Use of function diagrams in physiology education: Nessie the Nephron and Navigating the Lochs

Function diagrams focus on physiological concepts rather than associated structures and can serve as elaboration tools and mnemonic aids. A function diagram prototype of the gastrointestinal system was recently described (Wilson TE, Barrett KE. Adv Physiol Educ 45: 264-268, 2021). In this article, a functional diagram of the glomerulus, nephron, urinary system, and bladder is proposed. Colloquially named "Nessie the Nephron" to loosely capture the looping structure and elusive understanding of renal blood flow, glomerular filtration, and epithelial transport for the student, not to mention the nearly mythical countercurrent multiplier. "Navigating the Lochs" references Nessie's possible habitat and more importantly the movement and storage of the modified ultrafiltrate from the nephron. The primary analogies that form the structure of this function diagram are Rain Barrel, Soaker Hose, and Hose Nozzle (afferent and efferent blood flow and filtration pressure); Water Purification System (glomerular filtration barrier forming multiple step filtration process involving the capillary, basement membrane, and podocytes); Mixed Recycling Machine (proximal tubule individual, co-, and bulk transport); Desiccator and Briner (thin descending limb removal of water and thin/thick ascending limb removal of salt); Conveyor Belt Picker (distal nephron selective ion transport); and Concentrator (collecting duct water and urea transport). The primary analogies that elaborate Navigating the Lochs are Aqueduct and Cistern System (fluid movement and collection); and Pressure Gauge, Syringe Bulb, and Two-Valve Plumbing (bladder storage and micturition). Complementing these analogies is the rich potential for inclusion of clinical and comparative applications and examples to link previous knowledge and strengthen memories for future retrieval.NEW & NOTEWORTHY Function diagrams put the focus on physiology and physiological concepts rather than the associated anatomy and can serve as elaboration tools and mnemonic aids. The function diagram of the nephron can provide analogies for glomerular filtration, bulk and selective epithelial transport, and overall ability to create concentrated or dilute urine. The function diagram of the urinary system and bladder can provide analogies for moving and storing urine and finally micturition.