Welcome to HealthCareMagic. My name is Doctor Saleem Ur Rehman and I will like to answer your question.
First I will like to tell you about how fluid circulates in the body:
Basically body fluid is divided into Intracellular Fluids and Extracellular Fluids by semi-permeable membrane (which envelopes every cell). Extracellular fluid is further divided into Extravascular fluid (which bathes the cell) and Intravascular Fluid (fluid within the blood vessels)
Semi permeable means that only some ions are allowed to pass through the membranes. For example, Sodium is kept out of the cells and Potassium is concentrated inside the cells. Water is always distributed through a semi-permeable membrane in accordance with the relative solute concentrations of the compartments.
When you drink any fluid, it absorbed from the stomach and intestines and enters the extracellular compartment. From there it is distributed to the Intracellular compartment based on osmotic laws. As an elaboration, fluid will be distributed from your blood to the extravascular compartment through the capillary membranes. It will bath the cells and either enter the cells through cell membrane or be washed away by the lymphatic channels. These lymphatic channels open up into the vascular compartment.
Fluid is excreted from the body through kidneys (urine), skin (sweating), and lungs (breathing).
Fluid is retained when the intravascular compartment is either low in proteins
(which decreases the solute concentration causing a shift of water to the extravascular compartment) and the kidneys retain water to compensate for the resultant "under-filled" vessels. In such cases generalized fluid retention will occur, meaning that he whole body will be involved.
In certain cases, the lymphatic system
is blocked. These include surgeries, metastatic carcinomas (when the cancer cells deposit in the lymphatics), filariasis
, congenital defects and other nodal diseases.
The fluid retention in your grandmother's case seems to be due to systemic causes. These include Congestive Heart Failure
, Nephrotic Syndrome
and Nutritional Edema.
Her treatment will correspond to the underlying cause of edema. For example, in case of Congestive Heart Failure she will be given diuretics to increase the excretion of fluids through kidneys. Almost all causes are treated with a decrease in daily fluid intake (except in nutritional edema, where nutrition supplements, preferably proteins, are given to decrease edema)