HUBS192 Lecture 26 - Chemical Digestion Flashcards
what are the 3 main nutrients that undergo chemical digestion?
1) carbohydrates (sugars)
2) proteins
3) lipids (fats)
what are carbohydrates?
storage polysaccharides
e.g starch and glycogen
what are storage polysaccharides?
large complex chains of monosaccharides
-e.g glucose
what are the 3 types of disaccharides ingested from carbohydrates from the human diet?
1) sucrose
- glucose + fructose
2) lactose
- glucose + galactose
3) maltose
- glucose + glucose
what is sucrose?
glucose + fructose
what is lactose?
glucose + galactose
what is maltose?
glucose + glucose
are proteins a source of energy and if so/not what are they a source of?
no proteins are a source of amino acids
how many amino acids can be synthesised?
12 amino acids
what are the amino acids that can not be synthesised called?
essential amino acids
-must be acquired from the diet
what are the 2 sources of protein and what is the ratio of these 2 sources out of 100%?
- 50% diet
- 50% endogenous proteins
what are endogenous proteins?
proteins secreted into the intestine that are the digestive enzymes and the immunoglobulins
are lipids essential?
lipids are not essential
are lipids a source of energy?
lipids are an important source of energy
what do lipids contain in terms of vitamins?
fat soluble vitamins A,D, E and K
what is the function of lipids?
lipids slow down gastric emptying
what is the main component of lipids?
mainly triglycerides
what is a triglyceride?
glycerol back bone with 3 fatty acids attached
how many carbons are in a short fatty acid chain?
< 6 carbons
how many carbons are in a medium fatty acid chain?
6-12 carbons
how many carbons are in a long chain fatty acid?
12-24 carbons
why do we need chemical digestion?
because food is ingested in the form of large complex molecules and the nutrients from food can only be absorbed as small molecules, therefore, chemical digestion is required because it reduces the size of nutrients to allow them to be absorbed
where does chemical digestion occur?
occurs at the surface of food particles and utilises digestive enzymes
what are the monosaccharides in cellulose joined together by?
long chains of beta 1-4 glycosidic bonds
what are the names of the 2 stages of chemical digestion?
stage one = luminal digestion
stage two = contact digestion
what occurs in stage one of chemical digestion?
luminal digestion
- the initial digestion involving enzymes secreted into the lumen
- salivary glands –> salivary amylase
- stomach –> pepsin
- small intestine –> pancreatic enzymes (pancreatic amylase, trypsin, chymotrypsin, carboxypeptidase, lipase)
what occurs in stage two of chemical digestion?
contact digestion
- occurs in the small intestine
- completes digestion before absorption
- involves enzymes produced by enterocytes and attached to the brush border of enterocytes (lining the small intestine) –> sucrase, lactase and maltase
- disaccharides converted to monosaccharides
where does chemical digestion of proteins occur for luminal digestion?
- pepsin is secreted into the stomach
- trypsin, chymotrypsin , carboxypeptidase in the small intestine are secreted by the pancreas
what is the result of chemical digestion of proteins in luminal digestion?
converts proteins into polypeptides
what is the result of chemical digestion of proteins in contact digestion?
converts polypeptides into individual amino acids
what is the only stage of chemical digestion of lipids (fats)?
only luminal digestion, NO contact digestion
what are the enzymes involved with the chemical digestion of lipids?
pancreatic lipase is the main digestive enzyme but lingual lipase and gastric lipase have a minor role
why does lipid digestion require a more complex process?
because lipids (fats) are insoluble in water therefore the digestive enzymes can not be dissolved in the luminal fluid
what are the 4 stages of the chemical digestion of lipids (fats)?
1) emulsification
- motility
2) stabilisation
- bile salts
3) digestion (hydrolysis)
- enzymes
4) formation of micelles
- bile salts
what is the function of the emulsification stage of lipid (fat) digestion?
the motility breaks ups big lipid droplets into small droplets (0.5 - 1.0 um) and this increases the surface area for digestion
what are the 2 types of emulsification of lipids (fats) and where do each of these occur?
1) simple emulsion
- occurs in the stomach where the retropulsion motility pattern takes place
2) more complex emulsion
- where the bile salts stabilise the lipid droplets for a long period of time
where does stabilisation of lipids (fats) digestion occurs?
occurs in the small intestine
where are bile salts secreted by and where are they concentrated?
secreted by the liver and concentrated in the gallbladder
where are bile salts released and why?
released into the small intestine with the arrival of food
what is the composition of bile salts?
composed of a hydrophobic (water-hating) and a negatively charged hydrophilic side (water-loving)
what are the 2 functions of bile salts?
1) stabilise the emulsion in the small intestine
2) further increase the surface area of the emulsion droplets
where does the hydrolysis stage of lipid (fat) digestion occur?
occurs in the small intestine at the surface of emulsion droplets
what enzymes does the hydrolysis stage of lipid (fat) digestion) involve and where are these secreted from?
involves lipase and cofactor colipase that are both secreted by the pancreas
what is the function of colipase?
collapse anchors lipase to the surface of a emulsion droplet
what is the function of lipase?
lipase coverts triglycerides to monoglycerides and free fatty acids
what are the products of fat digestion that insoluble in water?
monoglycerides and long chain fatty acids
what is the function of the formation of micelles stage in lipid (fat) digestion?
to keep the product of fat digestion in solution through the formation of micelles
what are micelles?
micelles are small droplets (4-6 nm diameter) that consist of 20-30 molecules and contain:
- bile salts
- fatty acids
- monoglycerides
what does it mean that bile salts are amphipathic?
that the molecule has one side that is hydrophilic and one side that is hydrophobic
