6.1 Flashcards
Explain why digestion of large food molecules is necessary
large food molecules must be broken down into smaller molecule so that they can be absorbed across small intestine wall into blood
function of mouth
ingestion
- where food is taken into the body
- food is physically broken down by teeth (mechanical digestion)
- starch is broken down into sugars by salivary amylase (chemical digestion)
esophagus
- muscular tube which connects the mouth to the stomach
- moves food by peristalsis
stomach
- HCl provides acid condition (pH 2) which kills bacteria on food and provides optimum pH for stomach enzymes (eg. pepsin)
- pepsin breaks down proteins into amino acids
- mucus lining protects the stomach wall from autolysis (self-digestion)
liver
- produces bile
gall bladder
- stores bile
pancreas
- produces enzymes and secretes them into the small intestine
e.g. amylase, lipase
small intestine
- emulsification of lipids & neutralisation of stomach acids by bile
- chemical digestion of food by enzymes
- absorption of small soluble molecules into the blood
large intestine
- absorption of water (by osmosis) & minerals into the blood
rectum
- stores faeces
anus
- where faeces are secreted by process called egestion
draw & label digestive system
peristalsis
- the gut is made of smooth muscle which is not under conscious control & contracts rhythmically
- peristalsis is waves of muscle contractions which help move food along the gut
- contraction of circular muscles behind food help prevent it from being pushed backwards
- contraction of longitudinal muscles help move food forwards
- a special type of peristalsis in the small intestine called segmentation helps mix food with digestive enzymes
enzymes on digestion
- enzymes digest most macromolecules in food into monomers in the small intestine
- the pancreas secretes three types of enzyme into the lumen of the small intestine: amylase, lipase, endopeptidase
how do the three enzymes secreted by pancreas break down products into monomers
membrane bound digestive enzymes
- some enzymes catalyse hydrolytic reactions by mixing with the ingested food, however, as food moves continuously through the alimentary canal, the enzymes are either digested or lost in the faeces
- some enzymes are not mixed with the ingested food but are produced by and remain in the cells lining the small intestine, such as maltase
- maltase is produced by epithelial cells in the small intestine
- it remains bound to the plasma membrane on microvilli
- it catalyses the hydrolysis of maltose to glucose
- this means that maltase isn’t lost as food moves along the small intestine and it means that glucose is produced in the right location for absorption
cellulose digestion
- although humans can digest starch, glycogen, lipids, and nucleic acids, we cannot digest cellulose as we don’t have the enzymes cellulase or any cellulose-digesting bacteria
- however it is still an important component to our diet (even though we gain no energy from it)
- it is what we call fibre and it provides bulk to the food in the digestive system and it also aids the movement of food through the alimentary canal by peristalsis as it gives the smooth muscle of the gut something to push against
identify the tissue layers in the transverse section of small intestine to
absorption in small intestine (features)
microvilli/villi:
- greatly increase the surface area over which absorption takes place
epithelium:
- only one cell thick, reduces distance over which absorption takes place
capillaries:
- close to epithelium to reduce distance for absorption
lacteals (absorb lipids);
- close to epithelium today reduce distance for absorption
length:
- about 6m
- increases surface area and provides enough time for absorption to take place
different methods of absorption
simple diffusion
- substances can move b/w phospholipid molecules
facilitated diffusion
- involves channel proteins which lets solutes pass OR involves specific carries proteins that change shape to let solutes pass
active transport
- particles collide with protein pump
- protein pump is activated by ATP, which causes a shape change
- particles are released on föhr side of membrane
- ADP & Pi are released which reverts protein pump back to original shape
- occurs against a concentration gradient
endo- & exocytosis
- endo: the bulk transport of materials/large molecules into the cell
- exo: the bulk transport of materials/large molecules out of the cell
describe how fructose & glucose is absorbed
fructose is absorbed into epithelial cells by facilitated diffusion
glucose is absorbed by the sodium glucose co-transport mechanism
both are then absorbed into blood by facilitated diffusion
describe how amino acids are absorbed
di peptides and tripeptides are hydrolysed by membrane bound proteases into amino acids which are then actively transported into epithelial cells
they then diffuse into the blood
describe how lipids are absorbed
fatty acids and glycerol are absorbed into epithelial cells by simple diffusion because they are non polar and can pass through hydrophobic membrane into the blood
dialysis tubing model
- can model the digestion of the small intestine
- dialysis tubing is semi-permeable (to small molecules but not to large ones)
- the medium outside represents blood into which digested products are absorbed
- the movement of glucose mimics absorption via epithelial cells as the glucose moves from an area of high glucose concentration (inside tubing) to low glucose concentration (in beaker) = positive results
- if it was starch the result would be negative as starch is too large to diffuse through the dialysis tubing
