nutrition in humans

Question 1

ingestion

Answer 1

process of taking in food into the body through the mouth (eating)

Question 2

digestion

Answer 2

process whereby large, complex food molecules are broken down into smaller, soluble and diffusible molecules that can be absorbed into the body cells

Question 3

absorption

Answer 3

process whereby digested food substances/molecules are taken up through the membranes of the intestinal cells, into the bloodstream and into the body cells

Question 4

egestion

Answer 4

elimination of undigested food as faeces

Question 5

assimilation

Answer 5

conversion of absorbed food substance into protoplasm or used to provide energy

Question 6

peristalsis

Answer 6

rhythmic, wave-like muscular contractions in the wall of the alimentary tract (in oesophagus, stomach, and intestines)

function:
- allows food to be mixed with digestive juices
- helps the movement of food along the gut

Question 7

antagonistic muscles
longitudinal - outside
circular - inside

Answer 7

in front of the food bolus:

• > circular muscles relax while longitudinal muscles contract
• > gut wall dilates, becoming shorter and wider, to allow food to enter.

behind the food bolus:

• > circular muscles contracts while longitudinal muscles relax
• > gut wall constricts, causing the gut to be narrower and longer
• > food is pushed forward

Question 8

physical digestion

Answer 8

• involves the mechanical break up of food into smaller particles
• e.g. chewing, churning, peristalsis

Question 9

chemical digestion

Answer 9

• involves break down of large molecules in food into smaller, more soluble molecules that can be absorbed
• involves hydrolytic reactions catalysed by digestive enzymes

Question 10

mouth

Answer 10

physical digestion
teeth - chew, increase surface area to volume ratio of food for more enzymes to at on it per unit time
tongue - mixes food with saliva and rolls food into food bolus
mucin in saliva softens the food

chemical digestion
starch -salivary amylase-> maltose (pH 7)

Question 11

stomach

Answer 11

physical digestion
churning breaks up the food and allow it to mix with digestive juices

chemical digestion
proteins -pepsin-> polypeptide (pH2)
caseinogen -rennin-> casein (pH2)

hydrochloric acid:

• denatures salivary amylase (pH 7) and stops its enzymatic reaction.
• converts inactive enzyme pepsinogen and prorennin into pepsin and rennin respectively
• provides optimal pH of 1-2.5 for gastric enzymatic actions
• kills potentially harmful microorganisms in the food

Question 12

small intestine

Answer 12

physical digestion
bile emulsifies larger fat droplets into smaller fat droplets to increase surface area to volume ratio of fats for lipase to digest fats at a faster rate

chemical digestion
starch -pancreatic amylase-> glucose (pH8-9)
sucrose -sucrase-> glucose + fructose (pH8-9)
lactose -lactase-> glucose + galactose (pH8-9)

proteins -trypsin-> polypeptide -peptidase-> amino acids (pH8-9)

fats -lipase-> fatty acids + glycerol (pH8-9)

Question 13

absorption in small intestine

increase surface area to volume ratio

Answer 13

• numerous folds on the inner walls of small intestine
• inner walls of small intestine lined with numerous minute finger-like projections called villi, which further increases the surface area to volume ratio
• epithelial cells of villi have numerous microvilli

-> to increase surface area to volume ratio for efficient absorption of nutrients

Question 14

absorption in small intestine

shorter time

Answer 14

• one-cell thick wall of epithelium of villi

- > shorter distance hence shorter tike for nutrients to diffuse through

Question 15

absorption in small intestine

maintain a steep concentration gradient

Answer 15

• dense network of blood capillaries in each villus
• lacteal transport fats while blood capillaries transport glucose and amino acids away from the intestine
• continual transport of digested food substances maintain the concentration gradient for the absorption of digested food substances

-> to maintain a steep concentration gradient for faster diffusion of nutrients into the villi for faster absorption

Question 16

absorption in small intestine

provide sufficient time

Answer 16

• small intestine is long

- > to provide sufficient time for absorption of more nutrients.

Question 17

how are glucose and amino acids absorbed?

Answer 17

diffuse into the blood capillaries
they are absorbed via diffusion when there is a higher concentration of glucose and amino acids in the small intestine than the blood capillaries
they are absorbed via active transport when there is a lower concentration of these nutrients in the lumen of the small intestine than in the blood capillaries.

Question 18

how are glycerol and fatty acids absorbed?

Answer 18

diffuse into the epithelium, and combine to form minute fat globules which enter the lacteal

Question 19

how are water and mineral salts absorbed?

Answer 19

absorbed in the small and large intestines via osmosis and diffusion respectively

Question 20

hepatic portal vein

Answer 20

transport glucose and amino acids from the small intestine to the liver

Question 21

assimilation of carbohydrates

Answer 21

• glucose is transported by hepatic vein to different parts of the body to be used by the cells during tissue respiration to release energy for vital activities in the cells
• excess glucose is converted into glycogen for storage
• liver cells also convert some of the excess glucose into fasts, which is stored under the skin

Question 22

assimilation of amino acids

Answer 22

• liver synthesizes plasma proteins such as albumen, globulins and fibrinogen
• some amino acids pass through liver before being transported by hepatic vein to different parts of the body for cell division, growth and replace of worn-out parts and synthesis of enzymes and hormones
• excess amino acids are deaminated and converted into urea

Question 23

functions of liver

regulate blood glucose concentration

Answer 23

• the liver keeps the blood glucose concentration within narrow limits
• the liver is stimulated by insulin and glucagon to store and release glucose respectively

Question 24

functions of liver

production of bile

Answer 24

the liver produces bile, which emulsifies fats

Question 25

functions of liver

proteins synthesis

Answer 25

the liver uses amino acids to synthesise proteins such as prothrombin and fibrinogen

Question 26

functions of liver

deamination of excess amino acid

Answer 26

the excess amino acid is converted or deaminated to urea in the liver
the carbon residues of amino acids from deamination are converted to glucose in the liver

Question 27

functions of liver

storage of iron

Answer 27

when red blood cells are worn out, they are destroyed in the spleen. their haemoglobin is sent to the liver to be ‘recycled’
breakdown of haemoglobin produces iron which is stored in the liver and used in the synthesis of new red blood cells

Question 28

functions of liver

detoxification

Answer 28

it is the process of converting harmful substances into harmless products
enzyme alcohol dehydrogenase converts alcohol into acetaldehyde. acetaldehyde is used as a source of energy in cells.

Question 29

effects of excessive consumption of alcohol

Answer 29

• causes liver cirrhosis (liver cells destroyed and replaced with fibrous tissues) - patients may have bleeding in liver, eventually leading to liver failure/ death.
• depressant - slows down some brain function
• reduced self-control
• causes symptoms of ‘drunkenness’’ (blurred vision, poor muscular co-ordination, deteriorated judgement)
• frequent intake may lead to addiction
• stimulates acid secretion which increases the risks of gastric ulcers