chloride shift is followed by water shift into RBCs..why theres pressure difference that cause H2O shift?

Question

just studying in medical school..my lecturer ask that question..so im hoping for reasonable answers.

Answer 1

Sami has explained about the chloride shift. With the movement of the chloride ions into the cell to maintain its electronegativity, the osmolarity of the RBC increases thereby dragging H2O along with it.It is a passive movement.

Answer 2

The chloride shift describes the exchange of chloride anions for
bicarbonate anions across the erythrocyte's cell membrane.

To truly understand the purpose of the chloride shift, one must
first understand the transport system of carbon dioxide in the blood.
There are three primary ways that carbon dioxide is carried in the blood:
8% of carbon dioxide travels directly dissolved in plasma. The reason
that this amount is so low is that carbon dioxide's solubility in blood
plasma is very low - about 2.5 Volume Percent.
20% of carbon dioxide travels bound to proteins called carbamino
compounds. The remaining 72% of carbon dioxide is transported as
biocarbonate ion in the blood stream.

After carbon dioxide has diffused into erythrocytes, some of the
carbon dioxide binds to hemoglobin. Scientists refer to this carbamino
compound as carbaminohemoglogin. However, as noted in the above
percentages, most of the carbon dioxide does not react with the
hemoglobin. Instead, the carbon dioxide reacts with a water molecule.
Carbonic anhydrase catalyzes the following reaction:

Water+ Carbon dioxide ---->H2CO3.

H2CO3 then immediately divides into a proton and the bicarbonate anion.
The bicarbonate anion builds up inside the erythrocyte. Because of this
high diffusion gradient of biocarbonate anion across the cell membrane,
the bicarbonate anion diffuses out of the cell into the blood plasma.
Since negative charge is moving out of the cell, chloride anions must move
into the cell from the surrounding blood plasma in order to allow
electrical balance to be achieved between the inside and outside of the
cell.