PHIS 206 Lecture Notes - Lecture 26: Brush Border, Microvillus, Maltose
2 May 2018
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Lecture 26: Absorption
Absorption
• Surface Area Boost
o Folds 3↓ increase
o Villi 10↓ increase
o Microvilli 20↓ increase
o Increases surface area by 600 essentially more opportunity for absorption
o Blood that leaves the gut goes to the liver first
• Each villus has arterial, venous, and lymphatic supply (the lacteal)
• Villus has cells that can secrete water and fluids and cells that absorb nutrients
• High turnover of cells on villus
• ”Brush Border” on microvilli has digestive enzymes and absorption machinery
• Bottom of villus/dip are more for secretion and the upper villus is more for absorption
since the food is more near the top
• Cells are at a constant state of turnover (new cells come at the bottom and push the
bottom cells up)
• Cancer drugs go after high turnover cells (like villi, cells that absorb)
Carbohydrates
• Overall Goal
o Break down large carbohydrates (polysaccharides) into simple sugars
(monosaccharides)
Carbohydrate Digestion I
• First Step
o Polysaccharides such as amylose, amylopectin, and glycogen
o
o disaccharide maltose
o through actions of salivary and pancreatic amylases
Carbohydrate Digestion II
• Final digestion
o Disaccharides maltose, lactose, and sucrose
o
o monosaccharides glucose, galactose, and fructose
o through actions of particular enzymes on the brush border of the microvilli
Carbohydrate Absorption I
• Absorption
o Absorption into the cell utilizes carrier proteins to cross lipid membrane of
enterocyte.
o For glucose and galactose, a Na+-dependent secondary active transport
mechanism is utilized.
o For fructose, a facilitated diffusion protein does the job.
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