Gastroenterology Flashcards
Which structure is the remnant of the umbilical vein of the fetus?
Ligamentum Teres
Briefly outline the outflow and inflow of the liver
Inflow: Hepatic artery (25%), Portal vein (75%)
Outflow: Bile, 3 x Hepatic veins
What is the purpose of blood delivered to the liver by the Portal Vein?
Contains all of the products of digestion absorbed from the GI tract
So all useful and non-useful products are processed in the liver before being released back into the hepatic veins which join the IVC or stored in the liver for later use
What is the purpose of blood delivered to the liver by the Hepatic Artery?
Delivers oxygenated blood from the general circulation
What parts of the liver does the middle hepatic vein separate?
Anterior segment of the right hepatic lobe from the medial segment of the hepatic lobe.
How many hepatic segments are there?
8
List the micro-morphological and functional components of the liver.
Morphological - Lobules + Portal triads
Functional - Acinus, blood, and bile flow
What shape is a hepatic lobule and describe the structure of 1 hepatic lobule?
Hexagon - Each corner consists of a portal triad that links with 3 adjacent lobules. The center of the lobule is a central vein that collects blood from hepatic sinusoids. Within the lobule are rows of hepatocytes.
The center of the lobule is the central vein. Outline its drainage
Collects blood from the hepatic sinusoids → hepatic veins → systemic venous system
Within a lobule, there are rows of hepatocytes. What does each side of the row of hepatocytes face?
Each has a sinusoid-facing side → picks up stuff from the inflow of blood
Bile canaliculi facing side → Makes bile by taking nutrients, processing it, and shifting it across to the biliary canaliculi
What does a portal triad consist of? What is the function of each constituent?
Branch of hepatic artery -> Brings O2-rich blood into the liver to support hepatocytes’ increased energy demands.
Branch of portal vein -> Mixed venous blood from GIT (nutrients, bacteria, and toxins) and spleen (waste products). Hepatocytes process nutrients, detoxify the blood, and excrete waste.
Bile Duct -> Bile drains into bile canaliculi and then coalesce with cholangiocyte-lined bile-ducts around the lobule perimeter.
What type of cell are bile-ducts lined by and what is the function of this cell type?
Cholangiocytes. Their function is the modification of hepatic canalicular bile as it is transported along the biliary tree
Sinusoids are formed by the junction of what two vessels?
Branch of hepatic artery and branch of the portal vein
Through what vessels does blood flow through to get from the central vein to the right, left, or middle hepatic veins?
Central → Intralobular → Interlobular → Right, Middle or Left Hepatic Veins
What is the functional unit of the liver (in terms of micro-function) and what does it consist of?
Hepatic acinus. It consists of 2 adjacent 1/6th hepatic lobules sharing 2 portal triads. They extend into hepatic lobules as far as the central vein.
At what point does blood drain out of the hepatic acinus in the 3 zone model?
Point B (central vein)
Which zones in the 3 zone model receive the most oxygen and have the lowest toxin risk, respectively?
Zone 1: Highest oxygen concentration (also highest toxin risk)
Zone 3: Lowest toxin risk (also lowest oxygen concentration)
Do sinusoidal endothelial cells have a basement membrane?
No. This allows lipids and large molecule movement to and from hepatocytes
Describe the structure of the sinusoidal endothelium and how does this adapt the endothelium to its structure
Discontinuous, fenestrated endothelium
Allows lipids and large molecule movement to and from hepatocytes
What is the difference between a bile canaliculus and a bile duct?
Bile canaliculi are thin tubes that collect bile secreted by hepatocytes and they empty into a series of progressively larger bile ductules and ducts that eventually become the common hepatic duct
What are Kupfer cells and what are their functions?
