Functions of the liver Flashcards
Blood supply to the liver
supplied with oxygenated blood from the heart through the hepatic artery.
The blood leaves the liver through the hepatic vein, which carries deoxygenated blood.
This vein joins the vena cava, which returns the blood to the heart.
+ receives deoxygenated blood from the spleen, stomach, pancreas, gall bladder and intestines through the hepatic portal vein
hepatic portal vein
carries foods absorbed mainly in the small intestine
rich in amino acids, glucose, vitamins, minerals and other foods
75% of the total blood supplied to the liver
dual blood supply
liver receives oxygenated blood from the hepatic artery and deoxygenated blood from the hepatic portal vein
hepatocytes
As blood passes through the liver, the hepatocytes monitor the contents of the blood and remove many toxic substances such as alcohol and drugs before they can reach the rest of the body. Enzymes metabolise these toxins to render them harmless.
Liver lobules
consists of four lobes
internal structure of each lobe has around 100,000 lobules, each consisting of a central venule coming from the hepatic vein surrounded by six venules coming from the hepatic portal vein and six arterioles from the hepatic artery. These blood vessels are connected by sinusoids
sinusoids
tubes that resemble capillaries but have a discontinuous endothelium.
Hepatocytes
perform most of the liver functions, especially storage and metabolism
nucleus is round and found in the centre of the cell. These cells are capable of regenerating when exposed to toxic substances.
Plasma proteins
synthesised in hepatocytes mainly in the rough endoplasmic reticulum (rER) and processed in Golgi complexes.
detoxification reactions occur in the smooth endoplasmic reticulum (sER)
Kupffer cells
white blood cells (macrophages) that break down red blood cells.
are involved in the recycling of erythrocytes,
functions of hepatocytes
absorb most of the glucose and store it as glycogen
absorb fatty acids and metabolise to produce energy in the form of ATP
synthesise lipids such as triglycerides, cholesterol and phospholipids.
These lipids can be bound to proteins forming lipoproteins, which are now soluble in blood plasma and can therefore be transported in blood to all the body.
Amino acids entering the liver
transformed into other amino acids or are used in the synthesis of new proteins.
Endoplasmic reticulum and Golgi apparatus in hepatocytes
produce plasma proteins. These plasma proteins include fibrinogen used in blood clotting, and albumin that transports hormones and maintains the blood pH.
deamination
When amino acids are no longer necessary, hepatocytes remove the amine group from the acid group
The acid group of the amino acid is used to produce energy or new glucose molecules while the amine group is converted into ammonia. As ammonia is toxic, it is transformed into urea, which is then eliminated by the kidneys in urine.
detoxification
gets rid of drugs, hormones and other toxins
reaks down the substances into harmless compounds. If it cannot break them down, it attaches these substances to other organic groups (such a glycine), which allows the kidneys to recognise them as unwanted waste material and are therefore excreted.
metabolising alcohol
Ethanol is oxidised into acetaldehyde, a toxic substance, by the hepatic enzyme alcohol dehydrogenase. Acetylaldehyde is converted into a less toxic substance, acetate, by aldehyde dehydrogenase.
Acetate is then broken down to acetyl-CoA that can enter fatty acid metabolism or be used in the Krebs cycle. If acetaldehyde is not broken down immediately, it can combine with proteins that induce liver injury. Excess of alcohol can damage the liver, causing cirrhosis.
Red blood cells or erythrocytes
cells modified to increase their capacity in the transport of oxygen.
biconcave shape and have lost their nucleus and organelles.
rich in haemoglobin, a protein that binds oxygen
The biconcave shape
increases erythrocyte surface area:volume ratio, thus increasing the absorption of oxygen
The lack of nucleus
increases the amount of hemoglobin in each cell
cannot reproduce, therefore they must be produced in the bone marrow from undifferentiated cells.
production of erythrocytes
in the bone marrow and are liberated into the bloodstream.
die after approximately 120 days circulating in blood
Dead erythrocytes are engulfed by macrophages in the liver, spleen or bone marrow by phagocytosis.
In the liver, Kupffer cells recycle dead erythrocytes by phagocytosis
in the Kupffer cells…
hemoglobin is split into globin chains and heme groups. Globin is re-used in protein synthesis.
The heme group is transformed into iron and bilirubin. Iron is carried back to the bone marrow where it is used to produce new red blood cells.
Bilirubin is secreted into bile that will be used in the emulsification of fats
Cholesterol
membrane synthesis
a small portion is added to the membranes of hepatocytes
exported as lipoproteins or bile salts
precursor for important molecules: the bile salts, steroid hormones (such as oestrogen and progesterone), and vitamin D
cholesterol regulation
synthesis is regulated according to its concentration in cells
regulation is performed by the hormones glucagon (inactivating its synthesis) and insulin (activating its synthesis).
HDLs AND LDLs
insoluble in water
to be carried in blood to other tissues, need to be carried as plasma lipoproteins
HDL contain more protein, while LDL contain more lipids.
both produced in the plasma; however a small amount is synthesised in the liver.
The function of LDLs
to transport cholesterol from the liver to other organs.
The function of HDLs
to transport cholesterol from tissues to the liver.
atherosclerosis
Molecules of LDL deposit in the blood vessels and can become oxidised
Bile salts
emulsify fats
break fats down into smaller droplets to increase their surface area. allows enzymes (for example pancreatic lipase) to work better.
are reabsorbed from the intestines into the liver, but lots are lost in faeces.
Jaundice
condition when skin and white of the eyes turn yellow
caused by the presence of bilirubin in extracellular fluid.
liver is not able to remove the bilirubin from blood, its level may rise
Jaundice appears under several circumstances:
Increased destruction of red blood cells.
Immaturity in the conjugation of bilirubin (greater in premature babies).
Genetic diseases (e.g. Gilbert syndrome).
Defects in the secretion of conjugated bilirubin from hepatocytes (in liver damage).
Defects in transit of bilirubin to intestines (e.g. with bile duct obstruction)
Alcohol and cirrhosis
the damaged liver tissue is replaced by scar tissue
symptoms: weakness, fatigue, jaundice and bruising
liver regeneration
the replication of hepatocytes followed by the replication of other liver cells. Once cell proliferation is completed, the newly divided cells undergo restructuring and reformation of the extracellular matrix to complete the process.