Essential thrombocythemia (ET) is a rare chronic blood cancer (myeloproliferative neoplasm) characterised by the overproduction of platelets (thrombocytes) by megakaryocytes in the bone marrow. It may, albeit rarely, develop into acute myeloid leukemia or myelofibrosis. It is a type of myeloproliferative neoplasm (blood cancers) wherein the body makes too many white or red blood cells, or platelets). Signs and symptoms
Most people with essential thrombocythemia are without symptoms at the time of diagnosis, which is usually made after noting an elevated platelet level on a routine complete blood count (CBC). The most common symptoms are bleeding (due to dysfunctional platelets), blood clots (e.g., deep vein thrombosis or pulmonary embolism), fatigue, headache, nausea, vomiting, abdominal pain, visual disturbances, dizziness, fainting, and numbness in the extremities; the most common signs are increased white blood cell count, reduced red blood cell count, and an enlarged spleen. Cause
In ET, megakaryocytes are more sensitive to growth factors. Platelets derived from the abnormal megakaryocytes are activated, which, along with the elevated platelet count, contributes to the likelihood of forming blood clots. The increased possibility of bleeding when the platelet count is over 1 million is due to von Willebrand factor (vWF) sequestration by the increased mass of platelets, leaving insufficient vWF for platelet adhesion. A mutation in the JAK2 kinase (V617F) is present in 40–50% of cases and is diagnostic if present.
It also increases sodium and water absorption and potassium excretion in the intestines. Sodium
Cortisol promotes sodium absorption through the small intestine of mammals. Sodium depletion, however, does not affect cortisol levels so cortisol cannot be used to regulate serum sodium. Cortisols original purpose may have been sodium transport. This hypothesis is supported by the fact that freshwater fish use cortisol to stimulate sodium inward, while saltwater fish have a cortisol-based system for expelling excess sodium. Potassium
A sodium load augments the intense potassium excretion by cortisol. Corticosterone is comparable to cortisol in this case. For potassium to move out of the cell, cortisol moves an equal number of sodium ions into the cell. This should make pH regulation much easier (unlike the normal potassium-deficiency situation, in which two sodium ions move in for each three potassium ions that move out—closer to the deoxycorticosterone effect). Stomach and kidneys
Cortisol stimulates gastric-acid secretion. Cortisols only direct effect on the hydrogen-ion excretion of the kidneys is to stimulate the excretion of ammonium ions by deactivating the renal glutaminase enzyme. Memory
Cortisol works with adrenaline (epinephrine) to create memories of short-term emotional events; this is the proposed mechanism for storage of flash bulb memories, and may originate as a means to remember what to avoid in the future. However, long-term exposure to cortisol damages cells in the hippocampus; this damage results in impaired learning. Diurnal cycles
Diurnal cycles of cortisol levels are found in humans.