EDEMA
Edema is defined as the
swelling caused by excessive accumulation of fluid in the tissues. It may be
generalized or local. Edema that involves the entire body is called generalized
edema. Local edema is the one that occurs is specific areas of the body such as
abdomen, lungs and extremities like feet, ankles and legs. Accumulation of
fluid may be inside or outside the cell.
TYPES OF EDEMA
Edema is classified
into two types, depending upon the body fluid compartment where accumulation of
excess fluid occurs:
1. Intracellular edema
2. Extracellular
edema.
INTRACELLULAR EDEMA
Intracellular edema is
the accumulation of fluid inside the cell. It occurs because of three reasons:
1. Malnutrition
2. Poor metabolism
3. Inflammation of the
tissues.
1.
Edema
due to Malnutrition
Malnutrition occurs because
of poor intake of food or poor circulatory system, through which the nutritive
substances are
supplied. Due to the lack of nutrition, the ionic pumps of the cell membrane
are depressed leading to poor exchange of ions. Especially, the sodium ions
leaking into the cells cannot be pumped out. Excess intracellular edema.
2.
Edema
due to Poor Metabolism
Poor metabolism is caused
by poor blood supply. Poor blood supply leads to lack of oxygen. It results in
poor function of cell membrane and edema, as explained above.
3.
Edema due to Inflammation of Tissues
During inflammation of
the tissues, usually the permeability of cell membrane increases. This causes
the movement of many ions,
including sodium into the cells resulting in endosmosis and intracellular
edema.
EXTRACELLULAR EDEMA
Extracellular edema is
defined as the accumulation of fluid outside the cell.
Causes for
extracellular edema
1. Abnormal leakage of
fluid from capillaries into interstitial space.
2. Obstruction of
lymphatic vessels that prevents fluid return from interstitium to blood.
Conditions which lead
to extracellular edema
1. Heart failure.
2. Renal disease.
3. Decreased amount of
plasma proteins.
4. Lymphatic
obstruction.
5. Increased
endothelial permeability.
1.
Edema
due to Heart Failure
Edema occurs in heart
failure because of various reasons such as:
i. Failure of heart to
pump blood: Failure of the heart to pump blood from veins to arteries increases
venous pressure and
capillary pressure. This leads to increased capillary permeability and leakage
of fluid from blood into interstitial fluid, causing extracellular edema.
ii. Fall in blood pressure
during heart failure: It decreases the glomerular filtration rate in the
kidneys, resulting in
sodium and water retention. So, the volume of blood and body fluid increases.
This in turn increases
the capillary hydrostatic pressure. These two factors together increase the
accumulation of fluid causing extracellular edema.
iii. Low blood supply
to kidneys during heart failure: It increases renin secretion, which in turn
increases aldosterone
secretion. Aldosterone increases the reabsorption of sodium and water
from renal tubules
into ECF resulting in the development of extracellular edema.
Pulmonary Edema
Pulmonary edema is the
accumulation of fluid in pulmonary interstitium. In left heart failure, the
blood
is easily pumped into
pulmonary circulation by right ventricle. However, the blood cannot return from
lungs to left side of the heart because of weakness of this side of the heart.
This increases pulmonary vascular pressure leading to leakage of fluid from
capillaries into pulmonary interstitium. It causes pulmonary edema which can be
life threatening.
2.
Edema
due to Renal Diseases – Generalized Edema
In renal disease, the
kidneys fail to excrete water and electrolytes particularly sodium, leading to
retention of water and electrolytes. So, the fluid leaks from blood into interstitial
space causing extracellular edema. Initially, the edema develops in the legs,
but later it progresses to the entire body (generalized edema).
3.
Edema
due to Decreased Amount of
Plasma Proteins
When the amount of
plasma proteins decreases, the colloidal osmotic pressure decreases. Because of
this, the permeability of the capillary increases, resulting in increased
capillary filtration. So, more amount of water leaks out of the capillary. It
accumulates in the tissue spaces resulting in extracellular edema.
Amount of plasma
proteins decreases during the conditions like malnutrition, liver diseases,
renal
diseases, burns and
inflammation.
4.
Edema
due to Lymphatic Obstruction – Lymphedema
Lymphedema is the
edema caused by lymphatic obstruction. It is common in filariasis. During this
disease, the parasitic
worms live in the lymphatics and obstruct the drainage of lymph. Accumulation
of lymph along with cellular reactions leads to swelling that is very prominent
in legs and scrotum. Repeated obstruction of lymphatic drainage in these regions
results in fibrosis and development of elephantiasis.
Elephantiasis
Elephantiasis is a
disorder of lymphatic system, characterized by thickening of skin and extreme enlargement
of the affected area, most commonly limbs (legs), genitals, certain areas of
trunk and parts
of head.
5.
Edema
due to Increased Endothelial Permeability
The permeability of
the capillary endothelium increases in conditions like burns, inflammation,
trauma, allergic reactions and immunologic reactions, which lead to oozing out
of fluid. This fluid accumulates leading to development of edema.
PITTING AND
NON-PITTING EDEMA
Interstitial fluid is
present in the form of a gel that is almost like a semisolid substance. It is
because the
interstitial fluid is
not present as fluid but is bound in a proteoglycan meshwork. It does not allow
any free
space for the fluid movement
except for a diameter of about a few hundredths of a micron. Normal volume of
interstitial fluid is 12 L and it exerts a negative pressure of about 3 mm Hg.
It applies a slight
suction effect and
holds the tissues together. However, in abnormal conditions, where the
interstitial fluid volume increases enormously, the pressure becomes positive. Most
of the fluid becomes free fluid that is not bound to proteoglycan meshwork. It
flows freely through tissue spaces, producing a swelling called edema. This
type of edema is known as pitting edema because, when this area is pressed with
the finger, displacement of fluid occurs producing a depression or pit. When
the finger is removed, the pit remains for few seconds, sometimes as long as
one minute, till the fluid flows back into that area. Edema also develops due
to swelling of the cells or clotting of interstitial fluid in the presence of
fibrinogen.
This is called
non-pitting edema because, it is hard and a pit is not formed by pressing.
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