digestive system Flashcards
what does digestion do
food is broken down into small simple and soluble substances that can be absorbed and used by our body cells through digestion
processes of human nutrition
• ingestion (happens in mouth)
food is taken into the alimentary canal
• digestion (starts in mouth)
food is broken down into simple + soluble molecules
• absorption (large + small intestines)
absorbed food molecules enter the circulatory system (eg. glucose is absorbed into the bloodstream)
• assimilation
absorbed food molecules are taken up by body cells for metabolism (eg. glucose converts into glycogen stored in muscle cells)
• egestion
undigested + in absorbed materials are removed
if nitrogen is used as an index of proteins, express the following in terms of nitrogen intake (i) nitrogen in faeces (f) and nitrogen in urine (u)
• amount of proteins digested and absorbed:
• amount of proteins used in growth:
• amount of proteins digested and absorbed: i - p [urine is the amino groups from excess proteins hence is not absorbed]
• amount of proteins used in growth: i - p - u
what does the pancreas do
produces pancreatic juice containing enzymes to help digest food
produces insulin
what does the liver do
produces bile, helps to physically break down fat
what does the gallbladder do
stores bile from liver temporarily, doesn’t produce anything
what does the small intestine do
absorb digested foods
why is the small intestine so long
the length of the small intestine increases the surface area and time for the nutrients in the food to be digested and absorbed
2 types of digestion
physical and chemical digestion
swallowing procedure
the tongue rolls the food into a soft mass called bolus
1. the tongue rises to push the bolus towards the pharynx
2. the soft palate moves up to prevent the bolus from entering the nasal cavity
3. the larynx rises, and the epiglottis covers the opening to the trachea (to prevent it from entering)
4. the bolus enters the oesophagus
the food is moved along the alimentary canal from the oesophagus to the rectum through peristalsis
function of the epiglottis
prevents food from entering the lungs and obstructing the airway
what is physical digestion and the purpose of it
breaks down food into smaller pieces by physical actions (no change in the nature of the molecule)
helps to increase the total surface area of the food so as to promote chemical digestion (will later be further broken down into small molecules by chemical digestion)
where does physical digestion mainly occur
mainly occurs in mouth cavity (mastication) alimentary canal (churning and peristalsis (a wave-like muscular contraction)) small intestine (emulsification by bile)
what is chemical digestion and what does it require
complex food substances are broken down into simple food substances by chemical reactions (requires digestive enzymes to break chemical bonds)
what is food mixed with in the mouth cavity
saliva
what does saliva contain and what are the function of such substances
saliva contains salivary amylase (catalyses the hydrolysis of starch and water into maltose) mucus (helps to moisten and lubricate food to facilitate chewing and swallowing) water (dissolves soluble substances in food so we can taste it)
what do glands in the stomach secrete
gastric glands in the stomach secrete gastric juice
what does gastric juice contain and what are the functions of its substances
contains pepsin (protease that works best in acidic mediums, catalyses the hydrolysis of proteins into peptides)
hydrochloric acid (provides acidic medium for action of pepsin + kills most bacteria in food)
mucus (protects stomach wall from being digested by proteases + damaged by hydrochloric acid / food particles)
how does physical digestion occur in the stomach and what is the resulting substance + functions
the churning action of the stomach physically digests food into smaller pieces to increase the surface area for the action of digestive enzymes + mix the food w digestive enzymes
food is churned into a creamy liquid called chyme which is then released into the duodenum
what substances are involved in digestion in the small intestine
bile, pancreatic juice, intestinal juice
what is bile
(green alkaline fluid produced by liver and released thru the bile duct (can be temporarily stored in gallbladder))
what substances do bile contain and what are its functions
bile salts
emulsify lipids into small droplets (facilitates chem digestion by increasing the total surface area for lipase to act on)
sodium hydrogencarbonate
(alkaline, neutralises chyme as acids are unfavourable for the action of enzymes in the small intestine, and provides an alkaline medium instead)
where is pancreatic juice released
produced by pancreas, released through pancreatic duct into duodenum
what does pancreatic juice contain and what are the functions of its substances
pancreatic amylase,
proteases (trypsin for proteins; needs diff types due to diffs in active sites of proteins / peptides),
pancreatic lipase,
sodium hydrogencarbonate (neutralises acidic chyme + provides an alkaline medium for the action of enzymes in the small intestine)
where is intestinal juice produced and what are its properties
secreted by intestinal glands in the walls of small intestine, slightly alkaline
what does intestinal juice contain
contains mainly water / mucus / sodium hydrogencarbonate
what doesn’t intestinal juice contain
enzymes
where can enzymes be found in the small intestine (apart from chyme / digestive juices)
there are also enzymes embedded in the epithelium of the small intestine
they are on the cell membrane of the epithelial cells lining the inner wall of the small intestine (contains carbohydrases, eg. maltase / sucrase / lactase and proteases)
what are gallstones’ effect on fat digestion
• decrease in secretion of bile salts from the liver -> decrease in rate of emulsification of fats
• decrease in secretion of pancreatic lipase from the pancreas -> decrease in rate of hydrolysis of fats
• decrease in secretion of hydrogencarbonate (as both bile and pancreatic juice contain it) -> less able to provide an optimum pH for enzymes to function / they can’t really function (as proteins denature in acidic / hot conditions)
• leads to poor digestion of lipids (as some lipids may be left undigested / unabsorbed bc of the decrease in rate of hydrolysis of fats) which are then passed out of the body through egestion -> oily faeces
what food substance are enzymes
protein
how do enzymes aid digestion
act as a biological catalyst which speeds up metabolic reactions taking place inside or outside living cells
action of enzymes process
substrate molecule binds to active site to form a enzyme-substrate complex
substrate molecule is converted into its products
products leave active site, enzyme is released in its original form (can be reused and can bind to another substrate molecule)
3 main types of enzymes
carbohydrases (helps to catalyse the breakdown / hydrolysis of poly/disaccharides by breaking glycosidic bonds)
proteases (catalyse hydrolysis of proteins / polypeptides into peptides by breaking down / hydrolysing the peptide bonds // breakdown of peptides into amino acids by breaking peptide bonds) [some proteins cannot be hydrolysed into amino acids]
lipase (catalyse the hydrolysis of lipids into fatty acids + glycerol by breaking / hydrolysing ester bonds)
control setup for action of bile experiment
set up another test tube w/ identical volume of vegetable oil and distilled water, and add x drops of distilled water instead of bile
proves that the result in the test tube is actually caused by the bile
how are enzymes formed
through the assimilation of amino acids in our bodies to become different types of proteins, one of which are enzymes
the shape of an active site is ?? to the shape of the ???
complementary, substrate
what is an example of a food that cannot be digested
dietary fibre
how does absorption occur
food substances / minerals / vitamins / water can pass through the wall of the small intestine and enter the blood capillaries
where does absorption take place
in the small / large intestine (mostly in the small intestine)
what happens to the absorbed food substances
they are then caried to all parts of the body via the transport system
what systems are the transport system made out of
circulatory (for proteins / carbs)
lymphatic (for lipids)
what is the large intestine responsible for
to absorb minerals and most of the remaining water
what is produced in the large intestine and where is it stored
faeces are produced (a semi-solid waste)
it is temporarily stored in the large intestine until they are passed out through the anus
how is the bolus transported to the stomach
through peristalsis along the pharynx and the oesophagus
peristalsis also helps mix the food with digestive juices
