Digestion And Absorption Flashcards
What are salivary glands
Secretes salivary amylase, the enzyme which hydrolyses starch to maltose
Describe the role of the stomach
Food is mixed with gastric juice which is acidic
Kills microorganisms
Contains endopeptidases and exopeptidase which hydrolyse polypeptides to dipeptides
Describe the role of the pancreas
Secretes pancreatic juice containing amylase- endopeptidases, exopeptidase and lipases
Describe the role of the small intensive (ileum)
Adapted to provide a large surface area for the absorption of the products of digestion
Maltose enzymes are embedded in the epithelium cell membrane of the small intestine- hydrolyses maltose to glucose so available for rapid absorption
Also sucrose, lactase enzymes and dipeptidase enzymes
Describe the process for the complete breakdown of starch
Food enters the mouth and is broken up by teeth (mechanical digestion), then mixed with saliva
Salivary amylase starts hydrolyse glycosidic bonds in the starch producing maltose
In the stomach this salivary amylase is denatured due to acidic pH
In the small intestine, pancreatic amylase continues to hydrolyse starch to maltose
Maltose is then hydrolysed to glucose by maltase enzymes in the membrane of the epithelial cells- glucose can then be absorbed
In mammals, cellulose is not hydrolysed as the enzyme cellulose is not produced
Where is amylase located and what does it produce
Synthesised and secreted from salivary glands and pancreas
Starch to maltose
Where is maltase located and what does it make
Within the membrane of epithelium cell membrane of ileum
Maltose to glucose
Describe how glucose is absorbed from the ileum to the blood
- Na+ are actively transported out of epithelial cell into the blood by sodium potassium pump
- This creates a concentration gradient of Na+ between lumen of the ileum and the epithelial cell
- Na+ and glucose enter by facilitated diffusion using complementary cotransporter proteins
- Na+ diffuse into the cell down its concentration gradient
- Glucose moves into the cell against its concentration gradient down an electrochemical gradient
- Glucose moves into the blood by facilitated diffusion
AO2 application key points
Epithelial cells contain many mitochondria to produce the large amount of ATP they need for active transport
Human do not produce cellulase so they are unable to hydrolyse cellulose
Some people do not produce lactase they are unable to hydrolyse lactose
Lactose and all dissacharides are soluble so they lower water potential
Bacteria within the large intestine can produce these enzymes releasing the monosaccharides for the bacteria to absorb and assimilate for their own cellular respiration
Describe protein digestion
- Proteins are hydrolysed by enzymes called proteases. The process begins in the stomach
- Endopeptidases hydrolyse the peptide bonds within the polypeptide chain
- This produces many smaller/shorter polypeptide chains and increases the surface area for the next enzyme. This makes digestion more faster and efficient
- Exopeptidase hydrolyse the peptide bonds at the terminal ends of the protein, removing one amino acid at a time
- Exopeptidase are specific- one group are complementary to the N terminal ends and the other are complementary to the C terminal ends. Amino acids and dipeptides are produced
- The dipeptidases are embedded in the cell surface membrane of the epithelial cells- hydrolyse peptide bonds into amino acids which can now be absorbed by facilitated diffusion, active transport and cotransport
How are amino acids absorbed
Only amino acids are small enough to move across the epithelial cell membrane and be absorbed because they are monomers.- absorbed by facilitated diffusion and cotransport using specific protein
Where are lipids digested
Within the lumen of the ileum
What is the function of bile
Contains bile salts which emulsify fat droplets and form micelles- this increases the surface area of lipids for the action of lipase
Explain lipid absorption and digestion
- Lipid droplets are mixed with bile salts to form smaller droplets( emulsified)
- Increase surface area for a faster rate of 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
- At the smooth Endoplasmic reticulum- fatty acids, glycerol are recombined to form triglycerides
- St Golgi body- triglycerides are modified, proteins are added to form lipoproteins called chylomicrons
- Chlyomicrons are transported into a lymph vessel by exocytosis - they then enter the blood
