The liver is the body’s chemical factory: it stores and releases fuel, makes proteins, clears drugs and toxins and produces bile. This page explains its blood supply and main functions, how it handles glucose and lactate during exercise, and why exercise is a treatment for fatty liver disease.
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10Questions
Part 7 · Digestion and Metabolism · Chapter 32 of 47
Learning objectives
By the end of this page you should be able to:
List the main functions of the liver.
Describe the liver’s double blood supply and lobule structure.
Explain the liver’s role in glucose, fat and protein metabolism.
Describe bilirubin handling and the causes of jaundice.
Explain the lactate shuttle and Cori cycle in exercise.
Describe the effects of liver disease and the role of exercise in fatty liver.
Why it matters
Fatty liver disease is now one of the commonest chronic diseases, closely linked to obesity, diabetes and inactivity. Exercise is a first-line treatment.
People with advanced liver disease often lose muscle, become frail and have fluid in the abdomen, bleeding tendency and confusion. Physiotherapists help them stay mobile, sometimes while they wait for a transplant.
Functions of the liver
Figure 1 · What the liver does
A chemical factory with reserve capacity. Signs of liver failure appear only when most function is lost.
Blood supply and structure
Figure 2 · A double blood supply
Everything absorbed from the gut passes the liver first. That is why many drugs taken by mouth are partly broken down before reaching the body (first-pass metabolism).
Hepatocytes are arranged in plates radiating from a central vein. Blood from the portal vein and hepatic artery mixes as it flows through leaky capillaries called sinusoids, giving each hepatocyte direct contact with plasma. Bile flows the opposite way, towards bile ducts at the edge of each lobule.
Metabolic roles
Figure 3 · The liver as glucose buffer
The liver keeps blood glucose steady for the brain. Liver glycogen lasts roughly a day of fasting; then gluconeogenesis takes over.
Nutrient
Liver roles
Clinical link
Carbohydrate
Stores glycogen; releases glucose; makes new glucose
Low blood glucose in liver failure
Fat
Makes lipoproteins and cholesterol; makes ketones in fasting
Fatty liver when fat inflow exceeds output
Protein
Makes albumin and clotting factors; converts ammonia to urea
Low albumin, bleeding, confusion in liver failure
Drugs and hormones
Inactivates and prepares them for excretion
Drug doses may need adjusting
Lactate and the liver in exercise
Brooks summarises decades of work showing that lactate is not a waste product. It forms continuously, even with plenty of oxygen, and moves between cells as a fuel and a signal [1]. The heart and resting muscles burn it, and the liver turns it back into glucose [1].
Figure 4 · Lactate is shared, not wasted
Lactate is formed even with plenty of oxygen. It is a major fuel and the main substrate for making new glucose [1].
During prolonged exercise, liver glucose output rises to match muscle uptake. When liver glycogen runs low late in long events, blood glucose can fall, contributing to fatigue. Carbohydrate intake during exercise spares liver glycogen (Chapter 31).
Myth to retire
Lactate does not cause muscle soreness a day or two after exercise. Lactate clears within an hour of stopping. Delayed soreness comes from muscle micro-damage and inflammation (Chapter 27).
Bilirubin and jaundice
When old red cells are broken down, haem becomes bilirubin. The liver conjugates it and excretes it in bile, giving stool its colour. Jaundice, a yellow tinge to skin and eyes, occurs when bilirubin builds up.
Type
Cause
Clue
Pre-hepatic
Excess red cell breakdown
Anaemia; normal-coloured urine
Hepatic
Liver cell damage (hepatitis, cirrhosis)
Abnormal liver tests
Post-hepatic
Blocked bile ducts (stones, tumour)
Pale stool, dark urine, itch
Liver disease
In fatty liver disease, fat builds up in hepatocytes, usually with obesity, insulin resistance and inactivity. It is now often called metabolic dysfunction-associated steatotic liver disease. It can progress to inflammation, scarring and cirrhosis.
Consequence of cirrhosis
Why
Physiotherapy implication
Ascites
Raised portal pressure and low albumin
Breathlessness, reduced mobility; position for comfort
Bleeding tendency
Fewer clotting factors and platelets
Gentle manual techniques; fall prevention
Muscle wasting
Poor protein metabolism and intake
Resistance training and nutrition support
Confusion (encephalopathy)
Ammonia and other toxins reach the brain
Simple instructions; safety
Varices
Portal hypertension
Avoid heavy straining
Keating and colleagues pooled 12 controlled trials of regular exercise in fatty liver disease. Exercise reduced liver fat, even with minimal or no weight loss [2].
Figure 5 · Exercise reduces liver fat
Exercise is liver treatment even without weight loss. Benefits appeared at activity levels below obesity-management targets [2].
The benefit appeared at exercise levels below those usually recommended for weight management, though liver enzyme levels did not change clearly [2].
Practical skill · exercise for fatty liver
Combine regular aerobic activity with resistance training, building gradually [2]. Explain that the liver benefits even if the scale does not move much. In cirrhosis, check platelet count, varices status and fluid before progressing, and work with the medical team.
Clinical relevance for the physiotherapist
Fatty liver. Exercise reduces liver fat without needing major weight loss [2].
