Digestion and absorption Flashcards
what is digestion?
process which large molecules are hydrolysed by enzymes into smaller molecules which can be absorbed and assimilated
what is ingestion?
process by taking food into body through the mouth (eat)
what is assimilation?
the conversion of absorbed food into a substance required for the body
what is egestion?
final act of digestion which eliminates solid/liquid waste material from digestive tract via the anus
what is another term for egestion?
defecation
name the seven major parts of the digestive system
- salivary glands
- oesophagus
- stomach
- pancreas
- large intestine
- small intestine
- rectum
mnemonic for major parts of digestive system
- So
- Ollie
- Stopped (eating)
- Pringles
- Like
- Some
- Rookie
location/ function of salivary glands
- situated near mouth
- pass secretions via a duct in mouth which contains amylase
function of oesophagus
carries food from mouth to stomach
description/ function of stomach
- muscular sac with inner layer producing protease
- stores and digest food
location/ function of pancreas
- situated below stomach
- produces secretion called pancreatic juice containing protease, lipase and amylase
function of large intestine (colon)
- absorbs water from secretions of digestive glands
function of small intestine (ileum)
- digests food by enzymes
- inner walls folded into villi to aid absorption of products into bloodstream
functions of rectum
- temporary storage for faeces
- removed via anus in egestion
what is the overall name for enzymes used in digestion and what process do they use to split molecules?
- hydrolases
- hydrolysis: split molecules by adding water
what are the two stages to digestion?
- physical breakdown - churning
- chemical breakdown - digestion
what are three types of molecules digested?
- carbohydrates
- lipids
- proteins
which enzymes are involved in the digestion of carbohydrate?
- salivary amylase
- pancreatic amylase
- maltase (membrane-bound disaccharidase)
what pH does amylase work best in and how does the body maintain the optimum pH?
- alkaline conditions
- salivary amylase: contains mineral salts to keep pH at neutral
- pancreatic amylase: alkaline salts produced by pancreas and intestinal wall to maintain pH
explain the process of carbohydrate digestion
saliva enters mouth through glands
- mixes with food during chewing
- saliva contains salivary amylase which hydrolyses starch to maltose
- swallowed by stomach
- stomach acid denatures salivary amylase
- passed into small intestine
- mixes with pancreatic juice containing amylase which hydrolyses starch to maltose
- muscles in intestinal wall pushes food along ileum
- epithelial lining produced maltase (membrane-bound disaccharidase)
- hydrolyses maltose into alpha-glucose
name two others disaccharides that are digested in diet
- sucrose
- lactose
how is sucrose hydrolysed?
sucrase
- glucose + fructose
how is lactose hydrolysed?
- lactase
- glucose +galactose
what type of enzymes hydrolyse lipids?
- lipase
where is lipase produced and what does it do?
produces in pancreas
- hydrolyses ester bond in triglycerides - fatty acid + monoglyceride
how does lipase split the lipid up?
- split into micelles
- emulsified by bile salts
- surface area increased - increased enzyme reaction rate
how are micelles (triglycerides) absorbed?
- micelles come into contact with epithelial cells - release monoglycerides and fatty acids
- as they are non-polar, they diffuse across cell membrane
- recombine on SER to form triglyceride
- in Golgi triglycerides combines with cholesterol and lipoproteins to form chylomicrons
- secreted out of cell by exocytosis
- enter lacteals (lymphatic capillaries)
- emptied into blood stream via thoracic duct
- ## either used by blood or transported to liver and split into HDL and LDL
what enzymes are involved in protein digestion?
peptidases (proteases)
what three peptidases are used?
- endopeptidase
- exopeptidase
- dipeptidase
explain process of protein digestion
- endopeptidase hydrolyses peptide bonds between amino acids in central region to split into peptides
- exopeptidase hydrolyses peptide bonds between terminal amino acids to release dipeptides and single amino acids
- dipeptidase hydrolyses dipeptides into two monopeptide
what is dipeptidase described as?
membrane bound
