Liver Blood Flow Flashcards
liver
lobed organ located below diaphragm that functions to regulate chemical composition of blood
- receives oxygenated blood via hepatic artery, which is used to sustain liver cells
- also receives nutrient rich blood from the gut via the portal vein
- Deoxygenated blood is transported from the liver via the hepatic vein
liver functions
- processes the nutrients absorbed from the gut and hence regulates the body’s metabolic processes
- responsible for the storage and controlled release of key nutrients (e.g. glycogen, cholesterol, triglycerides)
- detoxification of potentially harmful ingested substances (e.g. amino acids, medications, alcohol)
- produces plasma proteins that function to maintain sustainable osmotic conditions within the bloodstream
- breakdown of red blood cells and the production of bile salts
hepatic lobules
liver is composed of smaller histological structures called lobules, which are roughly hexagonal in shape
- Each lobule is surrounded by branches of the hepatic artery (provide oxygen) and the portal vein (provide nutrients)
- These vessels drain into capillary-like structures called sinusoids, which exchange materials directly with the hepatocytes
- The sinusoids drain into a central vein, which feeds deoxygenated blood into the hepatic vein
- Hepatocytes also produce bile, which is transported by vessels called canaliculi to bile ducts, which surround the lobule
sinusoids
type of small blood vessel found in the liver that perform a similar function to capillaries. Sinusoids have increased permeability, allowing larger molecules (e.g. plasma proteins) to enter and leave the bloodstream.
- The surrounding diaphragm (basement membrane) is incomplete or discontinuous in sinusoids (but not in capillaries)
- The endothelial layer contains large intercellular gaps and fewer tight junctions (allowing for the passage of larger molecules)
liver regulating levels of nutrients in bloodstream
- Nutrients absorbed by the small intestine are transported by the hepatic portal vein to the liver for metabolism
- The liver converts these nutrients into forms that can be stored or used and mediates their transport to various tissues
- Nutrients stored within the liver include glycogen, iron, vitamin A and vitamin D
carbohydrate metabolism
- Excess glucose in the bloodstream (e.g. after meals) is taken up by the liver and stored as glycogen
- When blood glucose levels drop, the liver breaks down glycogen into glucose and exports it to body tissues
- When hepatic glycogen reserves become exhausted, the liver synthesizes glucose from other sources (e.g. fats)
- These metabolic processes are coordinated by the pancreatic hormones – insulin and glucagon
protein metabolism
- The body can not store amino acids, meaning they must be broken down when in excess
- Amino acid breakdown releases an amine group (NH2), which cannot be used by the body and is potentially toxic
- The liver is responsible for the removal of the amine group (deamination) and its conversion into a harmless product
- The amine group is converted into urea by the liver, which is excreted within urine by the kidneys
- The liver can also synthezise non-essential amino acids from surplus stock (via transamination)
fat metabolism
- The liver is the major site for converting excess carbohydrates and proteins into fatty acids and triglycerides
- It is also responsible for the synthesis of large quantities of phospholipids and cholesterol
- These compounds are then stored by the liver or exported to cells by different types of lipoproteins
- Low density lipoprotein (LDL) transports cholesterol to cells, for use in the cell membrane and in steroid synthesis
- High density lipoprotein (HDL) transports excess cholesterol from cells back to the liver (for storage or conversion)
- LDL is considered ‘bad’ as it raises blood cholesterol levels, while HDL lowers cholesterol levels and is therefore ‘good’
- Surplus cholesterol is converted by the liver into bile salts, which can be eliminated from the body via the bowels
detoxification
- Toxins are converted into less harmful chemicals by oxidation, reduction and hydrolysis reactions
- These reactions are mediated by a group of enzymes
- These conversions produce damaging free radicals, which are neutralized by antioxidants within the liver - The converted chemical is then attached to another substance (e.g. cysteine) via a conjugation reaction
- This renders the compound even less harmful and also functions to make it water soluble
- The water soluble compounds can now be excreted from the body within urine by the kidneys
plasma proteins
proteins in blood plasma and are produced by liver. are produced by the rough ER in hepatocytes and exported to blood via Golgi complex.
types of plasma proteins
- Albumins regulate the osmotic pressure of the blood (and hence moderate the osmotic pressure of body fluids)
- Globulins participate in the immune system (i.e. immunoglobulins) and also act as transport proteins
- Fibrinogens are involved in the clotting process (soluble fibrinogen can form an insoluble fibrin clot)
- Low levels of other plasma proteins have various functions (e.g. α-1-antitrypsin neutralizes digestive trypsin)
red blood cells
possess minimal organelles and no nucleus in order to carry more haemoglobin. have short lifespan and must be constantly replaced.
- liver is responsible for breakdown and recycling of its components
- components are used to either make new red blood cells or other important compound
Kupffer cells
specialized phagocytes within liver which engulf red blood cells and break them down
- break down haemoglobin into globin and heme groups (containing iron)
- globin is digested by peptidases to produce amino acids
- heme groups are broken down into iron and bilirubin (bile pigment)
jaundice
condition caused by excess of bile pigment (bilirubin) within body
- bilirubin is produced as part of the natural breakdown of haemoglobin by the liver
- normally, the liver conjugates this bilirubin to other chemicals and then secretes it into bile
- when there is an excess of bilirubin, it may leak out into surrounding tissue fluids
causes of jaundice
- liver disease: impaired removal of bilirubin by the liver may cause levels to build within body
- obstruction of gall bladder: preventing the secretion of bile will cause bilirubin levels to accumulate
- damage to red blood cells: increased destruction of erythrocytes will cause levels to rise
