Lecture 6: Digestion and Reabsorption of Carbs and Lipids Flashcards
What are the two paths for absorption of carbohydrates and proteins
Transcellular
Paracellular
Transverse folds of intestinal mucosa
Folds are large circular folds of mucosa
Folds of Kerckring
Villi line
Lumen of small intestine
Villi are lined by what kind of cells
Epithelial cells and goblet cells
What do goblet cells secrete?
Mucus
Where are villi longest and shortest?
Longest in duodenum
Shortest in terminus of ileum
What form the brush border?
The surface of epithelial cells lined with microvilli
Folds + villi =
Microvilli
What fold is SA increased by microvilli
600
What is turnover rate of epithelial cells
Every 3-6 days
Natural diet of horse, cattle, sheep
Grass
Grass is high in
Cellulose
Grain is high in
Starch
Chicken and pigs usually fed diets high in
Starch
Dogs are classified as
Omnivores
What diet do dogs do well on?
Diets of starch + soluble fibers
What is the primary source of energy for most cells?
Glucose
Monosaccharides definition
Simple sugars
Glucose, fructose, galactose, ribose are examples of
Monosaccharides
Sucrose, maltose, lactose are examples of
Disaccharides
Disaccharides definition
2 monosaccharides
Polysaccharides definition
Complex chains of sugars
Starch, cellulose, glycogen, hemicellulose are examples of
Polysaccharides
All ingested carbs must be digested to what for absorption?
Monosaccharides
What absorbs monosaccharides?
Enterocytes
How does digestion of carbohydrates begin?
Enzymatic cleavage makes chains shorter
What cleaves internal linkages of amylose (alpha 1,4 glycosidic bonds) in starch digestion?
Alpha-amylase
What cleaves linear or branched portions of amylose or glycogen in starch digestion?
Glucoamylase
In starch digestion, what is used to digest oligosaccharides? AKA Brush border enzyme
Alpha-dextrinase
What are the brush border enzymes in starch digestion?
Alpha-dextrinase, maltase, sucrase, lactase
What does maltase (brush border enzyme) do in starch digestion?
Converts maltose to 2 glucose units
What are the monosaccharides for absorption?*
Glucose, galactose, fructose
What enzymes digest cellulose/hemicellulose?
No mammalian enzymes for digesting these
What transports both glucose and galactose from intestinal lumen to enterocyte?
SGLT 1 (Na+/glucose co-transporter)
What transport method is using to transport fructose from intestinal lumen into enterocyte?
Facilitated diffusion
What transporter is fructose specific?
GLUT 5
What transport method is using to transport glucose, galactose, fructose from enterocyte into blood?
Facilitated diffusion
What specific transporter is used to transport glucose, galactose, and fructose from enterocyte into blood?
GLUT 2
What is deficient in lactose intolerance?
Lactase
What domestic species have dietary requirements for essential amino acids?
Dogs, cats, chickens, pigs, horses
What domestic species have dietary protein requirement only?
Cattle, sheep, goats
Why do cattle, sheep, goats only have a dietary protein requirement?
Microbes can take the dietary protein and make essential AA which will be absorbed in SI
In species that have dietary requirements for essential amino acids, what must be special about the protein in their diets?
Protein must be high quality
What does high quality protein mean?
Protein with essential amino acid profile
What form are amino acids usually provided in?
Protein
Essential AA P.V.T
Phenylalanine
Valine
Threonine
Essential AA T.I.M
Tryptophan
Isoleucine
Methionine
Essential AA H.A.L.L
Histidine
Arginine
Leucine
Lysine
Digestion of protein in the stomach is ultimately completed by
Endopeptidases and exopeptidases
What do exopeptidases do
Hydrolyze 1 AA at a time from C terminal end
Protein digestion begins where
Stomach
When is pepsinogen activated to pepin?
When pH is 1-2
Pepsin exopeptidase or endopeptidase?
Endopeptidase
What does endopeptidases do?
Hydrolyze interior bonds
What does HCl do to proteins?
Causes them to unfold and expose their peptide bonds to pepsin
In young ruminants, chief cells produce
Rennin
Enzyme that coagulates milk + reduces (decreases) passage rate in young ruminants
Rennin
Inactive enzymes
Zymogens
What does SI utilize in protein digestion?
Pancreatic proteases and brush border proteases
When digesta enters SI, what is released?
CCK
When digesta enters SI, CCK is released, which causes the release of
Zymogens
SI endopeptidases
Trypsin, chymotrypsin, elastase
SI exopeptidases
Carboxypeptidases A and B
What activates trypsinogen to form trypsin?
Enterokinase
What does trypsinogen form when activated?
Trypsin
What breaks down the proteins in the SI? Name all
Trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A and B
What activates other zymogens after initial release?
Trypsin
What is the final protein digestion step in SI?
Aminopeptidases at the brush border break down peptides further
AA move across basolateral membrane via
Facilitated diffusion
Carb products of digestion
Glucose
Galactose
Fructose
Protein products of digestion
Amino acids
Dipeptides
Tripeptides
Carbohydrate absorption mechanisms
Na+-glucose co transporter
Na+-galactose co transporter
Facilitated diffusion
Protein absorption mechanisms
Na+-amino acid co-transporter
H+-dipeptide co-transporter
H+-tripeptide co-transpower
Loss of appetite, vomiting, weakness, abdominal pain, dehydration, diarrhea are symptoms of
Pancreatitis
Prematurely activated enzymes can lead to local damage of exocrine pancreas, which leads to?
Pancreatitis
Insufficient production and secretion of digestive enzymes (which can be caused by long-term pancreatitis) is a cause of what?
Exocrine pancreatic insufficiency
Destruction of cells producing digestive enzymes is a cause of what?
Exocrine pancreatic insufficiency
Lack of digestion, malabsorption, weight loss, nutrient deficiencies are all symptoms of
Exocrine pancreatic insufficiency
Defect or absence of Na+/amino acid co-transporter is a cause of
Cystinuria
Crystal formation and calculi, urinary blockages, are symptoms of
Cystinuria
