Lecture 9 Flashcards
Oedema
Accumulation of abnormal amounts of fluid in the extravascular and intercellular tissue spaces of the body
What are the major factors regulating fluid movement between vascular and interstitial spaces (capillary exchange)?
Blood Hydrostatic Pressure (BHP)
Colloid Osmotic Pressure (COP)
Normally, fluid outflow from the arterial end is balanced by inflow at the venous end, with excess interstitial fluid drained by lymphatics.
How does Blood Hydrostatic Pressure (BHP) influence capillary exchange?
Higher BHP pushes fluid out of capillaries into interstitial tissues.
Accumulation of fluid increases interstitial hydrostatic pressure, eventually halting fluid movement out of the capillary.
What role does Colloid Osmotic Pressure (COP) play in capillary exchange?
Blood Osmotic Pressure (BOP) increases at the venous end as fluid leaves the arterial end, drawing fluid back into the capillary.
Interstitial Fluid Colloid Osmotic Pressure (IFOP) is usually low and insignificant
Which pressures facilitate fluid movement out of and into the capillary?
Out of capillary: Blood Hydrostatic Pressure (BHP) and Interstitial Fluid Osmotic Pressure (IFOP).
Into capillary: Blood Osmotic Pressure (BOP) and Interstitial Fluid Hydrostatic Pressure (IFHP).
What are the pressure changes that contribute to the development of oedema?
- BHP higher than IFHP
- BOP is lower then IFOP
What are the causes of increased BHP?
Impaired venous outflow (congestion) that may develop in
a number of situations:
* Secondary to deep venous thrombosis (DVT)
* Late stage of pregnancy
* Right ventricular failure (RVF)
* Left ventricular failure (LVF)
* Long haul flights
Mechanism of Oedema in DVT
Mechanism of Oedema during long haul flights
Mechanism of Oedema in Late-Stage Pregnancy
Mechanism of Oedema in Right Ventricular Failure (RVF)
Mechanism of Oedema in Left Ventricular Failure (LVF)
What are some causes of decreased BOP?
Excessive loss or reduced synthesis of albumin
- Nephrotic Syndrome
- Chronic Liver damage
Mechanism of Oedema in Nephrotic Syndrome
Mechanism of Oedema in Chronic Liver Damage and Malnutrition
Causes of Increased tissue/Interstitial Osmotic Pressure
A rise in osmotic pressure -> draws water out of the vessel and into the tissues
- Inflammation
What causes impaired lymphatic drainage and lymphoedema?
Usually localized.
Often from surgical removal of lymph nodes (e.g., after breast cancer surgery, causing arm swelling).
Can also result from lymphatic obstruction by parasites (e.g., filariasis)
Salt and water retention contribution to oedema
Generalised Oedema
If there is insufficient albumin in blood -> then blood osmotic pressure will be low
everywhere -> Oedema will be generalised
Can also occur if there is a widespread increase in blood hydrostatic pressure.
