SEMMELWEIS UNIVERSITY, Medical Biophysics II. Final - Practice topics ONLY Questions And Answers With Complete Solutions

Coulter principle. - Answer-The ability to count and measure the size of particles using an electric circuit. Particles are moved through a small aperture, their presence causes a narrowing of the aperture, which leads to an increase in resistance.By using constant I, According to Ohms law (U= I * R), when R increases, U increases and pulse is generated. Parts and functions of the Coulter-counter - Answer-- Two spaces with a small aperture in between, capillary (contains the electrolyte solution with the cells) - Measuring electrode, one in each of the spaces (closing the circuit and measuring voltage between the two spaces) - Pump (draws the solution into the smaller space, and out again, through the capillary) - Auxiliary electrode (signals when certain volume is reached, to initiate pumping out of the solution) - Integral Discriminator (filter out noise) - Differential Discriminator (mapped of the size distribution of the particles) How does the voltage pulse amplitude depend on particle size in the Coulter-counter? - Answer-Its proportional, bigger particle will form higher resistance, higher voltage pulse. How do you separate the red-blood-cell versus white-blood-cell signals in a Coulter-counter? - Answer-when you want to measure RBC, it's not necessary to separate them from the RBC b.c. the number of WBC is negligible (less than error of the measurement) By hemolyze RBC and measured them separately photochemically and subtracted the result from the coulter-counting measurement How do you separate the red-blood-cell versus platelet signals in a Coulter-counter? - Answer-By integral discrimination (the size of the platelets is much smaller)What is the role of differential discriminator in Coulter-counting? - Answer-Mapping the size distribution of the particle Why is dilution of blood is necessary in Coulter-counting? - Answer-Because the cells themselves do not conduct well, and so we dilute them with an electrolyte solution so changes in resistivity are noticed. Also, for practical reasons (e.g. we don't want the solution to dry up.) What solution is used for blood dilution in Coulter-counting? - Answer-Saline solution, for optimal osmotic pressure (keep the RBCs in their natural size) and for good conduction (NaCl) How does the matter flow density (flux) change if the concentration gradient is doubled? - Answer-It doubles, due to flicks first law: Jv=-Dxdeltac/deltax Name the parameters influencing the value of diffusion coefficient. - Answer-Size and shape of the particle as well as the temperature and viscosity of the medium. Can be calculated for spherical particles: D=kT/6 pi n r What diffuses faster: a potassium ion or a virus particle? - Answer-K+ ion due to smaller diffusion coefficient (smaller size) How does the average distance travelled by a diffusing particle depend on time? - Answer-Square root function (Distance average ^2 =6 * D * t) On what length scale is diffusion an effective transport process? - Answer-On a small scale