D.3: Functions of the Liver

Question 1

What are cells in the liver called?

Answer 1

Hepatocytes

Question 2

Hepatic artery

Answer 2

Carries oxygenated blood from the heart into the liver, subdivides into arterioles.

Question 3

Hepatic vein

Answer 3

Carries blood from the liver to the heart with levels of food.
Subdivides into venules.

Question 4

Hepatic portal vein (O2, how much of blood)

Answer 4

Carries nutrient rich blood from the stomach/intestines to the liver, subdivides into sinusoids

• low in O2 since it has been circulating from heart to stomach/intestines to liver
• most of blood circulating in the liver is from the hepatic portal vein

Question 5

What are Sinusoids?

Answer 5

Similar to capillaries, but wider and not always lined with cells, connects with venules, arterioles at some points

Question 6

Excess proteins and amino acids

Answer 6

Access proteins and amino acids are broken down (to be used as energy sources) in the liver as the body cannot store these (unlike glucose, which can be stored as glycogen)

• liver then processes the nitrogenous waste

Question 7

Lipids in the liver

Answer 7

Lipids in the liver are processed in one form and distributed in another form

E.g. chylomircons broken down, surplus cholesterol converted into bile salts

Question 8

What nutrients are stored in the liver when in excess? (And released when there is a deficit?)

Answer 8

Iron, retinol (v. A), calciferol (v. D)

Question 9

More about blood sugar level control

Answer 9

• 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 synthesises glucose from other sources (e.g. fats)
• These metabolic processes are coordinated by the pancreatic hormones – insulin and glucagon

Question 10

Recycling of rbcs in the spleen and liver

Answer 10

• When erythrocytes are at the end of their life cycle, they are broken down in the spleen and the liver.
• Most of the products of the breakdown are recycled.
• Old and damaged erythrocytes undergo changes in their plasma membrane (susceptible to recognition by macrophages such as kupffer cells)

(Erythrocytes have a lifespan of around 120 days)

Question 11

What are kupffer cells?

Answer 11

Kupffer cells are macrophages which line the sinusoids of the liver.

They engulf foreign particles and substances by phagocytosis (trap using arm-like filopodia cytoplasm then engulf)

Question 12

Kupffer cells in the process of breaking down erythrocytes

Answer 12

• Kupffer cells separate hemoglobin cells into a globin chain and a heme group.
• Heme group broken down further into iron and bilirubin.
• amino acids in globin chain recycled.
• bilirubin distributed into blood.
• iron bound to transferrin and transported to be stored in liver/spleen or to bone marrow for synthesis of new rbcs

Question 13

Where are rbcs synthesized?

Answer 13

Stem cells in bone marrow

Question 14

Heme group formation in rbcs

Answer 14

• Developing rbcs have many transferrin receptors which bind to transferrin
• transferrin bound to iron is brought into the rbc
• iron obtained from protein transferrin used to form heme group or stored in storage molecule called ferritin

Question 15

Bilirubin (yellow pigment) is produced by the breakdown of which proteins?

Answer 15

• hemoglobin (heme group)
• myoglobin
• cytochrome

Question 16

What is albumin?

Answer 16

• A protein which bilirubin binds to
• transports bilirubin to the liver when bilirubin is produced outside of the liver

Question 17

What happens to bilirubin in the liver?
(glucaronic, canaliculi)

Answer 17

• Since bilirubin is insoluble, it is made soluble by reacting with glucaronic acid
• water soluble form secreted into canaliculi (passages) along with water, electrolytes, cholesterol, bicarbonate, phospholipids and salts.
• this mixture is called bile, which enters the gall bladder to be later be secreted in the duodenum (to help break down fatty compounds/foods!!)

Question 18

What is jaundice?

Answer 18

• there is an issue with the metabolism or excretion of bilirubin
• results in the build-up of bilirubin in the blood
• concentration of bilirubin higher than 2.5 mg dl^(-1) (average conc. is 1.2 mg dl^(-1))
• not a disease, both often a sign of a disease

Symptoms:
- yellowing if the eyes and skin

Question 19

Example of a disease that may cause jaundice (+ explain)

Answer 19

• hepatitis/liver cancer: impaired removal of bilirubin by the liver may cause levels to build within the body
• obstruction of bile duct by gallstones: preventing the secretion of bile will cause bilirubin levels to accumulate
• pancreatic cancer
• Damage to red blood cells: increased destruction of erythrocytes (e.g. anemia) will cause bilirubin levels to rise

Question 20

What are some of the causes of jaundice in newborns?

Answer 20

• high turnover of new rbcs
• the liver of a newborn may still be developing and not be able to process the bilirubin fast enough
• is there is a lack of intestinal content, excess bilirubin can be absorbed (newborn is not feeding enough)

Question 21

Treatment of bilirubin

Answer 21

• patient is exposed to more uv lights: either under a “bili” light or patient spends time exposing skin to the sun
• underlying issue must be addressed

*note: when going under “bili” light, patient’s eyes are covered to prevent damage to the eyes (retina)

Question 22

What is cholesterol used for in the body?

Answer 22

• used in the synthesis of vitamin D
• used in the synthesis of steroid hormones
• used in production of bile
• structural component of membranes

Question 23

Liver and the production of cholesterol

Answer 23

• large quantity of cholesterol is synthesized every day by hepatocytes even though it is also absorbed from food in the intestine
• excess saturated fat results in increase in production of cholesterol

Question 24

Importance of hepatocytes in the production of plasma proteins

Answer 24

• the rough ER in hepatocytes synthesize 90% of proteins in the blood plasma (for example, albumin and fibrinogen)
• this is why hepatocytes have extensive networks of rough ER and golgi apparatus (estimated around 13 million ribosomes attached to the rER of a typical liver cell)

Question 25

Detoxification by the liver
(hydro-)

Answer 25

• livers absorb toxic substances from the blood and convert them into non-toxic or less toxic forms
• one way the liver does this is by converting hydrophobic forms of a compound into a hydrophilic form that can be excreted

Question 26

Examples of detoxification by the liver

Answer 26

• ammonia into urea
• alcohol is converted by the enzyme ethanol dehydrogenase
• biochemicals which are foreign to the body’s biochemistry