Renal Regulation of Blood Osmolarity

Abstract: The experiment was done to demonstrate the effect of ADH on the volume and concentration of urine in order to demonstrate the control of ADH over blood plasma osmolarity. Since non-invasive methods were preferred the volume and concentration of urine was used in place of drawing blood. The results that we our anticipating are that ADH levels in the group of subjects that ingested the 6 gm. Of NaCl would increase over time in response to the increased osmolarity of the blood from all of the salt.

Urine output would decrease and eventually the body would stabilize. Purpose: In this experiment, renal regulation of osmolarity will be demonstrated through the use of urinalysis. Materials and Methods: In this experiment, we assigned two groups. The first group was given 800ml of distilled to drink and the second was given 6mg of NaCl dissolved in a small amount of water. Both groups were instructed to note the time each time they voided from waking up until the control urine that was obtained just prior to the beginning of the experiment.

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They also were not to deviate from their normal activities of food and liquid consumption on this day. The control urine was the last urine prior to the experiment and was taken in a large specimen cup. The osmolarity of blood plasma is within normal range at 275-295 mosmol/L of blood. Due to the fact that urine is the end product of our filtered plasma, it was an appropriate and noninvasive vehicle to demonstrate how ADH secretion works in regulating osmolarity. The experiment began when the groups drank the entire solutions and the time was noted for that.

Once the experiment was in progress, the groups were instructed not to ingest anything until the lab was complete. During the 30 minute waiting periods between voiding there were three tests to perform on the urine samples. The control urine was used for the first set of data and time was measured since last void. The total amount of time to complete the experiment was 120 minutes, giving four test urines and five sets to examine and chart. The first test performed was to determine urinary output. The urine was poured completely into a beaker and measured in milliliters.

That measurement was put into the formula x ml/y min. Minutes were measured from the time of previous void until the current void. The second test was to determine the specific gravity. Normal specific gravity is 1. 003-1. 030 and measures the number of solutes in the solution. Therefore, if the number of solutes is increased the concentration of the urine is increased. We placed a drop of each test urine, including the control urine, on the tip of a refractometer and used the number shown. The final test was to measure the sodium ion concentration in the urine.

Ten drops of urine were placed into a test tube and first mixed with one drop of 20% potassium chromate turning the urine bright yellow. The urine is then mixed with 2. 9% silver nitrate drop by drop while shaking the test tube. Once the solution turned a orange brown color then the number of drops was recorded. The number of drops of 2. 9% silver nitrate was for the purpose of our experiment equal to one mg NaCl/ml. The amount of sodium in the plasma changes the irritability of neurons and cell membranes action potentials making it an important solute to test.

Each member of the experiment tracked their data and entered it into a spreadsheet. All the values for the four different labs were combined and averaged according to group to produce a larger sample size. The averages were graphed based on each test measured against time. The data, averages, and graphs are all included in the results section of this report. Theory: The experiment was based upon correct functioning of the hypothalamic osmoreceptors located in the supra-optic nucleus of the hypothalamus to sense a change in blood osmolarity.

This change should increase or decrease the amount of Antidiuretic Hormone (ADH) secreted should also increase, if the osmolarity decreases than ADH secretion should decrease. The purpose of executing this experiment was to essentially illustrate our body’s compensatory mechanisms via hormone regulation to maintain homeostasis. Osmolarity of bodily fluids need to be in their appropriate “normal ranges” in order for the body as a whole to maintain “normal or healthy” functions. A disruption of homeostasis will eventually lead to disease whether acute or chronic if the compensatory mechanisms within our bodies are not working ppropriately. Although the kidneys are the focus of the action, renal regulation of osmolarity goes well beyond the kidneys. The hormones involved in the process are ADH, aldosterone, and the few involved in the renin-angiotensin system. Due to the fact that ADH was the target of our experiment, we will begin with the anatomy and physiology involved with ADH. The cell bodies of the supra-optic nucleus of the hypothalamus are the site of synthesis of ADH, and the site of the osmoreceptors that detect changes in blood osmolarity. The posterior pituitary is the site of release for ADH.

When the osmoreceptors detect a change in osmolarity the number and intensity of the action potentials fired will change. An increase will cause an increase in action potentials fired from the supra-optic nucleus to the posterior pituitary via the infundibulum. Likewise, a decrease in osmolarity will decrease the action potentials fired. The synaptic vesicles of the posterior pituitary will then secrete the appropriate amount of ADH into the nearby capillaries for transport to the kidneys through the blood stream. Nephrons are the primary functional units of the kidneys. Martini, 959) They are responsible for reabsorbing water, organic molecules, and ions. They are also the site of secretion of drugs, toxins, acids, and ammonia. They consist of two parts: the renal corpuscle and the renal tubule. The beginning of a nephron is the renal corpuscle. This is where filtration begins. Blood is delivered to the glomerulus. Blood pressure forces water and solutes out of the capillaries into the capsular space leading into the tubules. The filtrate journeys on through the renal tubule where reabsorption begins.

