Final Exam GI Physiology: GI Tract Absorption Flashcards
What are the 9 general factors that influence the absorption or secretion of substances across membranes?
- Size
- Solubility
- Charge
- Concentration gradient
- Electrical gradient
- Available energy
- Area of membrane
- Transport protein availability
- Permeability of tight junctions
Why does the flow of water across intestinal mucosa decrease from duodenum to ileum to large intestine?
The tight junctions get gradually less “leaky”
How is absorption throughout the intestines similar to absorption in the proximal tubule?
Both are isosmotic
How is secretion by the GI tract different from secretion in the nephron?
GI tract secretes isotonic fluids into the lumen
How is flow through tight junctions accomplished?
Via active transport and facilitated transport (like in the nephron)
Does absorption take place in the mouth? In the esophagus?
Absorption does NOT take place at either of these organs
Can volatile fatty acids in their associated forms cross the rumen and reticulum (cecum and colon) mucosa?
Yes!
What are the 3 main VFAs?
Acetic, Proprionic, Butyric
The small intestine is a major site of _______ in the GI tract.
absorption
What are the electrolyte absorption mechanisms available in the GI tract?
Basolateral Na+- K+ ATPase pumps Na+-H+ antiports Cl- HCO3- antiports Na+ uniports Na+glucose symports Na+ amino acid symports
What do Basolateral Na+- K+ ATPase pumps do?
Pumps sodium into the basolateral interstitum to maintain a low cytoplasmic [Na+].
What do Na+-H+ antiports do?
A way of putting sodium into the absorptive cells of the GI tract. H+ secreted into lumen as Na+ is absorbed.
What do Cl- HCO3- antiports do?
A way of putting sodium into the absorptive cells of the GI tract.
HCO3- is secreted into lumen as Cl- is absorbed
What do Na+ uniports do?
A way of putting sodium into the absorptive cells of the GI tract.
Na+ enters and Cl- follows paracellularly
What do Na+glucose symports do?
A way of putting sodium into the absorptive cells of the GI tract.
Glucose diffuses into the basolateral interstitium and Cl- follows paracellularly.
What do Na+ amino acid symports do?
A way of putting sodium into the absorptive cells of the GI tract.
Amino acids diffuse into basolateral interstitium and Cl- follows paracellularly.
How is K+ absorbed in the small intestine?
Via simple diffusion (after osmosis) and solvent drag through tight junctions
What ports become abundant in the COLON?
Na+ uniports
The colon ______ K+.
secretes
What does the presence of aldosterone do at the activity of colon basolateral Na+K+ ATPase?
Aldosterone INCREASES the activity of colon basolateral Na+K+ATPase which INCREASES Na+ and H20 absorption, and INCREASES K+ secretion
Bacterial toxins can BLOCK electrolyte antiports. What does this do to the animal?
Inhibits water absorption
Promotes diarrhea and dehydration in young animals especially. This can lead to mortality.
Bacterial toxins can block electrolyte antiports. What do they do to Na+glucose and Na+amino acid symports?
Bacterial toxins do not affect these symports.
Because bacterial toxins do not block sodium-glucose and sodium-amino acid symports, what is an effective means of preventing life-threatening diarrhea?
ORS! Oral Rehydration Solutions rich in glucose and amino acids can prevent life-threatening diarrhea.
What promotes increased absorption of Ca++, Mg++, and (PO4)2-?
Calcitriol
What does calcitriol promote the absorption of?
Calcium, magnesium, and phosphate ions
What substance antagonizes the action of calcitriol?
CORTISOL is an antagonist of Calcitriol
In order to be absorbed, ingested polysaccharides must be hydrolyzed by an enzyme called ________ .
Amylase
T or F: Amylase CAN attack terminal glycosidic bonds.
False. Amylase cannot attack terminal glycosidic bonds
What are the two end products of hydrolyzation of ingested polysaccharide by amylase?
