GI Lecture 51 Flashcards
Absorption of carbohydrates, proteins, and lipids is highest where?
Duodenum
Absorption of calcium, folate, and iron is highest where?
Duodenum
Absorption of bile acids are highest where?
Terminal ileum
What carbohydrates are able to be absorbed?
monosaccharides
What is starch?
mixture of both straight and branch-chain polymers of glucose
Amylose
straight chain polymers
Amylopectin
branched-chain polymersq
Composition of Trehalose
2 glucose molecules
Composition of Sucrose
glucose and fructose
Composition of Lactose
glucose and galactose
What the three monosaccharides?
- glucose
- fructose
- galactose
Name a carbohydrate that can’t be digested?
cellulose
-due to beta 1,4 linkages
Products of amylase digestion
- alpha-limit dextrins
- maltose
- maltotriose
What digests alpha-dextrins?
-alpha dextrinase
What digests maltose?
-maltase
What digests maltotriose and sucrose?
-sucrase
What digests trehalose?
-trehalase
What digests lactose?
-lactase
SGLT1
simperer transports glucose or galactose against concentration gradient with sodium
What transporter allows glucose and galactose be reabsorbed?
GLUT2
Fructose transport (apical and basolateral)
- GLUT5 (apical)
- GLUT2 special (basolateral)
Lactose Intolerance
- Lack of lactase in the brush border
- lactose in lumen retains water and causes osmotic diarrhea
Congenital lactose intolerance
- lack of jejunal lactase
- replace lactose with sucrose or fructose diet
Glucose-galactose mal-absorption
- mutation of SGLT 1
- severe diarrhea
- fructose diet
Where and how is protein digestion started?
in the stomach with pepsin
Two class of proteases for protein digestion
- endopeptidases
- exopeptidases
Five major pancreatic proteases secreted as inactive proteases
- trypsinogen
- chymotrypsinogen
- proelastase
- procarboxypeptidase A
- procarboxypeptidase B
What activates trypsin?
enterokinase (brush border enzyme)
Into what must proteins be broken down into to be absorbed?
- amino acids
- dipeptides
- tripeptides
Explain absorption process of peptides and amino acids.
- transport with Na+ and H+ symporter
- dipeptides and tripeptides hydrolyzed into amino acids in epithelial cytosol
- amino acids exit cell through facilitated diffusion
Deficiency in single AA absorption
-compensated by absorption of di- and tri- peptides that are hydrolyzed in cells
Trypsinogen deficiency
- Diet of partially hydrolyzed proteins
- rare and serious
Cystinuria
- transporter for dibasic amino acids is absent in small intestine and kidney
- result of intestinal defect is feces excretion, renal defect is urine excretion
Major categories of lipid in the diet
- Triglycerides
- Phospholipids
- Cholesterol
- Vitamin A, D, E, K
Emulsification
- mixing of stomach churns dietary lipids into suspension of fine droplets
- stomach emulsification by dietary proteins
- small intestine emulsification by bile acids
Lipolytic enzymes in pancreatic juice
- Pancreatic lipase
- Phospholipase A2
- Cholesterol ester hydrolase
Pancreatic lipase
- hydrolyzes triglycerides to monoglycerides and fatty acids
- Bile acids inactivate pancreatic lipase, but collapse overrides this inactivation
Phsopholipase A2
- hydrolyzes phospholipids to lysolecithin and fatty acids
- secreted as proenzyme
Cholesterol ester hydrolase
- hydrolyzes cholesterol ester to free cholesterol and fatty acids
- and ester linkages of triglycerides
Composition of micelles
- interior = lipid digestion products
- exterior = bile salts
Lipid absorption inside cell
- lipid digestion products are re-estrified
- re-packaged with apoproteins into chylomicrons
- exocytosed and enter lymphatic capillaries
- empty into the thoracic duct an into bloodstream
Pancreatic Insufficiency
- results in defects of pancreatic enzyme secretion
- Abnormality of lipid digestion/absorption - results in steatorrhea
Acidity of duodenal contents
-pancreatic enzymes cannot function optimally at acidic pH
Deficiency of Bile salts
- No micelle formation/interferes with lipid digestion/absorption
- In ileal resection, bile lost in feces
Abetalipoproteinemia
- Failture to synthesize Apo B
- Chylomicrons are either not formed or unable to be transported into lymph
How many liters of fluid absorbed in small intestine?
7 Liters
How many liters of fluid absorbed in colon?
2 Liters
How many liters of fluid excreted in feces?
100 - 200 mL
There is a net absorption of ___ in ileum.
NaCl
There is a net absorption of ___ in jejunum.
NaHCO3-
Cholera
- makes the adenylyl cyclase constitutively active and produces cAMP and keeps Chloride channel open
- water follows and causes life-threatening diarrhea
Calcium Absorption
- Ca++ diffuses into cell from lumens side
- Parathyroid hormone needs to convert dietary vitamin D into 1,25- dihydroxycholecalciferol
- induces vitamin D- dependent Ca++ (calbindin D-28K)
- pumped into blood by Ca++ ATPase
Inadequate Ca++ absorption causes
- rickets in children
- osteomalacia in adults
Vitamin B12 Absoprtion
- binds to R protein
- pancreatic proteases degrade R proteins and B12 is transferred to Intrinsic Factor (IF)
- Vitamin B12-IF complex absorbed in ileum
Gastrectomy
- parietal cells are lost
- no B12 absorption
- pernicious anemia (problem with RBC count)
