Digestion

Question 1

what are the 6 steps of digestion

Answer 1

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

Question 2

what happens in the mouth

Answer 2

-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

Question 3

what is the role of the epiglottis

Answer 3

closes to prevent food from travelling down the trachea

Question 4

how does the food move down the oesophagus

Answer 4

peristalsis
osephagus is a hollow tube with muscular walls

Question 5

what happens in the stomach

Answer 5

-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

Question 6

why is important that the pepsinogen becomes active

Answer 6

prevents the protease from digesting chief cells

Question 7

what is pepsin

Answer 7

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

Question 8

what happens in the small intestine

Answer 8

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

Question 9

what is trypsin

Answer 9

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

Question 10

what happens in large intestine

Answer 10

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

Question 11

what is egestion

Answer 11

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

Question 12

what are exopeptidases

Answer 12

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

Question 13

what are endopeptidases

Answer 13

Hydrolyse bonds between amino acids in central region

Question 14

what are dipeptidases

Answer 14

hydrolyse bond between AA of two amino acids

Question 15

protein digestion in the stomach

Answer 15

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

Question 16

How can the proteins digestive enzyme cause harm

Answer 16

they can digest themselves in turn digesting body cells

Question 17

protein digestion in the small intestine

Answer 17

-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

Question 18

carb digestion in the mouth

Answer 18

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

Question 19

carb digestion in stomach

Answer 19

does not happen due to acidity of the stomach

Question 20

carb digestion in the small intestine

Answer 20

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

Question 21

lipid digestion in the small intestine

Answer 21

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

Question 22

where does absorption occur

Answer 22

the ileum

Question 23

what cover the inner layer of the ileum

Answer 23

finger-like projections called villi

Question 24

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

Answer 24

epithelium

Question 25

what are on the surface of the ileum

Answer 25

microvilli - these form a brush border

Question 26

how do the muscle layer of the digestive system change

Answer 26

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

Question 27

how is the ileum structurally adapted for digestion

Answer 27

-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

Question 28

how is the ileum structured for absorption

Answer 28

-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

Question 29

how are molecules absorbed- what methods

Answer 29

-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

Question 30

how is glucose absorbed from ileum to the blood

Answer 30

sodium-potassium pump

Question 31

describe the process of the sodium-potassium pump

Answer 31

-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

Question 32

is the absorption of glucose active or passive

Answer 32

overall active
however glucose into the blood is passive

Question 33

how are amino acids absorbed

Answer 33

-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

Question 34

how are fats absorbed

Answer 34

-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

Question 35

what enzyme digests lactose

Answer 35

lactase - produced in the microvilli of the epithelial cells

Question 36

what is the word equation of the action of lactase

Answer 36

lactose + water + lactase = beta glucose + galactose

Question 37

what happens if you are lactose intolerant

Answer 37

body produces little to no lactase

Question 38

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

Answer 38

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

Question 39

what are the symptoms of lactose intolerance

Answer 39

-nausea
-abdominal pain
-bloating
-diarrhoea

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

Question 40

how does excess lactose in the colon cause diarrhoea

Answer 40

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