Lecture 24: Mucosal Absorption-1 Flashcards
Are end products of carbohydrate and protein digestion hydrophilic or hydrophobic
Hydrophilic
What is active transport
Transport of molecules that requires ATP, against concentration gradient
What is the most important active transporter
Na/K pump
Numerous secondary active transporters depend on __gradient
Sodium
Secondary active co-transporters ligands are on the ___side
Same
Secondary active antiporter or exchanger ligands are on __sides
Opposite
What maintains the Na gradient
Na/K pump
What is the tertiary active transport
- Na/K maintains Na gradient
- Intracellular H is transported out via Na/H anti port
- Cl-/HCO3- exchange
What catalyzes H+ and bicarbonate production
Carboanydrase
What are the 3 forms of passive transport
- Transcellular
- Paracellular
- Facilitated diffusion
What is transceullar absorption
Ions following the electrochemical gradient through the ion channels in the apical membrane
What is paracellular absoprtion
Ions follow the electrochemical gradient and osmotic pressure through tight junctions
Tight junctions are freely permeable to __ and __
Water and small ions
What is facilitated diffusion
Spontaneous passive transport of molecules or ions across membrane specific transmembrane integral proteins
What transporter dose glucose and galactose use
SGLT-1
Where is SGLT-1 located
Next to glycocalyx enzymes on apical membrane
How is fructose transported across the membrane
Facilitated diffusion via GLUT-5
Once fructose is in cell it is phosphorylated and converted to ___
Glucose
Glucose is transported across the basolateral membrane via
Facilitated diffusion via GLUT-1
Glucose movement through the basolateral space is driven by ___
Diffusion
Describe how oral rehydration therapy works
Utilizes the Na+ glucose co-transporter and stimulates water reabsorption
Disorders of carbohydrate digestion and absorption are most commonly due to __deficiencies that prevent breakdown of carbohydrates to ___form
Enzyme, absorbable
How do unabsorbed carbohydrates cause diarrhea
Hold water and cause osmotic diarrhea
Proteins utilized what transporter on the apical membrane
Amino acid co-transporter (Na)
What are the four co-transporters
- Neutral AA
- Dibasic AA
- Dicarboxylic AA
- Imino (proline) AA
Transport of di and tripeptides are coupled to ___transport
H+
Digested proteins are released into basolateral side and capillaries as __
Free amino acids
How do free amino acids cross basolateral membrane
Facilitated diffusion
What is aminoaciduria
Result or pancreatic insufficiency where there is a defect in the transport of a specific amino acid
How does aminoacidura affect di and tripeptides
It doesn’t, di and tripeptides are facilitated by H+ transporter not amino acid transporter
What is cystinuria
Transporter for dibasic amino acids is absent or reduced causing dibasic amino acids to be lost in urine and feces. Could result in cysteine stones
What is responsible for facilitating the absorption and digestion of lipids
Micelles
How do Micelles get lipids into cell
Simple diffusion
How do long chain fatty acids get into cell
Facilitated diffusion
95% of ingested fat is removed by __
Small intestine
Describe the steps in absorption of micellar contents
- Micelles diffuse through apical membrane of the enterocyte
- Micelles adhere to enterocyte membrane
- Fatty acids, monoglycerides, phospholipids, cholesterol diffuse from the Micelles
What two pathways reassemble lipids intracellular
- Monoglyceride adulation pathway
- Phosphatidic acid pathway
What is the monoglyceride acylation pathway
2 monoglycerides and fatty acyl CoA= triglycerides
What is the phosphatidic acid pathway
Glycolysis—> P glycerol or diOH-acetone P—> alpha glycerolP—>triglycerides
What are chylomcirons
Transport vehicle for lipids in lacteals. Core of triglycerides and cholesterol surrounded by phospholipase and apoproteins
Fatty acids and monoglycerides are converted to ___ in ___
Triglycerides in the endoplasmic reticulum
What are apoproteins
Embedded in chylomicrons, serve as ligands for cell surface and cofactors for enzymes
Without apoproteins what happens to triglycerides
Accumulate in enterocytes
Chylomicrons are taken up by __
Lacteals
What are lacteals
Lymphatic vessels in villi that take up lipids
What is the draining sequence from lacteals
Lacteals to cisterna chyli-> thoracic duct-> external jugular vein
Intestinal lymph changes between __ and __ characters depending on ingesta processing
Watery, milky
How are bile acids recycled
- Bile acid transporter (Na-bile acid secondary active) in ileum
- Bile reabsorbed and returned to portal system
- Processed in liver and stored in gallbladder to be later released into SI
Known as enterohepatic circulation
If the liver does not recycle bile acids they will show up in the ___
Plasma
Complete or partial damage to the ___ will cause bile acid elevation as they bypass the liver which is known as ___
Portal blood flow, portosystemic shunt
Acquires shunts can result from ___
Liver disease
Congenital shunt in toy breeds
Extrahepatic shunt
Congenital shunt in large breed dogs
Intrahepatic
Accumulation of toxins and metabolic waste products from portosystemic shunts can result in ___
Hepatic encephalopathy
What is the main neurotoxic that builds up in hepatic encephalopathy
Ammonium
The bile acid tests what
Liver function and the degree of damage or inflammation
Describe the steps in bile acid testing
- 12 hour fast
- Prelimary blood draw
- Offer small meal
- 2 hours later take second sample
How should the bile test read if liver function is normal
Low initial and 2 hour levels
If the resting bile acid sample is elevated what does that indicated
Bile acids remain in circulation- liver disease, shunt, impaired gallbladder, gall stones
If the preliminary sample for bile acids is normal and the 2 hour test is elevated what does that mean
Bile acids are very slowly absorbed and escape into systemic circulation. The liver can handle bile acids between meals but not after meal
