Flashcards in GI digestion and absorption  Deck (21):
4 mechanisms of protein uptake
1. Sodium dep Co-transporters:
2. Sodium indep transporters:
3. Specific carriers for small peptides (di-, tri-) linked to H+ uptake
Primary bile acids are produced in the _____ from ____.
Secondary bile acids are formed in the ____ by _____.
Bile is recycled during meals by uptake in the ______
liver - cholesterol
intestines+Colon - bacteria
Distal ileum (enterohepatic circulation)
(note: bile acids + glycine + tuarine → bile salts)
Roles of pancreatic:
- How does fat get to the lacteals?
Lipase (w/ colipase help) anchor onto lipid droplets →
digest triglyceride droplets to monoglycerides + FA →
Bile salts solubilize the fat into micelles →
FFA are transported into enterocytes →
Triglycerides are resynthesized and chylomicrons form→
released into lacteals
Fat soluble Vitamins (Vit A, D, E, K) absorbed how?
same as fat digestion
Absorbed along length of small Int. and carried in micelles, form chylomicrons
Water soluble vitamins (B, C, niacin, folic acid, panthothenic acid, biotin) absorbed how?
1. simple diffusion
- biotin, folic acid
2. specific transporters
composition and formation of chylomicrons
triglycerides that are re-synthesized from absorbed monoglycerides and FA in the enterocytes and are packed
- also contain PL, cholesterol, apolipoproteins
How do chylomicrons exit the basolateral membrane and enter the Cardivascular system?
Golgi body incorporates them into secretory vesicles and get exocytosed and enter lacteals.
They will eventually enter the CVS via thoracic duct
Role of IF in B12 absorption
What happens if you have impaired B12 abs?
B12: imp for RBC production
IF from stomach binds B12 in duodenum →
B12-IF complex binds to receptor in terminal ileum for absorption (receptor is for IF)
_____L of fluid is put into the gut EVERY DAY. only ____ mls are lost.
Duodenum and jejunum responsible for abs of?
absorption of sugars and aa (with Na+ cotransport) →
Cl- follows → then water follows PARACELLULARL pathway
*water absorption is critically linked to Na+ absorption
Ileum responsible for abs of?
similar to upper sm int. (abs sugar + aa)
Has specialized absorption tasks (bile salt and B12)
H2O abs by TRANSCELLULAR pathway
Colon responsible for abs of?
what happens to K+?
Na+ and H2O
Epithelial ENaC on apical membrane is activated by aldosterone and increases Na+ reabsorption and consequently more H2O
this also increases K+ secretion across apical membrane
After the stomach, the Sm Int contents become _____ with respect to the blood
Which is more absorptive, jejunum, ileum, or colon?
(right out the gate!) 60-80%
Cl- absorption in the gut takes place where? active or passive?
Passive in proximal intestine
- to offset Na+ charge in intercellular space
- in distal ileum + colon, Cl- is exchanged for HCO3- to offset acids produced by bacteria
K+ absorption in the gut takes place where? active or passive?
paracellular movement in jejunum
(due to low K+ in intercellular space thanx to Na/K ATPase movement of K into cell)
transcellular in colon
(water gradient decreases w/ approach to colon)
Ca2+ and Mg2+ in the gut takes place where? active or passive?
two compete for uptake by cells
Ca2+ enters enterocytes PASSIVELY down [ ] gradient in prox intestines
- this Ca2+ gets stored in intracellularly and maintains gradient
- Ca2+ ATPase pumps it out to the blood
Vit D is absorbed by ____. Hydroxylated in the ____, and is converted to 25-OH D. This is hydroxylated again in the _____ in the presence of the hormone ______. Vit D stimulates the uptake of ______.
What is it?
3 things that can cause it
impaired digestion or defects in absorption
1. lactase deficiency
2. ileal resection
3. celiac disease (Sprue)
what is it?
what can cause it?
may be cause by Vibro cholerae
↑ cAMP levels in cell → activates CF Cl- channel (CFTR) on the luminal surface