The Concept of Renal Physiology

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Table of Contents

Introduction
Results
Discussion
References

Introduction

The kidney performs two key functions in the body, which are either homeostatic or endocrine. Homeostatic functions of the kidney involve the maintenance of a relatively constant extracellular environment. Maintenance of the osmolality of body fluids is imperative because it provides the optimum pH, which is indispensable for the routine function of the cells or organisms. This is achieved by the excretion of metabolic waste products such as uric acid, creatinine and urea. Water and electrolytes from dietary intake is also removed from the body. The kidneys maintain balance by “keeping the rate of excretion equal to the sum of net of intake plus endogenous production” (Rennker & Denker, 2007). The kidney can also control the excretion of water and solutes, for example, sodium, potassium, and hydrogen through alteration of tubular absorption and secretion.

There are considerable variations in the amount and osmolality of the daily urine production of an individual. The volume and rate of production of urine is directly proportional to the amount of fluid taken by the individual (Lyons, 2011). A low fluid intake results in a low volume of urine and vice versa.

The endocrine roles of the kidney involve the secretion of hormones, which participate in the control of “systemic and renal hemodynamics.” These include hormones such as prostaglandins, angiotensin II, and renin. Erythropoietin aids in the formation of red blood cells, whereas calcitriol, the key constituent of vitamin D takes part in metabolism of minerals (Rennker & Denker, 2007).

This paper looked at the homeostatic functions of the kidney paying detail to the renal and acid-base bodily processes. It investigated the rate of urine production, resultant specific gravities and pH in three different subjects.

Results

Experiment 1: The effect of water load on urine production rate and osmolar excretion rate

Table 1: The rate of urine production rates for three subjects (control subject, a water load subject and an isotonic saline subject).

Urine production rate	0	20	40	60	80	100
A control Subject	1.1	1.3	1.3	1.2	1.0	0.8
A water load subject	0.8	2.2	5.7	7.6	5.4	3.0
An isotonic saline subject	0.8	2.0	3.1	3.9	2.6	1.8

*Figure 1: A graph of urine production rate versus time*

The results shown in the above figures indicated that the water load subject had the highest rate of urine production, whereas the isotonic saline subject had a lower rate of urine production compared to the water load subject. However, the urine production rates of the control subject were lower than the water load and isotonic subjects’ rates.

Experiment 2: Chemical and Physical properties of urine

Table 2: The specific gravity of urine for the three subjects at 0 minutes and 60 minutes

Specific gravity	SG at time 0 minutes	SG at time 60 minutes
Control	1.017	1.021
Water load	1.017	1.003
Saline	1.019	1.008

The values in the figure above indicated that the specific gravity of urine was higher at 0 minutes than at 60 minutes. The SG at 0 minutes was identical (1.017) for the control and water load subjects, but was slightly higher (1.019) for the isotonic saline subject. However, at 60 minutes, the SGs for the water load and isotonic saline subjects were slightly lower (1.003 and 1.008) than the control subject’s specific gravity (1.021).

Table 3: Average values and ranges for the class urine data

Average	Range
6.026	5.3-7.5

Discussion

It was observed that the overall rate of urine production increased reaching a maximum (peak) and reduced in all subjects. That was because of continued kidney function. The water load subject displayed the highest rate of urine production. This was because the kidney had to get rid of excess water to maintain water balance. The isotonic saline subject, on the other hand, produced moderate quantities of urine because there was no excess water to be eliminated. The control subject displayed the lowest rate of urine production.

The antidiuretic hormone (ADH) played a key role in the maintenance of water balance. Osmoreceptor cells in the hypothalamus checked blood osmolality and activated the release of ADH (The vertebrate kidney, n.d.). Osmolality of the blood, volume of blood and certain receptors modulated the release of ADH. ADH acted on the kidney nephrons causing them to retain or release water. Water passed through the collecting ducts of the cell membrane through water channels called aquaporins (Lyons, 2011). “The key targets of ADH were the distal convoluted tubules and the collecting ducts of the kidney, where the hormone increased the permeability of the epithelium to water” (The vertebrate kidney, n.d.). In the negative feedback loop, as was the case in the water load subject, the high amount of water reduced the blood osmolality. Consequently, there was suppression of ADH release making the kidney absorb little water resulting in the production of large quantities of dilute urine (The vertebrate kidney, n.d.). The large amount of dilute urine was what resulted in the high rate of urine production. In the control subject, there was little water to be excreted. Therefore, the hormone raised the epithelium’s permeability to water, magnifying the reabsorption of the water. As a result, there was production of little amount of urine hence the low rate of urine production.

The renin-angiotensin-aldosterone pathway serves in the short-term mechanism of regulating fluid balance.

According to Jones, normal urine has a pH range of 4.5 to 8.0. However, the somewhat acidic of 6.0 is the standard (2010). All the subjects had normal urine ph values going by the average class pH value.

The specific gravity of normal urine is between 1.003 and 1.030. Specific gravity measures the quantity of solids in urine. A low SG indicates that few solids are present, whereas a high SG shows the presence of a large amount of solids (Jones, 2010). Therefore, the SG for all the three subjects was within the normal ranges, indicating that increasing the amount of water intake did not impact on the amount of solids in the urine. However, the SG at 0 minutes was higher than the SG at 60 minutes, indicating that the amount of solids in the urine reduced with the quantity of urine produced. Those results implied that as more urine was produced, more solids were eliminated together with it.

References

Jones, B. D. (2010). Comprehensive medical terminology (4^th ed). Clifton Park, NY: Cengage learning.

Lyons, I. (2011). Lecture notes: Biomedical science. Hoboken, NJ: John Wiley & Sons.

Rennker, H. G. & Denker B. M. (2007). Renal pathophysiology: The essentials (2^nd ed). Philadelphia, PA: Lippincott Williams & Wilkins.

The vertebrate kidney (n.d.). Web.

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