Flashcards in Physiology - Liver Structure and Function Deck (25)
What are the two major and minor lobes of the liver?
Major Lobes: Left and Right
Minor Lobes: Caudate and quadrate
Where is the porta and what does it contain?
On the inferior surface of the liver
Blood vessels: Hepatic artery, hepatic portal vein
Nerves: hepatic nerve plexus
Bile ducts: left and right hepatic ducts from the common hepatic duct
The porta hepatic contains the portal triad.
What makes up the portal triad?
Hepatic portal vein
Describe the biliary tree from the liver to the duodenum
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)
What is the function of the coronary ligament and what lies within its border?
Connects the liver to the inferior border of the diaphragm
The area inside the coronary ligament is the bare area of the liver.
What structures cover the liver?
The liver is covered by a connective tissue capsule.
Also mostly covered by peritoneum
What does the connective tissue capsule of the liver become on the inferior surface?
At the porta the connective tissue capsule becomes a branching network of septa which run through the liver providing support
How does the septa of the liver add to the histological shape of the parenchyma?
The septa divide the liver into hexagonal lobules
What structures follow the septa throughout the liver?
Vessels, ducts and nerves
What structures are located at the corners of each hexagonal lobule?
-Hepatic portal vein
What exist in the centre of hexagonal lobules in the liver?
These drain into hepatic veins and eventually into the inferior vena cava
Describe hepatic cords
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.
What type of capillaries are in the hepatic sinusoids?
This allows lots of exchange
How do blood and bile flow through the hepatic lobules?
Blood flows towards the central vein
Bile flows down bile canuliculi towards the hepatic bile ducts
Describe the flow of blood through the hepatic sinusoids
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.
What are the functions of hepatocytes?
Bile synthesis: Main function (bile salts)
What nutrients do the liver hepatocytes store?
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
How do hepatocytes play a role in detoxification?
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
What are the 6 components of bile?
(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)
What are bile pigments?
How does bilirubin colour bile, urine and faeces?
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
Describe the life cycle of bile acids
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
Why do you need a gallbladder?
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
Describe the histological layers of the gallbladder
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
Describe the control of bile secretion
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