Digestion and absorption Flashcards
What happens in digestion ?
Large biological molecules are hydrolysed to smaller molecules
Describe carbohydrate digestion
Mouth- salivary glands hydrolyses glycosidic bonds in starch to form maltose
The salivary glands produce the enzyme amylase
Small intestine-pancreatic amylase hydrolyses glycosidic bonds in starch to form maltose
Disaccharides attached to the epithelial calls lining the ileum hydrolyse glycosidic bonds in disaccharides to form monosaccharides
Pancreas- produce pancreatic amylase
Starch(polysaccharide) is hydrolysed to maltose (disaccharide) by the enzyme amylase which is produced by the salivary glands which releases into the mouth and it also produced by the pancreas and released into the small intestine membrane bound disaccharides are attached to the membrane of the epithelial cells in the ileum and breakdown disaccharides into monosaccharides
Describe lipid digestion
Lipids are not monomers so only need one enzyme to hydrolyse the ester bonds
Lipids are hydrolysed to monoglycerides and fatty acids by lipase
Lipase is made in the pancreas and it works in the small intestine
Bile salts produces by the liver emulsify large droplets of lipids into small droplets with a larger surface area for lipases to work on
The monoglycerides and fatty acids form micelles with bile salts
Describe protein digestion
Proteins are hydrolysed by three types of protease enzymes: endopeptidases exopeptidases and dipeptidases into amino acids
Endopeptidases hydrolyse bonds within a protein
Some endopeptidases are produced by the pancreas and secreted into the small intestine. Other types of endopeptidases are produced by the stomach cells and work in acidic conditions using hydrochloric acid in the stomach
Endopeptidases hydrolyse long polypeptides into short polypeptides increasing the number of terminal bonds for exopeptidases and speeds up full hydrolysis of proteins
Exopeptidases produced by the pancreas and secreted into the small intestine, hydrolyse the bonds at the end of proteins to remove single amino acids
Dipeptidases are located on the cell surface membrane of epithelial cells in the small intestine and separate dipeptides into two amino acids
What happens after hydrolysis ?
The smaller soluble products of digestion are absorbed from a part of the small intestine called the ileum
How is the ileum adapted ?
Very long and if folded into villi which increases surface area for absorption
Each villus has a good capillary network and a network tubes called a lacteal which is part of the lymph system. Both rapidly remove absorbed molecules, maintain a steep concentration gradient
The lining of the ileum is made of one layer epithelial cells and the capillaries are one layer of endothelial cells which ensures a short pathway for diffusion
Adaptations of the epithelial cells
The cells have folds in the cell membrane called microvilli further increasing the surface area
The membrane has more protein channels and carriers for more active transport facilitated diffusion and co transport
The cells contain more mitochondria for more ATP production allowing more active transport and co transport
The cells has more ribosomes RER and Golgi bodies for protein synthesis and modification to produce more membrane proteins
Absorption of the products of digestion
Na is actively transported out of the ileum cell into the blood using ATP which produces a concentration gradient
Na diffuses down the gradient through a carrier protein and it brings glucose with it by co transport
Glucose moves out the cell into the blood by facilitated diffusion
What are micelles ?
Lipid droplets surrounded by bile soluble in water
Micelles make the lipids soluble in the water solution in the lumen of the ileum and transport the fatty acids and monoglycerides to the cell membrane if the epithelial cells
What is the role of micelles ?
Once at the cell membrane of the epithelial cells the micelle releases the fatty acids and monoglycerides. As the fatty acids and monoglycerides are small and hydrophobic they cross the cell membrane by diffusion through the phospholipid bilayer
Once inside the cell the triglycerides are reformed in the SER. The triglyceride is transported to the Golgi body where the triglyceride is added to a protein modifying it into a structure called a chylomicron which is packaged into a vesicle and exported out of the cell
The chylomicrons move into lactealwhere they are transported around the body
