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3.3 Digestion and Absorption - Coggle Diagram
3.3 Digestion and Absorption
Enzymes
Petidases
Exopeptidases- produced in pancreas, act in small intestine. Hydrolyse peptide bonds on terminal or penultimate amino acids in the chain, producing single amino acids and dipeptides.
Endopeptidases- produced and act in stomach. Hydrolyse peptide bonds between amino acids in the middle of a protein molecule, forming a series of peptide molecules.
Dipeptidases- produced and act in small intestine. hydrolyse peptide bonds in dipeptides. Membrane-bound are part of the cell surface membrane of ileum lining cells
Carbohydrases
Amylase
Salivary amylase- produced in salivary glands, acts in mouth
Pancreatic amylase- produced in pancreas, acts in small intestine
Disaccharidases- produced and act in small intestine. Are located membrane-bound to the epithelium of the small instestine.
Hydrolyses the glycosidic bonds between saccharides
Lipases
Hydrolyse the ester bonds in triglycerides, often into monoglyceride and 2 fatty acids.
Produced in pancreas, act in small intestine
Fat emulsification and transport
Emulsification- lipids are broken up into tiny droplets called micelles by bile salts, produced in the liver. Increases SA of lipids to speed up lipase activity. Micelles are made up of monoglycerides and fatty acids that remain in association with the bile salts
Digestion and absorption
micelles come into contact with ileum epithelial cells. Micelles break down to release monoglycerides and fatty acids, which diffuse into the cell
Monoglycerides and fatty acids transport to smooth ER, and are reformed to triglycerides and are put into vesicles
Vesicles reach golgi apparatus where the triglycerides associate with cholesterol and lipoproteins to form chylomicrons.
Chylomicrons move out of epithelial cells by exocytosis and enter lymphatic capillaries called lacteals and pas via lymphatic vessels to enter the blood stream.
Absorption
Adaptations of ileum
Villi and microvilli- increases SA to increase rate of absorption.
One cell thick wall of small intestine- reduces diffusion distance
Contains muscle- maintains steep diffusion gradient as movement mixes ileum content.
Large number of capillaries- blood flow carries away absorbed molecules so steep conc. gradient maintained.
Large number of carrier proteins within epithelial cell membranes- Increases surface area, allows diffusion of large molecules such as glucose, increased number increases rate of absorption
Increased numbers of mitochondria in epithelial cells- production of many ATP molecules
Glucose absorption
Sodium ions leave epithelial cell by active transport into blood.
Low sodium conc in cell creates gradient.
Sodium ions diffuse from lumen of ileum into epithelial cell using cotransport protein. Glucose is the molecule Na is cotransported with in this case.
Glucose enters blood via facilitated diffusion, down its conc gradient.