Homeostasis is the maintenance of constant conditions within the internal environment of the body in order to sustain health and functioning, despite changes in the external environment. The kidney, a principal regulator of the internal environment of the body, establishes homeostasis by regulating the concentration of ions, water and blood volume, pH balance of plasma, and through the elimination of the waste products of metabolism (Tilley, 2003).
The functional unit of the kidney, the nephron, is composed of two key structures: the glomerulus and the renal tubule. The afferent and efferent arterioles supply blood to the glomerulus. As a network of ...view middle of the document...
Eventually, the solutes and fluid that remain in the renal tubule are excreted as urine (Crowder, 2010).
An analysis of urine can provide a clear indication of not only the health of the kidney, but the overall health of the body as well.
Four experiments were conducted to examine the production of urine under the following treatments: water, water and exercise, coffee, and V8.
In subjects undergoing the water treatment, the results should reveal an increased volume, a light color, an increase in pH, and a decrease in specific gravity. Excessive water in the body causes an imbalance of sodium and water content in the body, resulting in more dilute extracellular fluid and lowered osmotic pressure. This decrease in pressure is detected by osmoreceptors in the hypothalamus, inhibiting the release of ADH, and prevents the reabsorption of water which is excreted in the urine (Ira, 2009). The loss of water from the body into the urine causes the urine to become more dilute, thus lighter in color. Also, when the water levels present in the urine increase, the concentration of H+ ions will decrease. This causes the pH of the urine to increase. The specific gravity of the urine will decrease because the urine is more dilute.
In subjects undergoing the water and exercise treatment, the results should reveal a decreased volume, a darker color, a decrease in pH, and an increase in specific gravity. The sympathetic division of the autonomic nervous system is activated during physical exercise, causing the blood vessels that supply the kidneys to constrict. This constriction causes the glomerular filtration rate to decrease, which results in the production of less urine. Also, the constriction of the blood vessels supplying the kidneys produces a reduced blood supply to the kidneys, causing the release of renin and consequently the renin-angiotensin-Aldosterone cascade occurs (Ira, 2009). The Aldosterone acting on the kidneys promotes the retention of sodium which stimulates the release of ADH and causes the kidneys to retain water. When the water levels present in the urine decrease, the concentration of H+ ions will increase (Ira, 2009). This causes the pH of the urine to decrease. The specific gravity of the urine will increase because the urine is more concentrated.
In subjects undergoing the coffee treatment, the results should reveal increased volume, a light color, an increase in pH, and a decrease in specific gravity. Caffeine is chemically similar to adenosine, and therefore competitively binds to the same neurotransmitter, inhibiting the vasoconstriction effect of adenosine (Tilley, 2003). This allows an increase in the blood supply to the kidneys, increases the glomerular filtration rate, and results in the production of more urine. Also, caffeine works by inhibiting the release of ADH. When the release of ADH is inhibited, the reabsorption of water is prevented and the water is excreted in the urine (Ira, 2009). The...