D.3 LIVER FUNCTIONS

Question 1

The liver

Answer 1

is a lobed organ located below the diaphragm that functions to regulate the chemical composition of blood

Question 2

It receives oxygenated blood via

Answer 2

the hepatic artery, which is used to sustain liver cells (hepatocytes)

Question 3

t also receives nutrient rich blood from

Answer 3

the gut via the portal vein

Question 4

Deoxygenated blood is transported from the liver via

Answer 4

the hepatic vein

Question 5

The liver functions to

Answer 5

process the nutrients absorbed from the gut and hence regulates the body’s metabolic processes

• storage/controlled release of key nutrients
• detoxification
• plasma protein production
• breakdown of red blood cells
• the production of bile salts

Question 6

The liver is composed of smaller histological

Answer 6

structures called lobules, which are roughly hexagonal in shape

Question 7

Each lobule is surrounded by

Answer 7

branches of the hepatic artery (provide oxygen) and the portal vein (provide nutrients)

Question 8

lobules vessels drain into

Answer 8

capillary-like structures called sinusoids, which exchange materials directly with the hepatocytes

Question 9

The sinusoids drain into

Answer 9

a central vein, which feeds deoxygenated blood into the hepatic vein

Question 10

Hepatocytes also produce

Answer 10

bile, which is transported by vessels called canaliculi to bile ducts, which surround the lobule

Question 11

Sinusoids are

Answer 11

a type of small blood vessel found in the liver that perform a similar function to capillaries (material exchange)

Question 12

Sinusoids have

Answer 12

increased permeability, allowing larger molecules (e.g. plasma proteins) to enter and leave the bloodstream

Question 13

The increased permeability of sinusoids is important for liver function and is due to a number of structural features:

Answer 13

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)

Question 14

Nutrients stored within the liver include

Answer 14

glycogen, iron, vitamin A and vitamin D

Question 15

carbohydrate metabolism

Excess glucose in the bloodstream

Answer 15

(e.g. after meals) is taken up by the liver and stored as glycogen

Question 16

carbohydrate metabolism

When blood glucose levels drop,

Answer 16

the liver breaks down glycogen into glucose and exports it to body tissues

Question 17

carbohydrate metabolism

When hepatic glycogen reserves become exhausted

Answer 17

the liver synthesises glucose from other sources (e.g. fats)

Question 18

carbohydrate metabolism

The liver plays an important role in regulating the levels of nutrients in the bloodstream

Answer 18

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

Question 19

Protein Metabolism

A.A

Answer 19

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

Question 20

Protein Metabolism

Amine group

Answer 20

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

Question 21

Fat Metabolism

Answer 21

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

Question 22

Fat Metabolism

LDL

Answer 22

Low density lipoprotein (LDL) transports cholesterol to cells, for use in the cell membrane and in steroid synthesis

LDL is considered ‘bad’ as it raises blood cholesterol levels, while HDL lowers cholesterol levels and is therefore ‘good’

Question 23

Fat Metabolism

HDL

Answer 23

High density lipoprotein (HDL) transports excess cholesterol from cells back to the liver (for storage or conversion)

Question 24

Surplus cholesterol

Answer 24

is converted by the liver into bile salts, which can be eliminated from the body via the bowels

Question 25

triglyceride pathway

Answer 25

triglycerides are transported to cells by VLDL from liver to chylomicrons (from intestine) for energy use of storage (adipose tissue)

Question 26

cholesterol

Answer 26

transported to cells by LDL for use in plasma membranes and steroid synthesis, while excess cholesterol is moved from cells by HDL to be converted by liver into bile

Question 27

drugs and toxin in the bloodstream

Answer 27

Many of these toxic compounds are fat soluble, making them difficult for the body to excrete These compounds are converted into less harmful and more soluble forms, which are then excreted from the body by the liver

Question 28

The detoxification of compounds by the liver typically involves two sets of chemical pathways:

Answer 28

1. Toxins are converted into less harmful chemicals by oxidation, reduction and hydrolysis reactions These reactions are mediated by a group of enzymes known as the cytochrome P450 enzyme group These conversions produce damaging free radicals, which are neutralised by antioxidants within the liver 2. 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

Question 29

plasma proteins are produced by

Answer 29

Endoplasmic reticulum and Golgi apparatus in hepatocytes

Question 30

Plasma proteins are

Answer 30

proteins present in the blood plasma and are produced by the liver (except for immunoglobulins)

Question 31

plasma proteins are exported to

Answer 31

exported into the blood via the Golgi complex

Question 32

different types of plasma proteins

Answer 32

Albumins Globulins Fibrinogens

Question 33

Albumins

Answer 33

regulate the osmotic pressure of the blood (and hence moderate the osmotic pressure of body fluids)

Question 34

Globulins

Answer 34

participate in the immune system (i.e. immunoglobulins) and also act as transport proteins

Question 35

Fibrinogens

Answer 35

are involved in the clotting process (soluble fibrinogen can form an insoluble fibrin clot)

Question 36

RBC have a life span of X and thus

Answer 36

short lifespan (~120 days) and must be constantly replaced the liver is responsible for the break down of red blood cells and recycling of its components These components are used to make either new red blood cells or other important compounds (e.g. bile)

Question 37

Kupffer cells

Answer 37

specialised phagocytes within the liver which engulf red blood cells and break them down

Question 38

Kupffer cells break

Answer 38

down haemoglobin into globin and iron-containing heme groups

Question 39

Globin is digested by

Answer 39

peptidases to produce amino acids (which are either recycled or metabolised by the liver)

Question 40

Heme groups are broken down into

Answer 40

iron and bilirubin (bile pigment)

Question 41

The released iron must be complexed within a protein in order to avoid

Answer 41

oxidation to a ferric state

Question 42

Iron can be stored by the liver within

Answer 42

a protein shell of ferritin

Question 43

Iron can be transported to the bone marrow

Answer 43

(where new haemoglobin is produced) within the protein transferrin

Question 44

Jaundice is a condition caused by

Answer 44

an excess of bile pigment – bilirubin – within the body

Question 45

Bilirubin is produced as part

Answer 45

the natural breakdown of haemoglobin by the liver Normally, the liver conjugates this bilirubin to other chemicals and then secretes it in bile

Question 46

When there is an excess of bilirubin

Answer 46

it may leak out into surrounding tissue fluids

Question 47

Jaundice may be caused by

Answer 47

any condition which impairs the natural breakdown of red blood cells Liver disease – impaired removal of bilirubin by the liver may cause levels to build within the body Obstruction of the gall bladder – preventing the secretion of bile will cause bilirubin levels to accumulate Damage to red blood cells – increased destruction of erythrocytes (e.g. anemia) will cause bilirubin levels to rise

Question 48

consequences of jaundice

Answer 48

yellowish discoloration of the skin and whites of the eyes (sclera) Other common symptoms include itchiness, paler than usual stools and darkened urine

Question 49

Jaundice treatment

Answer 49

Other common symptoms include itchiness, paler than usual stools and darkened urine