Question

Explain what type of mechanism will be used to transport glucose from your intestine to your muscles. The relative levels of glucose are provided below.

a. Intestinal epithelium cell: high glucose to Interstitial fluid between intestinal cell and blood vessel: very low (blood vessels have “clefs” that glucose fits through to enter blood by bulk flow.)

b. Na+ is required for the transport into the intestinal epithelium cell. Why? How is the level of Na+ kept low in the intestinal cell?

Answer 1

a. Intestinal epithelium cell: high glucose to Interstitial fluid between intestinal cell and blood vessel: very low (blood vessels have “clefs” that glucose fits through to enter blood by bulk flow.)

In the transport of glucose from the epithelial cells to the interstitial fluid transport proteins are used that are present around the basolateral membrane. For such trans-epithelial transport to happen, the cells have to be polarised . In this case, the concentration of glucose in the intestinal epithelium cells is higher than that of the interstitial fluids. This implies, that movement has to be done in the direction of high concentration to low concentration. Since, the movement is from a higher to a lower concentration, it is with the gradient, and hence, movement will happen via facilitated diffusion.

b. Na+ is required for the transport into the intestinal epithelium cell. Why? How is the level of Na+ kept low in the intestinal cell?

Sodium is required for the transport of glucose, when glucose moves across the apical plasma membrane. This adds the free energy component in transport of glucose. The family of glucose transporters that are responsible in transport of glucose are sodium dependent. SOdium glucose transport occurs when glucose has to be transported uphill against the concentration gradient. This is an example of active transport.

How is the level of Na+ kept low in the intestinal cell?

Sodium is one of the major cations present in the extra cellular fluid. The level of sodium in blood would depend on the intake as well as excretion of a person. While considering concentration gradient, the concentration of both sodium and glucose have to be taken into consideration. The concentration of sodium is kept low in the intestinal cells because while glucose is being transported to, sodium binds to the transporters, and hence, moves out of the intestinal cells along with glucose. This raised the concentration of sodium in the extracellular fluid and lowers its concentration in the intestinal fluids. Also, concentration of chloride is kept high in the cells via the chloride channels, allowing a higher gradient of sodium in the extra cellular fluid.