Biomedical Technology and Dialysis Water Treatment Flashcards

The main difference between an arteriovenous shunt (AVS) and an arteriovenous fistula (AVF) is an:

Answer: AVF is entirely within the arm.

An arteriovenous fistula (AVF) is created surgically by connecting an artery directly to a vein, typically in the arm, forming a completely internal connection. In contrast, an arteriovenous shunt (AVS) historically involved an external tube connecting an artery and a vein, which had higher risks of infection and clotting. AVFs are now the preferred long-term vascular access for hemodialysis due to their lower complication rates.

Which of the following dialyzers is used currently?

Answer: Hollow tube

Modern dialyzers predominantly use a hollow fiber (or hollow tube) design. These dialyzers contain thousands of tiny, semi-permeable hollow fibers through which blood flows. Dialysate flows around the outside of these fibers, allowing for efficient exchange of waste products and excess fluid across the membrane. This design maximizes surface area for filtration.

Which of the following kidney structures connects with and delivers urine directly to the ureter?

Answer: Pelvis

The renal pelvis is the funnel-shaped structure located in the center of the kidney. It collects urine from the major calyces and acts as a reservoir before the urine flows into the ureter. Therefore, it directly connects with and delivers urine to the ureter for transport to the bladder.

All of the following substances are produced by the kidney EXCEPT:

Answer: aldosterone.

The kidneys produce several important substances, including renin (for blood pressure regulation), erythropoietin (for red blood cell production), and calcitriol (the active form of vitamin D). Aldosterone, however, is a hormone produced by the adrenal glands, not the kidneys, and plays a role in regulating sodium and potassium balance.

Which site in the hemodialysis pathway has the highest positive pressure?

Answer: Blood entering the dialyzer fibers

In hemodialysis, blood is pumped from the patient's artery into the dialyzer. To effectively push blood through the narrow dialyzer fibers and facilitate filtration, the pressure is highest at the point where the blood first enters these fibers. This high positive pressure helps drive the filtration process across the membrane.

The term "sieving coefficient of a membrane" refers to the:

Answer: fraction of solute that passes through the membrane by convection.

The sieving coefficient of a membrane quantifies the efficiency with which a solute passes through the membrane via convection, also known as solvent drag. It represents the ratio of the solute concentration in the ultrafiltrate to its concentration in the plasma. A sieving coefficient of 1 means the solute passes freely, while 0 means it is completely retained.

The ultrafiltration coefficient of a dialyzer refers to the:

Answer: fluid that passes through the membrane in 1 hour.

The ultrafiltration coefficient (Kuf) of a dialyzer measures its permeability to water. It indicates how much fluid (in milliliters) will be removed from the blood across the dialyzer membrane per hour for every mmHg of transmembrane pressure. This value is crucial for calculating and controlling the amount of fluid removed from a patient during dialysis.