L10 - Dig and abs of carb and protein Flashcards
What are the different dietary carbohydrates?
- Monosaccharides (monomers)
- Oligosaccharides (short polymers)
- Polysaccharides (long polymers)
What can/can’t the small intestine directly absorb?
- Can directly abs monomers (monosaccharides)
- Cant directly abs polymers
Where is dietary fibre primarily present in?
Primarily present in fruits, vegetables and cereals
Which forms of fibre does dietary fibre contain?
Insoluble and soluble forms of fibre
What are some characteristics of insoluble fibre?
- Non-water soluble
- Not easily fermented
- Cellulose and hemicellulose
- Aids the digestive system and ease elimination
What are some characteristics of soluble fibre?
- Water soluble
- Pectins, gums and mucilage
- Easily digested by bacteria in the colon
Examples of soluble fibre?
- Oat bran
- Barley
- Nuts
- Seeds
- Beans
Examples of insoluble fibre?
- Corn
- Kidney beans
- Turnips
- Green beans
What is starch?
A storage form for carbohydrates that is primarily found in plants
What does starch consist of?
Amylose and amylopectin
What is the linkage in amylose?
a-1,4 linkages
What is the linkage in amylopectin?
a-1,4 and a-1,6 linkages
What is the linkage in glycogen?
a-1,4 and a-1,6 linkages but more highly branched
What is amylose?
A straight chain glc polymer that typically contains multiple glc residues
What is amylopectin?
A branched glc polymer
Approx percentage of dietary carbohydrates that are disaccharides?
30%-40%
Approx percentage of dietary carbohydrates that are polysaccharides? (in the form of starch)
45%-60%
Example of disaccharides?
- Sucrose
- Lactose
- Maltose
Example of monosaccharides?
- Glucose
- Fructose
- Galactose
Examples of polysaccharides?
- Glycogen
- Starch
- Cellulose (structural)
- Chitin (structural)
Approx percentage of dietary carbohydrates that are monosacchardies?
5%-10%
Which monosaccharides join to form lactose (disaccharide)?
Glucose + Galactose
Which monosaccharides join to form maltose (disaccharide)?
Glucose + Glucose
Which monosaccharides join to form sucrose (disaccharide)?
Glucose + Fructose
What happens in the first step of the digestive process for dietary carbohydrates?
- Action of salivary amylase and pancreatic amylase
- Salivary and pancreatic acinar cells synthesise and secrete active a amylases
- Salivary amylase in the mouth initiates starch digestion, inactivated by gastric acid
- Pancreatic a amylase (which is induced by CCK) completes starch digestion in the lumen on the SI
What happens in the second step of the digestive process for dietary carbohydrates?
- Hydrolysis of oligosacc/ disacc to monosacc by brush-border hydrolytic enzymes
- Human SI has membrane proteins: lactase, maltase and sucrase-isomaltase (two enzymes - sucrase and isomaltase)
- Lactase breaks down lactose into glc and galactose
- Isomaltase breaks bonds which cannot be broken by amylase or maltase
What are the two steps of the digestive process for dietary carbohydrates?
- Intraluminal hydrolysis - of starch to oligosacc by salivary and pancreatic amylases
- Membrane digestion - of oligosacc to monosacc by brush-border disacc
What’s the action of sucrase?
- Cleaves the terminal a-1,4 linkages of maltose, maltotriose and a-limit dextrins
- Can split sucrose into glc and frc
What’s the action of maltase?
- Cleaves the terminal a-1,4 linkages of maltose, maltotriose and a-limit dextrins
- Can degrade the a-1,4 linkages in straight chain oligosacc to yield glc
What’s the action of isomaltase?
- Cleaves the terminal a-1,4 linkages of maltose, maltotriose and a-limit dextrins
- The only enzyme that can split the branching a-1,6 linkages of a-limit dextrins
Where does peak oligosacc dist and activity occur?
The proximal jejunum
- Considerably less activity in the duodenum and distal ileum
- None in LI
How are glc, galactose and frc absorbed by the SI?
Two step process:
- Uptake across the apical membrane into the epithelial cell
- Exit across the basolateral membrane
What is a-limit dextrin?
A short chain branched amylopectin remnant, prod by hydrolysis of amylopectin with a-amylase
What are the 4 major pathways that dig-abs can occur?
- Luminal proteases from stomach/ pancrase hydrolyse proteins to peptides and to aa, which are then abs
- Luminal proteases digest proteins to peptides, but enzymes present at the brush border digest the peptides to aa, which are then aa
- Luminal enzymes digset proteins to peptides, taken up as oligopeptides by enterocytes. Furhter dig of oligopeptides by cytosolic enzymes yields intracellular aa, moved by transporters across the basolateral memb into the blood
- Luminal enzumes digest dietary proteins to oligopeptides, which are taken up by enterocytes and moved directly into the blood
What are the 5 pancreatic enzymes that participate in protein digestion (but secreted as inactive proenzymes)
- Trypsinogen
- Chymotrypsinogen
- Proelastase
- Procarboxypeptidase A
- Procarboxypeptidase B
What is the activating agent for trypsinogen and what is its active form?
Act agent = Enterokinase
Act form = Trypsin
What is the activating agent for chymotrypsinogen and what is its active form?
Act agent = Trypsin
Act form = Chymotrypsin
What is the activating agent for proelastase and what is its active form?
Act agent = Trypsin
Act form = Elastase
What is the activating agent for procarboxypeptidase A and what is its active form?
Act agent = Trypsin
Act form = Carboxypeptidase A
What is the activating agent for procarboxypeptidase B and what is its active form?
Act agent = Trypsin
Act form = Carboxypeptidase B
