Edema is an accumulation of fluid in the body cavities and the skin such as the pleural cavity of the lungs in which it is called hydrothorax and pleural effusion.  Also fluid can accumulate in the peritoneal cavity causing a condition which is called ascites.  In addition, fluid can accumulate in the pericardial cavity in the heart causing pericardial effusion or accumulation of fluid in the heart covering layers.

An edema which affects the whole body is called anasarca.  Fluid can also accumulate in the skin which can be characterized by the production of depression in the skin after the application of pressure to the skin surface by a finger. 

The blood in the arteries is maintained there by two opposing forces that each works in a different direction.  The first is the hydrostatic pressure which the weight of the bloods exerts on the walls of the blood vessels tend to force the blood out of the arteries while the plasma colloid osmotic pressure tend to force the blood in the opposite direction inside the arteries. 

Th forces usually cancel each other under normal conditions.  Edema can result due to increased hydrostatic pressure as occurs in increased blood pressure or hypertension due to the accumulation of fluids in the arteries or it can occur due to high blood pressure that can result due to narrowing of the arteries such as occurs in the medical condition of pheochromocytoma. 

In pheochromocytoma chronic secretion of the hormones epinephrine and nrepinephrine causes sustained elevation in blood pressure.  Edema can be localized to a special tissue or it can be generalized  in the whole body.  Example of localized edema occurs in skin inflammation in which the edema occurs due to secretion of vasodilating compounds such as histamine by the inflammatory cells causing local formation of fluid accumulation at the site of inflammation. 

Also allergic reactions such as occurs in the allergic condition of anaphylaxis.  An edema in this condition occurs in the form of skin hives or wheals as a result to the dilatation of blood vessels by the action of vasoactive amines that are released by mast cells at the site of inflammation. 

Also due to the dilatation of the blood vessels a condition of low blood pressure such as shock can occur.  This condition can be corrected by the administration of epinephrine and norepinephrine which both function by narrowing the blood arteries.  Thus contributing to ameliorating the shock condition by raising the blood pressure in the arteries. 

The types of edema that were discussed so far are due to localized form of the edema which affects specific parts of the body.  Generalized edema is another type of edema in which there is universal acumulation of fluid in the body cavities.  This can occur due to sodium and water retention in the body by the action of the hormone aldosterone or it can be caused due to increased amount of water in the body by the action of the hormone vasopressin on the kidney to promote the conservation of water in the body with subsequent development of hypertension and edema.

One type of edema which occurs due to retention of sodium and water in the body is the cardiac edema.  In cardiac failure the ability of the heart to pump blood to the general circulation is impaired.  The net result to this condition is the development of hypovolemia with deficient blood perfusion of the body organs including the two kidneys which are the site where the response to the hypovolemia occurs.

As a result of the low blood prefusion to the renal artery a state of hypovolemia occurs in which the kidney cells begin to secrete the hormone renin in response to the hypovolemia .  Renin in turn stimulates the adrenal cortex to secrete the hormone aldosterone which functions to restore blood pressure to normal by increasing the amount of sodium and water in the blood.  It does so by stimulating the reabsorption by the kidney tubules.

As a result a generalized type of edema occurs which can be corrected by the administration of appropriate type of diuretics.  Also generalized edema can occur due to the lack of proteins in the blood.  This can occur due to liver failure or due to the nephrotic syndrome.  The lack of appropriate amount of the protein albumin in the blood can cause diminished plasma colloid osmotic pressure which allows for the hydrostatic pressure inside the arteries to overcome the plasma colloid osmotic pressure. 

This in turn allows for the fluid in the arteries to leak to the outer side of the arteries causing edema.  This type of generalized edema is especially manifested in liver failure in which proteins synthesis is diminished.  Also it is manifested by the nephrotic syndrome in which hypoproteinemia occurs due to the escape of large amount of proteins in the kidney glomeruli into the urine. 

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If you’re lying on the couch watching television, do you still burn calories? The answer, of course, is yes. Even when you are not physically active, various systems in your body are still functioning to keep you alive.

The most limited number of calories needed to keep essential organs working is referred to as your Basal Metabolic Rate (BMR). This includes things like keeping your heart beating and your blood circulating, maintaining breathing to provide oxygen, and supporting body temperature.

About seventy percent of your actual daily caloric use is BMR. An additional ten percent is for thermogenesis, the digestion of food and elimination of waste products. The final twenty percent is attributable to various physical activities, like standing, walking, and so forth. Your caloric expenditure can also be affected by things like illness, ambient temperature, and stress. For example, if you start to shiver because you’re cold, this is your body’s way of warming up. Short muscle contractions release heat energy, which helps to raise your body temperature. This muscle movement uses calories.

BMR tends to decrease as you age. This is one of the reasons it seems to be harder to get rid of a few extra pounds as you get older. Reduction in energy expenditure and reduction in lean body mass tend to reduce BMR by about 5% per decade after you reach adulthood. Strength training and regular physical activity can limit this decrease.

Lean body mass requires more caloric expenditure and therefore promotes a higher BMR regardless of your age. Studies estimate that for every pound of lean body mass (which includes everything in your body except fat), you require 16 calories per day to maintain your body weight. If an average man has 15% body fat (therefore a lean body mass of 85%) and he weighs 180 pounds, he needs approximately 2,700 calories per day to maintain his weight.

This number is only an estimate. Every person has a different body configuration and there are many factors that affect total calories used. It has become quite popular to use BMR calculators to estimate calorie requirements. There are dozens of BMR calculators on the internet, and they all use similar models and will probably give you similar results. However, it’s important to remember that these are all estimates. The BMR for the man in the example given above would be about 1,900 calories, which is very close to seventy percent of his estimated daily calorie requirement.

The only way to know your BMR for sure is to begin tracking your calorie intake and see how you do. If you start losing weight, then you’re consuming fewer calories than your body is using each day. On the other hand, if your weight isn’t changing, you may need to further restrict your intake or do more physical activity if you’re trying to lose weight.

BMR can give you an idea of caloric expenditure, but it’s only a tool. Continued good health depends on basic principles like eating appropriate amounts of nutritious food and getting regular exercise.

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