What is Starling's Law of Capillary forces? How does this explain why a nutritionally deficient child would have edema? - ANSWER Starling's Law describes how fluids move across the capillary membrane. There are two major opposing forces that act to balance each other, hydrostatic pressure (pushing water out of the capillaries) and osmotic pressure (including oncontic pressure, which pushes fluid into the capillaries). Both electrolytes and proteins(oncontic pressure) in the blood affect osmotic pressure, high electrolyte and protein concentrations in the blood would cause water to leave the cells and interstitial space and enter the blood stream to dilute the high concentrations. On, the other hand, low electrolyte and protein concentrations (as seen in a nutritionally deficient child) would cause water to leave the capillaries and enter the cells and interstitial fluid which can lead to edema. How does the RAAS (Renin-Angiotensin-Aldosterone System) result in increased blood volume and increased blood pressure? - ANSWER A drop in blood pressure is sensed by the kidneys by low perfusion, which in turn begins to secrete renin. Renin then triggers the liver to produce angiotensinogen, which is converted to Angiotensin I in the lungs and then angiotensin II by the enzyme Angiotensin-converting enzyme (ACE). Angiotensin IIstimulates peripheral arterial vasoconstriction which raises BP. Angiotensin II is also stimulating the adrenal gland to release aldosterone, which acts to increase sodium and water reabsorption increasing blood volume, while also increased potassium secretion in urine.