mammalian physiology and behaviour the liver. roles of the liver
TRANSCRIPT
Mammalian Physiology and Behaviour
THE LIVER
THE LIVER
ROLES OF THE LIVER
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
Control of Glucose in blood
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
Glucose and Glycogen
• Adrenaline has similar effect to Glucagon
• Insulin gets Hepatocytes to convert Glucose to Glycogen
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
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.
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
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
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
Synthesis of Cholesterol
• Cholesterol is made in the liver
• It has many useful functions in the body• Can you think of any?
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 wemost often hear about cholesterol?
Controlling Cholesterol
• It is present in the diet
• But when Cholesterol is absorbed in the intestines…
• The Liver will make less Cholesterol
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!
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
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)
Protein Metabolism
(e) Explain the roles of the liver in deamination, transamination and urea formation
Deamination = Breakdown of excess amino acidsTransamination = Conversion of one amino acid to
another(apart from essential amino acids)
Deamination
• Urea is produced from excess amino acids • Getting rid of the whole amino acid would
be wasteful, so the Nitrogen is removed (NH2) group and the rest is kept
• The NH2 is combined with Hydrogen to form ammonia
• The organic acid can be turned into things like carbohydrates and fats
Animation of Deamination
Ornithine Cycle
• Ammonia is highly toxic and solubleConverted to
urea by combining with CO2
Via several amino acids
In Ornithine cycle
Requires energy
ATP
ATP
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
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!
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
Bile Formation
• Most of the cholesterol is used to make bile
• About 1000 cm3 per day• Made in hepatocytes• Secreted into bile canaliculi• To bile duct• Then to duodenum• Some will be stored in gall bladder
Bile composition
• Major components are water and bile salts
• Bile salts made from ___________• Emulsify fats• What effect does this have?• Easier digestion and absorption
Bile composition
• Bile also contains cholesterol itself• Precipitates out to form gall stones• If there is too much cholesterol or
too little bile salts
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
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
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
Alcohol
• Ethanol is toxic• Damages cells• Liver protects by breaking ethanol
down into harmless substances
Alcohol Metabolism
The Krebs Cycle
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
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