4.5-CO-TRANSPORT AND ABSORPTION OF GLUCOSE IN THE ILEUM Flashcards
What does the epithelial cells lining the ileum possess?
microvilli
What are microvilli?
finger-like projections of cell-surface membrane
Approximately how long are microvilli?
0.6μm in length
What are microvilli collectively termed as?
‘brush border’
Why are microvilli collectively termed as ‘brush border’?
they look like bristles on a brush
What do the microvilli provide?
more surface area for insertion of carrier proteins through which diffusion, facilitated diffusion + active transport can take place
What is another mechanism to increase transport across membranes?
increase number of protein channels + carrier proteins in any given area of membrane
What is diffusion?
net movement of molecules/ions from region where they’re highly concentrated to region where their concentration lower
As carbohydrates and proteins are being ingested continuously what does this cause?
normally a greater concentration of glucose and amino acids within the ileum than in the blood
As there is normally a greater concentration of glucose and amino acids within the ileum than in the blood what does this mean?
a concentration gradient down which glucose moves by facilitated diffusion from inside ileum into blood
How is glucose absorbed into the blood continuously being removed?
blood is continuously being circulated by the heart
What is the glucose being absorbed into and why?
continuously being removed by cells as they use it up during respiration
As the blood is continuously being circulated, what does this maintain?
concentration gradient between inside of ileum and blood
As the concentration gradient between the inside of the ileum and the blood is maintained what does this mean?
rate of movement by facilitated diffusion across epithelial cell-surface membrane increased
At best what does diffusion only result in?
concentrations either side of intestinal epithelium becoming equal
As diffusion only results in the concentrations becoming equal, what does this mean?
not all the available glucose + amino acids can be absorbed in this way + some may pass out of body
However, why does the glucose + amino acids not pass out of the body?
glucose + amino acids also being absorbed by active transport
As glucose + amino acids are also being absorbed by active transport, what does this mean?
all the glucose + amino acids should be absorbed into blood
What is the actual mechanism of how glucose + amino acids being absorbed from the small intestine an example of?
co-transport
Why is the term co-transport used?
as either glucose/amino acids drawn into cells along with sodium ions that have been actively transported out by sodium-potassium pump
How co-transport happens #1
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
How co-transport happens #2
what is maintained as sodium ions actively transported out of epithelial cells?
maintains much higher concentration of sodium ions in lumen of intestine than inside than inside epithelial cells
How co-transport happens #3
sodium ions diffuse into epithelial cells down concentration gradient through different type of protein carrier (co-transport protein) in cell-surface membrane
As the sodium ions diffuse in through the second carrier protein, what do they carry with them?
carry an amino acid or glucose molecule with them
How co-transport happens #4
glucose/amino acid pass into blood plasma by facilitated diffusion using another type of carrier
Does sodium ions move down or against concentration gradient when moving into cell?
sodium ions move down concentration gradient
Does glucose molecules move down or against concentration gradient when moving into cell
glucose molecules move against their concentration gradient
What powers the movement of glucose + amino acids into the cells?
sodium ion concentration gradient rather than ATP directly
What type of active transport is it when the glucose/amino acid molecules move into the cell?
indirect
Why is it indirect active transport when the glucose/amino acid molecules move into the cell?
sodium ion concentration gradient rather than ATP that powers movement of the molecules
