1. Make a statement about the composition, color, odor, consistency, nitrogenous component, and amount and specific gravity of mammalian urine. How would you respond if asked about any one of these variables?
Urinalysis is a very important diagnostic procedure consisting of an evaluation of several physical and chemical properties of urine, estimation of its solute concentration, and microscopic examination of urine sediment.
It requires a mastery of laboratory techniques and thoughtful interpretation. It is beyond the scope of this book to provide detailed information for urinalysis, and only some general characteristics of urine are considered.Composition. Urine is formed to keep the composition of the ECF constant, and, generally, most substances that are present in ECF are also present in urine. Also, the composition of urine varies depending on whether substances are being conserved or excreted.
Color. Urine is usually yellow in color. The yellow color is derived from bilirubin that was excreted into the intestine and reabsorbed into the portal circulation as urobilinogen. Much of the urobilinogen is reexcreted by the liver into the intestine, but urobilinogen that bypasses the liver can be excreted by the kidneys into the urine. The various bilinogens are colorless but are spontaneously oxidized on exposure to oxygen. Thus urobilinogen, when partially oxidized, is known as urobilin, and is largely responsible for the yellow color of urine.
Odor. The odor of urine is characteristic for a species and is probably influenced by diet. For example, the characteristic odor imparted to human urine after the ingestion of asparagus is caused by the formation of asparagine (the amide form of the amino acid, aspartic acid).
Consistency. Urine has a watery consistency in most species. Horse urine is somewhat thick and syrupy, however, because of the secretion of mucus from glands in the pelvis of the kidneys and the upper part of the ureters.
The urine of the horse has high concentrations of carbonates and phosphates, which seem to precipitate on standing. The secretion of mucus provides a carrier for the precipitated carbonates and phosphates and prevents their collection in the renal pelvis.Nitrogenous component. The principal nitrogenous constituent of mammalian urine is urea. Urea is formed by the liver from ammonia, which is produced during amino acid metabolism. The body expends considerable energy in producing urea so that the toxicity of ammonia can be avoided. As compared with ammonia, urea is relatively nontoxic at normal concentrations.
Amount and specific gravity. The amount of urine excreted daily varies with diet, work, external temperature, water consumption, season, and other factors. Marked pathologic variations may occur. The specific gravity of urine varies with the relative proportion of dissolved matter and water. In general, the greater the volume, the lower the specific gravity. Volume and specific gravities for several domestic animals and humans are shown in Table 11-4.
| TABLE 11-4 VOLUMES AND SPECIFIC GRAVITIES OF URINE | ||
| ANIMAL | VOLUME (mL/kg BODY WEIGHT/DAY) | SPECIFIC GRAVITY MEAN AND RANGE |
| Cat | 10-20 | 1.030 (1.02-1.040) |
| Cattle | 17-45 | 1.032 (1.030-1.045) |
| Dog | 20-100 | 1.025 (1.016-1.060) |
| Goat | 10-40 | 1.030 (1.015-1.045) |
| Horse | 3-18 | 1.040 (1.025-1.060) |
| Sheep | 10-40 | 1.030 (1.015-1.045) |
| Swine | 5-30 | 1.012 (1.010-1.050) |
| Human | 8.6-28.6 | 1.020 (1.002-1.040) |
| From Reece WO. Kidney function in mammals. In: Reece WO, ed. Dukes’ Physiology of Domestic Animals. 13th edn. Ames, IA: Wiley-Blackwell, 2015. | ||
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