The Digestive System

Question 1

The organs of the digestive system are structured and arranged so that they can carry out six basic activities. What are these?

Answer 1

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 2

What do body cells require to function normally?

Answer 2

• Simple sugars.
• Amino acids.
• Fatty acids.
• Vitamins.
• Minerals.
• Water.

Question 3

What is mechanical digestion?

Answer 3

The physical breakdown of food into small particles. The aim is to increase surface area, thus allowing for more effective chemical digestion, as the chemicals can access more of the food.

Question 4

Where does mechanical digestion occur in the body?

Answer 4

• The teeth cut tear and grind the food.
• Churning action in the stomach breaks the food down further.
• The gall bladder releases bile into the small intestine.
• Bile salts act as emulsifying agents, breaking fat down into smaller droplets.

Question 5

What is chemical digestion?

Answer 5

The breakdown of food to small molecules by chemicals. During this, chemicals break down large complex molecules into smaller, simpler molecules which are then small enough to be absorbed into the blood stream.

Question 6

What are the following split into?

• Carbohydrates?
• Proteins?
• Lipids?
• Nucleus acids?

Answer 6

• Carbohydrates split into monosaccharides such as glucose, fructose, and galactose.
• Proteins are split into peptides and animo acids.
• Lipids are split into fatty acids and glycerol.
• Nucleic acids split into nucleotides.

Question 7

What is the alimentary canal?

Answer 7

The tube via which food passes through the body, consisting of the mouth, oesophagus, stomach, and intestines; also called the digestive tract.

Question 8

What occurs at the mouth?

Answer 8

Ingestion occurs at the mouth. Here the food is chewed in a process called mastication.

Question 9

Explain saliva and its role in chemical digestion?

Answer 9

As food is chewed it is mixed with saliva (a fluid that is secreted into the mouth by three pairs of salivary glands). Saliva contains mucus to lubricate the food and a digestive enzyme, salivary amylase, which begins chemical digestion of starch into the disaccharide maltose.

Question 10

What are the functions of the following teeth?

• Incisors?
• Canines?
• Premolars and molars?

Answer 10

• Incisors: chisel-shaped teeth used for biting or cutting.
• Canines: conical teeth used for tearing.
• Premolars and molars: broad crowns with rounded cusps used for crushing and grinding food.

Question 11

What is the role of the toung for digestion?

Answer 11

After chewing the tongue shapes the food into a bolus. To swallow the tongue moves upwards and backwards, pushing the bolus to the back of the mouth, the pharynx which leads to the oesophagus.

Question 12

Where does the oesophagus carry food too?

Answer 12

From the throat to the stomach.

Question 13

What is the role of the oesophagus in the digestion of food?

Answer 13

As the bolus enters the pharynx and oesophagus, the circular muscles behind it contracts to narrow the tube. The contraction of successive bands of circular muscle causes the constriction to move in a wave called Peristalsis. This movement pushes the food in front of it, assisted by the secretion of mucus that lubricated the inner lining.

Question 14

What is the stomach?

Answer 14

A muscular organ that receives food from the oesophagus and mixes it with acid and enzymes to form chyme.

Question 15

Explain how mechanical digestion occurs in the stomach?

Answer 15

Mechanical digestion achieved by waves of muscular contraction that move along the stomach wall.

Unlike the rest of the alimentary canal, the stomach has an oblique muscle layer, enabling it to contract in a variety of ways to churn the food and mix it with the stomach juices until it is converted to chyme.

Question 16

Explain how chemical digestion occurs in the stomach?

Answer 16

The stomach lining, mucosa, is specialised for the secretion of gastric juice by gastric glands located in narrow, tube-like structures called gastric pits.

Gastric juice is a digestive juice contains hydrochloric acid, mucus, and digestive enzymes, each of which are secreted by a different type of cell in the gastric pits. Gastric juice is responsible for chemical digestion in the stomach, which is mainly the start of protein digestion.

Question 17

Why are nutrients not absorbed into the bloodstream through the stomach?

Answer 17

Because the internal surface is covered by a thick layer of mucus.

Question 18

What is the pyloric sphincter?

Answer 18

A ring of smooth muscle between the stomach and the duodenum.

Question 19

What prevents the stomach contents from moving through freely?

Answer 19

The constriction of the pyloric sphincter prevents stomach contents from moving unless pushed along by peristalsis.

Question 20

Where does the small intestine receive material from?

Answer 20

It receives material pushed through the pyloric sphincter from the stomach.

Question 21

What are the three regions of the small intestine?

Answer 21

The duodenum, the jejunum and ileum.

Question 22

Provide detail about the duodenum.

Answer 22

• First part and shortest section.
• Extends from the bottom end of the stomach in a curve around the pancreas.
• Most of the chemical digestion occurs here before the chyme moves further along the small intestine.

Question 23

Provide detail about the jejunum.

Answer 23

• Middle section.

- Its lining allows effective absorption of carbohydrates and proteins.

Question 24

Provide details about the ileum.

Answer 24

• Final part.

- B12, bile salts, and any remaining products of digestion are absorbed.

Question 25

How does mechanical digestion occur in the small intestine?

Answer 25

Mechanical digestion continues in the small intestine through segmentation. Segmentation is contractions of the circular muscle narrow the intestine which helps break up the bolus and mix it with juices and bile.

Question 26

Digestion continues in the small intestine under the influence of…

Answer 26

• Pancreatic juice: secreted by the pancreas via the pancreatic duct.
• Bile: produced by the liver but stored in the gall bladder and secreted into the small intestine via the bile duct.
• Intestinal juice: secreted by glands in the lining of the small intestine.

Question 27

Pancreatic juice:
Where does it enter?
What does it do?
What enzymes does it contain?

