1.9 Storage and Metabolic Role of Liver

The liver is the largest gland in the body and performs over 500 vital functions. It plays a central role in metabolism, storage, detoxification, and the production of bile. It is also a major site for the storage of nutrients and the regulation of blood composition.

Definition

Liver: The liver is the largest internal organ and the largest gland in the human body. It is a reddish-brown, wedge-shaped organ located in the upper right quadrant of the abdominal cavity, just below the diaphragm. It has two main lobes: the larger right lobe and the smaller left lobe.

Metabolic Role: The liver regulates most chemical levels in the blood and performs a wide range of metabolic functions, including carbohydrate metabolism, protein metabolism, lipid metabolism, and detoxification.

Storage Role: The liver stores glycogen, vitamins (A, D, B12), iron, and other substances for later use by the body.

Main Idea

The liver is the chemical factory of the body. It processes nutrients absorbed from the small intestine, stores them, converts them into usable forms, and releases them into the blood as needed. It also detoxifies harmful substances and produces bile for fat digestion.

Core Concept

• Largest gland in the body
• Two lobes — right (larger) and left (smaller)
• Blood supply — hepatic artery (oxygenated) and hepatic portal vein (nutrient-rich)
• Functions — over 500 vital functions
• Storage — glycogen, vitamins, iron
• Metabolism — carbohydrates, proteins, fats
• Detoxification — drugs, alcohol, toxins
• Bile production — for fat digestion

Detailed Explanation

Structure of the Liver

• Located in the upper right quadrant of the abdominal cavity.
• Just below the diaphragm.
• Protected by the rib cage.

• Right lobe — larger
• Left lobe — smaller

Blood Supply: The liver has two distinct sources of blood:

• The lobes contain thousands of lobules (small lobes).
• These lobules connect with many bile ducts.
• Bile ducts are tubes that transport bile from the liver to the small intestine.

• All blood leaving the stomach and intestines passes through the liver.
• The liver processes this blood and breaks down, balances, and creates nutrients.
• It also metabolizes drugs into forms that are easier to use or nontoxic.

Storage Role of the Liver

The liver stores several important substances:

• Excess glucose is converted into glycogen for storage.
• Glycogen can later be converted back to glucose for energy.
• This helps balance and maintain blood glucose levels.

• Vitamin A — stored in large amounts; essential for vision.
• Vitamin D — stored; essential for calcium absorption.
• Vitamin B12 — stored; essential for red blood cell production.

• The liver stores iron from the breakdown of hemoglobin.
• Iron is used to make new hemoglobin.

Metabolic Role of the Liver

The liver performs over 500 vital functions. The most important metabolic functions include:

Detailed List of Liver Functions

• Production of bile, which helps carry away waste and break down fats in the small intestine during digestion.
• Production of certain proteins for blood plasma e.g., serum albumin, globulins, and fibrinogen.
• Production of cholesterol and special proteins to help carry fats through the body.
• Conversion of excess glucose into glycogen for storage (glycogen can later be converted back to glucose for energy) and to balance and make glucose as needed.
• Regulation of blood levels of amino acids, which form the building blocks of proteins.
• Processing of hemoglobin for use of its iron content (the liver stores iron).
• Conversion of poisonous ammonia to urea (urea is an end product of protein metabolism and is excreted in the urine).
• Clearing the blood of drugs and other poisonous substances.
• Regulating blood clotting.
• Resisting infections by making immune factors and removing bacteria from the bloodstream.
• Clearance of bilirubin from the breakdown of red blood cells. If there is an accumulation of bilirubin, the skin and eyes turn yellow (jaundice).

Excretion of By-Products

When the liver has broken down harmful substances, its by-products are excreted into the bile or blood.

• Enter the intestine.
• Leave the body in the form of feces.

• Filtered out by the kidneys.
• Leave the body in the form of urine.

