12.9 Digestion and Absorption Flashcards
what is the digestive system
a tube that extends from the mouth through the body to the anus
each organ of this system has a…
specialised role to perform in the breakdown and absorption of food molecules and absorption of water
what are digestive juices and where are they produced
produced by the gland cells of the digestive system and they release hydrolytic enzymes and other molecules that facilitate digestion
what do these enzymes do (from digestive juices)
hydrolyse large insoluble food molecules (polymers) into smaller soluble molecules (monomers) which can then be absorbed through the lining of the intestine
polypeptides and proteins are hydrolysed by what and into what
hydrolysed into amino acids by proteases
carbohydrates are hydrolysed by what and into what
hydrolysed into simple sugars by carbohydrases
fats are hydrolysed by what and into what
hydrolysed into glycerol, fatty acids and monoglycerides by lipases
what are the 4 glands
- salivary glands
- stomach
- pancreas
- Ileum
what enzymes do salivary glands excrete
salivary amylase
what enzymes does stomach excrete
endopeptidases (pepsin) and exopeptidases
what enzymes does pancreas excrete
pancreatic amylase, lipases and exopeptidases
what enzymes does ileum excrete
membrane bound dipeptidases and dissacharides
ingest meaning
food going in
egest meaning
food going out
excretion meaning
getting rid of metabolic waste (from reactions) + happens in liver and kindeys
role of the salivary glands
secretes salivary amylase (the enzyme which hydrolyses starch to maltose)
role of the stomach
food is mixed with gastric juice which is acidic
- kills microorganisms
- contains endopeptidases and exopeptidases which hydrolyses polypeptides to dipeptides
role of the pancreas
secretes pancreatic juice containing amylase (and other carbohydrates), endopeptidases (pepsin), exopeptidases, lipases
role of the small intestine (ileum)
- adapted to provide a large SA for the absorption of the products of digestion
- maltase enzymes are embedded in the epithelium cell membrane of the small intestine. this enzyme hydrolyses maltose to glucose, so it is available for rapid absorption
- also sucrase, lactase enzymes and dipeptidase enzymes
digestion of starch
- 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 this salivary amylase is denatured due to acidic pH
- in the small intestine pancreatic amylase continues to hydrolyse the starch to maltose
- maltose is then hydrolysed to glucose by maltase enzymes in the membrane of the epithelial cells. the glucose can then be absorbed
- in mammals, cellulose is not hydrolysed as the enzyme cellulase is not produced
where is amylase located
synthesised and secreted from salivary glands and pancreas
product of reaction catalysed by the enzyme amylase
starch to maltose
where is maltase located
within the membrane of epithelium cell membrane of ileum (membrane-bound dissacharidase ‘maltase’)
product of reaction catalysed by the enzyme maltase
maltose to glucose
describe the role of the enzymes of the digestive system in the complete breakdown of starch (4)
1 salivary / pancreatic amylase hydrolyses starch into maltose
2 by hydrolysing glycosidic bonds
3 maltose is hydrolysed into glucose
4 by maltase
only what can be transported across the epithelial cell membrane
only monosaccharides (monomers)
why can only monosaccharides (monomers) can be transported across the epithelial cell membrane
they are small enough and are complementary to the binding sites of specific carrier / channel proteins that move specifically complementary monomers across the epithelial cell membrane
how are the monosaccharides (monomers) transported across the epithelial cell membrane
the monosaccharides (glucose, fructose, galactose) are absorbed by facilitated diffusion and co-transport using specific carrier proteins (due to their specifically shaped binding sites)
describe how glucose is absorbed from the ilium into the blood (5)
1 Na+ (sodium ions) are actively transported out of epithelial cell into the blood (by sodium potassium pump)
2 this creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell)
(cotransporter proteins have 2 binding sites complementary to Na+ and glucose. only when both molecules bind will the molecules be moved across the membrane)
3 Na+ and glucose enter by facilitated diffusion using (complementary) cotransporter proteins
4 Na+ diffuse into the cell down its concentration gradient
5 glucose moves into the cell against its concentration gradient / down an electrochemical gradient
6 glucose moves into the blood by facilitated diffusion
endo meaning
within
exo meaning
out
process of protein digestion
1 proteins / polypeptides are hydrolysed by enzymes called proteases. this process begins in the stomach
2 endopeptidases hydrolyse the peptide bonds within the polypeptide chain
3 this produces many smaller / shorter polypeptide chains and increases the SA (conc of substrate) for the next enzyme. this makes digestion faster and more efficient. this enzyme has acidic optimum pH and so it doesn’t denature in the stomach acid
4 exopeptidases hydrolyse the peptide bonds at the terminal ends of the protein, removing 1 amino acid at a time
5 exopeptidases are specific: 1 group are complementary to the N terminal end and another group are complementary to the C terminal end. amino acids and dipeptides are produced.
6 the dipeptidases - enzymes embedded in the cell surface membrane of the epithelial cells. these hydrolyse dipeptides into amino acids which can now be absorbed by facilitated diffusion, active transport and cotransport.
describe how amino acids are absorbed from the ilium into the blood (5)
1 Na+ (sodium ions) are actively transported out of epithelial cell into the blood (by sodium potassium pump)
2 this creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell)
3 Na+ and amino acid enter by facilitated diffusion using (complementary) cotransporter proteins
4 Na+ diffuse into the cell down its concentration gradient
5 amino acids moves into the cell against their concentration gradient / down an electrochemical gradient
6 amino acids moves into the blood by facilitated diffusion
Process of lipid digestion
- lipids are only digested within the lumen of the ileum
- in the stomach the lipids are churned into fat droplets
- bile is produced in the liver, stored in the gall bladder and is released into the small intestine with the food
- bile contains bile salts, which emulsify fat droplets (and form micelles)
- this increases SA of the lipids for that action of lipase enzymes
- this makes digestion of lipids faster and more efficient
- lipases hydroxide lipids into glycerol, fatty acids and monoglycerides
Process of lipid digestion and absorption
- lipids droplets are mixed with bile salts to form smaller droplets (emulsified)
- (smaller droplets) increase SA for faster hydrolysis by lipase
- triglycerides hydrolysed into glycerol, fatty acids and monoglycerides
- bile salts, glycerol and fatty acids form micelles
- micelles make fatty acids soluble in water and bring fatty acids to the surface of the epithelial cell membrane
- fatty acids enter the epithelial cell by simple diffusion (micelles do not cross the cell membrane)
- At SER fatty acids, glycerol are recombined to form triglycerides
- at Golgi apparatus triglycerides are modified, proteins are added to form lipoproteins (chyloproteins) and packaged into vesicles (chyloproteins are water soluble and so can be carried into the blood)
- chylomicrons are transported into a lymph vessel by exocytosis they then can enter the blood
