Digestion Flashcards
Definition of digestion
large molecules are being hydrolysed by enzymes into smaller molecules which can be absorbed across cell membranes
what do the salivary glands do?
secrete salivary amylase = catalyses the hydrolysis of starch into maltose
what does the oesophagus do?
moves food from mouth to stomach, thick muscular walls
what does the stomach do?
inner layer = produces enzymes especially pepsins.
Other glands secrete mucus = prevents self digestion from HCL
what does the pancreas do?
pancreatic juice: containing proteases, lipase and amylase
what does the small intestine do? (ileum)
walls secrete enzymes. Has villi/microvilli for absorbing substances into bloodstream
what does the large intestine do and what does the rectum do?
large: absorb H2O forms faeces
rectum: faeces are stored and periodically egested
what is the difference between absorption and assimilation?
absorption: taking soluble molecules into the body
assimilation: incorporating absorbed molecules into body tissues
what is the difference between physical and chemical breakdown?
physical: large food broken down physically i.e. by teeth or churning of stomach. Gives large SA
chemical: hydrolysis of large insoluble molecules by enzymes
describe the process of carbohydrate digestion
- saliva contains amylase = catalyses hydrolysis of starch to maltose
- food in stomach, acidic = amylase denatures
- food passed to ileum + mixed with pancreatic juice (pancreatic amylase) = continues hydrolysis of starch
- in ileum, epithelial lining has maltase (a membrane bound disaccharidase)
- glucose absorbed into epithelial cells with sodium via cotransporter (carrier) protein
name 3 membrane bound disaccharidases
maltase, sucrase and lactase
What maintains the pH7 in ileum
alkaline salts produced by pancreas
name the enzyme which hydrolyses proteins, where it hydrolyses them and which part and the products
endopeptidase: stomach
- central peptide bonds broken
= product: polypeptides
+ inactive pepsinogen becomes active pepsin (endopeptidase) at low pH
name the enzyme which hydrolyses polypeptides, where it hydrolyses them and which part and the products
exopeptidase: pancreatic juice
- terminal peptide bonds broken
= dipeptides
name the enzyme which hydrolyses dipeptides, where it hydrolyses them and which part and the products
dipeptidase: membrane bound (cell surface)
- bonds between dipeptides
= amino acids
What is the term called when bile salts spilt lipids into micelles and what does it achieve? (step 1 of lipid digestion)
emulsification: increase SA of lipids so hydrolysis of lipase is quicker
what bonds are hydrolysed by pancreatic juice and where are they packaged? (step 2 of lipid digestion)
ester bonds broken = form monoglycerides and fatty acids and packaged in micelles
when do micelles break down and release their contents before entering epithelial cell (in lumen) or in the epithelial cell? (step 3 of lipid digestion)
before
How do monoglycerides + fatty acids move into epithelial cells and why this route? (step 5 of lipid digestion)
simple diffusion as they are nonpolar
what happens at the endoplasmic reticulum (step 6 of lipid digestion) ?
monoglycerides and fatty acids recombined to make triglycerides
what happens at the golgi apparatus? (step 7 of lipid digestion)
triglycerides associate with cholesterol + lipoproteins to form chylomicrons
how do chylomicrons exit the epithelial cells? (step 8 of lipid digestion)
by exocytosis
when chylomicrons exit the epithelial cells where do they enter? (step 9 of lipid digestion)
the lacteals (part of lymphatic capillaries) then into the blood
how do fatty acids diffuse into cells from chylomicrons ? (step 10 of lipid digestion)
triglycerides in chylomicrons hydrolysed by enzyme in endothelial cells in capillaries
