GI digestion and absorption [4]

Question 1

4 mechanisms of protein uptake

Answer 1

1. Sodium dep Co-transporters:
2. Sodium indep transporters:
3. Specific carriers for small peptides (di-, tri-) linked to H+ uptake
4. Pinocytosis

Question 2

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 ______

Answer 2

liver - cholesterol
intestines+Colon - bacteria

Distal ileum (enterohepatic circulation)

(note: bile acids + glycine + tuarine → bile salts)

Question 3

Roles of pancreatic:
Lipase
Colipase
Micelles
- How does fat get to the lacteals?

Answer 3

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

Question 4

Fat soluble Vitamins (Vit A, D, E, K) absorbed how?

Answer 4

same as fat digestion

Absorbed along length of small Int. and carried in micelles, form chylomicrons

Question 5

Water soluble vitamins (B, C, niacin, folic acid, panthothenic acid, biotin) absorbed how?

Answer 5

either by:

1. simple diffusion
   - biotin, folic acid
2. specific transporters
   - B12

Question 6

composition and formation of chylomicrons

Answer 6

Lipoprotein particles:
triglycerides that are re-synthesized from absorbed monoglycerides and FA in the enterocytes and are packed
- also contain PL, cholesterol, apolipoproteins

Question 7

How do chylomicrons exit the basolateral membrane and enter the Cardivascular system?

Answer 7

Golgi body incorporates them into secretory vesicles and get exocytosed and enter lacteals.
They will eventually enter the CVS via thoracic duct

Question 8

Role of IF in B12 absorption

What happens if you have impaired B12 abs?

Answer 8

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)

Pernicious anemia

Question 9

_____L of fluid is put into the gut EVERY DAY. only ____ mls are lost.

Answer 9

9L, 100-200mls

Question 10

Duodenum and jejunum responsible for abs of?

Answer 10

absorption of sugars and aa (with Na+ cotransport) →
Cl- follows → then water follows PARACELLULARL pathway

*water absorption is critically linked to Na+ absorption

Question 11

Ileum responsible for abs of?

Answer 11

similar to upper sm int. (abs sugar + aa)
but!
Has specialized absorption tasks (bile salt and B12)
H2O abs by TRANSCELLULAR pathway

Question 12

Colon responsible for abs of?

what happens to K+?

Answer 12

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

Question 13

After the stomach, the Sm Int contents become _____ with respect to the blood

Answer 13

iso-osmotic

Question 14

Which is more absorptive, jejunum, ileum, or colon?

Answer 14

jejunum

(right out the gate!) 60-80%

Question 15

Cl- absorption in the gut takes place where? active or passive?

Answer 15

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

Question 16

K+ absorption in the gut takes place where? active or passive?

Answer 16

Passive,
paracellular movement in jejunum
(due to low K+ in intercellular space thanx to Na/K ATPase movement of K into cell)
or
transcellular in colon
(water gradient decreases w/ approach to colon)

Question 17

Ca2+ and Mg2+ in the gut takes place where? active or passive?

Answer 17

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

Question 18

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 ______.

Answer 18

intestine
liver
kidney
PTH
Ca2+

Question 19

Osmotic diarrhea
What is it?
3 things that can cause it

Answer 19

impaired digestion or defects in absorption

1. lactase deficiency
2. ileal resection
3. celiac disease (Sprue)

Question 20

Secretory diarrhea
what is it?
what can cause it?

Answer 20

may be cause by Vibro cholerae

↑ cAMP levels in cell → activates CF Cl- channel (CFTR) on the luminal surface

Question 21

Oral rehydration therapy

Answer 21

antibiotics + KHCO to prevent hypokalemia and met acidosis

Glucose + NaCl to facilitate abs of electrolytes and water