An echocardiogram--or echo--is a diagnostic test used to take pictures of the heart and surrounding blood vessels.It is more detailed than an X-ray and uses sound waves versus radiation.n echocardiogram--or echo--is a diagnostic test used to take pictures of the heart and surrounding blood vessels.
The term simple diffusion refers to a process whereby a substance passes through a membrane without the aid of an intermediary such as a integral membrane protein. The force that drives the substance from one side of the membrane to the other is the force of diffusion. In order for substances to pass through a cell membrane by simple diffusion it must penetrate the hydrophobic core of the phospholipid bilayer. The types of molecules that can do this are themselves substantially hydrophobic in nature such as carbon dioxide, oxygen or ethanol. In the figure below the green triangle indicates a concentration gradient of carbon dioxide. The blue arrow indicates the direction of net flow of carbon dioxide.
Molecular diffusion, often simply called diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles. Diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration. Once the concentrations are equal the molecules continue to move, but since there is no concentration gradient the process of molecular diffusion ha