Nutrient Digestion and Absorption of Carbohydrates and Proteins Flashcards
List the principle dietary constituents.
- carbohydrates
- proteins
- fats
- vitamins
- minerals
- water
True or False.
The body can absorb disaccharides.
False.
The body can only absorb monosaccharides.
Name three monosaccharides.
- glucose
- fructose
- galactose
How are disaccharides absorbed?
- brush border enzymes break down the glycosidic bonds
What will happen if disaccharides are not broken down?
- they will affect the osmotic relationship
- This will make water move into the lumen
- thus causing diarrhoea
What are the break-down products of lactose and which enzyme catalyses the reaction?
- glucose and galactose
- catalysed by lactase
What are the break-down products of sucrose and which enzyme catalyses the reaction?
- glucose and fructose
- catalysed by sucrase
What are the break-down products of maltose and which enzymes catalyses the reaction?
- glucose and glucose
- catalysed by maltase
Name three polysaccharides.
- Starch
- Cellulose
- Glycogen
What is starch composed of?
- glucose monomers linked by alpha-1,4-glycosidic bonds
What is cellulose composed of?
- glucose monomers linked by beta-1,4-glycosidic bonds
What is glycogen composed of?
- glucose monomers linked by alpha-1,4-glycosidic bonds
What lines the lumen of the intestines?
- villi, each containing microvilli
What separates the epical membranes of the villi and the basolateral membranes of the microvilli?
- a tight junctional complex
- attachment proteins
How many transport proteins would a polar molecule need to pass from the lumen into the bloodstream?
- A minimum of two
Describe the absorption of glucose.
- glucose accumulates until the blood glucose concentration exceeds 5mmol/L
- passes through the sodium-coupled glucose transporter 1 (SGLT1)
- then is transported through the basolateral membrane by GLUT-2
What two carbohydrates pass through the SGLT1 transporter?
- glucose
- galactose
Describe how fructose is absorbed.
- via the GLUT-5 transporter in the epical membrane
- via the GLUT-2 transporter in the basolateral membrane
What is the action of enzymes on proteins for digestion?
They hydrolyse the peptide bonds and reduce proteins to amino acids.
Name the two types of peptidase.
- endopeptidase
- exopeptidase
Explain the difference between endopeptidase and exopeptidase.
Endopeptidase - hydrolyses the peptide bonds in the middle of the chain
Exopeptidase - can only hydrolyse the terminal groups of the chain
Describe the absorption of amino acids.
- they are transported through the sodium amino acid transporter (SAAT1) at the epical membrane
- the amino acids then must travel through another transporter on the basolateral membrane
True or False.
70% of protein uptake is in amino acid form.
False.
70% of protein uptake is in dipeptide or tripeptide form.
Describe the absorption of dipeptides.
- the peptide must couple with hydrogen
- travels through the PepT1 transporter
- the peptide travels through an unknown transporter in the basolateral membrane
What happens to the hydrogen absorbed during the absorption of dipeptides?
- the hydrogen is transported out via NHE3 transporter
- it is released into the acid microclimate which exists around the microvilli
- the low pH attracts the hydrogen to keep it near the microvilli
