carbohydrate absorption

Question 1

where does absorption of carbs occur? (3)

Answer 1

in:
1) duodenum
2) jejunum
3) mainly via brush border of intestine (microvilli)

Question 2

significance of microvilli brush border?

Answer 2

surface of epithelium has 200,000 folds per square mm

HUGE SA to facilitate absorption

absorption capacity go our microvilli brush border exceeds our dietary intake

Question 3

maximum dietary intakes in humans?

Answer 3

males- 37g (9 tablespoons)
females- 25g (6 tablespoons)

Question 4

what facilities absorption in the epithelial cells of the small intestine?

Answer 4

microvilli brush border by increasing surface area

Question 5

how do glucose + galactose enter the intestinal epithelial cells from the lumen of the intestine? (5)

Answer 5

1) through the apical BORDER
2) via active transport
3) against conc. gradient
4) using sodium dependant co- transporters
5) sodium potassium pump REQUIRED ENERGY

Question 6

what is the name of the sodium dependant co transporter glucose/ galactose use to move from lumen to epithelial cells?

Answer 6

SGLT1

Question 7

how do glucose and galactose leave the epithelial cells?

Answer 7

1) through the basolateral side
2) by facilitated diffusion
3) using glucose co transporters
4) into the circulation
5) NO ENERGY REQUIRED

Question 8

what is the name of glucose co transporter molecule glucose/ galactose use to leave the epithelial cells into the bloodstream?

Answer 8

GLUT-2

Question 9

glucose absorption is dependant on?

Answer 9

sodium
SGLT1 (bind sodium + glucose)
that is how glucose is transported

active transport

Question 10

how many types of GLUT transporter are there?

Answer 10

14 types
all cell specific

Question 11

how does fructose enter and leave the epithelial cells?

Answer 11

enters- carried by GLUT-5 transporter
leaves- using GLUT-2 transporter

facilitated diffusion (No energy)

Question 12

what does the transporter acc do?

Answer 12

bind glucose/ sodium
carry that molecule
change their shape
can wedge themselves into lipid bilayer of cell membrane
release that molecule into cell

Question 13

rest of sugars apart from glucose/ galactose?

Answer 13

can be transported using facilitated diffusion (No energy used)

Question 14

so how does the process of glucose/ galactose entering from apical border actually go down?

Answer 14

sodium inside cells leaves into lumen
increases conc gradient into lumen
attaches to SGLT1
which also attaches to glucose
enters into epithelial cells

sodium released from SGLT1= releases energy
glucose also released from SGLT1
so glucose moves to bind to GLUT2
to leave basolateral border
into circulation

Question 15

how is fructose absorbed?

Answer 15

fructose (fruit sugar) only needs something to modify its shape
doest need sodium or energy release
enters using GLUT5
released inside epithelial cell
carried on GLUT2 to enter bloodstream

Question 16

factors affecting carbs absorption:

Answer 16

1) more na+ concentration in intestinal lumen
INCREASE rate

2) thyroid hormones INCREASE rate

3) mineralocorticoid e.g. Aldosterone INCREASE rate

4) in tact mucosa INCREASES rate (inflammation + injury decrease)

Question 17

why may the mucosa of epithelial cells not be intact?

Answer 17

if are affected by:
injury/ inflammation
crohns disease
trauma REDUCES absorption DECREASES rate