digestion

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describe how we process food.
ingestion > digestion > absorption > egestion
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what does physical digestion involve?
breaking food into smaller pieces to enable ingestion and increase S.A. for chemical ingestion
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what does chemical digestion involve?
breaking down large insoluble molecules into small. soluble ones and it is carried out by enzymes
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what is the human digestive system?
an interface with the environment as substances can enter the body through it
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what do the salivary glands do?
pass secretions into the mouth that lubricate food so that it can be swallowed
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what does the oesophagus do?
carries food from the mouth to the stomach
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how is it adapted?
thick muscle wall means food is propelled down by peristalsis
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what does the stomach do?
muscle churns food into a liquid and glands secrete gastric juices to kill bacteria, lubricate food, and digest proteins.
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what does the pancreas do?
secretes pancreatic juices to digest proteins, lipids, and starch
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what does the small intestine do?
digests food into the wall where it is moved along by peristalsis and absorbed into the blood stream
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what does the large intestine do?
absorbs water to form semi-solid faeces
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what does the rectum do?
stores faeces before they are removed by the rectum
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how is the small intestine adapted for absorption?
the inner surface is highly folded with villi and the epithelial cells are further folded by being covered in microvilli
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where is amylase produced and what does it break down?
produced in the salivary glands and pancreas and breaks down starch to maltose by hydrolysing the glycosidic bonds
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what do pancreatic juices contain?
protease, lipase, and amylase
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where is maltase secreted?
in the small intestine
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where is sucrase secreted?
in the epithelial lining of the small intestine
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where is lactase secreted?
in the epithelial cell of the small intestine
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how are monosaccharides absorbed from the gut lumen to the blood?
by facilitated diffusion and active transport
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describe the process.
sodium ions moved by AT into blood > carrier proteins transport sodium ions + glucose into cell by facilitated diffusion > glucose transported by facilitated diffusion into the blood
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when is glucose transported?
in the presence of sodium ions
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describe the process in terms of conc.
low conc of sodium ions in cell cytoplasm > high conc of glucose in cell
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what is cholera?
-water borne. -causes by the bacterium vibrio cholerae. -transmitted through contaminated water.
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what is the main symptom?
severe watery diarrhoea
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describe the process of infection.
bacteria burrow into epithelial lining through mucus > cholera toxin produced and binds to carb receptors on gut epithelial cells > chloride ion channels opened > chloride ions pass into gut lumen by facilitated diffusion >
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continue explaining.
water follows by osmosis due to low potential in lumen because of high no of ions
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why is there severe diarrhoea?
because there is so much water in the lumen
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how is the symptom of dehydration explained?
water and chloride ions enter the epithelial cells because of a low potential in the cell, so water moves by osmosis which removes water from the blood
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why is treating diarrhoea ineffective with just drinking water?
it doesn't replace the ions lost by the small intestine
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why can't it be treated with an IV drip?
lack of equipment/training/money
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what does ORT do?
replace the water and ions containing sodium to replace electrolytes and glucose
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why does it contain glucose?
to provide energy and stimulate the uptake of ions
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why does increased glucose make diarrhoea worse?
it means a lower water potential in the lumen do more water is drawn into the bloodstream
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how should glucose be given instead?
orally so that energy levels are increased
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what can be used in its place and why?
starch because it has no osmotic effect and can slowly be broken down to glucose
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what can be used as a source of starch?
rice flour because it is readily available and provides amino acids and other nutrients that help the uptake of sodium ions
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what is the problem and how is it overcome?
hard to swallow and instead starch can be partially digested by amylase which makes it more soluble/smaller, therefore making a more viscous drink.
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when does lactose intolerance result?
when a person provides insufficient lactase so lactose can't be digested and instead accumulates in the gut
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what are the symptoms?
-bloating. -flatulence. -diarrhoea.
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why can't it be absorbed from the gut into the bloodstream?
it is too large
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what does accumulated lactose cause?
it causes the water potential of the guts content to drop
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where does water move?
into the gut then faeces by osmosis
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what happens to the lactose?
it is digested by bacteria which are normally present instead of by lactase
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what do bacteria produce?
-hydrogen and methane which explains the bloating and flatulence. -lactic acid which lowers potential causing diarrhoea and makes the stomach inflamed causing a stomach ache.
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Card 2

Front

what does physical digestion involve?

Back

breaking food into smaller pieces to enable ingestion and increase S.A. for chemical ingestion

Card 3

Front

what does chemical digestion involve?

Back

Preview of the front of card 3

Card 4

Front

what is the human digestive system?

Back

Preview of the front of card 4

Card 5

Front

what do the salivary glands do?

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