Lecture 50: Digestion & Absorption of Carbs & Protein Flashcards
Name the two paths for absorption and briefly describe each path.
Transcellular- cross luminal membrane into the cell (via passive diffusion or a transporter
Paracellular- move across tight junctions BETWEEN cells
Villi line the lumen of the small intestine. What is their purpose?
Increase surface area (villi longest in the duodenum, shortest in the ileum)
**Surface of the epithelial cells are lined with microvilli= brush border
the turnover rate of epithelial cells in the small intestine is how long?
3-6 days, one of the fastest rates in the whole body
_______ is the primary source of energy for most cells.
Glucose
Either injest in the diet, make from precursors, or convert it from other metabolites
What are the 4 enzymes that digest carbohydrates? Name them and give a brief description of each.
1) a-amylase: all mammals make, it cleaves the internal linkages of amylose (1,4- glycosidic bonds)
2) Glucoamylase: cleaves linear or branched portions of amylose or glycogen
3) a- dextrinase: for oligosaccharides, brush border enzyme
4) Maltase: specific for cleaving maltose, brush border enzyme
What are the 3 monosaccharides that can be absorbed?
glucose
galactose
fructose
How are glucose and galactose transported from the intestinal lumen into the enterocyte? What is the specific name of the transporter?
Na+-dependent co-transport for glucose and galactose
SGLT 1 is a Na+/glucose co-transporter that transports both glucose and galactose into the cell
How is fructose transported from the intestinal lumen into the enterocyte? What is the specific name of the transporter?
Facilitated diffusion is used for transporting fructose from intestinal lumen into enterocyte
GLUT-5: fructose specific transporter
How are fructose, glucose, and galactose transported from the enterocyte into the blood??
Facilitated diffusion using the GLUT 2 transporter
What happens if there is a failure to digest carbohydrates to their absorbable forms?
Carbs will remain in the lumen and “hold” water to remain isosmotic, this leads to osmotic diarrhea
Name the 10 essential amino acids and which species require them in their diet
Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
Methionine
Histidine
Arginine
Leucine
Lysine
Doga, cats, chickens and pigs require in the diet
Digestion of protein is ultimately completed by _________ and ___________.
endopeptidases
exopeptidases
Explain the beginning of the protein digestion process in the stomach.
- Pepsinogen is activated to pepsin (endopeptidase) which hydrolyses interior bonds
- HCl causes protein to unfold and expose peptide bonds to pepsin
What is an essential enzyme produced by young ruminants that coagulates milk?
Rennin
Don’t confuse with Renin
Which enzyme will cleave bonds of oligosaccharides released from starch?
A) a-amylase
B) Maltase
C) a-dextrinase
a-dextrinase
***Oligosaccharides is another name for dextrins
Amino acids move across the basolateral membrane via what type of transport?
Facilitated diffusion