Cirrhosis. Address muscle wasting and frailty; adapt for ascites and bleeding risk.
Exercise testing. Raised lactate reflects metabolic strain and fuel shuttling, not just lack of oxygen [1].
Drugs. Liver disease prolongs drug effects; watch for sedation and falls.
Jaundice with itch and pale stools. Report; may indicate blocked bile ducts.
Assessment and application
Situation
Interpretation
Action
Overweight patient with fatty liver, frustrated by slow weight loss
Liver benefits anyway [2]
Encourage aerobic and resistance exercise
Patient with cirrhosis, thin limbs, swollen abdomen
Sarcopenia and ascites
Graded strength work; positioning; liaise with team
New confusion in a patient with liver disease
Possible encephalopathy
Urgent medical review
Athlete worried about lactate after intervals
Lactate is a fuel and clears quickly [1]
Reassure; cool-down
Common mistakes
Calling lactate a waste product [1].
Telling patients exercise helps fatty liver only if they lose weight [2].
Blaming lactate for next-day soreness.
Ignoring bleeding risk and ascites in cirrhosis.
Forgetting the liver clears many drugs.
Exam preparation
Long answer
Describe the functions of the liver. Add a note on jaundice.
Functions (Figure 1).
Blood supply and lobule (Figure 2).
Carbohydrate, fat and protein metabolism (Figure 3 and table).
Bilirubin metabolism and types of jaundice.
Clinical: fatty liver and exercise [2].
Short notes
Portal circulation.
Cori cycle and lactate shuttle [1].
Jaundice.
Exercise in fatty liver [2].
Viva and practical
“What proportion of liver blood comes from the portal vein?” — about three quarters.
“Is lactate waste?” — no, it is a fuel and glucose precursor [1].
“Does exercise help fatty liver without weight loss?” — yes [2].
OSCE: plan exercise for a patient with cirrhosis and ascites.
Current evidence
Exam and traditional teaching
Lactate is the end-product of anaerobic glycolysis and causes fatigue and soreness.
What the evidence adds
Lactate is continuously formed, shuttled and used as fuel and as a precursor for glucose [1].
Exercise reduces liver fat independently of weight loss [2].
What the student should understand
The liver and muscles share fuel constantly. Moving more is good for both.
Check yourself
10 questions on this page. Tap one to see the answer and the reasoning.
Q1. According to lactate shuttle theory, lactate is formed:
(A) Only without oxygen
(B) Continuously, even under aerobic conditions
(C) Only in the liver
(D) Never in healthy people
Answer: (B) Lactate forms continuously under aerobic conditions [1].
Q2. Which is NOT a role of lactate described by Brooks?
(A) Major energy source
(B) Major gluconeogenic precursor
(C) Signalling molecule
(D) Cause of delayed-onset muscle soreness
Answer: (D) Lactate serves as fuel, gluconeogenic precursor and signal [1].
Q3. In the Cori cycle, lactate from muscle is converted to glucose in the:
(A) Kidney only
(B) Liver
(C) Brain
(D) Lungs
Answer: (B) Lactate is the major gluconeogenic precursor, largely used by the liver [1].
Q4. Some clinicians now view raised blood lactate in illness as a marker of:
(A) Lack of oxygen only
(B) Metabolic strain rather than simply stress
(C) Liver cancer
(D) Dehydration only
Answer: (B) Lactatemia is being reframed as a ‘strain’ biomarker [1].
Q5. In the meta-analysis of exercise in fatty liver disease, exercise reduced:
(A) ALT strongly
(B) Liver fat
(C) Bilirubin only
(D) Nothing
Answer: (B) There was a pooled benefit on liver fat [2].
Q6. The liver fat benefit of exercise occurred:
(A) Only with large weight loss
(B) With minimal or no weight loss
(C) Only with diet alone
(D) Only in children
Answer: (B) Benefit occurred with minimal or no weight loss [2].
Q7. The effect of exercise on the liver enzyme ALT was:
(A) A large fall
(B) No significant effect
(C) A rise
(D) Not measured
Answer: (B) There was no effect on ALT [2].
Q8. Benefits in fatty liver were seen at exercise levels:
(A) Far above guidelines
(B) Below current obesity-management recommendations
(C) Only in athletes
(D) Only with resistance training
Answer: (B) Benefit appeared below current exercise recommendations for obesity [2].
Q9. Which liver product is a major fuel and glucose precursor during exercise recovery?
(A) Bilirubin
(B) Glucose made from lactate
(C) Albumin
(D) Urea
Answer: (B) Lactate is converted back to glucose (gluconeogenesis) [1].
Q10. A practical message for patients with fatty liver is:
(A) Exercise only helps if weight falls
(B) Regular exercise helps the liver even without weight loss
(C) Avoid exercise
(D) Only medicines help
Answer: (B) Exercise is a valid, low-cost therapy for fatty liver [2].
Keating SE, Hackett DA, George J, Johnson NA. Exercise and non-alcoholic fatty liver disease: a systematic review and meta-analysis.Journal of Hepatology. 2012;57(1):157–166.
doi:10.1016/j.jhep.2012.02.023PMID 22414768Systematic review and meta-analysis
