Digestion-physical process to increase the SA:V ratio of the food
Absorption- small, monomer units are absorbed into the blood, where it is carried away
Assimilation-rebuilding/ utilising nutrients
Defecation- removing materials that weren't broken down, different to excretion
Endopeptidase-hydrolyses bonds in the middle of a peptide
Exopeptidase- breaks terminalpeptide bonds
Maltase- hydrolyses maltose into twoalphaglucose molecules
Sucrase- hydrolyses sucrose into fructose and glucose
Lactase- hydrolyses lactose into galactose and glucose
Amylase- hydrolyses starch (polysaccharide) into maltose (disaccharide)
Maltase, sucrase and lactase are membrane-bounddisaccharidases.
Bile- produced in the liver, stored in the gall bladder
Emulsification is when bile breaks up large droplets if fat into smaller droplets of fat, increasing the SA:V ratio for digestion, making it easier for lipase to hydrolyse the triglyceride into smaller molecules (e.g. glycerol, fatty acids, monoglycerides).
The mouth releases salivaryamylase, which hydrolyses starch into maltose.
The stomach (pH 1-2) releases pepsin, which hydrolyses largepolypeptides into amino acids, and smallerpolypeptides.
The pancreas releases proteases, amylase and lipase, which hydrolyses starch, largepolypeptides and triglycerides into amino acids, maltose, fatty acids, monoglycerides and glycerol.
The ileum (on microvilli which are found in the small intestine) releases sucrase, maltase and lactase which hydrolyses sucrose, maltose and lactose into their monosaccharides.
Ileum of a small intestinal cell:
Thin layer of cells
Large surface area (many found on microvilli)
Glucose and amino acids are absorbed by the bloodstream which is part of the circulatory system
Fatty acids are absorbed by the lacteal which is part of the lymphatic system
Absorption of amino acids:
Sodium ions (Na+) are actively removed from the cell via the sodium-potassium pump which requires ATP.
Amino acids are removed from the cell by via facilitated diffusion into the capillaries.
This maintains a concentrationgradient.
Na+ and amino acids in the lumen (outside the cell) both bind to the co-transport protein.
The co-transport protein changes shape, transporting the molecules across the membrane.Na+ ions go down the conc. gradient and amino acids either go against or down the conc. gradient.
Lipid absorption:
Fatty acids and monoglycerides (from fat digestion) leave micelles and enter the epithelial cell.
Fatty acids link to form triglycerides.
Fatty globules combine with proteins to form chylomicrons (inside the golgi apparatus).
Chylomicrons are extruded from the epithelial cell (via exocytosis of vesicle) and enter a lacteal.
Lymph in the lacteal (part of the lymphatic system) transports chylomicrons away from the intestine.