Answer 27

• Enters the duodenum through the common bile duct.
• Neutralises the acidic chyme and contains the following enzymes.
• Pancreatic amylase: breaks down starch into the disaccharide maltose.
• Trypsin: which splits proteins into peptides.
• Pancreatic Lipases: enzymes that break down fats into fatty acids and glycerol.
• Ribonuclease and Deoxyribonuclease: enzymes that digest RNA and DNA.

Question 28

Bile:
Where does it enter?
What does it do?

Answer 28

Secreted into the small intestine through the common bile duct.

• Contains bile salts which act like a detergent and emulsify fats, breaking them down into tiny droplets. This is a form of mechanical digestion, as it increases the surface area on which the lipases can act to bring about the chemical digestion of fat.

Question 29

Intestinal juice:
Where does it enter?
What does it do?
What enzymes does it contain?

Answer 29

• Secreted by glands in the lining of the small intestine.
• Contains many enzymes that complete the digestion of carbohydrates, proteins, and lipids.
• Peptidase to break down peptides into amino acids.
• Sucrase, lactase, and maltase to break down sucrose, lactose, and maltose, respectively, into the monosaccharides, glucose, fructose and galactose.
• Lipases to break down lipids into fatty acids and glycerol.

Question 30

What are the products of digestion.

Answer 30

• The complex carbohydrates will have been broken down into simple sugars.
• The proteins into amino acids.
• The fats into fatty acids and glycerol.

Question 31

How are these products absorbed in the body.

Answer 31

They are absorbed through the wall of the small intestine into the blood.

Question 32

Efficient nutrient absorption requires the small intestine to have a large surface area. How is this achieved?

Answer 32

• The small intestine is very long- about 6-7m.
• The inner lining, known as the mucosa, has folds the extend to the interior of the small intestine.
• The mucosa has small, finger-like projections called villi that extend from the folded surface.
• The cells covering the outside of the villi have tiny, microscopic projections from their external surfaces called microvilli.

Question 33

How is the structure of a villus ideally suited to its function?

Answer 33

• Each villus is about 1mm long.
• Each villus is covered by a single layer of cells.
• Inside the villus is a lymph capillary, called a lacteal which is surrounded by a network of blood capillaries.
• Absorption is further enhanced by the continual movement of the villi brought about by the muscular movements of the intestinal wall. This constantly brings the villi into contact with different parts of the intestinal contents, which are constantly changing as new material comes and goes.

Question 34

Function

Answer 34

Bacteria in the large intestine break down much of the remaining organic compounds. Some bacteria produce vitamins, which are then absorbed through the walls into the blood. Mineral nutrients are also absorbed.

Question 35

What is faeces?

Answer 35

The semi-solid material left after water absorption and bacterial action makes up the faeces.

Question 36

What does faeces contain?

Answer 36

Faeces contains water, undigested food material, bacteria, bile pigments (which gives faeces their colour), and the remains of cells that have broken away from the internal lining of the alimentary canal.

Question 37

What is the effect of having a large meal on the digestive system?

Answer 37

Greater stretching of the stomach, and material is pushed into the small intestine much more quickly than when the stomach is less distended.

Question 38

What is the effect of high protein and/ or fat content in foods?

Answer 38

Slows the movement from stomach to small intestine.

Question 39

What is the effect of alcohol and caffeine on the digestive system?

Answer 39

Stimulate movements of the stomach.

Question 40

Constipation definition.

Answer 40

A condition in which defecation is difficult with faeces being hard and dry.

Question 41

Constipation cause.

Answer 41

Occurs if the movements of the large intestine are reduced and the contents remain there for a long period of time. As water is absorbed, the faeces become drier and harder than usual. May be caused by a lack of roughage in the diet. Roughage is important because it stimulates the movements of the alimentary canal. Other causes may be lack of exercise or emotional problems.

Question 42

Diarrhoea definition.

Answer 42

The frequent passing of watery faeces.

Question 43

Diarrohea cause.

Answer 43

It is caused by irritation of the small or large intestine, which increases peristalsis so that the contents of the intestines move through before there is adequate absorption of water. Such irritation may be the result of:

• A bacteria, e.g., salmonella.
• A virus, e.g., rotavirus.
• A parasite, e.g., giardia.
• Cancer such as bowel cancer.
• Coeliac disease,
• Lactose intolerance.

Question 44

Why is soluble fibre important in the diet?

Answer 44

Soluble fibre intake has been linked to lower cholesterol levels in blood, decreased risk of heart disease and cancer, and beneficial effects on blood glucose levels. Fats in the intestines are trapped by soluble fibre, thereby helping to prevent their absorption by the body. This is thought to be the reason that soluble fibre helps to lower cholesterol levels. Good sources of soluble fibres are fruits, vegetables, oat bran, barley, and soy products.

Question 45

What is bowel cancer?

Answer 45

Also known as colorectal cancer. Is an uncontrolled growth of cells in the wall of the large intestine. Research suggests that bowel cancer may be linked to diet, high alcohol consumption and smoking, a diet high in red and processed meat, and low in fibre, being overweight or obese and physical inactivity.

Question 46

What is coeliac disease?

Answer 46

An autoimmune disease due to the immune system reacting to gluten.

People with coeliac disease are unable to tolerate a protein called gluten, which is found in wheat, rye, and barley. If such people eat food containing gluten, their immune system responds by damaging or destroying the villi in the small intestine. Without healthy villi, nutrients cannot be absorbed, and the person becomes malnourished no matter how much food they eat.

Symptoms: muscle cramps, joint pain, or tingling in the legs may appear to have nothing to do with nutrition or digestion. The symptoms are many and vary from person to person.

Coeliac disease is inherited. There is no cure; the only treatment is to follow a gluten-free diet.