Digestion & Absorption Flashcards
What are the 5 main functions of the human gut?
- Ingestion
- Mechanical digestion
- Chemical digestion
- Absorption & assimilation
- Egestion
What is the digestive system?
- a muscular tube that extends from the mouth through the body to the anus
-each organ has a special role to breakdown and absorb food and water
Where are digestive juices produced and what do they do?
-produced by gland cells
-release hydrolytic enzymes and other molecules that facilitate digestion
What do hydrolytic enzymes do?
-hydrolyse large insoluble food molecules (polymers) into smaller soluble molecules (monomers) which can then be absorbed through the lining of the intestine
What are polypeptides & proteins hydrolysed by and into?
-hydrolysed into amino acids
-by proteases
What are carbohydrates hydrolysed by and into?
-into simple sugars
-by carbohydrases
What are fats hydrolysed by and into?
-hydrolysed into glycerol, fatty acids and monoglycerides
-by lipases
What are the 4 glands?
-salivary glands
-stomach
-pancreas
-ileum
What is the enzyme, if the gland is salivary gland?
-salivary amylase
What is the enzyme if the gland is the stomach?
-endopeptidases (e.g pepsin) and exopeptidases
What is the enzyme if the gland is the pancreas?
-pancreatic amylase, lipases & exopeptidases
What is the enzyme if the gland is ileum?
-membrane bound dipeptidases & disaccharides
What structures are involved in digestion?
-salivary glands
-oesophagus
-pancreas
-liver
-gallbladder
-stomach
-small intestine
-large intestine- absorption of water
-rectum
Describe the function of salivary glands
Secrete salivary amylase (the enzyme which hydrolyses starch to maltose)
What is the function of the stomach?
-food is mixed with gastric juice which is acidic
-this kills microorganisms
-this also contains endopeptidases and exopeptidases which hydrolyses polypeptides to dipeptidases
Describe the function of the pancreas
-secretes pancreatic juice containing amylase (and other carbohydrases), endopeptidases (e.g pepsin) and exopeptidases
Describe the structure and function of the small intestine (ileum)
-adapted to provide a large surface area for the absorption of the products of digestion
-maltase enzymes are embedded in the epilethelium cell membrane of the small intestine, this enzyme hydrolyses maltose to glucose so s available for rapid absorption
-There are also sucrose, lactase and dipeptidases enzymes
What is digestion?
-A process where large molecules are hydrolysed by enzymes into small molecules, which can be absorbed into the blood/ lymph and then be assimilated into biological molecules
Describe how starch is broken down
-food enters the mouth and is broken up by teeth (mechanical digestion), then mixed with saliva
-salivary amylase starts to hydrolyse glycosidic bonds in the starch producing maltose (chemical digestion)
-in the stomach, the salivary amylase is denatured due to acidic PH
-in the small intestine, pancreatic amylase continues to hydrolyse starch into maltose
-maltose is then hydrolysed to glucose by maltase enzymes in the membrane of epilethial cells, the glucose can then be absorbed
In mammals, cellulose isn’t hydrolysed as the enzyme cellulase isn’t produced
describe maltase/ microvilli
-maltase is a membrane protein (of epilethial cell lining villi) = the membrane has small folds called microvilli, increasing surface area for disaccharides (maltase, lactase, sucrose) and dipeptidases (hydrolyse dipeptidases to amino acids)
Which 2 enzymes are involved in starch digestion
Amylase and maltase
Where is amylase found?
Synthesised and secreted from salivary glands and pancreas
Where is maltase found?
Within the membrane of epilethial cell membrane of ileum
What is the product of a reaction catalysed by amylase?
Starch to maltose (hydrolyse)
What is the product of a reaction catalysed by maltase?
Maltose to glucose (hydrolyse)
Where are microvilli found?
Cell membrane of epilethial cell
Explain how starch is digested/absorbed
-starch hydrolysed by amylase to maltose
-amylase denatured in stomach
-pancreas adds amylase into small intestine
-small intestine lining maltase hydrolyses maltose into glucose
-then absorbed and assimilated
Describe how carbohydrates can be absorbed
-only monosaccharides/monomers are small enough to be transported across the epilethial cell membrane and are complimentary to the binding sites of specific carrier/ channel proteins that move specifically complimentary monomers across the epilethial cell membrane
-monosaccharides (glucose, fructose and galactose) are absorbed by facilitated diffusion and co-transport using specific carrier proteins (due to their specific shaped binding sites)
How is glucose absorbed?
-to the epilethial cell (across microvilli membrane) by co-transport with Na+ ions
describe the roles of the enzymes of the digestive system in the complete breakdown of starch (4)
- Salivary/ pancreatic amylase hydrolyses starch into maltose
- By hydrolysing glycosidic bonds
- Maltose is hydrolysed into glucose
- By maltase
Describe how glucose is absorbed from the ilium into the blood (5)
- Na+ (sodium ions) are actively transported out of epilethial cell into the blood (by sodium potassium pump)
- This creates a concentration gradient of Na+ (between lumen of the ileum and the epilethial cell)
- Na+ and glucose enter by facilitated diffusion using (complimentary) cotransporter proteins
- Na+ diffuse into the cell down its concentration gradient
- Glucose moves into the cell against its concentration gradient
- Glucose moves into the blood by facilitated diffusion
describe the process of absorption/ draw a diagram
AO2 (page 6)
Describe the process of protein digestion (6)
- Proteins are hydrolysed by proteases and this begins in the stomach
- endopeptidases hydrolyse the peptide bonds within the polypeptide chain (middle of chain)
- This produces many shorter polypeptide chains and increases surface area for the next enzyme = faster and more efficient digestion
- exopeptidases (ends of chains) hydrolyse peptide bonds at ends of proteins, removing amino acids one by one
- exopeptidases are specific, amino acids and dipeptidases are produced
- Dipeptidases- enzymes embedded into cell surface membrane of epilethial cells, these hydrolyse dipeptides into amino acids which can now be absorbed by facilitated diffusion, active transport and co transport
Draw an endopeptidase
Draw an exopeptidase
