Describe possible alteration of starling forces with examples and consequences

Answer 1

Starling forces are influenced by 3 factors: hydrostatic pressure, oncotic pressure and vascular permeability.

I will use Edema (excess fluid in the interstitial space) as an example because it involves all 3 factors that affect starling forces

1. Edema & Hydrostatic Pressure: Recall, plasma fluid moves from an area of higher hydrostatic pressure to an area of lower hydrostatic pressure. Edema occurs from high capillary hydrostatic pressure, such as in the setting of heart failure, where too much fluid is accumulating in the vessels due to the heart's weakened ability to keep pumping blood forward. This extra fluid accumulated in the capillaries increases the capillary hydrostatic pressure, and thus fluid moves from the capillaries into the interstitial space, causing edema (most notably in the legs). Heart failure --> increased hydrostatic pressure --> fluid moves out of the capillaries into interstitial space --> edema.
2. Edema & Oncotic Pressure: Plasma fluid moves from an area of lower oncotic pressure, to an area of higher oncotic pressure. Edema occurs from low capillary oncotic pressure such as in hypoproteinemia (or too little protein in the blood, most notably albumin). In this pathological state, the interstitial fluid has a higher oncotic pressure relative to the blood. Hypoproteinemia --> low oncotic pressure --> fluid moves out of the capillaries into the interstitial space --> edema.
3. Edema & Vascular Permeability: Increased vascular permeability causes fluid to leak out of capillaries and into the interstitial space. If you have holes in your watering hose, water will leak out; this is something to think of when it comes to vascular permeability. Vascular permeability is increased by vasodilation (from inflammation or infection) or capillary damage (from trauma), which make the capillaries "leaky." infection/inflammation or tissue trauma --> increased vascular permeability --> fluid leaks out of capillaries into the interstitial space --> edema

From these examples, you can see how each hydrostatic P, oncotic P and vascular permeability work to affect starling forces. Hope this helps :)