Chapter 9 - The Digestive System

Question 1

What is the alimentary canal?

Answer 1

The continuous tube that runs from the mouth to the anus. Together, with associated organs like the pancreas and gall bladder, the alimentary canal makes up the digestive system.

Question 2

What are the six main functions of the digestive system?

Answer 2

1. Ingestion of food and water
2. Mechanical digestion of food
3. Chemical digestion of food
4. Movement of food along the alimentary canal
5. Absorption of digested food and water into the blood and lymph
6. Elimination of material that is not absorbed

Question 3

Identify, label and describe each part of the digestive system

Answer 3

Mouth cavity 
Salivary glands 
Pharynx 
Oesophagus 
Liver 
Gall bladder
Stomach 
Pyloric sphincter 
Duodenum 
Pancreas 
Small intestine 
Appendix 
Caecum 
Large intestine ; ascending column, transverse column and descending column
Rectum 
Anus

Question 4

What are the four types of teeth?

Answer 4

• incisors (four, at the front of the mouth) chisel shaped teeth used for biting or cutting.
• canines (two, either side of the incisors) teeth used for tearing.
• premolars (four, on the side of the jaw)
• molars (six, at the back of the mouth) crushing and grinding food

Question 5

Explain the mechanical and chemical digestion that occurs in the stomach

Answer 5

Mechanical - waves of muscular contraction to churn and mix the food with the gastric juices.

Chemical - the enzyme pepsin breaks down long chains of amino acids (proteins) to form polypeptides. Pepsin works in very acidic solutions (gastric juices) that can kill many bacteria that enter the stomach.

Question 6

Explain the mechanical and chemical digestion that occurs in the small intestine

Answer 6

Mechanical - muscular contractions, bule salts emulsify lipids

Chemical - intestinal juice (secreted by the intestines), pancreatic juice (secreted by the pancreas) and bile (produced by the liver but stored in the gall bladder).
Intestinal juice contains many enzymes that complete the digestion of carbohydrates, proteins and lipids

Pancreatic juice neutralises gastric juices and contains

• pancreatic amylase (breaks down starch)
• trypsin (breaks down protein)
• ribonuclease and deoxyribonuclease (breaks down RNA and DNA)
• pancreatic lipases (breaks down fats into fatty acids and glycerol)

Question 7

What are villi?

Answer 7

Villi are found in the mucosa of the small intestine. They resemble small finger like projections that work to absorb nutrients. Inside each villus is a lymph capillary called a lacteal which is surrounded by a network of blood capillaries.

Question 8

What is the function of a lacteal?

Answer 8

Active :

• amino acids are absorbed by active transport into blood capillaries
• simple sugars (glucose) are absorbed by active transport into blood capillaries

Passive

• fatty acid and glycerol are absorbed by simple diffusion.
• water and water soluble vitamins are absorbed by diffusion.

Question 9

Explain the mechanical and chemical digestion that occurs in the mouth

Answer 9

Mechanical - chewing helps the food break down into smaller pieces

Chemical - saliva, which contains starch amylase, begins starch digestion

Question 10

How does diet affect the absorption of food in the alimentary canal?

Answer 10

A large meal = the alimentary has to work harder and is stretched - digestion may take longer than usual.

A smaller meal = the alimentary can work quickly.

Constipation - constipation can be caused by lack of roughage.

Diarrhoea - bacteria that produce food poisoning may cause diarrhoea.

Bowl cancer - high alcohol consumption or smoking can cause uncontrolled growth of cells in the large intestine. Eating a diet high in red meat, processed meat and being over weight also increases the risk of bowl cancer.

Coalic disease - people who are unable to tolerate a protein called gluten because it destroys the villi. Coalic disease is inherited.

The importance of soluble fibre in the diet - lower cholesterol levels in the blood, decreased risk of heart disease and cancer and beneficial effects on blood glucose levels. Good sources of soluble fibres are fruits, vegetables, oat, bran, barley and soy products.