Kidney always so simple; in cartilaginous fish and some amphibians, there is also a shorter duct, similar to the amniote ureter, which drains the posterior (metanephric) parts of the kidney, and joins with the archinephric duct at the bladder or cloaca. Indeed, in many cartilaginous fish, the anterior portion of the kidney may degenerate or cease to function altogether in the adult. In the most primitive vertebrates, the hagfish and lampreys, the kidney is unusually simple: it consists of a row of nephrons, each emptying directly into the archinephric duct. Invertebrates may possess excretory organs that are sometimes referred to as
Underactive bladder et al. (2014). "Pathophysiology and animal modeling of underactive bladder." Int Urol Nephrol 46 Suppl 1: 11-21. van Koeveringe, G. A., K. L. Rademakers, et al. (2014). "Detrusor underactivity: Pathophysiological considerations, models and proposals for future research. ICI-RS 2013." Neurourol Urodyn 33(5): 591-596. Underactive bladder Underactive bladder syndrome (UAB) describes symptoms of difficulty with bladder emptying, such as hesitancy to start the stream, a poor or intermittent stream, or sensations of incomplete bladder emptying. The physical finding of detrusor pressurization of insufficient strength or duration to ensure timely and efficient bladder emptying is properly termed "detrusor underactivity" (DU) (Abrams et