- Swelling in the tissues caused by excessive accumulation of fluid.
- Can be generalized and local.
- In generalized edema, entire body is involved.
- Local edema occurs in some specific body areas.
- Areas like abdomen, lungs, feet, ankles, legs are involved.
- There is accumulation of fluid which may be outside and inside the cell.
- Depending on accumulation of excess fluid, it is of two types.
- Accumulation occurs in the body compartment.
- They are: a) intracellular and b) extracellular.
A) Intracellular Edema
- It is the condition of fluid accumulation inside the cell.
- It occurs due to
ii) Poor metabolism and
iii) Inflammation of the tissues.
Edema due to malnutrition
- Occurs due to poor intake of food and poor circulatory system.
- Nutritive supply of the substances cannot occur.
- This leads to poor exchange of ions.
- This poor exchange occurs due to depressed ionic pumps in cell membrane.
- Sodium ions mostly cannot be pumped out that leak into the cells.
- Sodium gets excess inside the cells due to poor pumping action.
- This causes endosmosis resulting in edema i.e., intracellular.
Edema due to poor metabolism
- Blood supply won’t be proper.
- This causes poor metabolism.
- This also leads to lack of oxygen.
- In this condition, cell membrane can’t function properly.
- Thus, edema occurs.
Edema due to inflammation of tissues
- Permeability of cell membrane increases as inflammation occurs.
- Many ions including sodium moves inside the cells.
- This results to endosmosis and finally intracellular edema results.
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B) Extracellular Edema
- Outside the cell if fluid accumulates, called extracellular edema.
- Caused when fluid from capillaries leaks into interstitial space.
- This leaking of fluid is abnormal.
- Also, lymphatic vessels obstruction hampers fluid return.
- The return of fluid generally occurs from interstitium to blood.
Following conditions lead to extracellular edema
- Lymphatic obstruction
- Increased endothelial permeability.
- Decreased plasma proteins level.
- Renal disease.
- Failure of heart.
Edema due to lymphatic obstruction
- Also called lymphedema.
- Common in cases of filariasis caused by some parasitic worms.
- Parasitic worms block or obstructs the drainage of lymph.
- They are found living in the lymphatic.
- This results in lymph accumulation along with cellular reaction.
- The condition finally leads to swelling mostly in legs and scrotum.
- Fibrosis results as lymphatic drainage is obstructed repeatedly in this part.
- Hence, development of elephantiasis occurs.
- In elephantiasis, skin thickens and affected area enlarges extremely.
- Mostly affects limbs (legs), genitals, certain areas of trunk and parts of head.
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Edema due to increased endothelial permeability
- In burns, inflammation, trauma, allergic reactions, immunologic reactions endothelial permeability increases.
- This leads to oozing out of the fluid.
- Fluid released in this way thus accumulates developing edema.
Edema due to decreased plasma proteins level
- Decreased plasma proteins decreases colloidal osmotic pressure.
- This increases capillary permeability which increases capillary filtration.
- Thus, more amount of water leaks out of the capillary.
- Leaked water accumulates in the spaces of tissues.
- This finally results to extracellular edema.
- Conditions like malnutrition, liver diseases, renal diseases, burns and inflammation cause decrease in plasma proteins.
Edema due to renal diseases
- Retention of water and electrolytes cannot occur in some renal diseases.
- It occurs as the kidney fails to excrete water and the electrolytes (mostly sodium).
- Thus, from blood fluid leaks into interstitial space causing extracellular edema.
- Initiation of edema development occurs in legs.
- Then, it slowly progresses to the entire body.
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Edema due to heart failure
- Various reasons are responsible for causing edema in heart failure.
- They are as follows:
a) Failure of heart to pump blood
- Increase in venous pressure and capillary pressure as heart cannot pump blood from veins to arteries.
- Capillary permeability increases which cause leakage of fluid from blood into interstitial fluid.
- This results to extracellular edema.
b) Fall in blood pressure during heart failure
- Glomerular filtration rate decreases which results in sodium and water retention.
- This increases the volume of blood and body fluid.
- This in turn increases the hydrostatic pressure of capillary.
- These both factors togetherly increase the accumulation of fluid.
- Thus, extracellular edema occurs.
c) Low supply of blood to kidneys during heart failure
- Renin secretion increases in this condition.
- Thus, aldosterone secretion becomes more.
- Reabsorption of sodium and water from renal tubules into ECF increases.
- This results in the development of extracellular edema.
- If fluid accumulates in pulmonary interstitium, it is called pulmonary edema.
- In left heart failure, right ventricle pumps blood to pulmonary circulation.
- This blood cannot return from lungs to the left side of the heart.
- This is because of weakness of this side of the heart.
- Thus, pulmonary vascular pressure increases.
- This causes leaking of fluid from capillaries to pulmonary interstitium.
- Thus, pulmonary edema occurs which may be life threatening.
Edema and Its Types