Nutrient Digestion - Carbohydrates, Proteins, Fats, Vitamins and Minerals Flashcards
What are the only three sugars that can be taken up across the gut epithelia?
Monosaccharides - glucose, galactose and fructose
What bonds are broken between disaccharide monomers to form simpler molecules?
Glycosidic
Disaccharides are broken down to their constituent monomers through the use of what?
Brush border enzymes
What are the three dietary disaccharides and their constituent monomers?
Lactose - glucose and galactose
Sucrose - glucose and fructose
Maltose - glucose monomers
What are the enzymes responsible for breaking down disaccharides into their constituent monomers?
Lactase breaks down lactose
Sucrase breaks down sucrose
Maltase breaks down maltose
The alpha-1,4-glycosidic bonds between the glucose monomers of starch are broken down by what?
The bonds are hydrolysed by amylases in saliva and in the pancreas
Why can’t animals break down cellulose?
The beta-1,4-glycosidic bonds between the glucose monomers of cellulose can only be broken down by cellulase, which is an enzyme that no animals have the capability to express
What breaks down glycogen?
Alpha-amylase
What are the three mechanisms through which monosaccharides are absorbed across intestinal epithelial cells?
Transcellular
Paracellular
Vectorial Transport
What is the route that most nutrients will take when absorbed across intestinal epithelial cells?
Transcellular - lipid soluble molecules which can cross apical and basolateral membranes
What route of absorption across intestinal epithelial cells involves molecules of the right shape and size crossing through the tight junctions between epithelial cells?
Paracellular
What transport mechanism is used for water soluble molecules which cannot transport across the lipid membrane?
Vectorial transport
What transport mechanism involves the use of transporter proteins?
Vectorial transport
What are peptides?
Polymers of amino acids, 3-10 amino acids in length
Polymers of amino acids in chains with a length of 10 or more amino acids are what?
Proteins
What bonds need to be hydrolysed between proteins in order to convert them to peptides and amino acids for digestion?
Peptide
What enzymes hydrolyse peptide bonds?
Proteases and peptidases
Where do endopeptidases act?
Somewhere in the middle of the protein
Where do exopeptidases act?
Only on the terminal amino acids of a protein, removing amino acids one at a time
How are amino acids and small peptides absorbed across gut epithelia?
Transported in/out by a pump
What does the SAAT1 pump do?
Binds to a sodium molecule and an amino acid at the apical membrane and pumps both into the cell
The movement of sodium through the cell and the ion gradient it creates causes what?
The movement of water in the same direction as sodium, through the tight junctions
What is PepT1?
A protein coupled transporter which transports dipeptides and tripeptides as well as a hydrogen ion into the cell
What can penicillin transport into the gut epithelial cells?
Tripeptides
Almost all fat is ingested in the form of
triacylgylcerol
What is triacylglycerol broken into during digestion?
Monoglyceride and fatty acids
All fat digestion takes place _ through the use of _
in the small intestine
through the use of pancreatic lipase
What will happen when pancreatic lipase is digesting triaclyglycerols which are present as large lipid droplets?
Pancreatic lipase is water soluble but not lipid soluble so can only work on the outer surface of the lipid droplet, it will therefore be unable to digest all the fat
What is the name for fat in stools?
Steatorrhoea
What does emulsification of ingested fats do?
Divides large lipid droplets (triaclyglycerols) into smaller droplets, increasing surface area available to pancreatic lipase and making fat digestion more manageable
What three things does emulsification require?
Mechanical disruption
Smooth muscle contraction
An emulsifying agent
What is the purpose of an emulsifying agent?
To stop the reformation of smaller lipid droplets into large lipid droplets
What is the purpose of bile salts and phospholipids in fat digestion?
Both prevent the re-formation of small droplets of fat produced by emulsification into larger droplets
Bile salts and phospholipids are secreted in
bile
What feature of bile salts and phospholipids makes them effective at preventing the reformation of large lipid droplets?
They are amphipathic - non-polar portions associate with non-polar interior of the droplet leaving the polar portions exposed at the surface which repel other small lipid droplets
What are the components of micelles?
Bile salt
Monoglyceride
Fatty acids
Phospholipids
What is the purpose of micelles in fat digestion?
Enhance fat absorption by taking fat molecule to the microvilli of the epithelia for absorption
What happens once fatty acids and monoglycerides enter the smooth ER after entering epithelial cells?
They are reformed into triacylglycerol droplets which are emulsified
What are the fat soluble vitamins?
A, D, E and K
What are the water soluble vitamins and how are they absorbed?
B group, C and folic acid
Absorbed by passive diffusion or carrier-mediated transport
How is vitamin B12 absorbed?
It binds to an intrinsic factor in the stomach to form a complex which is absorbed via a specific transport mechanism in the distal ileum
What does a vitamin B12 deficiency cause?
Pernicious anaemia
What percentage of daily ingested iron is absorbed across the intestine into the blood?
10%
Iron ions are incorporated into what, in order to be stored intracellularly?
Ferritin
For how long does iron stay bound in ferritin?
Until the cell containing the ferritin dies, at which point the iron is expelled from the body
What happens to unbound iron?
It is transported across the serous membrane where it binds to transferrin and is taken to the liver for storage
What 3 pairs of glands secrete saliva?
Parotid
Submandibular
Sublingual
What are the components of saliva?
Water Mucins Alpha-amylase Electrolytes Lysozyme
What are the functions of water in saliva?
Softens, moistens and dilutes particles
What is the function of mucins in saliva?
To combine with water to form mucous which acts as a lubricant
What is the function of alpha-amylase in the saliva?
Catalyses the breakdown of polysaccharides into disaccharides + glucose
What is the function of electrolytes in the saliva?
Control the tonicity and pH
What is the function of lysozyme in the saliva?
Bacteriocidal - cleaves the polysaccharide component of any bacterial cell wall ingested
