triiodothyronine (T3). (If this does not occur it can lead to hypothyroidism, chronic fatigue, weight gain and memory problems)
25. Creates Glucose Tolerance Factor from chromium, niacin and glutathione. It’s needed for the hormone insulin to properly regulate blood-sugar levels.
26. Manufactures bile salts which emulsify fats and the fat-soluble vitamins A, D, E, and K for proper absorption.
27. Activates B vitamins into their biologically active coenzyme forms.
28. Stores various nutrients, especially A, D, B-12 and iron for release as needed.
29. Manufactures carnitine from lysine and other nutrients. Carnitine is the only known bionutrient which can escort fats into the mitochondria where they are used to generate ATP energy. The mitochondria generate 90% of the ATP energy at the cellular level.
30. Converts lactic acid to glycogen. (It’s produced when glucose is metabolized through the energy production cycle via anaerobic respiration, and is what leads to sore muscles after exercise.)
31. Serves as the main glucose buffer, preventing high or low extremes of blood sugar. The When blood sugar is low, the liver converts stored glycogen into glucose, releasing it into the bloodstream to raise blood sugar levels. When blood sugar is high, the liver will convert the excess into stored glycogen or fat.
32. Chief regulator of protein metabolism (linked to amino acid conversions.)
33. Produces cholesterol (High and Low Density Lipoproteins)
34. Converts essential fatty acids such as GLA, EPA, and DHA into the lipoprotein forms necessary to allow transport via the bloodstream .
35. Main poison-detoxifying organ in the body. The liver breaks down every substance toxic to the body including metabolic wastes, insecticide and pesticide residues, drugs, alcohol, etc.
36. Removes ammonia, a toxic by-product of animal protein metabolism, from the body (by conversion to urea to be filtered out by the kidneys.)
37. Breaks down hormones after they have served their function (if the liver does not break down insulin fast enough, hypoglycaemia results because the circulating insulin continues to lower blood sugar.)
Although you could arguably classify the entire breakdown of chemicals as one function, as each breakdown requires at least one specific enzyme (and many require coenzymes/cofactors) it is clear to see why they are classed as separate functions. I find it fascinating how this 2kg mass of cells can carry out so many functions that are fundamental to our survival.
Some estimates put the number of liver functions at over 100! How many other functions of the liver can you find?