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(3.3) Digestion & Absoprtion - Coggle Diagram
(3.3) Digestion & Absoprtion
Digestion
process in which large molecules are hydrolysed by enzymes into small molecules which can be absorbed & assimilated
Physical Breakdown
if food is large, broken into smaller pieces via teeth - makes it possible to ingest & increases surface area for chemical digestion
muscles in stomach wall contract to churn it, physically breaking it up
Chemical Digestion
hydrolyses large insoluble molecules -> small soluble molecules
via enzymes
carbohydrases
= carbohydrates -> monosaccharides
lipases
= lipids -> glycerol & fatty acids
proteases
= proteins -> amino acids
Carbohydrate Digestion
amylase
produced in mouth & pancreas
hydrolyses alternate glycosidic bonds -> maltose
maltase
produced in ileum lining
hydrolyses maltose -> alpha glucose
saliva contains
salivary amylase
hydrolyses starch in mouth -> maltose. contains mineral salts (maintains pH neutral) food enters stomach & acid denatures amylase. food enters small intestine mixes with pancreatic juice. contains
pancreatic amylase
hydrolyse remaining starch -> maltose. food pushed along ileum,
maltase
on CSM of epithelial cells, hydrolyses maltose -> alpha glucose
sucrase
hydrolyses single glycosidic bond in sucrose -> glucose & fructose
lactase
hydrolyses single glycosidic bond in lactose -> glucose & galactose
Lipid Digestion
lipases
produced in pancreas & hydrolyse ester bonds
triglycerides -> glycerol & fatty acids
emulsification
= lipids split up into
micelle
droplets by
bile salts
(produced by liver)
increases lipids SA to speed up lapses
Protein Digestion
peptidases
hydrolyse large, complex molecules
endopeptidases
= hydrolyse peptide bonds between amino acids in central region of protein -> peptide molecules
exopeptidases
= hydrolyse peptide bonds on terminal amino acids of peptide molecules formed by endopeptidases -> dipeptides & amino acids
dipeptidases
= hydrolyse bond between 2 amino acids (membrane bound to CSM of ileum's epithelial cells)
Structure of the Ileum
villi
= foldings of ileum wall, thin walls & network of blood capillaries (increase SA of ileum & increase absorption rate)
situated between lumen of intestines & blood/tissues of body
Adaptations of villi
increase SA for diffusion
thin walls = reduce diffusion distance
contain muscle & can move = as products are absorbed, new material replaces it (increases efficiency)
maintains diffusion gradients
well supplied with blood vessels = blood carries away absorbed molecules, maintains diffusion gradient
microvilli
= finger like projections on CSM of epithelial cells (further increase SA)
Absorption
Amino acids & Carbohydrates
Na+ out of epithelial cells (active transport) by
NaK Pump
into blood. takes place in protein carrier molecule in CSM of epithelial cells
maintains higher conc Na+ in lumen of intestine than inside epithelial cells
Na+ diffuse into epithelial cells down this conc gradient by co-transport protein in CSM. Na+ carry either amino acid/glucose into cell with them
amino acid/glucose pass into blood plasma by facilitated diffusion using another carrier
amino acids/glucose move against their own conc gradient using Na+ conc gradient = indirect form of active transport
Triglycerides
monoglycerides & FA still associated with bile salts from digestion =
micelles
form
micelles come into contact with epithelial cells of villi, break down & release monoglycerides & FA, they're non-polar & diffuse across CSM -> epithelial cells
monoglycerides & FA epithelial cells -> endoplasmic reticulum (form triglycerides)
triglycerides endoplasmic reticulum -> Golgi apparatus, associate with cholesterol & lipoproteins -> form chylomicrons
chylomicrons
= particles adapted for lipid transport
chylomicrons mover epithelial cells -> lymphatic capillaries (
lacteals
) via
exocytosis
-> bloodstream -> cells