Physiology - Liver Structure and Function

Question 1

What are the two major and minor lobes of the liver?

Answer 1

Major Lobes: Left and Right

Minor Lobes: Caudate and quadrate

Question 2

Where is the porta and what does it contain?

Answer 2

On the inferior surface of the liver

Blood vessels: Hepatic artery, hepatic portal vein
Lymphatic vessels
Nerves: hepatic nerve plexus
Bile ducts: left and right hepatic ducts from the common hepatic duct

Question 3

The porta hepatic contains the portal triad.

What makes up the portal triad?

Answer 3

Hepatic artery
Hepatic portal vein
Hepatic ducts

Question 4

Describe the biliary tree from the liver to the duodenum

Answer 4

Left and Right hepatic ducts join to form the common hepatic duct
The common hepatic duct joins the cystic duct from the gallbladder to form the common bile duct
The common bile duct joins the pancreatic duct.
These both flow out the major duodenum papilla (Sphincter of Oddi)

Question 5

What is the function of the coronary ligament and what lies within its border?

Answer 5

Connects the liver to the inferior border of the diaphragm

The area inside the coronary ligament is the bare area of the liver.

Question 6

What structures cover the liver?

Answer 6

The liver is covered by a connective tissue capsule.

Also mostly covered by peritoneum

Question 7

What does the connective tissue capsule of the liver become on the inferior surface?

Answer 7

At the porta the connective tissue capsule becomes a branching network of septa which run through the liver providing support

Question 8

How does the septa of the liver add to the histological shape of the parenchyma?

Answer 8

The septa divide the liver into hexagonal lobules

Question 9

What structures follow the septa throughout the liver?

Answer 9

Vessels, ducts and nerves

Question 10

What structures are located at the corners of each hexagonal lobule?

Answer 10

Portal triad:

• Hepatic artery
• Hepatic portal vein
• Hepatic ducts

Question 11

What exist in the centre of hexagonal lobules in the liver?

Answer 11

Central vein

These drain into hepatic veins and eventually into the inferior vena cava

Question 12

Describe hepatic cords

Answer 12

Hepatic cords radiate out from central veins like spokes on a wheel.
They are lined by (composed of) hepatocytes.
Bile canuliculi (cleft like lumen) lie between cells in each cord.
Spaces between hepatic cords are hepatic sinusoids and contain blood channels.

Question 13

What type of capillaries are in the hepatic sinusoids?

Answer 13

Discontinuous capillaries

This allows lots of exchange

Question 14

How do blood and bile flow through the hepatic lobules?

Answer 14

Blood flows towards the central vein

Bile flows down bile canuliculi towards the hepatic bile ducts

Question 15

Describe the flow of blood through the hepatic sinusoids

Answer 15

Blood comes from the alimentary canal through the hepatic portal vein. (Oxygen depleted but Nutrient rich)
Oxygenated blood that is nutrient deprived comes from the heart through the hepatic artery.

In the hepatic sinusoids these two sources mix giving both oxygen and nutrient rich blood.
As this blood travels through the hepatic sinusoids it exchanges with the hepatocytes and eventually drains into the central vein.

Question 16

What are the functions of hepatocytes?

Answer 16

Bile synthesis: Main function (bile salts)
Nutrient storage
Nutrient interconversion
Detoxification

Question 17

What nutrients do the liver hepatocytes store?

Answer 17

We eat more food than we require so nutrients are stored in the liver for a rainy day.

Glucose: converted to glycogen. Enough stored to run maybe 18 miles. Then you hit “the wall”
Fat: once your liver can’t store any more glycogen you start storing fat. Theres no limit to this (steatosis)
Vitamin B12: Enough for 3 years
Vitamins ADEK: Plenty stored
Copper: stored here safely so that oxygen free radicals aren’t causing havoc
Iron: also stored

Question 18

How do hepatocytes play a role in detoxification?

Answer 18

Particularly metals

Conjugated so that they are rendered harmless
We can then pass them without damaging other parts of our body
This system works for most things but isn’t perfect

Question 19

What are the 6 components of bile?

Answer 19

Bile Acid
Lecithin
Cholesterol
(These three are synthesised in the liver and emulsify fat)

Bile pigments: bilirubin
Toxic metals: Detoxified in liver
Bicarbonate: Neutralise acid chyme (produced in duct cells not hepatocytes)

Question 20

What are bile pigments?

How does bilirubin colour bile, urine and faeces?

Answer 20

Breakdown products of old/damaged erythrocytes

Bilirubin (predominant bile pigment) extracted from blood by hepatocytes and secreted into bile = Yellow Bile

Bilirubin is modified by bacterial enzymes to give brown pigment = Brown faeces

Reabsorbed Bilirubin is excreted in urine = Yellow urine

Question 21

Describe the life cycle of bile acids

Answer 21

Synthesised in the liver from cholesterol.
Before secretion they are conjugated with glycine or taurine to produce bile salts. (Increased solubility)

Secreted bile salts are reabsorbed through the enterohepatic circulation.
Liver -> bile duct -> duodenum -> distal ileum -> hepatic portal vein -> liver
Absorbed near transporters for vitamin B12 complex

Question 22

Why do you need a gallbladder?

Answer 22

When your not eating no CCK is being produced
Duodenal papilla (Sphincter of Oddi) is closed
Bile is being produced all the time
This bile starts to back up in the biliary tree

Gallbladder exists as a storage vessel
It absorbs water so that the bile is concentrated

Question 23

Describe the histological layers of the gallbladder

Answer 23

Mucosa has ruggae much like the stomach
Muscularis externa has smooth muscle so that bile can be pushed out into the duodenum
Serosa is the connective tissue layer

Question 24

Describe the control of bile secretion

Answer 24

Sphincter of Oddi:

• Controls release of bile and pancreatic secretion into duodenum
• When no CCK sphincter closed
• Bile builds up and backs into gallbladder
• Storage and concentration by absorption of Na and H2O

Presence of fat in duodenum causes release of CCK:

• Sphincter of oddi relaxes
• Smooth muscle of gallbladder contracts

Question 25

How is H2O absorbed from bile by the gallbladder?

Answer 25

Sodium potassium pump moves sodium out of epithelial cell and potassium in.
Potassium allowed to flow back out through channel
Sodium concentration inside the cell is low.
Sodium channel on apical surface takes sodium into cell
Water follows the movement of sodium from apical surface to basolateral surface