Volume and clearance: Kidneys and excretory systems

Abstract

Abstract for Section 10.1: Kidneys and their evolutionary precursor organs are indisputable for the survival of mammalians to invertebrates like Drosophila. These organs are responsible for clearing of water-soluble exogenous and also endogenous metabolites with a potential for toxicity in settings of overload. Such substances are for instance ammonium ions (from protein metabolism), ureic acid (from nucleic acid metabolism), and creatinine (end product of muscle proteins). These substances are called urophenic. In situations of kidney failure these substances are retained and cause severe toxicity in the patients (uremia). Further, water and ions are secreted which have important functions in cells: Na+ (sodium), K+ (potassium), HCO3- (bicarbonate), and phosphate and calcium. Especially Na+ ions are recognized by specialized kidney tubular cells and indicate the volume state of the organism. At the same time, the body must retain its homeostasis and retain its crucial fluids and molecules. The kidney is thus a major checkpoint for blood clearance, blood homeostasis, blood volume, blood pressure, and its pH. Abstract for Section 10.2: Main functions of the urinary system are elimination of metabolic wastes that otherwise accumulate and harm the integrity of the body, maintenance of homeostasis and osmoregulation, acid-base regulation and hormone production. Different species have developed different urinary sytems to adapt to the environment they are living in.