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what is nutrition
the process by which organisms obtain food and energy for growth, repair and maintenance of the body.
what is digestion
large food molecules broken down into smaller, soluble molecules that can be absorbed into the body cells.
state what is chemical and physical digestion
chemical:
the breaking down of large molecules in food, such as proteins, starch and fats, into small soluble molecules that can be absorbed
physical
the mechanical break-up of food into smaller pieces which increases
increases surface area-to-volume ratio of food so digestive enzymes can act on food more efficiently
processes that occur in the mouth
food in the mouth stimulates salivary glands to secrete saliva
chemical:
saliva contains salivary amylase digest starch in the mouth into maltose
the optimum pH for salivary amylase is 7 where the enzyme is most active
physical
saliva is mixed with food to soften it
chewing breaks food up into smaller pieces which increases surface area-to-volume ratio for salivary amylase to work on
tongue rolls food into boil which are swallowed and passed down into the oesophagus through the pharynx
peristalsis in oesophagus pushes each bolus of food down into the stomach.
processes that occur in the stomach
presence of food in stomach stimulates gastric glands in the stomach lining to secrete gastric juice
physical:
peristalsis in the stomach wall churns and breaks up the food. it also mixes the food well with gastric juice
chemical
gastric juice in the stomach contains hydrochloric acid and the enzyme pepsin which is a protease
pepsin digests proteins into polypeptides
additional
hydrochloric acid provides a low pH environment in the stomach which is the optimum pH for protease to digest proteins. it also kills potentially harmful microorganisms in food. it also stops the action of salivary amylase by denaturing it
mucus layer on top of the stomach lining protects the stomach wall against being digested by the enzymes it produces. mucus also moistens the food for easy movement
food remains in the stomach for 3-4 hours partially digested food become liquified, forming chyme. chyme passes into the duodenum in small amounts.
processes that occur in the small intestine
chyme entering the duodenum triggers secretion of:
pancreatic juices containing pancreatic amylase, pancreatic lipase and pancreatic protease into the duodenum from pancreatic duct.
bile from the gall bladder into the duodenum from the bile duct. bile emulsifies fats into tiny fat droplets, increasing surface area-to-volume ratio of fat molecules for easier digestion (physical)
acidic chyme from stomach is neutralised by the alkaline fluids from the pancreas, gall bladder and small intestine, achieving pH 8.
entering ileum:
intestinal juices containing intestinal protease, maltase, lipase, digest food (be specific in answering) to be absorbed into the bloodstream from the epithelium of the small intestine .
processes that occur in the large intestine, anus and rectum
undigested food enters the large intestine
water is reabsorbed from undigested food
undigested food is stored in rectum as feces and excreted through the anus
adaptations of small intestine for absorption
inner surface has many finger-like projections called villi which increases surface area of absorption
epithelium of villus is only one cell thick to provide a short diffusion distance for nutrients to pass through
cells of epithelium of villus have many microvilli to further increase surface area-to-volume ratio for absorption
each villus has many blood capillaries to allow blood to transport the absorbed glucose and amino acids away to maintain a diffusion gradient
each villus contains a lacteal to transport fatty acids and glycerol away so a steep diffusion gradient is maintained
the epithelial cells contain many mitochondria to provide energy for the active transport of nutrients into the villi
glucose and amino acids - diffusion and active transport
glycerol and fatty acids - diffusion
what is assimilation
the process where some of the absorbed nutrients are converted into new cytoplasm to provide energy
glucose after absorption
most absorbed sugars are converted into glycogen and stored in the liver and muscle cells
some glucose is transported by the blood leaving the liver and is distributed around the body to be used by cells during cellular respiration to produce energy
excess glucose is transported back to the liver and stored as glycogen
amino acids after absorption
amino acids that enter the cell are converted into new cytoplasm that is used for growth and repair of worn-out parts of the body
amino acids are also used to form enzymes and hormones
in the liver, excess amino acids have their amino groups removed and converted into urea — deamination
urea is removed from the body in urine. remains of deaminated amino acids are converted into glucose in the liver
fats after absorption
fats are absorbed into the lymphatic capillaries, which join to form larger lymphatic vessels. these discharge fats into the bloodstream
blood carries fats to all parts of the body especially the liver
when there is enough glucose, fats are not broken down and are used to build protoplasm
when glucose is in short supply, fats are broken down to provide energy needed for vital activities in the body
excess fat is stored in adipose tissues beneath the skin and around the heart and kidneys. adipose tissues protect organs by acting as shock absorbers
functions of liver
production of bile
deamination of amino acids
regulation of blood glucose concentration
breakdown of hormones
detoxification (such as alcohol)
what is a hormone
a chemical substance produced in very small quantities by an endocrine gland. it is transported in the bloodstream to target organs where it exerts its effects.
can influence the growth, development and activity of an organism
effects of alcohol consumption on the digestive system
stimulates acid secretion in the stomach -excess stomach acid increase risk of gastric ulcers
too much alcohol may lead to cirrhosis of liver -a disease where liver cells are destroyed and replaced with fibrous tissue, making the liver less able to function
may lead to liver failure and death
social implications of drinking
causes alcohol addiction, which causes alcoholics to
end up neglecting work and family
exhibit violent behavior
be at a higher risk of committing crimes
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