👉🏻Definition & Types:
🔹OEDEMA〰️Swelling. Abnormal/excessive accumulation of free fluid in the interstitial tissue spaces & serous cavities.
🔹Accumulation of fluid (abnormally) inside the cell is intracellular edema/hydropic degeneration.
🔹Accumulation in body cavities:
- Peritoneal Cavity – Ascitis
- Pleural Cavity – Hydrothorax (T.B)
- Pericardial cavity – Hydropericardium
🔹PITTING & NON-PITTING EDEMA:
➡️ When interstitial fluid volume increases, most of the fluid becomes free that is not bound to proteoglycan meshwork. This type of edema is called pitting edema because when this area is pressed with finger, fluid gets displaced producing depression or a pit as seen in SUBCUTANEOUS TISSUES.
➡️ Edema also develops due to swelling of the cells/clotting of interstitial fluid in the presence of fibrinogen. This is called Non-pitting/solid edema because its hard & a pit is not formed by pressing.
- e.g. – Myxodema
- – Elephantiasis
🔹 Pathogenesis of Edema:
➡️ Causative mechanisms that produce edema are:
- ⬇️ Plasma oncotic pressure
- ⬆️ capillary hydrostatic pressure
- Lymphatic obstruction
- Sodium & Water retention
- ⬆️ capillary permeability
- Tissue factors
These mechanisms interfere with normal fluid balance of plasma, interstitial fluid & lymph flow.
- It is exerted by total amount of plasma proteins that tend to draw fluid into the vessels normally.
- A fall in the total plasma protein level (<5g/dl), results in lowering of plasma oncotic pressure in a way that it can no longer counteract the effect of hydrostatic pressure of blood.
- Therefore, increased outward movement of fluid from capillary wall & decreased inward movement of fluid from the interstitial space causing edema.
- Hypoproteinaemia usually produces generalized edema
- Hypoalbuminaemia – <2.5g/dl albumin concentration has 4 times higher plasma oncotic pressure than globulin
- In hypoalbuminaemic states, the decreased plasma oncotic pressure disturbs the equilibrium between plasma and interstitial fluid, with the result that there is a decrease in the movement of the interstitial fluid back into the blood at the venular end of the capillaries. The accumulation of interstitial fluid is seen clinically as oedema. The relative decrease in plasma volume results in a fall in renal blood flow. This stimulates the secretion of renin, and hence of aldosterone, through the formation of angiotensin. This results in sodium retention and thus an increase in ECF volume, which potentiates the oedema.
There are many possible causes of hypoalbuminaemia; a combination of which may be implicated in individual cases. For example, to list few of them👇🏻
- Oedema of renal disease (Nephrotic syndrome, Acute glomerulonephritis)
- Ascitis of liver disease e.g. in Cirrhosis.
- Protein losing enteropathy
➡️ Fluid from capillary wall to interstitial space by counteracting the force of plasma oncotic pressure.
➡️ Edema results when hydrostatic pressure at Venular end of capillary wall(12mmHg) becomes more than the plasma oncotic pressure, resulting in no reabsorption of fluid at the Venular end.
- Example, edema of Cardiac disease – Congestive cardiac failure, constrictive pericarditis
- Cirrhosis of liver
- Passive congestion – e.g. mechanical obstruction due to thrombosis of veins of lower legs, varicosities, pressure by pregnant uterus, tumours etc.
- Postural edema e.g. ⬆️ Venous pressure (Edema of feet & ankle)
➡️ Lymphoedema is caused due to obstruction of lymphatic channels causing localized edema.
- e.g. removal of axillary lymph nodes in radical mastectomy for carcinoma of breast cancers.
- Rupturing of main lymphatic channel causing chylothorax & chylous ascitis
– Inflammation of Lymphaties:
- Filariasis (infection with Wuchereria Bancrofti) – Chronic lymphoedema of scrotum & legs
– Abnormal development of lymphatic channels:
- Milroy’s disease/hereditary lymphoedema
- Edema comfined to one or both lower limbs.
Forces acting in the interstitial space –
1. Oncotic Pressure
⬆️ Vascular permeability & inadequate removal of proteins by lymphatics
2. Tissue Tension
Lowered (e.g. loose subcutaneous tissues of eyelids & external genitalia)
Dr. Mehnaz Memon🖊
References: Textbook of Pathology, Harsh Mohan; Internet; https://basicmedicalkey.com/plasma-proteins-and-enzymes/