Liver

Liver

The liver is one of the most important organs of our digestive system. It performs many functions related to digestion, storage of nutrients, removal of harmful substances, formation of urea, and production of important blood proteins.

1. Location, colour and size of the liver

The liver is a dark reddish-brown coloured gland. It is located just below the diaphragm, mainly in the right upper portion of the abdominal cavity.

The diaphragm is the dome-shaped muscular sheet that separates the chest cavity (thoracic cavity) from the abdominal cavity.

The liver is the largest gland in the human body. In an adult, it weighs approximately 1.2–1.5 kg.

Remember:

Liver = Largest gland of the human body.

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2. Lobes of the liver

The liver is described here as a bilobed gland, meaning it has two main lobes.

Bi = two

Lobed = having lobes

Therefore, bilobed = having two lobes.

Each lobe is covered by a thin protective covering known as Glisson's capsule.

Glisson's capsule

Glisson's capsule is made up of connective tissue.

Its main purpose is to cover, support and protect the liver tissue.

So:

Liver → Lobes → Glisson's capsule → Connective tissue

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3. Hepatic lobules

Each lobe of the liver is further divided into many small structural and functional units called hepatic lobules.

The word hepatic means related to the liver.

Therefore:

> Hepatic lobule = Structural and functional unit of the liver

A hepatic lobule is approximately polygonal in shape, meaning it has several sides.

Think of the organization as:

Liver → Lobes → Hepatic lobules → Hepatic cells

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4. Structure of a hepatic lobule

A hepatic lobule contains several important structures.

At its centre is a central vein.

Around this central vein, liver cells called hepatic cells or hepatocytes are arranged in the form of cords.

So imagine the central vein as the centre of a wheel, with rows of liver cells arranged around it.

Hepatic cells

Hepatic cells are the main functional cells of the liver. They perform several important metabolic functions and also produce bile juice.

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5. Sinusoids

There are small spaces between the cords of hepatic cells. These spaces are called sinusoids.

Blood flows through these sinusoids.

Thus:

Hepatic cell cords → Sinusoids between them → Blood flows through sinusoids

Sinusoids allow close contact between the flowing blood and liver cells, helping the liver process substances carried in the blood.

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6. Portal area

At the junction between adjacent hepatic lobules, there is a triangular portal area.

This area contains a branch of each of the following:

Structure Main role

Hepatic artery Brings oxygen-rich blood to the liver

Hepatic portal vein Brings nutrient-rich blood from digestive organs

Bile duct Carries bile produced by hepatic cells

These three structures occurring together are commonly referred to as a portal triad.

Easy memory trick

A – V – D

A = Hepatic Artery

V = Hepatic portal Vein

D = Bile Duct

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7. Kupffer cells

Special cells called Kupffer cells are found in the liver sinusoids.

Kupffer cells are phagocytic cells.

Phagocytosis means the process in which a cell engulfs and destroys unwanted particles or microorganisms.

You can think of Kupffer cells as the liver's clean-up or defence cells.

They help remove:

toxic or unwanted substances,

microorganisms,

cellular debris, and

old or worn-out blood cells.

Thus, Kupffer cells contribute to the liver's defence and cleaning functions.

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8. Production of bile juice

One of the important digestive functions of the liver is the production of bile juice.

Hepatic cells → produce bile

The bile produced by liver cells is collected and transported through the bile ducts.

It is then stored and concentrated in a small sac-like organ called the gall bladder.

Important distinction

Liver PRODUCES bile.

Gall bladder STORES bile.

Students sometimes mistakenly say that the gall bladder produces bile. It does not.

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9. Common bile duct

The duct coming from the gall bladder joins the hepatic duct associated with the liver.

Together, they ultimately contribute to the formation of the common bile duct, which carries bile toward the small intestine.

A simple flow to remember is:

Liver → Bile → Bile ducts → Gall bladder/storage → Common bile duct → Small intestine

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10. Function of bile in digestion

Bile performs two particularly important functions.

A. Emulsification of fats

Bile helps break large fat globules into many tiny fat droplets.

This process is called emulsification of fats.

Importantly, emulsification is a physical breakdown, not digestion of fat by an enzyme.

Why is this useful?

