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Biology - AS Level > Digestion > Flashcards

Digestion Flashcards

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1
Q

what are the 6 steps of digestion

A

-ingestion
-mastication
-chemical digestion
-absorption
-assimilation
-egestion

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2
Q

what happens in the mouth

A

-food ingested
-food broken up by teeth (mastication)
-salivary glands produce salivary amylase- hydrolyses starch to maltose
-saliva lubricates food and maintains ph 7
-food shaped into a bolus and swallowed

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3
Q

what is the role of the epiglottis

A

closes to prevent food from travelling down the trachea

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4
Q

how does the food move down the oesophagus

A

peristalsis
osephagus is a hollow tube with muscular walls

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5
Q

what happens in the stomach

A

-conditions are very acidic - ph 2
-due to production of HCl from oxyntic cells in gastric pits
- the presence of HCl provides ideal conditions for protease to act and kills bacteria that may be present in food
-chief cells secrete inactive pepsinogen - comes active when comes into contact with HCl and converted to pepsin
-food stays in the stomach for a number of hours and muscles turn the food into semi-solid mixture called chyme

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6
Q

why is important that the pepsinogen becomes active

A

prevents the protease from digesting chief cells

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7
Q

what is pepsin

A

endopepptidase enzyme - hydrolyses peptide bonds in AA in the central region of the molecule
this produces a series of shorter peptides

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8
Q

what happens in the small intestine

A

duodenum- 1st 20 cm and entry controlled by the pyloric sphincter muscle and many secretions are added to the chyme
-bile emulsifies fats - increasing the SA for enzymes to act on
also contains hydrogen carbonate which neutralises the acidity from the stomach to ph 7- that is required for enzymes in the duodenum
-pancreatic juice contains pancreatic amylase - starch to maltose
and also contains inactive trypsinogen is secreted and is activated by enterkinase- activate to trypsin
-lipase enzymes also present
-helps to maintain ph
-exopeptidases somewhere but Newby didn’t say where
ileum- 5m - all chemical digestion is competed here
-carb digestion - occurs on membrane of the microvilli of epithelial cells - disaccharidases act on disaccharide sugars converting them to monosaccharides
Absorption takes place here also

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9
Q

what is trypsin

A

formed from inactive trypsinogen and activated by enterkinase
it is an endopeptidase enzyme that hydrolyses middle of AA chain

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10
Q

what happens in large intestine

A

large amounts of water absorbed here making the gut less fluid
huge numbers of bacteria present
bacteria can synthesis a number of vitamins - eg vit K which are used by the body

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11
Q

what is egestion

A

remaining gut contents removed as solid faeces
-mostly water with bacteria - living and dead and indigested food - mostly cellulose and lignin

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12
Q

what are exopeptidases

A

hydrolyses bonds on the terminal ends of the amino acids and release dipeptidases and single AA

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13
Q

what are endopeptidases

A

Hydrolyse bonds between amino acids in central region

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14
Q

what are dipeptidases

A

hydrolyse bond between AA of two amino acids

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15
Q

protein digestion in the stomach

A

-pepsinogen released in inactive form
-becomes activated when come into contact with HCl - pepsin
-pepsin as an endopeptidase breakes down polypeptides into shorter peptides

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16
Q

How can the proteins digestive enzyme cause harm

A

they can digest themselves in turn digesting body cells

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17
Q

protein digestion in the small intestine

A

-duodenum
- inactive trypsinogen- enters via pancreatic duct
-walls of duodenum secrete enterokinase which actives trypsinogen into trypsin
-trypsin is an endopeptidase enzyme
-polypeptides are converted to shorter peptides
-ileum
-bound to epithelial cells - dipeptidases are secreted to break down peptides/dipeptides into amino acids

18
Q

carb digestion in the mouth

A

-saliva contains salivary amylase
-hydrolyses some starch to maltose- disaccharide and reducing sugar- breaks glycosidic bonds in molecule

19
Q

carb digestion in stomach

A

does not happen due to acidity of the stomach

20
Q

carb digestion in the small intestine

A

duodenum
-pancreas - pancreatic juices - contain pancreatic amylase
-hydrolyses remaining starch to maltose
ileum
-disaccharidase enzymes
-maltase- hydrolyses maltose to alpha glucose
-sucrase- hydrolysis sucrose into alpha glucose and fructose
-lactase- hydrolysis lactose into beta glucose and galactose

