B15.4 - Liver

Question 1

What is excretion?

Answer 1

• removal of waste products of metabolism (synthesis and breaking down of molecules) from the body

Question 2

What are the main metabolic waste products in mammals?

Answer 2

• carbon dioxide:
  
  • waste products of cellular respiration
  • excreted from the lungs
• bile pigments:
  
  • formed from breakdown of haemoglobin from old RBCs
  • excreted in bile from liver to small intestine via gall bladder and bile duct
• nitrogenous waste products (urea):
  
  • formed from breakdown of excess amino acids
  • produced by all mammals
  • ** fish produce ammonia, birds/insects produce uric acid (water insoluble) **

Question 3

What is the liver?

Answer 3

• second largest organ of the body that is involved in homeostasis
  
  • just below diaphragm
• 5% of body mass
• is able to regenerate very quickly

Question 4

What is the hepatic artery?

Answer 4

• carries oxygenated blood to the liver
• provides O2 for respiration

Question 5

What is the hepatic vein?

Answer 5

• returns to the heart with deoxygenated blood

Question 6

What is the hepatic portal vein?

Answer 6

• branched vessel that carries blood (less O2 saturation) to the liver
• carries nutrients, glucose (products of digestion) from the intestines (ileum/duodenum)
  
  • 75% of the blood flowing through liver comes from the hepatic portal vein

Question 7

What is the bile duct?

Answer 7

• takes bile (secreted by the liver to emulsify/breakdown fat in the duodenum) and sends it to the gall bladder

Question 8

What is the overall structure of the liver?

Answer 8

• hepatic vein
• hepatic artery
• hepatic portal vein
• bile duct
• gall bladder

Question 9

What is the gall bladder?

Answer 9

• stores bile and releases it into the duodenum via the bile duct

Question 10

What are hepatocytes?

Answer 10

• liver cells
• large nuclei
• prominent Golgi apparatus
• many mitochondria
  
  • metabolically active cells
• divide and replicate
  
  • liver can be regenerated very quickly

Question 11

What is the internal structure of the liver?

Answer 11

• lobules
• central vein
• sinusoids
• Kupffer cells
• bile canaliculi

Question 12

What are lobules?

Answer 12

• the four lobes of the liver are further divided into lobules
• they are made up of millions of hepatocytes
  
  • ** allows for blood to flow past as many cells as possible **
• branches of hepatic artery/portal vein and bile duct are connected to the lobule

Question 13

What is the central vein?

Answer 13

• connects to the hepatic vein
• each lobule has a central vein in the middle

Question 14

What are sinusoids?

Answer 14

• spaces where the blood from the two hepatic blood vessels are mixed
  
  • increases oxygen content of the blood from the hepatic portal vein

Question 15

What happens when the blood runs through sinusoids?

Answer 15

• they pass the hepatocytes and remove harmful substances/O2 from the blood
  
  • these are broken down by hepatocytes into less harmful substances that then re-enter the blood

Question 16

What are Kupffer cells?

Answer 16

• attached to the walls of sinusoids
• remove bacteria and break down old red blood cells
  
  • act as resident macrophages
  • ingest foreign particles and helps to protect against disease

Question 17

What are Kupffer cells?

Answer 17

• attached to the walls of sinusoids
• remove bacteria and break down old red blood cells
  
  • act as resident macrophages
  • ingest foreign particles and helps to protect against disease

Question 18

What is the bile canaliculi?

Answer 18

• hepatocytes secrete bile and release it into the bile canaliculi
  
  • the bile then drains into the bile duct and takes it to the gall bladder

Question 19

What are the functions of the liver?

Answer 19

• carbohydrate metabolism
• deamination of excess amino acids
• detoxification

Question 20

How does the liver metabolise carbohydrates?

Answer 20

• increase in glucose level = release of insulin from beta cells
  
  • glycogenesis (storing glucose as glycogen)
• decrease in glucose = release of glucagon from alpha cells
  
  • gluconeogenesis
  • glyogenolysis

Question 21

How does the liver carry out deamination of amino acids?

Answer 21

• hepatocytes synthesise most plasma proteins
• transamination = conversion of one animal acid into another
  
  • if a diet does not contain the required balance of amino acids
• deamination = removal of amine group from a molecule
• ** body cannot store proteins or amino acids **
• remove amino group —> convert to ammonia —> urea
  
  • excreted by the kidneys
  • remaining amino acids are used for cellular respiration or converted into lipids
• ** ammonia produced is involved in the ornithine cycle **

Question 22

What is the ornithine cycle?

Answer 22

• converts ammonia to urea in the mitochondria of hepatocytes
  
  • ammonia is combined with CO2 to form urea
  • 2NH3 + CO2 —> CO(NH2)2 + H2O
• it then diffuses through the phospholipid bilayer of the hepatocytes and transported to the kidneys

Question 23

How does the liver carry out detoxification?

Answer 23

• where the liver breaks down other harmful substances like alcohol, drugs and unwanted hormones
  
  • e.g. hydrogen peroxide (enzyme catalase breaks it down into O2 and H2O)
• ethanol:
  
  • hepatocytes contain alcohol dehydrogenase that breaks it down to ethanal and then ethanoate acetic acid (build up fatty acids, cellular respiration
  • ** excess alcohol can cause liver cirrhosis (cells die and scar tissue blocks blood flow) **
• paracetamol:
  
  • excess can lead to liver and kidney failure
• insulin:
  
  • broken down by liver as excess insulin causes blood sugar level problems