Cardiovascular Module Cardiovascular Physiology Lect. Six Microcirculation & Lymphatics (Edema formation) Prof. Dr. Najeeb Hassan Mohammed
The microcirculation and the lymphatic system
The microcirculation and lymphatic system
Microcirculation and Lymphatic system Objectives: 1. Define the term hydrostatic and oncotic (colloid osmotic) pressures and state how it is interact in maintenance of interstitial fluid. 2. State and explain briefly the effects on tissue fluid formation in a vascular bed of: altered capillary hydrostatic pressure, decreased plasma protein concentration, elevated central venous pressure, increased capillary permeability, and obstruction of lymph drainage. 3. Define the term edema.
Types of Capillaries Permits exchange of nutrients and wastes. Continuous: Intercellular channels or clefts. Fenestrated: Intercellular pores. Discontinuous (sinusoidal): Have large, leaky capillaries.
Formation and drainage of the interstitial fluid: The IF is continuously formed and drained by the capillaries, and it contains almost the same constituents of the plasma except the plasma proteins. Factors that affect tissue fluid formation and drainage: The Starling's forces (the hydrostatic and osmotic forces that act across the capillary walls) The capillary permeability.
Overall Fluid Movement (Starling forces) P c = Hydrostatic pressure in capillary P i = Colloid osmotic pressure of interstitial fluid P i = Hydrostatic pressure in interstitial fluid P p = Colloid osmotic pressure of blood plasma. P c + P i (fluid out) - P i + P p (fluid in)
The Starling's forces: The hydrostatic capillary pressure: outwards, averages 35 mmhg (arteriolar ends) and 12 mmhg (venular ends). The interstitial fluid pressure: inwards, averages 1 mmhg. The plasma colloid osmotic pressure or oncotic pressure: inwards. plasma albumin. averages 25 mmhg. The interstitial fluid colloid osmotic pressure: outwards. averages 3 mmhg.
Lymphatic System 3 basic functions: Transports interstitial (tissue) fluid back to the blood. Transports absorbed fat from small intestine to the blood. Helps provide immunological defenses against pathogens.
EDEMA It is due to accumulation of excessive amounts of interstitial fluid (mostly in the dependent parts of the body by the effect of gravity), and this has 2 main causes: Excessive leakage of fluid from the capillaries. Inadequate lymph drainage.
Non-pitting edema (Elephantiasis) Pitting edema
EDEMA Excessive leakage of fluid from the capillaries: An increase of the capillary hydrostatic pressure: (elevation of the venous pressure (heart failure)). Hypoproteinaemia: decrease of synthesis of plasma proteins (severe liver disease). Undernutrition. excessive loss of plasma proteins (nephrotic syndrome, severe burns). An increase of capillary permeability: inflammation, bacterial infections, allergic reactions. prolonged ischemia and certain toxins. Excessive retention of salt in the body: renal and cardiac edema.
EDEMA Inadequate lymph drainage. blockage of the lymph vessels: which leads to accumulation of both fluid and protein in the tissue spaces (lymphedema (non-pitting edema)). Cancer, after certain surgical operations (e.g. radical mastectomy). infection with filaria worms which obstruct the lymphatics, causing massive swelling of the affected organ commonly the legs (elephantiasis).
Elephantiasis
In Summary Edema is excessive accumulation of ECF resulting from: High blood pressure Venous obstruction Leakage of plasma proteins into ECF Myxedema (excess production of glycoproteins in extracellular matrix) from hypothyroidism Low plasma protein levels resulting from liver disease Obstruction of lymphatic drainage
thank you M.B.Ch.B Academic Degrees Bachelor of Medicine and Bachelor of Surgery/chirurgery بكالوريوس طب وجراحة عامة