1. Mammalian Physiology and Behaviour THE LIVER

2. ROLES OF THE LIVER

3. Carbohydrate Metaoblism (c) Explain the roles of the liver in carbohydrate metabolism and the production of glucose from amino acids. Interconversion of glucose and glycogen Conversion of other substances to glucose

4. Control of Glucose in blood

5. Glucose and Glycogen Glycogen is stored in the liver (25%) and the muscles (75%) Glucagon causes the breakdown of Glycogen to Glucose In the Hepatocytes This is called Glycogenolysis

6. Glucose and Glycogen Adrenaline has similar effect to Glucagon Insulin gets Hepatocytes to convert Glucose to Glycogen

7. Conversion of Substances to Glucose Non-carbohydrates can be converted to glucose E.g. amino acids, fats, lactate and pyruvate Where do lactate and pyruvate come from? This is called GLUCONEOGENESIS Occurs in very low blood sugar situations when there is no more Glycogen

8. Lipid Metabolism (d) Explain the roles of the liver in fat metabolism, including the use of fats in respiration, the synthesis of triglycerides from excess carbohydrate and protein, the synthesis and regulation of cholesterol, and the transport of lipids to and from the liver as lipoproteins.

9. Fats for Energy Fats can be respired to produce ATP Most tissues respire fats in preference to glucose (especially cardiac muscle) Fats are split to fatty acids and glycerol Fatty acids are converted to acetyl coenzyme A This is used in the Krebs cycle

10. Synthesis of Triglycerides The liver converts unneeded carbohydrates and proteins to fats Fats are stored in adipose tissue Why can’t fats be transported in the blood? They are insoluble Transported as Lipoproteins

11. Lipoproteins Most fats are transported as Low Density Lipoproteins (LDLs) Hydrophobic lipids in the centre Polar lipids and proteins on the outside Cholesterol combined with fatty acids

12. Synthesis of Cholesterol Cholesterol is made in the liver It has many useful functions in the body Can you think of any?

13. Functions of Cholesterol Stability and fluidity of membranes Synthesis of steroid hormones Deposited in the skin for waterproofing Used to make Vitamin D Used to make bile slats Yet with all these uses how do we most often hear about cholesterol?

14. Controlling Cholesterol It is present in the diet But when Cholesterol is absorbed in the intestines… The Liver will make less Cholesterol

15. Controlling Cholesterol Cholesterol presence reduces the activity of an enzyme that produces it from acetyl coenzyme A So dietary cholesterol doesn’t significantly affect blood cholesterol!

16. High Blood Cholesterol? It is saturated fats in the diet that can raise blood cholesterol This is because they increase the rate of production in the liver

17. Transport of Cholesterol Transported as: Low Density Lipoproteins (LDLs) Very Low Density Lipoproteins High Density Lipoproteins (HDLs) LDLs = Deposition of cholesterol on blood vessel walls HDLs = Protect against deposition of cholesterol (may even remove it)

18. Protein Metabolism (e) Explain the roles of the liver in deamination, transamination and urea formation Deamination = Breakdown of excess amino acids Transamination = Conversion of one amino acid to another (apart from essential amino acids)

19. Deamination Urea is produced from excess amino acids Getting rid of the whole amino acid would be wasteful, so the Nitrogen is removed (NH 2 ) group and the rest is kept The NH 2 is combined with Hydrogen to form ammonia The organic acid can be turned into things like carbohydrates and fats Animation of Deamination

20. Ornithine Cycle Ammonia is highly toxic and soluble Converted to urea by combining with CO 2 Via several amino acids In Ornithine cycle Requires energy ATP

21. Synthesis of Plasma Proteins (g) Describe the production, and explain the roles, of the plasma proteins fibrinogen, globulins and albumin. All plasma proteins are soluble (globular) They include: Fibrinogen, Globulin and Albumin All made in the Liver

22. Plasma Proteins Fibrinogen and prothrombin are involved in blood clotting Albumin maintains the water level in the blood Globulin is most of the other globular proteins in blood plasma Synoptic = link to tissue fluid formation!

23. Globulins Immunoglobulins are made by immune system not liver Others are made by liver and help in transporting substances e.g. thyroxine, insulin, phospholipids, lipids, cholesterol, iron, vitamins A/E/B12/D/K

24. Bile Formation Most of the cholesterol is used to make bile About 1000 cm 3 per day Made in hepatocytes Secreted into bile canaliculi To bile duct Then to duodenum Some will be stored in gall bladder

25. Bile composition Major components are water and bile salts Bile salts made from ___________ Emulsify fats What effect does this have? Easier digestion and absorption

26. Bile composition Bile also contains cholesterol itself Precipitates out to form gall stones If there is too much cholesterol or too little bile salts

27. Breakdown of haemoglobin RBCs only last _________ Broken down in the spleen and liver Haemoglobin is broken down into Haem and Globin. Globin broken down to amino acids Heam broken down to Iron and bilirubin

28. Breakdown of haemoglobin Iron stored in Liver Bilirubin secreted into bile If bilirubin can’t be secreted into bile It stays in the blood And causes jaundice

29. Alcohol What is the alcohol that is found in alcoholic drinks? Ethanol How is it absorbed by the body? Lipid soluble so can pass straight through membranes

30. Alcohol Ethanol is toxic Damages cells Liver protects by breaking ethanol down into harmless substances

31. Alcohol Metabolism

32. The Krebs Cycle

33. Excessive Alcohol Consumption Damages Liver cells Metabolism of alcohol produces reduced NAD Stops oxidised NAD requiring reactions Including oxidation of fatty acids Fatty acids are deposited in hepatocytes Reducing their efficiency

34. Cirrhosis Liver cells die Replaced by fibrous tissue Lobule structure is destroyed Blood supply structure goes Blood can flow straight through without entering sinusoids Lots of damaging effects because Liver carries out so many functions