Seeing Throughout Blood Circulatory to Understand Drugs Delivery System

それが十回と言われているように、ナノ粒子は生物医学アプリケーション内の多くの利点があります。薬物送達アプリケーションでは、ナノ粒子はテレサと、キャリアと、薬自体となることができます。

        Studying drug delivery system will combine some basic knowledge in Physics, Chemistry and Biology as interdisciplinary of science and engineering. Targeting medicines into specific tissue or part of body needs  some considerations such as in which way the drugs will be delivered, what kind of media that ensures the drugs reaching the their destination, drugs biocompatibility to not be detected as “alien or invader” by immune system, etc. So, it becomes necessity to understand blood circulatory since blood is main “transporter” in our body. 

        As a living creature, human has specialized system to control blood circulatory called cardiovascular system. The cardiovascular system is an elaborate network that performs two major tasks: It delivers oxygen and nutrients to body organs and removes waste products of metabolism from tissue cells. Its major components are the heart “a hollow muscular pump” and a circulatory system of large and small elastic vessels or conduits that transport blood throughout the body. The circulatory system is an intricate network of vessels that supplies blood to all body organs and tissues. The part of the network that delivers blood to all parts of the body except the lungs is called the systemic circulation, while the flow of blood through the lungs is referred to as the pulmonary circulation.

       Blood that has been oxygenated in the lungs is pumped out of the heart through the aorta which branches off into numerous arteries that deliver oxygen-rich blood to various tissues. The arteries are further subdivided into smaller tubes, the arterioles, which in turn branch off into even smaller vessels, the capillaries. It is in the capillaries that the exchange of substances between the blood and the tissues takes place. The capillaries carrying blood that now has lower oxygen content merge to form the venules, which in turn converge into successively larger veins. Then, venous blood enters to heart and is pumped to lungs, performing next circulation.

         The lymph system is an accessory to the circulation functioning to return excess fluid filtered into the interstitial space back to the circulation. The lymph system also contains lymph nodes and other tissue in which mature lymphocytes proliferate.

         Mean blood pressure is greatest in aorta and the large elastic arteries. They also experience the greatest pulse pressure. Pulse pressure and average pressure decline as the blood enters the smaller muscular arteries and disappears within the arterioles. The capillaries have no pulse pressure. Capillary pressure is highest at their arterial ends and declines precipitously to their venous end. In the venous system, the slope of decline ebbs and lowest pressure is seen in the vena cave. In fact, the pressure goes below zero (a negative or pulling pressure) when the ventricle relaxes.

         Based on Starlings law, hydrostatic pressure is greatest at the arterial end of capillaries. This forces water and dissolved substances out into the interstitial fluid. Net filtration pressure (NFP = Hydrostatic Pressure –Osmotic Pressure) is 10 mmHg. As fluid is lost, the hydrostatic pressure decreases, becoming only 17 mmHg at the venous end. The osmotic pressure is not remaining same, there is now an inward pressure of 8 mmHg, (NFP = -8). This returns most, but not all of the lost fluid to the circulation. The remainder must be collected and returned by the lymphatic system.

        Cross sectional area is the greatest in the capillary component producing the slowest velocity. This facilitates transport from capillaries to interstitial fluid. Cross sectional areas are lower, and velocities are higher in the arteries and veins, since cross sectional area corresponds geometrically to the surface area, about 50 m2 in both the systemic tissues and the lungs.

        By understanding how the blood being circulated, hopefully gives information used as a consideration in designing nanomedicine and how its delivery system goes on. Parts of body is not like a hard drive that we can access as much as we want since they have specific register address (almost zero error communication). But, every organ is connected by vessels containing blood as media transport of essential substances and as protector from hazardous materials that may disturb parts of body. The  drugs may be removed, relocated or destroyed before they reach their destination