21
Q

lipid digestion in the small intestine

A

where lipid digestion begins
-duodenum- bile made by liver and stored in gall bladder enters via bile duct
-bile emulsifies fats - breaks them down to smaller droplets
-physical digestion
-larger SA for enzymes to act
-pancreatic juice contains lipase enzymes
-hydrolyse lipids into
-fatty acids
-glycerol
-monoglycerides

22
Q

where does absorption occur

A

the ileum

23
Q

what cover the inner layer of the ileum

A

finger-like projections called villi

24
Q

what is the layer of cells covering the villi and that comes into contact with the food

A

epithelium

25
Q

what are on the surface of the ileum

A

microvilli - these form a brush border

26
Q

how do the muscle layer of the digestive system change

A

varies in thickness due to how much food is needed to be used along eg the solidity of the food

27
Q

how is the ileum structurally adapted for digestion

A

-microvilli have digestive enzymes bound to them
-large SA means large SA of enzymes available to digest the food
-each villus has muscle fibres which contract to increase contact with food and enzymes
-all to help digestion happen faster

28
Q

how is the ileum structured for absorption

A

-large SA is achieved by the ileum being very long, and the presence of villi and microvilli
-epithelial cells have lots of mitochondria - provide energy for the active transport of molecules like glucose
-villi contain capillaries to transport molecules away quickly, maintaining a conc gradient
-each villus has a lymph vessel to absorb lipids
-epithelial cell layer is thin- short diffusion pathway
-villi are moved by muscle fibres, increasing contact with food and epithelium

29
Q

how are molecules absorbed- what methods

A

-first by diffusion as there is a greater conc of molecules in the ileum and less in the blood so a conc gradient is established
-however if diffusion contains the concs will become equal
- therefore glucose and amino acids are absorbed into the blood by active transport

30
Q

how is glucose absorbed from ileum to the blood

A

sodium-potassium pump

31
Q

describe the process of the sodium-potassium pump

A

-Na+ ions are actively transported out of the epithelial cells and into the blood - protein carries do this
- there is now a larger conc of Na+ ions in the lumen of the gut than inside the epithelial cells
-Na+ ions diffuse into the epithelial cells through another protein carrier which also carry glucose molecules
-glucose then diffuses through another protein carrier into the blood by facilitated difffusion

32
Q

is the absorption of glucose active or passive

A

overall active
however glucose into the blood is passive

33
Q

how are amino acids absorbed

A

-sodium-potassium pump transports Na+ ions out of the cell via active transport
-amino acids and Na+ ions bind to carrier protein
-as the Na+ ions diffuse into the cell the amino acids are carried alongside
-the amino acids then diffuse to the other end of the cell
-they are then transferred to the capillaries by facilitated diffusion

34
Q

how are fats absorbed

A

-after digestion the monoglycerides and fatty acids remain associated with bile salts and form structures called micelles
-at the epithelial cell membranes the micelles break down
-release the monoglycerides and fatty acids
-as they are lipid soluble they diffuse across the cell membrane
-when in the cell they are transported to the ER where they are recombined to form triglycerides
-they are then transported to the Golgi and associate with cholesterol and lipoprotiens to form chylomicrons
-chylomicrons leave the cell va EXOCYTOSIS as they are too large to leave via any other method
-chylomicrons enter lacteals - the lymph- in the villus
- they are then deposited into the blood by the subclavian vein

35
Q

what enzyme digests lactose

A

lactase - produced in the microvilli of the epithelial cells

36
Q

what is the word equation of the action of lactase

A

lactose + water + lactase = beta glucose + galactose

37
Q

what happens if you are lactose intolerant

A

body produces little to no lactase

38
Q

what happens to lactose in the body of someone who is lactose intolerant

A

it remains undigested in the SI
passes into the LI
then it is digested by E.coli bacteria- has own lactase in plasma
the E.coli ferments the glucose and galactose to acetate, ethanol, hydrogen gas and CO2

39
Q

what are the symptoms of lactose intolerance

A

-nausea
-abdominal pain
-bloating
-diarrhoea

caused by the hydrogen and carbon dioxide gas produced by the bacteria

40
Q

how does excess lactose in the colon cause diarrhoea

A

the presence of lactose lowers water potatenial
and the water is not absorbed into the blood

Biology - AS Level (17 decks)

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