Digestive system · metabolism

The liver — the body's chemical factory

The largest internal organ in the human body works nonstop: it keeps blood sugar in check, turns toxic ammonia into urea, breaks down alcohol and drugs, makes bile and blood proteins, stores vitamins — and on top of that it can grow back. Look inside, plan your own day of meals and see how the liver smooths out sugar spikes.

This page is educational and is not medical advice. The models are simplified and describe a healthy adult; the numbers are approximate and vary from person to person. For health questions, see a doctor.

Process

Breaking down proteins produces ammonia, NH₃ — toxic, especially to the brain. The liver locks it up in the urea cycle and releases harmless urea into the blood, which the kidneys remove in urine. Click NH₃ molecules in the drawing or use the button.

NH₃ in blood (diagram)0 molecules

Urea produced0 moleculeseach one costs 3 ATP

Drugs

The liver processes most drugs with enzymes from the cytochrome P450 family so the body can get rid of them. That's why the dose on the leaflet matters: too much of a drug (e.g. acetaminophen/paracetamol) can seriously damage the liver, and some drugs and foods (e.g. grapefruit juice) change how these enzymes work.

Regeneration

A healthy liver grows back even after about ⅔ of its mass is removed. That's why a living donor can give part of their liver, e.g. to a child or a relative — after a few months both parts work as full organs.

Time after surgery: 0 wk

03 mo6 mo

Liver volume100 %

Cell divisionresting

The myth of Prometheus

In the Greek myth, the Titan Prometheus stole fire from the gods and gave it to humans. As punishment he was chained to a rock, and every day an eagle ate his liver, which grew back each night. That's a legend — a real liver rebuilds itself over weeks, not overnight.

Glycogen

≈ 100 g

A glucose reserve for roughly a day without food (see the “Blood sugar” mode).

Vitamin A

≈ 80–90% of body stores

Stored in special stellate cells; usually enough for many months.

Vitamin D

first activation step

The liver converts it into the form that circulates in the blood (25-OH-D) and stores part of the reserve.

Vitamin B12

several years' supply

The liver holds a large share of the few milligrams of B12 in the body.

Iron

in ferritin

The protein ferritin stores iron, including iron from old red blood cells, so the bone marrow can build new ones.

Copper

storage and outflow

The liver builds copper into proteins and gets rid of the excess in bile.

Albumin

≈ 10–15 g per day

The main blood plasma protein: it keeps water inside the vessels and carries bilirubin and drugs, among other things. See Blood.

Clotting factors

fibrinogen, prothrombin…

Most clotting proteins are made in the liver; some of them need vitamin K. See Blood.

Fatty liver

Excess fat builds up in liver cells — often with excess weight, type 2 diabetes or drinking alcohol; in the early stage it can often be reversed.

Cirrhosis

After years of damage (e.g. from alcohol, viral hepatitis or fatty liver), healthy tissue is replaced by scar tissue, and the liver loses its ability to work and to grow back.

How does it work?

The liver sits in the upper right quadrant of the abdomen, under the diaphragm, partly shielded by the ribs. The gallbladder is tucked underneath it. Its double blood supply is unique: the portal vein brings all the blood draining from the intestines, stomach, pancreas and spleen, and the hepatic artery brings oxygen-rich blood. As a result, everything absorbed from the gut goes to the liver first, and only then to the rest of the body.

The liver is made of tens of thousands of lobules, each about 1–2 mm across. Blood flows through them in sinusoids from the edge (the portal triads) to the central vein, passing plates of liver cells — hepatocytes. Bile flows the opposite way: through bile canaliculi between hepatocytes toward the small ducts in the triads.

Sugar under control

After a meal the pancreas releases insulin, and the liver turns the extra glucose into glycogen. Between meals, glucagon tells it to break glycogen down and release glucose into the blood. As the reserve shrinks (late at night, and especially after about a day without food), the liver makes a growing share of glucose from scratch out of lactate, glycerol and amino acids — this is gluconeogenesis. Muscles have glycogen too (about 400 g), but they use it themselves: they can't release glucose into the blood.

glucose ⇄ glycogen to the right: insulin (after a meal) · to the left: glucagon and adrenaline (between meals, during exercise)

ΔG ≈ (absorption from the gut + liver output − liver storage − use by tissues) · Δt / Vmode 2 model: change in blood glucose concentration; V ≈ 16 L is the space in which glucose dissolves (1 g ≈ 6 mg/dL)

Detoxification

2 NH₃ + CO₂ → CO(NH₂)₂ + H₂Othe urea cycle in a nutshell: one nitrogen atom comes straight from ammonia, the other from aspartate (an amino acid); 3 ATP molecules supply the energy

CH₃CH₂OH ADH→ CH₃CHO ALDH→ CH₃COO⁻ → CO₂ + H₂Oethanol → acetaldehyde (toxic) → acetate → carbon dioxide and water. The ADH enzyme runs “at full speed” even at low concentrations, so the amount of alcohol drops roughly linearly over time (zero-order kinetics): about 0.1 g per kg of body mass per hour.

Pigment from old red blood cells

heme → biliverdin → bilirubin → conjugated bilirubin (with glucuronic acid)green → yellow; in the gut, bacteria turn it into stercobilin (brown stool), and some returns to the blood and the kidneys excrete it as urobilin (yellow urine)

Simplifications: the drawings are schematic. The sugar model is a few simple equations (absorption from the gut, insulin, glucagon, a glycogen store of about 100 g, gluconeogenesis) for a healthy adult — it does not predict any particular person's blood sugar. The “no buffer” mode is a thought experiment: you can't live without a liver. The alcohol curve shows the amount of ethanol in the body (in grams) for an example adult, not the blood concentration. The regeneration curve is an average — it varies from person to person.

Keys

Q W E R T — modes 1–5
1 2 — view within a mode
Space — the mode's main action (start, pause, next)
← → — time of day, step or week
B — liver buffer on/off
N — labels (mode 1)
Z — add bile (mode 4)
Delete — remove the selected meal

Did you know…?

A bruise changes color through the same chemistry as in the liver: scavenger cells break down heme from the spilled blood into green biliverdin and then into yellow bilirubin — that's why an old bruise turns greenish-yellow.
At any moment the liver holds about 10% of all the blood in the body — roughly half a liter.
About 95% of bile acids are reabsorbed in the gut and return to the liver. The same batch circulates like this several times a day, so the liver doesn't have to keep making new ones.

Challenges

Keep glucose in range for 24 hoursMode 2: plan a day with at least three meals so that glucose never leaves 70–140 mg/dL, and play it to the end (until 6:00).
Turn off the liver buffer and watch sugar swingMode 2: turn off the buffer and play the day until glucose falls below 70 or jumps above 160 mg/dL.
Turn ammonia into ureaMode 3: feed enough NH₃ into the urea cycle to make 5 urea molecules.
Follow an old red blood cell to bilirubinMode 4: go through all the steps — from the blood cell to the color of stool and urine.
Rebuild the liver after removing a lobeMode 5: remove a lobe and move time forward until the liver regains at least 95% of its volume.