Maltose and maltotriose
Can maltose and maltotriose (hydrolysis products of ingested polysaccharides) be absorbed across the mucosal membrane?
NO, maltose and maltotriose cannot be absorbed across the mucosal membrane.
What is responsible for the hydrolysis of maltose and maltotriose?
Brush border oligosaccharides (glucoamylase and dextrinase)
What are ingested disaccharides (sucrose and lactose) hydrolyzed by?
Brush border sucrase hydrolyzes sucrose and lactose. The end products are glucose and fructose.
What are ingested disaccharides (sucrose and lactose) hydrolyzed by other than brush border sucrase?
Brush border lactase also hydrolyzes sucrose and lactose. The end products are glucose and galactose.
How are glucose and galactose absorbed?
Via Na+glucose symport
How is fructose absorbed?
Via facilitated diffusion
How do glucose, galactose and fructose exit, so they can ultimately enter portal circulation?
Glucose, galactose and fructose exit via BASOLATERAL PORTS which facilitate their diffusion.
What is ingest protein hydrolyzed by?
Pancreatic proteases
Results in amino acids and oligopeptides
What are oligopeptides hydrolyzed by?
Brush border oligopeptidases
Results in amino acids, dipeptides and tripeptides
How are amino acids absorbed?
Via Na+amino acid symports
How are dipeptides and tripeptides absorbed?
Via symports with intracellular peptidases
Results in amino acids
How do amino acids exit in order to ultimately enter portal circulation?
Amino acids exit via basolateral ports which facilitate their diffusion
Colostrum is rich in antibodies and contains a trypsin inhibitor. What does this trypsin inhibitor do?
It inhibits proteolysis in the small intestine
How long postpartum does the trypsin inhibitor in colostrum work?
No more than 2 days postpartum
What do absorptive cells do when encountered by colostral antibodies within 2 days postpartum?
Absorptive cells endocytose colostral antibodies intact!
What is ingested triacylglycerol (lipid) emulsified by?
Bile acids and phospholipid lecithin emulsify triacylglycerol.
Results in small droplets of triacylglycerol
What are the small droplets of triacylglycerol hydrolyzed by?
Pancreatic enzymes (lipase, colipase, phospholipase, and cholesterolesterase) hydrolyze the small droplets of triacylglycerol.
What is the result of hydrolysis of small triacylglycerol lipid droplets by pancreatic enzymes?
Free fatty acids Monoacylglycerols Glycerol Cholesterol Lysolecithin Fat soluble vitamins
How are mixed micelles formed?
By using bile acids, phospholipids and products of small droplet triacylglycerol lipid hydrolysis.
What is the “core” of mixed micelles made up with?
LCFA (long chain fatty acids), MG (monoacylglycerol), lysolecithin, cholesterol, and fat soluble vitamins
Are short chain and medium chain fatty acids found in the core of a mixed micelle?
NO. Only LONG CHAIN FATTY ACIDS
Is glycerol a component of the core of a mixed micelle?
NO. Glycerol is not found in mixed micelles, even though it is a products of lipid hydrolysis.
Micelles diffuse from lumen to _________ ________ membrane.
Mucosal cell membrane. The contents are diffused readily.
Where are most micellar contents absorbed?
In the JEJUNUM
Where are bile acids reabsorbed?
In the TERMINAL ILEUM
What happens to the products of lipid hydrolysis once within the mucosal cell (brought here by mixed micelle)
They are RE-ESTERIFIED to form:
Triacylglycerols
Cholesterolester
Phospholipid
What happens to the re-esterified triacylglycerol, cholesterolester, and phospholipid inside the mucosal cell?
They are put together with ingested fat soluble vitamins, cholesterol, phospholipids and proteins to make a heterogenous lipid droplet called a CHYLOMICRON
Chylomicrons are too big to be taken up by small intestinal capillaries. Instead, they are taken up by ______ and transferred to plasma via the ________ duct.
LACTEALS take up chylomicrons and are transferred to plasma via the THORACIC DUCT
