The large intestine and the liver

Saving water, and the body's chemical factory

What is left after absorption moves into the large intestine by peristalsis. Its three parts are the caecum, the colon and the rectum. More water is absorbed here, so the material becomes solid faeces.

Faeces hold undigested material, many bacteria, broken gut cells, bile pigments and water. They are stored in the rectum and expelled through the anus: egestion.

The liver lies to the right of the stomach and weighs about 1.5 kg in an adult. It makes bile, which is stored in the gall bladder and sent to the duodenum by the common bile duct.

The large intestine does no digestion: it saves water and stores waste. The liver does dozens of jobs, but its digestive job is making bile.

Key terms

Caecum

Joins the small intestine to the large intestine; the appendix is at its blind end.

Faeces

Undigested material, bacteria, gut cells, bile pigments and water.

Gall bladder

A sac on the liver that stores bile.

Urea

Made by the liver from ammonia, removed in urine.

Short questions with model answers

1. Q1. Justify the importance of the liver and pancreas in digestion. (Detailed Answer 4)

   • Liver.
   • Pancreas.

   Without bile, fats are poorly digested; without pancreatic juice, all three food types are.

2. Q2. Why can an infected appendix be dangerous? (p. 7 box)

   • Where it is.
   • What can happen.

   It can burst and spread infection, so it is removed by surgery.

Common mistakes

• ✗ The gall bladder makes bile.

  ✓ The liver makes bile; the gall bladder only stores it.

• ✗ The large intestine digests the rest of the food.

  ✓ It absorbs water and stores faeces; digestion is finished in the small intestine.

• ✗ Faeces are only undigested food.

  ✓ They also contain bacteria, broken gut cells, bile pigments and water.

MCQs

1. 1. The three parts of the large intestine are:

   1. (a) Duodenum, jejunum, ileum
   2. (b) Pharynx, oesophagus, stomach
   3. (c) Caecum, colon, rectum
   4. (d) Liver, pancreas, gall bladder
   Show answer

   (c) p. 8.

2. 2. Bile is stored in the:

   1. (a) Gall bladder
   2. (b) Pancreas
   3. (c) Stomach
   4. (d) Rectum
   Show answer

   (a) p. 8.

3. 3. The liver converts ammonia into:

   1. (a) Glycogen
   2. (b) Bile salts
   3. (c) Vitamin A
   4. (d) Urea
   Show answer

   (d) p. 8: less toxic urea, excreted in urine.

4. 4. Undigested material becomes solid in the large intestine because:

   1. (a) Enzymes harden it
   2. (b) More water is absorbed from it
   3. (c) Bile freezes it
   4. (d) Acid is added
   Show answer

   (b) p. 8.

5. 5. The liver makes vitamin A from:

   1. (a) Carotene
   2. (b) Urea
   3. (c) Glycogen
   4. (d) Ammonia
   Show answer

   (a) p. 8; carotene is found in carrots and mangoes (p. 7 box).

Quick revision

• The large intestine (caecum, colon, rectum) absorbs water and stores faeces until egestion.
• The liver makes bile; the gall bladder stores it; bile salts emulsify fats.
• The liver also stores glycogen and vitamins, makes urea, breaks toxins and old red cells, and makes vitamin A.