Describe possible causes and consequences of dehydration hypotonic hydration and edema?

Answer 1

Dehydration

When water output exceeds intake over a period of time and the body is in negative fluid balance, the result is dehydration. Dehydration is a common sequel to hemorrhage, severe burns, prolonged vomiting or diarrhea, profuse sweating, water deprivation, and diuretic abuse. Dehydration may also be caused by endocrine disturbances, such as Diabetes mellitus or diabetes insipidus. Early signs and symptoms of dehydration include a "cottony" or sticky oral mucosa, thirst, dry flushed skin, and decreased urine output(oliguria). If prolonged, dehydration may lead to weight loss, fever, and mental confusion. Another serious consequence of water loss from plasma is inadequate blood volume to maintain normal circulation and ensuing hypovolemic shock.

In all these situations, water is lost from the ECF). This is followed by the osmotic movement of water from the cells into the ECF, which equalizes the osmolality of the extracellular and intracellular fluids even though the total fluid volume has been reduced. Though the overall effect is called dehydration, it rarely involves only a water deficit, because most often electrolytes are lost as well.

Hypotonic Hydration

When the ECF osmolality starts to drop (usually this reflects a deficit of Na+), several compensatory mechanisms are set into motion. ADH release is inhibited, and as a result, less water is reabsorbed and excess water is quickly flushed from the body in urine. But, when there is renal insufficiency or when an extraordinary amount of water is drunk very quickly, a type of cellular overhydration called hypotonic hydration may occur. In either case, the ECF is diluted-its sodium content is normal, but excess water is present. Thus, the hallmark of this condition is hyponatremia (low ECF Na+), which promotes net osmosis into the tissue cells, causing them to swell as they become abnormally hydrated. This leads to severe metabolic disturbances evidenced by nausea, vomiting, muscular cramping, and cerebral edema. Hypotonic hydration is particularly damaging to neurons. Uncorrected cerebral edema quickly leads to disorientation, convulsions, coma, and death. Sudden and severe hyponatremia (as in overhydrated athletes) is treated by intravenous administration of hypertonic saline to reverse the osmotic gradient and "pull" water out of the cells.

Edema

Edema (ĕ-de′mah; "a swelling") is an atypical accumulation of fluid in the interstitial space, leading to tissue swelling. Edema may be caused by any event that steps up the flow of fluid out of the blood or hinders its return.

Factors that accelerate fluid loss from the blood include increases in capillary hydrostatic pressure and permeability. Increased capillary hydrostatic pressure can result from incompetent venous valves, localized blood vessel blockage, congestive heart failure, or high blood volume. Whatever the cause, the abnormally high capillary hydrostatic pressure intensifies filtration at the capillary beds.

Increased capillary permeability is usually due to an ongoing inflammatory response. Recall that inflammatory chemicals cause local capillaries to become very porous, allowing large amounts of exudate (containing not only clotting proteins but also other plasma proteins, nutrients, and immune elements) to form.

Edema caused by hindered fluid return to the blood usually reflects an imbalance in the colloid osmotic pressures on the two sides of the capillary membranes. For example,hypoproteinemia (hi″po-pro″te- ĭ-ne′me-ah), a condition of unusually low levels of plasma proteins, results in tissue edema because protein-deficient plasma has an abnormally low colloid osmotic pressure. Fluids are forced out of the capillary beds at the arterial ends by blood pressure as usual, but fail to return to the blood at the venous ends. Thus, the interstitial spaces become congested with fluid. Hypoproteinemia may result from protein malnutrition, liver disease, or glomerulonephritis(in which plasma proteins pass through "leaky" renal filtration membranes and are lost in urine).

Although the cause differs, the result is the same when lymphatic vessels are blocked or have been surgically removed. The small amounts of plasma proteins that seep out of the bloodstream are not returned to the blood as usual. As the leaked proteins accumulate in the IF, they exert an ever-increasing colloid osmotic pressure, which draws fluid from the blood and holds it in the interstitial space. Because excess fluid in the interstitial space increases the distance nutrients and oxygen must diffuse between the blood and the cells, edema can impair tissue function. However, the most serious problems resulting from edema affect the cardiovascular system. When fluid leaves the bloodstream and accumulates in the interstitial space, both blood volume and blood pressure decline and the efficiency of the circulation can be severely impaired.