B elow is a sketch of a lumen (non-blood), the epithelial lining and the nearby

Question

Below is a sketch of a lumen (non-blood), the epithelial lining and the nearby vascular supply. This concept occurs in many of the body’s systems. The goal in this model is for substances (such as ions, water, peptides, sugars, fats, drugs, etc) to move from the lumen into the blood.

Sodium is absorbed in this model.

1)aWhat type of transporter is shown, explain? (ex: “this channel that uses simple diffusion because…”)

b)What types of transporters need to be added to the basal side of the epithelial cell to allow each ion to be absorbed into the blood. List the transporter and describe the transportation method being used.

c)If this transporter malfunctions, what organelles would you consider investigating to see if the organelle(s) have a role in the malfunction (explain your reasoning)

2)a)Synthetic EPO (initially used to help treat various anemic diseases, but more popularly known as a blood doping agent used in sport) was taken. Concentrations of this showed up in the non – blood lumen. How does it then reach the blood? (Synthetic EPO is a large hydrophilic molecule). Please draw or explain the mechanism (provided information about EPO is sufficient to answer the question)

b) If K+ ECF concentration increased to be more than ICF concentration, how would this change your story for how Na+ is absorbed?

c)Does Ek change, if so how, if not why?

d)If this cell were electrically active, would the change in K+ concentration have any influence on it’s ability to depolarize, if yes, how, if not, why.

e)Does this change affect the relation of Vm rest to threshold and the ability of the cell to depolarize?

f)In this new state of increased K+ concentration in the ECF, a chemical from the anterior pituitary is released, what type of cell signaling molecule is this?

Explanation / Answer

1. (a) GLUT2 transporter is used in the basal and lateral membrane. Glucose moves into the epithelium with facilitated diffusion. But in case of glucose with Na+ a secondary transport is required which is called Na+/Glucose Cotransporter.

1. (b) The types of transporters that need to be added to the basal side of epithelial cell to allow each ion to be absorbed in the blood are:

Cotransporters help to transport Cl- ions into the epithelium and the transportation method is diffusion due to the presence of a gradient.

Another Cotransporter Na+/K+ ATPase creates a concentration gradient of Na+ which helps to move Na+, K+ and Cl- ions inside the epithelium. As Na+ concentration increases the Na+/K+ ATPase pumps Na+ out and pushes K+ in .

(c) The organelle that is involved in the transportation is Endoplasmic reticulum. They are the only organelles involved in transportation of materials into and out of the plasma membrane of the cell. If there is a problem in transportation of ions into and out of the cell then it is likely that there is a malfunction in the Endoplasmic Reticulum

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