4.5-CO-TRANSPORT AND ABSORPTION OF GLUCOSE IN THE ILEUM

Question 1

What does the epithelial cells lining the ileum possess?

Answer 1

microvilli

Question 2

What are microvilli?

Answer 2

finger-like projections of cell-surface membrane

Question 3

Approximately how long are microvilli?

Answer 3

0.6μm in length

Question 4

What are microvilli collectively termed as?

Answer 4

‘brush border’

Question 5

Why are microvilli collectively termed as ‘brush border’?

Answer 5

they look like bristles on a brush

Question 6

What do the microvilli provide?

Answer 6

more surface area for insertion of carrier proteins through which diffusion, facilitated diffusion + active transport can take place

Question 7

What is another mechanism to increase transport across membranes?

Answer 7

increase number of protein channels + carrier proteins in any given area of membrane

Question 8

What is diffusion?

Answer 8

net movement of molecules/ions from region where they’re highly concentrated to region where their concentration lower

Question 9

As carbohydrates and proteins are being ingested continuously what does this cause?

Answer 9

normally a greater concentration of glucose and amino acids within the ileum than in the blood

Question 10

As there is normally a greater concentration of glucose and amino acids within the ileum than in the blood what does this mean?

Answer 10

a concentration gradient down which glucose moves by facilitated diffusion from inside ileum into blood

Question 11

How is glucose absorbed into the blood continuously being removed?

Answer 11

blood is continuously being circulated by the heart

Question 12

What is the glucose being absorbed into and why?

Answer 12

continuously being removed by cells as they use it up during respiration

Question 13

As the blood is continuously being circulated, what does this maintain?

Answer 13

concentration gradient between inside of ileum and blood

Question 14

As the concentration gradient between the inside of the ileum and the blood is maintained what does this mean?

Answer 14

rate of movement by facilitated diffusion across epithelial cell-surface membrane increased

Question 15

At best what does diffusion only result in?

Answer 15

concentrations either side of intestinal epithelium becoming equal

Question 16

As diffusion only results in the concentrations becoming equal, what does this mean?

Answer 16

not all the available glucose + amino acids can be absorbed in this way + some may pass out of body

Question 17

However, why does the glucose + amino acids not pass out of the body?

Answer 17

glucose + amino acids also being absorbed by active transport

Question 18

As glucose + amino acids are also being absorbed by active transport, what does this mean?

Answer 18

all the glucose + amino acids should be absorbed into blood

Question 19

What is the actual mechanism of how glucose + amino acids being absorbed from the small intestine an example of?

Answer 19

co-transport

Question 20

Why is the term co-transport used?

Answer 20

as either glucose/amino acids drawn into cells along with sodium ions that have been actively transported out by sodium-potassium pump

Question 21

How co-transport happens #1

Answer 21

sodium ions actively transported out of epithelial cells by sodium-potassium pump into blood
takes place in one type of protein- carrier molecule found in cell-surface membrane of epithelial cells

Question 22

How co-transport happens #2

what is maintained as sodium ions actively transported out of epithelial cells?

Answer 22

maintains much higher concentration of sodium ions in lumen of intestine than inside than inside epithelial cells

Question 23

How co-transport happens #3

Answer 23

sodium ions diffuse into epithelial cells down concentration gradient through different type of protein carrier (co-transport protein) in cell-surface membrane

Question 24

As the sodium ions diffuse in through the second carrier protein, what do they carry with them?

Answer 24

carry an amino acid or glucose molecule with them

Question 25

How co-transport happens #4

Answer 25

glucose/amino acid pass into blood plasma by facilitated diffusion using another type of carrier

Question 26

Does sodium ions move down or against concentration gradient when moving into cell?

Answer 26

sodium ions move down concentration gradient

Question 27

Does glucose molecules move down or against concentration gradient when moving into cell

Answer 27

glucose molecules move against their concentration gradient

Question 28

What powers the movement of glucose + amino acids into the cells?

Answer 28

sodium ion concentration gradient rather than ATP directly

Question 29

What type of active transport is it when the glucose/amino acid molecules move into the cell?

Answer 29

indirect

Question 30

Why is it indirect active transport when the glucose/amino acid molecules move into the cell?

Answer 30

sodium ion concentration gradient rather than ATP that powers movement of the molecules