nutrition in humans Flashcards
ingestion
process of taking in food into the body through the mouth (eating)
digestion
process whereby large, complex food molecules are broken down into smaller, soluble and diffusible molecules that can be absorbed into the body cells
absorption
process whereby digested food substances/molecules are taken up through the membranes of the intestinal cells, into the bloodstream and into the body cells
egestion
elimination of undigested food as faeces
assimilation
conversion of absorbed food substance into protoplasm or used to provide energy
peristalsis
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
antagonistic muscles
longitudinal - outside
circular - inside
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
physical digestion
- involves the mechanical break up of food into smaller particles
- e.g. chewing, churning, peristalsis
chemical digestion
- involves break down of large molecules in food into smaller, more soluble molecules that can be absorbed
- involves hydrolytic reactions catalysed by digestive enzymes
mouth
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)
stomach
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
small intestine
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)
absorption in small intestine
increase surface area to volume ratio
- 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
absorption in small intestine
shorter time
- one-cell thick wall of epithelium of villi
- > shorter distance hence shorter tike for nutrients to diffuse through
absorption in small intestine
maintain a steep concentration gradient
- 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
absorption in small intestine
provide sufficient time
- small intestine is long
- > to provide sufficient time for absorption of more nutrients.
how are glucose and amino acids absorbed?
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.
how are glycerol and fatty acids absorbed?
diffuse into the epithelium, and combine to form minute fat globules which enter the lacteal
how are water and mineral salts absorbed?
absorbed in the small and large intestines via osmosis and diffusion respectively
hepatic portal vein
transport glucose and amino acids from the small intestine to the liver
assimilation of carbohydrates
- 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
assimilation of amino acids
- 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
functions of liver
regulate blood glucose concentration
- the liver keeps the blood glucose concentration within narrow limits
- the liver is stimulated by insulin and glucagon to store and release glucose respectively
functions of liver
production of bile
the liver produces bile, which emulsifies fats
