Functions of the liver

Question 1

Blood supply to the liver

Answer 1

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

Question 2

hepatic portal vein

Answer 2

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

Question 3

dual blood supply

Answer 3

liver receives oxygenated blood from the hepatic artery and deoxygenated blood from the hepatic portal vein

Question 4

hepatocytes

Answer 4

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.

Question 5

Liver lobules

Answer 5

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

Question 6

sinusoids

Answer 6

tubes that resemble capillaries but have a discontinuous endothelium.

Question 7

Hepatocytes

Answer 7

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.

Question 8

Plasma proteins

Answer 8

synthesised in hepatocytes mainly in the rough endoplasmic reticulum (rER) and processed in Golgi complexes.
detoxification reactions occur in the smooth endoplasmic reticulum (sER)

Question 9

Kupffer cells

Answer 9

white blood cells (macrophages) that break down red blood cells.
are involved in the recycling of erythrocytes,

Question 10

functions of hepatocytes

Answer 10

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.

Question 11

Amino acids entering the liver

Answer 11

transformed into other amino acids or are used in the synthesis of new proteins.

Question 12

Endoplasmic reticulum and Golgi apparatus in hepatocytes

Answer 12

produce plasma proteins. These plasma proteins include fibrinogen used in blood clotting, and albumin that transports hormones and maintains the blood pH.

Question 13

deamination

Answer 13

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.

Question 14

detoxification

Answer 14

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.

Question 15

metabolising alcohol

Answer 15

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.

Question 16

Red blood cells or erythrocytes

Answer 16

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

Question 17

The biconcave shape

Answer 17

increases erythrocyte surface area:volume ratio, thus increasing the absorption of oxygen

Question 18

The lack of nucleus

Answer 18

increases the amount of hemoglobin in each cell

cannot reproduce, therefore they must be produced in the bone marrow from undifferentiated cells.

Question 19

production of erythrocytes

Answer 19

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

Question 20

in the Kupffer cells…

Answer 20

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

Question 21

Cholesterol

Answer 21

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

Question 22

cholesterol regulation

Answer 22

synthesis is regulated according to its concentration in cells
regulation is performed by the hormones glucagon (inactivating its synthesis) and insulin (activating its synthesis).

Question 23

HDLs AND LDLs

Answer 23

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.

Question 24

The function of LDLs

Answer 24

to transport cholesterol from the liver to other organs.

Question 25

The function of HDLs

Answer 25

to transport cholesterol from tissues to the liver.

Question 26

atherosclerosis

Answer 26

Molecules of LDL deposit in the blood vessels and can become oxidised

Question 27

Bile salts

Answer 27

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.

Question 28

Jaundice

Answer 28

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

Question 29

Jaundice appears under several circumstances:

Answer 29

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)

Question 30

Alcohol and cirrhosis

Answer 30

the damaged liver tissue is replaced by scar tissue

symptoms: weakness, fatigue, jaundice and bruising

Question 31

liver regeneration

Answer 31

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.