EDEMA Physiology Slideshow – MBBS Lectures – Physiology Lectures

Learning Objectives

•By the end of lecture, students should be able to:
–Define edema
–Explain and categorize the types of edema
–Summarize the causes of edema
–Explain the physiological basis of development of edema

Fluid Distribution

•60% of lean body weight is water
•2/3 is intracellular
•1/3 is extracellular (mostly interstitial)
•5% of total body water is in blood plasma

Edema

•Edema is caused by mechanisms that interfere with fluid balance in plasma, interstitial fluid and lymph flow
•Presence of excess fluid in body tissues
•Abnormal and excesses amount of fluid in the interstitial tissue spaces is called edema
•Occur in
–Extracellular fluid Compartment
–Intracellular fluid Compartment

Intracellular Edema

•Conditions
–Hyponatremia
–Depression of metabolic system of tissues
–Lack of adequate nutrition to cells
•May extend to entire tissue like edema of leg
•May leads to death of tissue

•Decreased blood flow, inadequate supply of nutrients and oxygen
•Unable to maintain tissue metabolism
•Depressed ionic pump
•Sodium that leaks into the cell is pumped back by Na/K pump
•Na/K pump depressed Na does not move out of cell and also osmotic drag leads to edema of cell

Inflammation

•Intracellular edema can also occur in inflamed tissue
•Because of increased vascular permeability
•Ions like Na and other ions move into the cell
•Causes osmotic drag

Extracellular Edema

•Fluid accumulate in extracellular spaces
•Causes
–Leakage of fluid from ECF to tissue spaces
–Failure of lymphatics to return fluid back to circulation–lymphedema

Filtration=Kfx (Pc-Pif-πc+πif)
•Change in capillary filtration rate leads to edema
•Increased filtration coefficient
•Increased hydrostatic pressure
•Decreased plasma colloid osmotic pressure

Lymphedema

•Blockage or absence of lmphatics
•Plasma protein accumulates in interstitium
•Not removed increases colloid osmotic pressure
•Drags water from capillaries to interstitium

Blockage of lymph return

•Cancer
•Infections (e.g., filaria nematodes)
•Surgery
•Congenital absence or abnormality of lymphatic vessels

Increased Capillary Pressure

A. Excessive kidney retention of salt and water

1. Acute or chronic kidney failure
2. Mineralocorticoidexcess
   B. High venous pressure and venous constriction
3. Heart failure
4. Venous obstruction
5. Failure of venous pumps
   (a) Paralysis of muscles
   (b) Immobilization of parts of the body
   (c) Failure of venous valves
   C. Decreased arteriolar resistance
6. Excessive body heat
7. Insufficiency of sympathetic nervous system
8. Vasodilator drugs

Decreased Plasma Proteins

•Loss of proteins in urine (nephroticsyndrome)
•Loss of protein from denuded skin areas

1. Burns
2. Wounds
   •Failure to produce proteins
3. Liver disease (e.g., cirrhosis)
4. Serious protein or caloric malnutrition

Increased Capillary Permeability

•Immune reactions that cause release of histamine and other immune products
•Toxins
•Bacterial infections
•Vitamindeficiency, especiallyvitaminC
•Prolonged ischemia
•Burns

Edema in Heart failure

•Heart fails to pump blood received from veins and to be sent to arteries
•Increased venous pressure and capillary pressure–capillary filtration→ EDEMA
•↓CO→↓BP, causes ↓ excretion of salt and water →↑ blood volume→↑capillary filtration→ EDEMA
•↓ excretion of salt and water →↑release of renin, angiotensin II and aldosterone →↑ blood volume

Edema in Heart failure

•Untreated heart failure leads to edema
•When only left sided heart failure occurs pulmonary capillary pressure increases leading to pulmonary edema
•Untreated pulmonary edema is life threatening leading to death

Edema In Renal Diseases

•NaClremains in ECF do not enter the cells
•Kidney diseases →↓ excretion of salt and water →↑ blood volume →↑capillary filtration→ EDEMA
•Leads to
1.↑interstitial fluid volume–ECF edema
2.Hypertension–↑blood volume

Edema by Decreased Plasma Proteins

•Decreased Plasma Proteins
1.Decreased plasma protein production
2.Loss of protein from plasma
•↓Plasma colloid osmotic pressure &↑capillary pressure–ECF edema
•Causes
1.Nephroticsyndrome–protein loss
2.Cirrhosis of liver–insufficient synthesis and increase portal pressure

Safety Factors That Normally Prevent Edema

•Lowcomplianceofinterstitium–interstitialfluidpressureisnegative(3mmhg)
•Lymphflowincrease10-50fold(7mmhg)
•Washdownofinterstitialfluidproteinreducesinterstitialfluidcolloidosmoticpressureandraisescapillaryfiltration(7mmhg)

Low Compliance

•Interstitial fluid hydrostatic pressure in subcutaneous tissues < atmospheric pressure −3 mmHg
•Small suction in the tissues keeps the tissues together
•Compliance in interstitial tissue is low–prevents edema
•↑ Interstitial fluid hydrostatic pressure opposes capillary filtration → filtration of fluid into tissues.

Low Compliance

•For development of edema, ISF hydrostatic pressure must rise 3mmHg
•Compliance will increase–fluid accumulate in tissue
•In positive tissue pressure range, safety factor is lost–edema occurs
•Interstitium is in gel form, fluid is bound in proteoglycan filaments–no free fluid spaces

Insterstitial fluid in GEL form

•Gel prevents free flow of fluid because of entrapment in proteoglycan filaments
•ISF pressure rises to positive pressure range, cusesaccumulation of free fluidin tissues
•pitting edema–one can press thumb against tissue area and push the fluid out of the area–ECF edema
•Nonpittingedema–tissue cells swell instead of the interstitiumor fluid in the interstitiumbecomes clotted with fibrinogen and cannot move freely within tissue spaces

Lymph Flow

•lymphatic system return fluid and proteins back to circulation
•If plasma protein and fluid stays in instertitiumplasma volume would have rapidly depleted resulting in interstitial edema
•Lymph flow can increase 10-50 fold
•lymphatics takes away large amounts of fluid and proteins preventing the positive interstitial pressure
•Safety factor caused by increased lymph flow –7 mm Hg

Washout of proteins

•Interstitial fluid colloid osmotic pressure increases because of proteins
•Lowering interstitial fluid proteins reduces net filtration force prevent EDEMA
•Safety factor is about 7 mm Hg.

Safety factor

•Low tissue compliance in negative pressure range 3mmHg.
•Increased lymph flow 7 mmHg
•Washdownof proteins from interstitial spaces is 7 mmHg
•Total safety factor against edema –17 mmHg
•Capillary pressure in a peripheral tissue rise by 17 mmHg i.e.double the normal value to cause EDEMA

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