Lecture 50-Digestion And Absorption Of Carbohydrates And Proteins Flashcards
Define digestion
Chemical and mechanical breakdown of ingested food into absorbable molecules
Define absorption
Movement of macronutrients, water, electrolytes from intestinal lumen into blood
What are the two paths for absorption?
Transcellular (cross luminal membrane into cell transporter)
Paracellular (moving across tight junctions between cells)
For transcellular absoprtion how do cells cross the luminal membrane into cell?
Passive diffusion
What is the turnover rate for epithelial cells?
Every 3 to 6 days
One of the highest turnover rates
What is the surface of epithelial cells lined with?
Microvilli
Brush border
What are the villi lined with?
Epithelial cells and goblet cells
Where is the vili the longest? Shortest?
Duodenum
Ileum
What is the function goblet cells?
Secrete mucous
What lines the lumen of small intestine
Villi
What are the folds of Kerckring?
Structure of intestinal mucosa
Folds are large circular folds
Increase SA and slow movement of digesta
What is the primary source of energy for most cells?
Glucose
How is glucose supplied in diet?
Monosaccharide
Disaccharide
Polysaccharide
Which species do not have an enzyme made to digest cellulose?
Horse, cattle, sheep
What must all ingested carbohydrates first be for absoprtion by enterocytes?
Monosaccharides
How does digestion of carbohydrates begin?
Begin by enzymatic cleavage and ultimate release of ologiosaccahradies etc.
What does glucoamylase (AKA amyloglucosidase) cleave?
Linear or branched portions of amylase or glycogen
What does alpha-amylase in salivary glands and pancreas cleave?
Internal linkages of amylose
What are the four brush border enzymes?
Maltase
Alpha-dextrinase
Sucrase
Lactase
What monosaccharides for absorption?
Glucose
Galactose
Fructose
What is special about cellulose, hemicellulose?
No mammalian enzyme for digesting these
Need microbial enzymes to digest
What is SGLT 1? What does it transport?
SGLT 1 is a Na+/glucose co-transporter
Transports both glucose and galactose
What is used for transporting fructose from intestinal lumen into enterocyte?
Facilitated diffusion
Which transporter is fructose-specific?
GLUT 5
What is used for transporting glucose, galactose, and fructose from enterocyte into blood?
GLUT 2
what is the transporter that goes from intestinal lumen into the enterocyte?
Na-dependent co-transport for glucose and galactose
What is lactose intolerance?
A lactase deficiency
What leads to osmotic diarrhea?
Remain in lumen and “hold” water to remain Isosmotic
Which species have dietary requirements for essential amino acids?
Dogs, horses, cat, chickens, pigs
Which species have dietary protein requirement?
Cattle, goat, sheep
In what form are amino acids usually provided?
Protein
How must proteins be digested?
Via enzymes (general term: proteases)
What are the digestion of proteins ultimately completed by?
Endopeptidases and exopeptidases
Where does protein digestion begin?
Stomach
What is activated to pepsin? This hydrolyzes interior bonds
Pepsinogen
What causes protein to unfold and exposes peptide bonds to pepsin
HCl
Young ruminants have chief cells that produce ______.
Rennin
What does rennin do?
Enzyme coagulates milk
At what pH is pepsin activated?
Low pH
When digesting proteins in the small intestine, what are used as proteases?
Pancreatic and brush border
As digesta enters SI, CCK is released which causes the release of ________/
Zymogens (inactive enzyme)
What is trypsinogen activated by to form trypsin?
Enterokinase
Where is enterokinase found?
On the brush border
What does trypsin activate?
Other zygmogens
What are three endopeptidases:
trypsin, chymotrypsin, elastase
What do exopeptidases act on?
Act on carboxyl end of proteins
What is the final digestion step in the SI?
Aminopeptidases at the brush border
Release either single AA or dipeptides/tripeptides
What can absorb amino acids, dipeptodes and tripeptides?
Enterocyte
How do amino acids move across the basolateral membrane ?
Facilitated diffusion
What are proteins products of digestion?
Amino Acids
Dipeptides
Tripeptides
Where are proteins absorbed?
Small intestine
What mechanisms are associated with proteins?
Na+ amino acid cotransport
H dipeptide cotransport
H tripeptides cotransport
What are carbohydrates products of digestion?
Glucose
Galactose
Fructose
Where is the site of absoprtion for carbohydrates?
Small intestine
What mechanisms are associated with carbohydrates?
Na glucose cotransport
Na galactose cotransport
Facilitated diffusion
What are lipids products of digestion?
Fatty acids
Monoglycerides
Cholesterol
Where are lipids absorbed?
Small intestine
Where are bile salts absorbed?
Ileum
What are three general disorders do protein digestion and absorption?
Pancreatitis
Exocrine pancreatic insufficiency
Cystinuria
What is cystinuria?
Defect or absence of Na/amino acid co-transporter
Can contribute to crystal formation and calculus, leading to urinary blockages
What is exocrine pancreatic insufficiency?
Insufficient production and secretion of digestive enzymes
Destruction of cells producing enzymes
Lack of digestion, malabsorption, weight loss, nutrient deficiencies
What can prematurely activated enzymes lead to?
Local damage of exocrine pancreas
edema, inflammation
What does pancreatitis cause?
Deficiency of pancreatic enzymes and fluid in initial stages
An increase in steroid hormones, increase glucose and circulating TG (associated with inflammation of pancreas)
