L7: functions and secretions of the liver

Question 1

Major functions of the liver

Answer 1

• produces bile needed to digest fat and absorb vitamins A, D, E, K
• metabolises nutrients from all food to produce energy when needed
• removes and destroys old RBCs

Question 2

What makes bile?

Answer 2

Made by liver hepatocytes and transported to the gallbladder via hepatic bile ducts,

Question 3

Important functions of bile

Answer 3

• helps the digestion and absorption of fats using bile salts
• elimination of insoluble waste products such as bilirubin and excess cholesterol
• helps neutralise gastric acid in the duodenum using bicarbonate

Question 4

What is bile composed of?

Answer 4

Bile salts, waste products, electrolytes, water

Question 5

When is the gallbladder empty and full?

Answer 5

• stores bile produced by the liver. concentrates it by removing water
• after meals the gallbladder is empty and flat
• before a meal, the gallbladder may be full of bile
• it contracts during a meal and ejects bile into cystic duct

Question 6

What does the gallbladder do in response to CCK?

Answer 6

Contracts to eject stored bile into the small intestine through a series of tubes called ducts.

Question 7

What happens if you remove the gallbladder?

Answer 7

Bile helps digest fats, but the gallbladder is not essential. Removing the gallbladder in an otherwise healthy individual typically causes no observable problems with health or digestion though there may be a small risk of diarrhoea and fat malabsorption.
The bile will just go straight from the liver into the intestine - not as concentrated so not as effective

Question 8

Blood supply of the liver

Answer 8

Hepatic vein - drains into vena cava, sends blood back to the heart
Hepatic artery - 20% of blood supply; branch of the aorta; oxygenated blood
Hepatic portal vein - 80% of blood supply; absorbed nutrients; toxins; connects the small intestine, pancreas and spleen to liver

Blood from both sources mix in the sinusoids which are specialised capillaries of the liver

Question 9

Flow of blood and bile in the liver

Answer 9

Blood flows into the central vein and bile flows into ducts (via canaliculi) in opposite directions.

Question 10

What make up the portal triad?

Answer 10

Hepatic portal vein, hepatic artery, bile duct

Question 11

How do bile salts come together to make micelles?

Answer 11

Bile salts are amphipathic: hydrophobic/lipophilic tail and hydrophilic/lipophobic head
Individual unit is wedge-shaped.
So in water a sphere is created
Sphere = micelle, occurs when there is a high concentration of bile salts
So ‘fatty’ things can travel in the middle of them.

Question 12

How does the liver remove insoluble waste products from the body using bile salts?

Answer 12

An insoluble waste products e.g. excess cholesterol or fat soluble toxins are sent by the liver to the intestine by solubilising them in bile salt micelles.

Question 13

How is bilirubin formed?

Answer 13

RBCs get broken down by splenic phagocytes or hepatic macrophages into globulin, haem and iron.
They convert the haem into unconjugated bilirubin which is a yellowish/green pigment. It is quite insoluble.

Question 14

How is bilirubin excreted?

Answer 14

Splenic phagocytes put it in the bloodstream where it is picked up by albumin, reducing its toxicity.
The albumin helps transport it to the liver. Hepatocytes pick up the bilirubin and conjugate it by binding it to glucuronic acid to form conjugated bilirubin, which is now soluble.
Conjugated bilirubin moves into bile ducts and into bile, into gallbladder, to SI where it is not absorbed and enters the faeces.
Gives faeces their brown colour.

Question 15

What is jaundice?

Answer 15

Excessive blood bilirubin

Bilirubin can accumulate in skin, sclera, mucous membranes

Question 16

Different causes of jaundice

Answer 16

• excessive RBC breakdown (pre-hepatic jaundice). E.g. transfusion reactions, sickle cell anaemia etc.
• impaired hepatocytes uptake/conjugation/excretion (hepatic jaundice). E.g. hepatitis, cancer, cirrhosis etc.
• impaired bile flow out of liver due to an obstruction (post-hepatic jaundice)? E.g. gallstones (obstructive), inflammation etc.

Question 17

Relevance of liver to dentistry

Answer 17

Young patient who had chronic liver disease with severely bilirubin stained (green) teeth that started mineralising before liver transplant at age 2.5 years.
Dental tissue formed after a liver transplant can be normal.

Congenital biliary atresia - permanently stained green teeth. Occurs before birth. Occurs when there is an inadequate pathway for bile to drain from liver to intestine, so it backs up into liver and eventually rest of body.

Question 18

What is the enterohepatic circulation?

Answer 18

Once in the intestine, waste products from the liver are excreted in faeces. When the bile salts have finished helping they are returned back to the liver to be used again and again, the enterohepatic circulation. Sent to the liver via the hepatic portal vein. Most is reabsorbed.