Imagine one large drop of oil. An enzyme can act only on its exposed surface. If that large drop is divided into hundreds of tiny droplets, the total surface area increases.

Therefore:

Large fat globule → Bile → Many small fat droplets → Increased surface area → Lipase acts more efficiently

B. Makes the intestinal contents alkaline

The food entering the small intestine from the stomach is acidic.

Bile helps create a more alkaline environment, which is suitable for the action of several digestive enzymes in the small intestine.

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11. Storage of excess glucose

After eating carbohydrate-rich food, the amount of glucose in our blood may increase.

The liver can take up excess glucose and convert it into glycogen for storage.

Excess glucose → Glycogen → Stored in liver

When the body needs glucose later, stored glycogen can be broken down to help maintain the supply of glucose.

Think of the liver as a glucose storage bank.

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12. Deamination of excess amino acids

Proteins are digested into amino acids.

Unlike excess glucose, excess amino acids cannot simply be stored as proteins for later use in the same way.

The liver removes the nitrogen-containing amino group from excess amino acids. This process is called deamination.

A simplified sequence is:

Excess amino acids → Deamination in liver → Ammonia → Urea

Why convert ammonia into urea?

Ammonia is highly toxic.

The liver converts it into urea, which is much less toxic. Urea is then carried by blood to the kidneys, where it is removed from the body through urine.

So remember:

Liver forms urea → Kidneys excrete urea

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13. Role in vitamins

The liver is closely involved in the metabolism and storage of several vitamins. In the wording of your textbook passage, it is involved with vitamins:

A, D, K and B₁₂

These vitamins are important for functions such as vision, bones, blood clotting and formation of blood cells.

For school answers, follow the terminology and wording prescribed in your textbook.

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14. Formation of blood proteins

The liver produces several important plasma proteins and clotting proteins.

Two mentioned in your passage are:

Prothrombin

Prothrombin is important for blood clotting.

Fibrinogen

Fibrinogen is also essential for blood clot formation. During clotting, fibrinogen is converted into fibrin, which helps form a mesh at the injured area.

Therefore:

Liver → Prothrombin + Fibrinogen → Important for blood clotting

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15. Liver as a haemopoietic organ

Haemopoiesis means formation of blood cells.

During early development, especially during fetal life, the liver acts as an important haemopoietic organ.

In other words, the developing liver helps in the production of blood cells.

After birth, the bone marrow becomes the major site of blood-cell production.

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16. Detoxification

The liver is sometimes described as the body's chemical processing centre because many potentially harmful substances are chemically modified or processed there.

Kupffer cells also contribute to the liver's protective function by removing microorganisms, debris and old blood cells from blood passing through the sinusoids.

Therefore, the liver plays an important role in detoxification and defence.

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Complete structure in one flow

LIVER

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Largest gland — about 1.2–1.5 kg

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Located below the diaphragm, mainly on the right side

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Two main lobes

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Covered by Glisson's capsule

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Lobes divided into hepatic lobules

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Each lobule contains hepatic cells arranged around a central vein

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Between hepatic cell cords are sinusoids

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Blood flows through sinusoids

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Sinusoids contain Kupffer cells

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Hepatic cells produce bile

Functions of the Liver — Quick Revision

Function What the liver does

Bile production Hepatic cells produce bile

Fat digestion support Bile emulsifies fats

Alkaline medium Bile helps make intestinal contents alkaline

Glucose storage Excess glucose is stored as glycogen

Protein metabolism Excess amino acids undergo deamination

Urea formation Toxic ammonia is converted to urea

Vitamin-related functions Involved with vitamins A, D, K and B₁₂

Blood proteins Produces prothrombin and fibrinogen

Haemopoiesis Helps form blood cells during early development

Defence/clean-up Kupffer cells remove microorganisms and old cells

Detoxification Helps process and remove harmful substances

Most important exam points

Remember these five connections:

Hepatic lobule = structural and functional unit of liver

Hepatic cells = produce bile

Gall bladder = stores bile

Sinusoids = spaces through which blood flows

Kupffer cells = phagocytic clean-up cells

And the metabolic sequence:

Excess glucose → Glycogen

Excess amino acids → Deamination → Ammonia → Urea

These two sequences are particularly useful for remembering the metabolic functions of the liver.