(Original post by Awesomnia)
Hepatic Artery - from aorta to liver, supplies liver with oxygenated blood.
Hepatic Portal Vein - from small intestine to live, supplies liver with nutrient rich blood.
Hepatic vein - takes all blood from liver to vena cava.
Bile Duct - takes bile from liver to gall bladder and duodenum.
Liver made of many lobules (100,000 in humans) which are circular with a central vein in the middle. Blood from the two arteries flows from the edge of the lobule to the centre like the spokes of a wheel. This blood passes through channels of liver cells (hepatocytes) called sinosoids. Other channels between these rows of hepatocytes are bile canaliculi, which transport bile made the the hepatocytes to the bile duct, at the edge of the lobule. Large phagocytic macrophages called Kupffer cells line the sinosoids and destroy any bacteria that flows past them. The hepatocytes have microvilli to increase surface area.
- glucose in absorbed from blood into hepatocytes.
- if insulin is in blood, it acts on hepatocytes causing them to convert glucose to glycogen (glycogenesis
- if glucagon (or adrenaline) is in the blood, it acts of hepatocytes causing them to convert glycogen to glucose (glycogenolysis
- after a long time without food, glucagon and adrenaline cause gluconeogenesis
, which is the conversion of substances into glucose.
- eg, amino acids deaminated, turned to pyruvate, condensation reaction to glucose.
Lipids are energy dense and are stored in adipose tissue. They can be used as a respiratory substrate by all tissues except for nervous tissue and red blood cells, which must use glucose.
Fat --> Energy:
- Triglycerides hydrolyzed to fatty acids and glycerol by lipase (lipolysis) inside hepatocytes.
- Glycerol can go straight into glycolysis as a substrate.
- Fatty acids broken down to coenzyme A, which is used in the Krebs cycle to make ATP.
Triglycerides are non-polar and so are not water-soluble. They can, however, be transported in blood plasma if they are surrounded by proteins to make a lipoprotein, which can be either 'low density lipoproteins' LDLs or 'high density lipoproteins' HDLs. Cholesterol can be transported as either, but LDL cholesterol can build up plaques leading to atherosclerosis, whereas HDL cholesterol can actually remove plaques from artery walls. So, a high ratio of HDLs to LDLs can reduce the risk of cardiovascular disease.
- Cell membranes (helping maintain mechanical stability, regulate fluidity, and maintain impermeability to to hydrophilic molecules).
- Making steroid hormones eg, testosterone/oestrogen.
- Waterproofing skin.
- Making vitamin D, when skin is exposed to UV light.
- Making bile salts.
The liver can make it's own cholesterol, but the amount changes depending on how much is in your diet, so it can regulate cholesterol levels a little bit.
Too much bad cholesterol can cause gall stones and cardiovascular disease.
- Transamination - converting one amino acid to another. (essential amino acids cannot be synthesied in this way)
- Deamination - amino acids can't be stored, so amine group (ammonia) is removed, leaving an organic acid which can enter the Krebs cycle. The ammonia is toxic, so enters the ornithine cycle to make urea, which is less toxic. This urea is released from hepatocytes into the blood, where it enters the urine through the kidneys.
Plasma Protein Synthesis:
Fibrinogen: - blood clotting
- globular, soluble protein.
- in a wound, exposed collagen causes platelets to cause prothrombin into thrombin. Thrombin then catalyses the removal of some amino acids from fibrinogen, which can then polymerise to make fibrin.
- Fibrin is insoluble and forms a mesh around the wound where red blood cells and platelets will get caught.
- This stops blood escaping and stops pathogens entering the wound.
- this is the term for most globular proteins.
- some globulins are made in the immune system eg immunoglobulins (antibodies)
- some globulins made in the liver, which help to transport other molecules in blood plasma such as hormones and lipids.
- Too large to enter tissue fluid through pores in capillaries.
- Albumin lowers the solute potential of the blood plasma.
- At the arterial end of a capillary, the relative hydrostatic pressure is high which forces water out and into the tissue fluid.
- At the venous end, the relative hydrostatic pressure is still trying to force water out, however it is now lower than the solute potential (caused by albumin). This means that the net flow of water is back into the capillary.
- If this didn't occur, then water wouldn't enter back into the capillary, and you would oedema would occur. Kwashiorkor sufferers get oedema because they don't have enough protein in their diet to synthesise enough albumin.
- bile salts, made from cholesterol, which emulsifies fats
- cholesterol, makes bile salts water soluble so they are more effective at emulsification. Too much cholesterol migt cause gall stones, which can block the bile duct, and have to be removed with surgery or ultrasound treatment.
- bilirubin, an excretory product.
Erythrocytes (red blood cells) are broken down by the spleen and liver, and the haemoglobin spilts into haem and globin. The globin can be converted to amino acids and used for protein synthesis. The haem group is broken into iron and bilirubin. Iron is stored in the liver, and bilirubin is excreted in bile. Jaundice is a disease where bilirubin isn't excreted efficiently, and a symptom is yellow skin (because bilirubin is yellow and can appear in your skin). Newborn (often premature) babies have jaundice as their liver is not yet fully formed.
Breaks down drugs and hormones, so they have a time limited effect.
-Ethanol is toxic.
- in hepatocytes, enzyme alcohol dehydrogenase converts ethanol to ethanal.
- Enzyme aldehyde dehydrogenase converts ethanal to ethanoate.
-Ethanoate can enter the Krebs cycle.
This metabolism produced a lot of reduced NAD, which disrupts other metabolic reactions, eg, fatty acid breakdown. This means that fats are stored in hepatocytes, causing 'fatty liver
Alcohol also destroys hepatocytes, and the repair often leaves blood supply damaged, with some blood passing straight through the liver without going near any hepatocytes. Hepatocytes may not be replaced properly, and fibrous tissue is laid down in their place. This damage is known as cirrhosis of the liver
, and means that liver cells cannot convert ammonia to urea efficiently. This can cause damage to the central nervous system resulting in coma or death.