Liver Structure (M5)

Comprehensive flashcards covering the gross and microscopic structure of the liver, blood circulation, hepatocyte functions, detoxification pathways, and the ornithine cycle.

What is the largest internal organ in the human body?

The liver.

Which blood vessel supplies oxygenated blood from the aorta to the liver?

The hepatic artery.

Why is an abundant supply of oxygen from the hepatic artery essential for hepatocytes?

Liver cells are highly active and carry out hundreds of metabolic processes requiring energy in the form of $ATP$, which is supplied through aerobic respiration.

Which vessel delivers deoxygenated, nutrient-rich blood from the digestive system to the liver?

The hepatic portal vein.

Why must blood entering via the hepatic portal vein pass through the liver before circulating to the rest of the body?

Concentrations of absorbed digestive products are uncontrolled and may contain ingested toxins that must be adjusted and detoxified before entering systemic circulation.

Through which vessel does blood leave the liver to rejoin the vena cava?

The hepatic vein.

What fourth major vessel connects to the liver that is not a blood vessel?

The bile duct.

Where is bile stored before release into the small intestine, and what are its two digestive roles?

Bile is stored in the gall bladder; in the small intestine, it emulsifies fats and neutralises stomach acid.

Which excretory bile pigment produced from haemoglobin breakdown is eliminated from the body via faeces?

Bilirubin.

How is the human liver divided macroscopically and microscopically?

It is divided into $2$ lobes, which are further divided into cylindrical lobules.

What cylindrical structural unit of the liver is depicted in this diagram?

A liver lobule.

What are the inter-lobular vessels?

Smaller branches of the hepatic artery and hepatic portal vein that run parallel to and between liver lobules.

What are sinusoids in the liver?

Chambers lined with hepatocytes where oxygenated and deoxygenated blood from the hepatic artery and hepatic portal vein mix together.

What are Kupffer cells and what is their primary function?

Specialised macrophages located inside the sinusoids whose primary function is the breakdown and recycling of red blood cells ($RBC$).

Into what micro-vessels do hepatocytes first secrete bile before it reaches the bile duct?

Bile canaliculi.

What vessel located at the centre of each lobule collects modified blood from the sinusoids and merges into the hepatic vein?

The central vein (or intra-lobular vessel).

What microscopic liver lobule structure is illustrated in this diagram?

A section of a lobule detailing hepatocytes, sinusoids, Kupffer cells, bile canaliculi, and associated vessels.

What are the structural features of hepatocytes (liver cells)?

They are relatively unspecialised, have a simple cuboidal shape with many microvilli on their surface, and contain very dense cytoplasm.

Which vitamins and minerals are stored by hepatocytes in the liver?

Vitamins $A$, $D$, and $B_{12}$, as well as iron.

In what form does the liver store excess carbohydrates in hepatocyte cytoplasm?

Glycogen (as glycogen granules).

By which four chemical mechanisms can the liver render toxic substances harmless?

Oxidation, reduction, methylation, or combination with another molecule.

What reaction does catalase carry out in hepatocytes, and what is its turnover number?

It converts hydrogen peroxide into oxygen and water, with a turnover number of five million ($5 \times 10^6$).

What is the function of the Cytochrome P450 group of enzymes in the liver?

They break down drugs, including cocaine and various medicinal drugs.

What two-step enzymatic oxidation process breaks down alcohol in hepatocytes?

Ethanol is oxidised to ethanal by ethanol dehydrogenase, and ethanal is further oxidised to ethanoic acid (ethanoate) by ethanal dehydrogenase, reducing $NAD$ to $NADH$ at each step.

How does excessive alcohol intake lead to the development of a 'fatty liver'?

Detoxifying excess alcohol consumes most available $NAD$, leaving insufficient $NAD$ to oxidise fatty acids for respiration; fatty acids are converted back to fats and stored in hepatocytes, enlarging the liver.

What two long-term conditions can develop from unresolved alcohol-induced fatty liver?

Alcohol-related hepatitis and cirrhosis.

Why must excess amino acids undergo deamination rather than being stored or directly excreted?

Amino acids cannot be stored because their amino groups are toxic, and directly excreting them would waste the usable energy in their carbon skeleton.

What are the chemical products of the deamination reaction in the liver?

Ammonia ($NH_3$) and an organic keto acid.

What cyclic metabolic pathway is depicted in this sticky-note diagram?

The ornithine cycle.

What two substances combine with ornithine in the first step of the ornithine cycle, and what molecule is produced?

Ammonia ($NH_3$) and carbon dioxide ($CO_2$) combine with ornithine to produce citrulline (releasing $H_2O$).

What reaction converts arginine back into ornithine in the final step of the ornithine cycle?

Arginine reacts with water to release urea and regenerate ornithine.

Why does the liver convert ammonia into urea via the ornithine cycle?

Ammonia is highly soluble and toxic, whereas urea is less soluble and less toxic, allowing it to be safely transported in the blood to the kidneys for excretion.