Digestion And Absorption

• salivary/pancreatic amylase hydrolyses starch into maltose • by hydrolysing glycosidic bonds • maltose is hydrolysed into glucose • by maltase

• Na+ (sodium ions 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 ilium and the epithelial cell) • contransporter proteins have 2 binding sites complementary to Na+ and glucose • Na+ and glucose enter by facilitated diffusion using a complementary contransporter protein • 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

• endopeptidases hydrolyse peptide bonds within the polypeptide producing shorter polypeptides • this increases surface area for expertises to act on • exopeptidases hydrolyse peptide bonds at the end of polypeptides producing amino acids (or dipeptides) • dipeptidases hydrolyse the peptide bond in a dipeptide producing 2 amino acids • amino acids can be absorbed

• smaller droplets have a larger surface area to volume ratio • more surface for lipase to act • faster hydrolysis of triglycerides into glycerol, fatty acids and monoglycerides

• micelles are bile salts and fatty acids • make the fatty acids more soluble in water • carry fatty acids to cell lining of the ileum • maintain higher concentration of fatty acids at cell lining than inside the cell • fatty acids only absorbed by simple diffusion

• fatty acids and glycerol recombine to form triglycerides at smooth endoplasmic reticulum • triglycerides are modified by addition of proteins to make chylomicrons and then packaged into vesicles at the Golgi apparatus • chylomicrons are transported into lymph/lacteal vessel by exocytosis