save my exam digestion Flashcards
what is digestion
large, insoluble biological molecules in food (such as starch, proteins) are hydrolysed into smaller, soluble molecules that can be absorbed across the cell membranes into the bloodstream and delivered to cells in the body
enzymes
essential for the process of digestion as they catalyse the hydrolysis
used either to provide cells with energy (via respiration) or to build other molecules for cell growth, repair and function
what are carbohydrates hydrolysed into
simple sugar
what are protrins hydrolyssed into
amino acids
wat are lipids hydroysd into
mixture of glycerol and fatty acids
what the human digestive system contains
Glands - the salivary glands and glands in the pancreas produce digestive juices
The stomach and small intestine - the sites of digestion
The liver - produces bile
Small intestine - the site of absorption
Large intestine - site of water reabsorption
three types of digestive enzyme
carbohydrases, proteases and lipases
amylase
carbohydrase that hydrolyses (breaks down) starch into maltose
then hydrolysed into glucose by the enzyme maltase
Amylase is made in the salivary glands, the pancreas and the small intestine
maltase
disaccharidase which is found in cell-surface membranes of the epithelial cells lining the small intestine
other disaccharidases in the cell-surface membrane of the epithelial cells in the small intestine: sucrase and lactase, that hydrolyse sucrose and lactose respectively
This allows the absorption of monosaccharides into epithelial cells of the small intestine which pass them into the blood stream
Digestion of Proteins by Proteases
begins in the lumen of the stomach by protease enzymes
endopeptidase hydrolyses peptide bonds within proteins
enzyme is secreted along with hydrochloric acid
partially digested food moves from the stomach into the small intestine
pancreatic juices
endopeptidases and exopeptidases
endoppetidases
hydrolyse peptide bonds within polypeptide chains to produce dipeptides
exopeptidases
hydrolyse peptide bonds at the ends of polypeptide chains to produce dipeptides
dipeptidases
found within the cell surface membrane of the epithelial cells in the small intestine. These enzymes hydrolyse dipeptides into amino acids which are released into the cytoplasm of the cell
emsulsifaction
stomach, solid lipids are turned into a fatty liquid consisting of fat droplets
fatty liquid arrives in the small intestine, bile (containing bile salts) which has been made in the liver and stored in the gallbladder is secreted
bile salts bind to the fatty liquid and breaks the fatty droplets into smaller ones via emulsification
Emulsification helps to increase the surface area of the fatty droplets for action of digestive enzymes
diegstion of lipids
The digestion of lipids takes place solely in the lumen of the small intestine
Lipase enzymes break down lipids (fats) to glycerol and fatty acids
Lipase enzymes are produced in the pancreas and secreted into the small intestine by the pancreas
co trasnport for absorption of amino acids
carrier molecules) are found within the cell-surface membrane of the epithelial cells in the ileum
transport amino acids only when there are sodium ions present
every sodium ion that is transported into the cell, an amino acid is transported in
via facilitated diffusion
molecules down their concentration gradient
Amino acids diffuse across the epithelial cell and then pass into the capillaries
concentration gradient of sodium ions from the lumen of the ileum into the epithelial cell is maintained by the active transport of sodium ions out of the cell and into the blood via a sodium-potassium pump at the other end of the cell
absorption of monossaccharide
lucose carrier proteins in the cell-surface membrane of the small intestine work in a similar way to the amino acid carrier proteins
Sodium ions and glucose molecules are co-transported into the epithelial cells via facilitated diffusion
The glucose molecules diffuse across the epithelial cell and enter the capillary at the other end of the cell by facilitated diffusion
The concentration gradient of sodium ions is maintained by actively transporting sodium ions out of the epithelial cells into the blood
micelles in the absoprtion of lipids
micelles break down and add to a pool of fatty acids and monoglycerides that are dissolved in the small intestine solution surrounding the epithelial cells. These freely dissolved molecules enter the epithelial cell by diffusion
They are non-polar molecules so they can diffuse through the phospholipid bilayer of the cell membrane
hort fatty acid chains
move directly into the blood via diffusion
longer fatty acid chains recombine with monoglycerides and glycerol to form triglycerides
chylomicrons
spherical ‘case’ made of phospholipids and lipoproteins that hold the non-polar triglycerides inside, hidden from the aqueous environment of the cytoplasm and blood
Cholesterol and phospholipids are also found within chylomicrons
ransported to a lacteal
via exocytosis
enter the bloodstream