Intermediate Level

Metabolic Functions of the Liver

Carbohydrate Metabolism:

Protein Metabolism:

Lipid Metabolism:

Storage Functions of the Liver

Detoxification Functions of the Liver

Liver and Blood Regulation

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Liver is the largest gland in the body.
• 2. It has two lobes: right (larger) and left (smaller).
• 3. Blood supply: hepatic artery (oxygenated) and hepatic portal vein (nutrient-rich).
• 4. Liver contains thousands of lobules.
• 5. Liver stores glycogen, vitamins (A, D, B12), and iron.
• 6. Liver converts excess glucose to glycogen.
• 7. Liver converts glycogen back to glucose when needed.
• 8. Liver produces bile for fat digestion.
• 9. Liver produces plasma proteins (albumin, globulins, fibrinogen).
• 10. Liver converts ammonia to urea.
• 11. Liver detoxifies drugs, alcohol, and toxins.
• 12. Liver produces clotting factors.
• 13. Liver removes bacteria from the bloodstream.
• 14. Liver clears bilirubin from the blood.
• 15. Liver performs over 500 vital functions.

Remember

• - Liver = largest gland
• - Lobes = right (larger) and left (smaller)
• - Blood supply = hepatic artery + hepatic portal vein
• - Stores = glycogen, vitamins (A, D, B12), iron
• - Converts = excess glucose → glycogen
• - Produces = bile, plasma proteins, clotting factors
• - Converts = ammonia → urea
• - Detoxifies = drugs, alcohol, toxins
• - Clears = bilirubin from blood
• - Removes = bacteria from bloodstream
• - Over 500 functions

Common Mistakes

• 1. Thinking the liver only produces bile — It performs over 500 functions.
• 2. Believing the liver stores glucose as glucose — It stores glucose as glycogen.
• 3. Confusing hepatic artery and hepatic portal vein — Hepatic artery brings oxygenated blood; hepatic portal vein brings nutrient-rich blood.
• 4. Thinking ammonia is excreted directly — Ammonia is converted to urea in the liver.
• 5. Forgetting the role of the liver in clotting — The liver produces clotting factors.
• 6. Mixing up the lobes of the liver — Right lobe is larger; left lobe is smaller.
• 7. Believing the liver is not involved in immunity — The liver removes bacteria from the blood.
• 8. Confusing bilirubin and biliverdin — Biliverdin is converted to bilirubin.
• 9. Thinking the liver stores only glycogen — It also stores vitamins and iron.
• 10. Believing the liver is not essential for survival — It is essential; liver failure is fatal.

Quick Revision

The liver is the largest gland in the body. It has two lobes (right larger, left smaller) and receives blood from the hepatic artery (oxygenated) and hepatic portal vein (nutrient-rich). The liver stores glycogen, vitamins (A, D, B12), and iron. It converts excess glucose to glycogen and breaks down glycogen to glucose. It produces bile for fat digestion, plasma proteins (albumin, globulins, fibrinogen), and clotting factors. It converts toxic ammonia to urea. It detoxifies drugs, alcohol, and toxins. It clears bilirubin from the blood and removes bacteria from the bloodstream. The liver performs over 500 vital functions. By-products are excreted in bile (feces) or blood (urine).

60-Second Revision

• Liver = largest gland; right and left lobes
• Blood supply = hepatic artery + hepatic portal vein
• Stores = glycogen, vitamins (A, D, B12), iron
• Converts = glucose ↔ glycogen
• Produces = bile, plasma proteins, clotting factors
• Converts = ammonia → urea
• Detoxifies = drugs, alcohol, toxins
• Clears = bilirubin
• Removes = bacteria
• Over 500 functions
• Warning: Liver stores glucose as glycogen, not glucose; ammonia is converted to urea

NEXT TOPIC

• Chapter:
• 1. Digestive System of Man

• Topic:
• 1.10 COMPOSITION AND ROLE OF BILE

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