Describe the major functions of the urinary system.
List the three processes that take place in the nephron (i.e., filtration, reabsorption, and secretion).
Describe the role of the nephron in urine production.
Describe the composition of normal urine.
Perform a virtual urinalysis of three samples of urine using the dipstick method and analyze the urinalysis for evidence of abnormality by comparing the results to a standard reference chart.
Urine characteristics
The urinary system has many important functions. Most of these functions are related directly to urine production and include filtration of blood, removal of nitrogenous wastes, blood volume and blood pressure regulation, acid-base balance and electrolyte regulation. Urine formation is critical to our health and is the responsibility of the nephron - the structural and functional unit in the kidney. Most of them (85%) are located in the cortex and some are located at the junction with the medulla. Each kidney has approximately one million nephrons.
Each kidney filters approximately 1 liter of blood per minute. Blood is filtered from the glomerulus, a capillary bed, into the glomerular capsule through hydrostatic pressure. The fluid, now called filtrate, then enters the renal tubule where it is then termed tubular fluid. 99% of the filtrate created will be reabsorbed during the process of urine formation.
Urine can be characterized by its composition, volume, specific gravity, color, transparency, and smell. Determining both physical characteristics and chemical composition of urine provides a great deal of information about the health of the individual. Characteristics of urine change, depending on influences such as water intake, exercise, environmental temperature, nutrient intake, and other factors. These characteristics include:
Urine volume is an important number regulated by the kidneys. Volume of urine can range up to 18L/day, but a normal urine volume is about 1-2L/day. This volume can increase (taking a diuretic, developing diabetes (mellitus and insipidus), drinking a lot of water when staying inside and resting) or decrease (working outside on a hot day without access to water, too many aquaporins or increasing permeability of collecting duct to water). Changes in urine output are known as:
Analysis of a patient's urine (urinalysis) is an easy, non-invasive, and quick way to determine if some diseases or infections are present. The presence of glucose, blood (erythrocytes), leukocytes, excess protein, or ketones is abnormal and indicates infection or disease.
McGraw Hill Online Lab 3: Urinalyses