Sinusoidal macrophage cells attached to endothelial cells
Phagocytosis; they eliminate and detoxify substances arriving in the liver from portal circulation
What is another name for ito or perisinusoidal cells? List all the functions of these cells
Hepatic stellate cells
Store vitamin A in liver cytosolic droplets
Activated (fibroblasts) in response to liver damage
Deposit collagen in the ECM
What does a cholangiocyte secrete into bile?
HCO3- and H20
What cell type makes up 80% of liver mass?
Hepatocyte
Summarise the main hepatocyte functions
Metabolic and catabolic functions - make + use carbohydrates, lipids, and proteins
Secretory and excretory functions - Synthesis and secretion of proteins, bile, and waste products
Detoxification and immunological functions - breakdown of ingested pathogens and processing of drugs
List 3 non-sugar molecules that can be used to produce glucose via gluconeogenesis
Amino acids (from liver and renal cortex)
Lactate (from anaerobic glycolysis in RBCs and muscles)
Glycerol (lipolysis)
What is the Cori cycle?
The process where lactate from muscles is transported to the liver and converted to glucose to then return to muscles to be metabolized back into lactate
Outline the reactions of the Cori Cycle
Lactate produced via anaerobic glycolysis in a muscle cell (myocyte) is transported to the liver and is converted to pyruvate via lactate dehydrogenase
Pyruvate then converted to glucose via gluconeogenesis, releasing 6 ATP in the process
Glucose via glycolysis to pyruvate → lactate in muscle cells and the cycle starts over again
Where do amino acids undergo protein synthesis and what are some examples of the proteins that are produced?
Liver
Plasma proteins, Clotting factors, and Lipoproteins
Briefly explain what transamination is using alanine and alpha-ketoglutarate as an example
Keto acids can be converted into multiple non-essential amino acids depending on the specific transaminase enzyme responsible for the conversion. This will occur in the liver
Alanine + alpha-keto glutarate → Glutamate + Pyruvate
Outline the glucose-alanine cycle
Pyruvate is produced from anaerobic glycolysis in muscle cells and then transported to the liver where it is converted to alanine via an aminotransferase enzyme. Nitrogen is also transported to the liver in the form of glutamine made from glutamate and ammonia catalyzed by glutamine synthetase.
- Alanine converted goes from pyruvate to glucose via gluconeogenesis. Glucose is returned to muscle cells for glycolysis.
- Alanine is also converted to glutamate. Glutamate is converted to urea, which gets deaminated and returned to the blood.
How are fatty acids from triglyceride breakdown converted into acetyl CoA?
Beta-oxidation
How can Acetyl CoA be used as an alternative tissue energy source before running it through the TCA cycle?
2 Acetyl CoA can be converted into Acetoacetyl CoA via the enzyme thiolase
Add another Acetyl CoA to Acetoacetyl CoA to get HMG CoA
HMG CoA can be cleaved to form a free Acetoacetate and another Acetyl CoA
What is the main energy reserve stored in the liver and muscle?
Glycogen
What is the main function of LDLs, VLDLs, and HDLs?
LDLs - Transport cholesterol to tissues
VLDLs - Transport fatty acids to tissues.
HDLs - Transport endogenous cholesterol from tissues to the liver.
What are the major functions of cholesterol?
Maintaining cell membrane integrity.
Steroidogenesis (synthesis of steroid hormones)
What do hepatocytes store (besides glycogen, lipids, and proteins)?
Fat-soluble vitamins -> vitamin A, D, E, K.
Vitamin B12
Store iron as ferritin (available for erythropoiesis)
Copper
What vitamin is essential for blood clotting?
Vitamin K
Outline how hepatocytes carry out detoxification
Phase 1 (modification) - P450 enzymes used. Toxins are made to be more hydrophilic. Reactions classified into oxidation, reduction, and hydrolysis. Phase 2 (conjugation) - Attach water-soluble side chain to the toxin to make it less reactive.
What is the majority of bile made of?
97% Water
What are the bile pigments?
Bilirubin (yellow) and biliverdin (green)
