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3.3 digestion and absorption - Coggle Diagram
3.3 digestion and absorption
lesson 1: digestive system
function
to hydrolyse large insoluble molecules into small soluble molecules and absorb these into the blood/lymph
digestion
physical digestion
breaking down food into smaller pieces e.g chewing by teeth/churning by stomach. increases surface area for chemical digestion by enzymes
chemical digestion
hydrolysis of large insoluble molecules into smaller soluble molecules catalysed by digestive enzymes
digestive enzymes
large biological molecules (mostly polymers) are progressively hydrolysed to their monomers: this may be in several stages (polymers to dimers to monomers)
carbohydrases
hydrolyse carbohydrates to (ultimately monosaccharides)
peptidases
hydrolyses proteins (polypeptides) to ultimately amino acids
lipases
hydrolyse lipids (triglycerides) to fatty acids and monoglycerides
key words
ingestion
taking food into the body
egestion
getting rid of undigested food
excretion
getting rid of waste products from metabolic reactions
assimilation
incorporation of products of digestion into larger molecules that are part of the body e.g amino acids used for protein synthesis
structure
mouth (chews food- physical digestion)
salivary glands (produce amylase)
tongue (helps chew food)
epiglottis
oesophagus
liver (produces bile salts)
stomach (contains hydrochloric acid, breaks down food and maintains optiumum pH for exopeptidases)
gall bladder (stores bile to raise pH before entering small intestine)
pancreas (produces digestive enzymes)
small intestine made of duodenum and ileum (further hydrolyses food molecules and site of absorption into blood)
large intestine made of colon and rectum (absorbs water and vitamins, propels faeces towards rectum)
appendix
anus
lesson 2: digestive enzymes
biological molecules structure (recap from topic 1)
starch
polysaccharide made of glucose, contains 1,4 and 1,6 glycosidic bonds, can be branched or unbranched - branched has more ends for carbohydrases to act on
polypeptides
primary structure (sequence of amino acids in polypeptide chain), secondary structure (alpha helix hydrogen bonds), tertiary structure (3D specific shape maintained by hydrogen disulphide and ionic bonds between amino acid R groups)
triglycerides
1 glycerol and 3 fatty acids, contain ester bonds, fatty acids can be saturated or unsaturated
digestion of carbohydrates by carbohydrases
starch + (amylase) --> maltose + (maltase) --> glucose
starch is hydrolysed by amylase (breaks glycosidic bonds) which is produced in the salivary glands and the pancreas (not membrane bound) this produces maltose
maltose is then hydrolysed by maltase (breaks glycosidic bonds) which is produced in the pancreas (membrane bound in epithelium of ileum) this produces glucose
begins in the mouth continues in the duodenum completed in the ileum
digestion of polypeptides by peptidases
polypeptide + (endopeptidase) --> shorter polypeptide + (exopeptidases) --> dipeptide + (dipeptidase) --> single amino aicds
long polypeptide chain is hydrolysed by endopeptidase which are produced in the stomach and pancreas-not membrane bound (peptide bonds between amino acids in the middle of the polypeptide chain are broken) producing shorter polypeptide chains
shorter polypeptide chains are hydrolysed by exopeptidase which are produced in the pancreas- not membrane bound (peptide bonds on the terminal (end) amino acids are hydrolysed) producing dipeptides
dipeptides are hydrolysed by dipeptidases which break the peptide bond between the amino acids producing single amino acids
starts in the stomach continues in the duodenum fully digested in the ileum
digesttion of lipids/triglycerides by lipases
triglycerides are hydrolysed by lipase which is produced in the pancreas - not membrane bound (hydrolyse the ester bonds in the triglyceride) producing 2 fatty acids and a monoglyceride
triglyceride + (lipase) --> monoglyceride + 2 fatty acids
action of bile salts (produced in the liver) they emulsify lipids/triglycerides to form micelles which increase surface area for lipase to act on
lesson 3: bile salts and adaptations of the ileum
bile salts
salts produced by the liver as part of a mixture called bile, they emulsify large lipid globules into smaller droplets which increases the surface area for chemical digestion of lipids by lipase
adaptations
villi and microvilli: increases surface area, diffusion rate is faster
capillary network: carries products of digestion away which maintains concentration gradient, speeds up diffusion
epithelium is 1 cell thick: short diffusion distance
muscles to mix food in the ileum: maintains concentration gradient
epithelial cells with many mitochondria to make ATP for active transport of glucose and other products of digestion
epithelial cells many transport proteins in cell surface membrane for facilitated diffusion and active transport of glucose and other products of digestion
lesson 4: digestion absorption and transport of lipids
micelles
carry glycerol, fatty acids and monoglycerides to membrane of intestinal epithelial cell
chylomicron
triglycerides contained in lipoprotein outer layer
triglycerides - hydrophobic core
lipoprotien = hydrophobic outer layer
process
1) bile salts emulsify lipid globules forming small lipid droplets
2) lipase hydrolyses lipids into fatty acids and a monoglyceride
3) fatty acids and monoglycerides associate with bile salts and form micelles (increased solubility in water)
4) micelles transport fatty acids and monoglycerides to cell surface membrane of epithelial cells and break down releasing fatty acids and monoglycerides
5) fatty acids and monoglycerides diffuse across the cell surface membrane into the epithelial cells
6) in the endoplasmic reticulum fatty acids and monoglycerides are recombined to make triglycerides
7) in the golgi apparatus triglycerides are modified and combined with lipoproteins and phospholipids to form chylomicron then packaged into vesicles
8) chylomicrons are released out of the cell by exocytosis
9)chylomicrons diffuse into lacteal/lymph capillary found at the centre of each villus
10) chylomicrons are transported in the lymph system until they enter the blood stream
11) chylomicrons travel in the bloodstream until they reach tissues where the triglycerides are needed, they then break down to release triglycerides
12) lipases in the cell surface membranes of endothelial cells hydrolyse triglycerides into fatty acids and monoglycerides
fatty acids and monoglycerides diffuse across endothelial cells and into other tissues
lesson 5: co transport of amino acids/glucose
1) sodium ions actively transported out of epithelial cell via sodium potassium pump to lower the sodium concentration, increase concentration gradient
2) much higher concentration of sodium ions in the lumen of the ileum than the epithelial cells
3) sodium ions diffuse into epithelial cells down concentration gradient via carrier protein, as the sodium ions diffuse through they carry amino acids/glucose into the cell with them
4) glucose/amino acids pass into the blood plasma via facilitated diffusion down the concentration gradient