Raynaud's disease and thromboangitis obliterans (Buerger's disease) are caused by reduced blood flow to the extremities. Raynaud's disease involves intermittent vasoconstriction of arteries in fingers and toes in response to cold or stress, causing discoloration and pain. Buerger's disease causes inflammation and blood clots in lower extremity arteries and veins, which can lead to gangrene if untreated. Both diseases require lifestyle modifications like avoiding cold and tobacco to prevent attacks and progression. Treatment involves medications to improve circulation, surgery to relieve symptoms, and amputation in severe cases of Buerger's disease.