Human digestive system

Question 1

Define nutrition

Answer 1

Nutrition is the process by which organisms obtain food and energy for growth, repair and maintenance of the body

Question 2

Define digestion

Answer 2

Digestion is the process that breaks down complex food substances into simple, soluble molecules that are small enough to be absorbed into body cells

Question 3

Where does food digestion take place

Answer 3

Alimentary canal

Question 4

Define physical digestion

Answer 4

Physical digestion is the mechanical breakdown of food into smaller particles to increase surface area to volume ratio for faster rate of chemical digestion

Question 5

Define chemical digestion

Answer 5

Chemical digestion is the breakdown of large food molecules into small soluble molecules catalysed by digestive enzymes through hydrolytic reactions

Question 6

What is ingestion

Answer 6

The act of taking food into the mouth

Question 7

What is the optimum pH in the mouth

Answer 7

6.5-7.5

Question 8

What glands and enzymes are present in the mouth

Answer 8

Salivary gland
- Salivary amylase

Question 9

What enzyme actions occur in the mouth

Answer 9

• Starch > Maltose (Amylase)

Question 10

What is peristalsis

Answer 10

Rhythmic, wave-like, muscular contractions of the oesophagus

Question 11

What does gastric juice contain

Answer 11

• HCl
• Pepsin

Question 12

What is the purpose of HCl in the stomach

Answer 12

• Provides acidic medium suitable for stomach enzymes
• Kills bacteria in food
• Denatures salivary amylase
• Converts inactive forms of enzymes to active forms (pepsinogen > pepsin)

Question 13

What glands and enzymes does the stomach contain

Answer 13

Gastric gland
- Pepsin

Question 14

What enzyme actions occur in the stomach

Answer 14

Proteins > Polypeptides (Pepsin)

Question 15

What are the glands and enzymes in the small intestine

Answer 15

Pancreas
- Pancreatic amylase
- Pancreatic lipase
- Trypsin

Intestinal gland
- Maltase
- Sucrase
- Lactase
- Intestinal lipase
- Peptidase

Question 16

What is the optimal pH in the stomach

Answer 16

2

Question 17

Are the liver, gall bladder and pancreas part of the alimentary canal

Answer 17

NO

Question 17

What are the features and functions of bile

Answer 17

• Alkaline greenish-yellow liquid
• Does not contain digestive enzymes
• Emulsifies fats, which physically breaks them down to increase surface area to volume ratio for faster digestion by lipase
• Creates alkaline environment suitable for enzymes
• Contains bile salts
• Contains bile pigments

Question 18

Describe digestion of food in the stomach

Answer 18

• Stomach is a muscular elastic bag
• Food is churned and mixed with gastric juice by peristaltic stomach contractions
• Partly digested food becomes liquefied, forming chyme
• Chyme passes into small intestine

Question 19

What does the small intestine consist of

Answer 19

• Duodenum
• Jejunum
• Ileum

Question 20

What does the liver produce

Answer 20

Bile

Question 21

What enzyme actions occur in the small intestine

Answer 21

• Starch > Maltose (Amylase)
• Emulsified fats > Fatty acids + Glycerol (Lipase)
• Proteins > Polypeptides (Trypsin)
• Maltose > Glucose (Maltase)
• Sucrose > Glucose+Fructose (Sucrase)
• Lactose > Glucose+Galactose (Lactase)
• Polypeptides > Amino acids (Peptidase)

Question 22

What is the optimum pH in small intestine

Answer 22

8.5

Question 23

Describe digestion in the small intestine

Answer 23

• Duodenum receives chyme from stomach and secretions from glands
• Digestion takes place in the duodenum
  By the end of digestion,
• All carbohydrates digested to monosaccharides
• All fats digested to fatty acids and glycerol
• All proteins digested to amino acids

Question 24

What enzymes does pancreatic juice contain

Answer 24

- Pancreatic amylase - Pancreatic lipase - Trypsin

Question 24

What enzymes does intestinal juice contain

Answer 24

- Maltase - Lactase - Sucrase - Intestinal lipase - Peptidase

Question 24

What are the adaptations of the small intestine for absorption

Answer 24

Long - Provides sufficient time for absorption of materials Inner walls have many transverse folds with villi, each villi made up of many microvilli - Increases SA:V ratio for faster absorption of digested substances by diffusion Epithelium of villus is one cell thick - Decrease distance for digested substances to diffuse over, increases rate of absorption Consists of a dense network of blood capillaries - Continuous transport of digested substances maintains steep concentration gradient for faster absorption

Question 25

How are glucose and amino acids absorbed at small intestine

Answer 25

- Glucose and amino acids are absorbed by facilitated diffusion into blood capillaries - Also absorbed by active transport when blood capillaries have higher concentration of glucose and amino acids than intestinal lumen - Blood capillaries join to form venules - Venules join to form the hepatic portal vein, which carries mainly glucose and amino acids to liver to be processed

Question 25

How are fatty acids and glycerol absorbed at the small intestine

Answer 25

- Fatty acids and glycerol diffuse into epithelial cells - They then recombine and form minute fat globules before diffusing into lacteal - fat globules transported away by lacteal

Question 25

Define assimilation

Answer 25

Assimilation is the utilisation of absorbed nutrients and how the body deals with excess nutrients

Question 26

Describe assimilation of glucose

Answer 26

- Glucose is a substrate for respiration - Pancreas produces insulin, which stimulates liver to stimulate conversion of excess glucose to glycogen - Pancreas produces glucagon when blood glucose levels are low to stimulate conversion of glycogen to glucose

Question 26

Describe assimilation of amino acids

Answer 26

- Excess amino acids are deaminated in the liver - Their amino group is removed and converted into urea - Remaining carbon residue is converted to glucose

Question 27

Describe assimilation of lipids

Answer 27

- Excess fats are stored in adipose tissue under the skin - Fat droplets collect in cytoplasm of adipose cells

Question 28

Describe what happens after absorption in small intestine

Answer 28

- Undigested and unabsorbed matter enters large intestine - Movement of undigested materials along large intestine is by peristalsis - Large intestine absorbed most of the water and mineral salts into bloodstream - Results in the formation of faeces - Mucus secreted by large intestine binds faeces together - Faeces temporarily stored in rectum - Once it accumulates, rectal wall contracts to egest faeces

Question 29

What are the functions of the liver

Answer 29

- Bile production - Blood glucose regulation - Protein synthesis (Riobosomes in liver synthesise plasma proteins) - Deamination of excess amino acids - Breakdown of red blood cells (Liver breaks down haemoglobin and stores released iron) - Detoxification (Liver produces alcohol dehydrogenase that breaks down alcohol to acetaldehyde, which can be broken down further to glucose) (Hydrogen peroxide is also broken down into water and oxygen by enzyme catalase in liver)

Question 30

What are some effects of excessive alcohol consumption

Answer 30

- Depresses motor centre of brain, resulting in longer reaction times - Affects area of cerebrum, resulting in reduced self-control - Leads to cirrhosis of liver, where liver cells are destroyed and replaced with fibrous scar tissue, increasing chances of liver failure