1.1 nutrition in humans

describe the function of the teeth

break large pieces of food into smaller pieces to increase the surface area-to-volume ratio of the food so that enzymes can act on it more effectively (physical digestion)

describe the function of the tongue

mixed the food with saliva + moves food to the back of the mouth when swallowing

describe the function of salivary glands

secrete saliva into the mouth (chemical digestion of starch to maltose using salivary amylase)

describe the function of the oesophagus

it has circular and longitudinal muscles which pushes food down the alimentary canal

describe peristalsis in terms of the wave-like contractions of the muscles to mix and propel the contents of the alimentary canal

• when circular muscles contract, longitudinal muscles relax and they constrict the lumen (ie gut becomes narrower and longer

  • food is squeezed/pushed forward

• when longitudinal muscles contract, circular muscles relax and they shorten and widen the lumen

describe the physical digestion in the stomach

increases the SA-vol ratio of ingested food so that digestive enzymes can act on the food particles more effectively

describe the chemical digestion in the stomach

stomach secretes protease which digests proteins into polypeptides

what are the functions of the (hydrochloric acid) acidic environment in the stomach?

• stops the action of salivary amylase by denaturing it

• provides a low pH (2) environment for protease to digest proteins (optimum environment)

• kills potentially harmful microorganisms in food

describe the function of the duodenum

it is the first part of the small intestine (connects stomach to food)

describe the function of the pancreas

produces pancreatic juice which contains digestive enzymes (PAL)

state the chemical digestion (in SI) using the pancreatic juice (PAL)

proteins to polypeptides (by protease)

starch to maltose (by pancreatic amylase)

fats to fatty acids and glycerol (by lipase)

describe the function of the gall bladder

• bile is stored temporarily here

• when the gall bladder contracts, the bile flows into the duodenum via the bile duct

describe the function of the liver (for digestion)

secretes and produces bile which aids in the emulsification of fats from big fat droplets (+ bile salts) to tiny fat droplets

described the function of the liver (deamination)

excess amino acids are transported to the liver. their amino groups are removed and converted into urea. urea is removed from the body in the urine. the remains of any delaminated amino acids are converted into glucose in the liver. any excess glucose formed in this way is converted into glycogen.

describe the function of the ileum

absorb digested nutrients

describe the function of the large intestine

water and mineral salts are absorbed from undigested food material

describe the function of the colon, rectum, anus in relation to egestion

the colon absorbs about 90% of the remaining water and mineral salts from the undigested food material. faeces are stored temporarily in the rectum. when the rectum contracts, the faeces are egested through the anus.

describe the functions of amylase in digestion (list substrates and end-products)

salivary/pancreatic amylase digests starch → maltose

describe the functions of maltase in digestion (list substrates and end-products)

maltase digests maltose → glucose

describe the functions of protease in digestion (list substrates and end-products)

protease digests proteins → polypeptides, and polypeptides → amino acids

describe the functions of lipase in digestion (list substrates and end-products)

lipase digests fats → fatty acids + glycerol

state the adaptations of the small intestine.

• inner surface of the ileum is folded extensively and has numerous minute finger-like projection called villi (singular: villus)

• epithelium / wall of the villus is only one cell thick

• each villus has many blood capillaries

• each villus contains a lacteal

• epithelial cells have many microvilli

• epithelial cells contain many mitochondria

describe the function of the inner surface of the ileum being folded extensively and having numerous minute finger-like projections called villi

to increase the surface area for absorption

describe the function of the epithelium being only one cell thick

to provide a short diffusion distance for the nutrients to pass through

describe the function of each villus having many blood capillaries

to allow the blood to transport the absorbed glucose and amino acids (via diffusion and active transport) in order to maintain a diffusion gradient

describe the function of each villus containing a lacteal

to transport the absorbed fats away and maintain a steep diffusion gradient

describe the function of the epithelial cells having many microvilli

to further increase the surface area of the small intestine for absorption

describe the function of the epithelial cells containing many mitochondria

to provide energy for active transport of nutrients into the villi

state the function of the hepatic portal vein as the transport of blood rich in absorbed nutrients from the small intestine to the liver

the hepatic portal vein transports blood rice in absorbed nutrients (mainly sugars and amino acids) from the small intestine to the liver

state the role of the liver in conversion of glucose to glycogen and vice versa

excess glucose is converted to glycogen for storage / breaks down stored glycogen to glucose and releases into bloodstream

state the role of the liver in fat digestion

the liver secretes and produces bile (containing bile salts) which aids in the physical digestion (emulsification) of fats whereby big fat droplet + bile salts → tiny fat droplets.

state the role of the liver in metabolism of amino acids and formation of urea

the liver metabolises excess amino acids through deamination.

• during deamination, the amino group (NH₂) is removed from amino acids and converted into urea

• urea is then transported in the blood to the kidneys for excretion in urine

define and describe deamination

the process by which amino groups (NH₂) are removed from amino acids and converted into urea

• the remains of the deaminated amino acids are converted into glucose in the liver. any excess glucose formed in this way is converted into glycogen.

describe how the liver regulates blood glucose concentration after a heavy meal.

when blood glucose concentration rises above normal, insulin (a hormone) is secreted. the liver converts glucose into glycogen for storage, and blood glucose concentration decreases back to normal.

describe how the liver regulates blood glucose concentration during fasting.

when blood glucose concentration falls below normal, glucagon (a hormone) is secreted. the liver converts glycogen into glucose to be released into the bloodstream, and blood glucose concentration increases back to normal.

what is detoxification?

the process of converting harmful substances into harmless ones (harmful substances may be absorbed into the blood from the gut; these substances are made harmless by the liver cells)

state the role of the liver in breakdown of alcohol

liver cells contain an enzyme which breaks down alcohol to compounds that can be used in respiration, providing energy for cell activities.

state the role of the liver in the breakdown of hormones

hormones, after they have served their purpose, are broken down in the liver.

outline the effects of alcohol consumption on the brain

• slower reaction time

• reduced self control

outline the long-term effects of excessive alcohol consumption on the brain

• ‘wet brain’

  • alcohol interferes with the absorption of vitamin B1 (in the SI), which is a part of an enzyme needed to break down sugar to release energy for brain activities

• shrinkage of brain volume (esp the region associated with memory and reasoning)

• (during pregnancy) may intefere with the development of the foetus’ brain, which may lead to lifelong physical, mental and behavioural problems

outline the social implications of excessive alcohol

• may neglect their work and families

• may exhibit violent behaviour, esp towards families

• may commit crimes