26 Flashcards
Epithelial cells (Enterocytes) in the small intestine make
digestive enzymes : True or False?
True - not nearly as many as the pancreas tho
Main nutrients that undergo chemical digestion
- Carbohydrates (Sugars)
- Proteins
- Lipids (Fats)
What are carbohydrates ?
- important source of energy
- 250-800mg per day in a western diet
- storage poly sac arises
- large complex chains of monosaccharides (glucose is a monosaccharide)
Most common source of carbohydrates
Starch (plants)
- also glycogen (a carbohydrate in itself - can breakdown into glucose)
Composition of ingested carbohydrates - starch and glycogen
- long chains of glucose joined by α 1-4 glycosidic bonds
(α amylose can digest it - enzyme specifically snips that bond)
Examples of disaccharides injested and their compositions
- sucrose
- glucose and fructose
- lactase
- glucose and galactose
- maltose
- glucose and glucose
We invest a limited amount of which monsaccaride?
Glucose
Structure of sucrose
Strucutre of glucose
How many grams per day of protein do we invest in out food
Ingest 70-100 g per day of proteins in food
Proteins are not normally a source of energy
Ya
Pre it’s are required for
Amino acids
How many amino acids can/ cant be synthesised
12 can by synthesised - non esential
Others cannot be synthesised
Sources of protein
- 50% diet
- 50% endogenous proteins
- recycled and taken back into body
- secreted into intestine
- enzymes
- imunoglibns
Ingested proteins are
Long chains of amino acids linked by polypeptide bonds
How many grams of lipids per day
100 – 150g per day
What do ingested lipids provide (non-essential)
- Important source of energy
- Fat soluble vitamins A, D, E & K
- Slow gastric emptying
Of the lipids in our body.. they are mainly
triglycerides
- Glycerol back bone with 3 fatty acids attached
Fatty acids have _____ chain lengths
Variable
Classifications of the variable chain length
- short chain fatty acids < 6 carbons
- medium chain fatty acids - 6 to 12 carbons
- long chain fatty acids - 12 - 24 carbons
Why do we need chemical digestion?
We Ingest nutrients in form of large complex molecules
- Carbohydrates
- Proteins
- Lipids
We can only absorb nutrients as small molecules
Chemical digestion reduced the size of nutrients to allow them to be absorbed
Unitised digestive enzymes
Why is mechanical digestion needed before chemical digestion
- chemical digestion occurs at the surface of food particles
- Mechanical digestion breaks up food increases surface area
available for chemical digestion
- Mechanical digestion breaks up food increases surface area
Is there a large amount of cellulose in diet
Yes
What is cellulose - what is its structure and how does it differ from simple starch
- Structural polysaccharide of plants
- Long chains of β 1- 4 glycosidic bonds
Two stages of chemical digestions
- luminal digestion
- contact digestion
Optimal pH of salivary enzymes
Alkaline
Optimal pH of gastric enzymes
Acidic
Optimal ph of small intestinal enzymes
Alkaline
Luminal digestion
Initial digestion involving enzymes secreted into lumen
- Salivary glands – salivary amylase
- Stomach – pepsin
- Small intestine – Pancreatic enzymes
- Pancreatic amylase, trypsin, chymotrypsin, carboxypeptidase,
lipase
Contact digestion
- In small intestine
- Completes digestion before absorption
- Involves enzymes produced by enterocytes and attached to brushborder of enterocytes
Chemical digestion of carbohydrates - luminal
- Salivary and pancreatic amylase
- Polysaccharides converted to oligosaccharides and disaccharides
Chemical digestion of carbohydrates - contact digestion
- Contact digestion - brush border - disaccharidases
- Disaccharides converted to monosaccharides
- Involves the enzymes
- Sucrase, lactase, maltase and others
- Bound to brushborder
Chemical digestion of protein - luminal digestion
- Pepsin in stomach
- Precursor pepsinogen secreted by chief cells
- Trypsin and chymotrypsin (Peptide bonds) small intestine
- Carboxypeptidase (COOH terminus) small intestine
- Secreted by pancreas
- Converts proteins into polypeptides
Chemical digestion of proteins - contact digestions
- Involves peptidases
- Many types attached to brush border
- Convert polypeptides into individual amino acids
Chemical digestion of lipids - features
Occurs in lumen of small intestine
- NO contact digestion
- Pancreatic lipase main digestive enzyme
- Lingual lipase and gastric lipase have minor role
The problem with lipid digestion
- Digestive enzymes that break down lipids dissolved in aquious luminal fluid
- No problem for carbohydrates and proteins (they are Soluble in water)
- Lipids (fats) insoluble in water
- Requires a more complex process
4 stages of chemical digestion for fats
Emulsification
- motility
Stabilisation
- bile salts
Digestion (hydrolyisis)
- enzymes
Formation of micelles
- bile salts
Emulsification - The 1st stage of fat digestion -what happens and where
Motility breaks up lipid droplets into small droplets
- Forms and emulsion
- Droplets 0.5 -1.0 µm
- Increases surface area for digestion
Occurs in
- stomach - retropulsion
- simple emulsion
- small intestine - segmentation
- more complex emulation
- bile salts stabilise droplets
Stabilization - The 2nd stage of fat digestion - where does it occur - what helps it
- Occurs in small intestine
- Bile salt
Stabilization - The 2nd stage of fat digestion
Bile salts
- what are they secreted by
- when are they released
- what is their properties
- what do they do in emulsion?
- Secreted by liver & concentrated in gallbladder
- Released into small intestine with arrival of food
- Have a hydrophobic (water hating) and a negatively charged hydrophilic side (water loving)
- Stabilize the emulsion in small intestine Also reduce the size of the emulsion droplets
- Further increase in surface area
Hydrolysis - the 3rd stage of lipid digestion - where does it occur? What enzyme does it involve? What does the enzyme convert it too?
- occurs in small instestine at the surface of emulsion droplets
- involves lipase and cofactor - colipase
- both secreted by pancreas
- colipase anchors lipase to surface of droplet
- lipase converts triglycerides to
- monoglyceride
- free fatty acids
Formation of micelles the 4th stage of fat digestion
- Products of fat digestion are insoluble in water, especially
- Monoglycerides
- Long chain fatty acids
- Kept in solution through formation of micelles
- Micelles are
- Small droplets (4-6 nm diameter)
- Consist of 20-30 molecules
- Bile salts
- Amphipathic
- Fatty acids
- Monoglycerides
- Bile salts
