human digestive system Flashcards
digestion of starch in mammals
Amylase (produced by salivary glands / pancreas)
hydrolyses starch to maltose
Membrane-bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose
Hydrolysis of glycosidic bond
digestion of disacharides
Membrane-bound disaccharidases hydrolyse disaccharides to 2 monosaccharides:
○ Maltase - maltose → glucose + glucose
○ Sucrase - sucrose → fructose + glucose
○ Lactase - lactose → galactose + glucose
● Hydrolysis of glycosidic bond
Describe the digestion of lipids in mammals, including action of bile salts
● Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets
● This increases surface area of lipids for faster lipase activity
● Lipase (made in pancreas) hydrolyses lipids (eg. triglycerides) → monoglycerides + fatty acids
● Hydrolysis of ester bond
digestion of protein
● Endopeptidases - hydrolyse internal (peptide) bonds
within a polypeptide
smaller peptides
○ So more ends / surface area for exopeptidases
● Exopeptidases - hydrolyse terminal (peptide) bonds at
ends of polypeptide → single amino acids
● Membrane-bound dipeptidases - hydrolyse (peptide)
bond between a dipeptide → 2 amino acids
● Hydrolysis of peptide bond
co transport
Na+ actively transported from epithelial cells lining ileum toblood (by Na+/K+ pump)
● Establishing a concentration
gradient of Na+ (higher inlumen than epithelial cell)
● Na+ enters epithelial cell down its concentration gradient with monosaccharide or amino acid against its concentration gradient
● Via a co-transporter protein
● Monosaccharide or amino acid moves down a
concentration gradient into
blood via facilitated diffusion
Describe the absorption of lipids by a mammal, including the role of micelles
Bile salts combine with monoglycerides and fatty acids to form micelles
○ Micelles make monoglycerides and fatty acids (more) soluble in water
○ Micelles carry fatty acids and monoglycerides to cells lining the ileum, where they break down to
release them This maintains a high concentration of fatty acids and monoglycerides near cells lining the ileum
● Monoglycerides / fatty acids are absorbed (into epithelial cell) by diffusion (as they’re lipid soluble)
● Triglycerides reformed in (epithelial) cells and aggregate into globules
● Globules coated with proteins forming chylomicrons which are then packaged into vesicles
● Vesicles move to cell membrane and fuse with it, releasing chylomicrons via exocytosis
○ Chylomicrons enter lymphatic vessels and eventually return to blood circulation