In respect to water, the variable site for reabsorption is the distal convoluted tubule (DCT), which is also conveniently the site of the ADH receptors. So when the osmolarity of blood changes and this registers with the osmoreceptors of the hypothalamus, they send the ADH via an action potential down the infundibulum to the posterior pituitary to be released at the synaptic vesicle into the blood stream. The ADH travels through the blood to the receptor site at the DCT and tells the nephron whether to retain more or less water.

If the kidneys are retaining water it is reabsorbed back into the plasma for circulation leading to an increased blood volume and lower osmolarity. Conversely, if they are losing water it is excreted via the urine, there is a decreased blood volume, and osmolarity is increased. Once the tubular fluid has passed through the DCT it is dumped into a collecting duct, which is the last point of the nephron, and all the individual collection ducts converge into a larger papillary duct for passage to the ureters, the bladder, and out of the body.

Aldosterone, like ADH, has target cells in the kidneys. Specifically it acts upon the sodium ion pumps and sodium channels in cell membranes along the DCT and collecting duct (Martini, 974). It is made and secreted from the zona glomerulosa, the outer portion, of the adrenal cortex. The main job of aldosterone is to retain sodium ions in the blood and to eliminate potassium ions. Unlike ADH, the target cells for aldosterone are found in salivary glands, sweat glands, and the pancreas as well so clearly this hormone is a powerful contributor to regulating the osmolarity of the blood.

The amount of sodium ions in the blood are a major component in osmolarity and if aldosterone controls the retention of sodium in the body then it is important to consider this hormone in connection with ADH. The expression “water follows salt” is accurate in the relationship of how aldosterone works on increasing blood volume. When the target cells are stimulated in the kidney the sodium is retained back into the plasma and as a secondary effect more water is retained. Aldosterone’s effects are most dramatic when normal levels of ADH are present.

In addition, the sensitivity of the taste buds to salty foods is increased which will lead to more salt ingested into the body. (Martini, 615,999) The renin-angiotensin system is designed to maintain normal blood volume and blood pressure. It can control secretion of both ADH and aldosterone and it involves several target sites. It begins with renin, which is formed and secreted at the juxtaglomular apparatus of the kidney in response to a decreased blood flow to the kidneys or sympathetic stimulation from the vasomotor nerves that regulate blood flow and renal resistance by altering the constriction or dilation of arterioles.

Renin acts as an enzyme and converts angiotensinogen secreted from the liver into angiotensin I. Angiotensin I travels through the blood stream to the lungs where it is modified to Angiotensin II. Angiotensin II then circulates back to the adrenal cortex stimulating aldosterone release. When it reaches the supra-optic nucleus of the hypothalamus, it triggers ADH release. It also signals thirst, leading to increased fluid intake. In the presence of aldosterone, the DCT and the other target cells begin retaining sodium and eliminating potassium leading to fluid retention.

The ADH also leads to fluid retention. To conclude the system, increasing the fluid retention will then increase the blood volume and blood pressure causing normal flow back to the kidneys. Another set of hormones worth mentioning are the Natriuretic Peptide Hormones. They are secreted by cardiac muscle cells of the atria in response to high blood pressure and high blood volume detected by stretching the muscle cells. They are antagonistic to all of the previously mentioned hormones, thus inhibiting ADH secretion, Aldosterone secretion, Angiotensin II secretion.

This will in turn, decrease thirst, sodium and water reabsorption by the kidneys, lower plasma sodium content, plasma volume, and blood pressure. (Kirkpatrick, 2010) All of the hormones mentioned in this description are controlled by interrelated negative feedback mechanisms. The body is a complex compilation of systems working together for the common goal of maintaining homeostasis. Results: Attached there are spreadsheets of raw data for each of the four lab classes. There are 6 separate tables for the averages of the data.

Three tables showing averages for each specific test for the water drinkers, and three tables for the salt drinkers. Finally the averages are graphed against time to show the differences between the two groups. The averages for urinary output for the water consumption raised significantly from the control urine. In the salt consumption group, urinary output decreased over the 120 minutes. Looking at the averages and graphs for specific gravity, the specific gravity of the water group dipped down by the 60 minute mark and then started increasing slightly.

The salt group numbers fell marginally for the 30 minute test and then rose up and stayed increased for the experiment. Finally, the urine sodium content shows similar results to the specific gravity test. The water group values dipped drastically at the 60 minute test and started rising gradually. The salt group values rose incrementally over the full time. Conclusions: In conclusion, the results of this experiment prove the theory that was discussed regarding the effect of ADH on osmolarity and how the kidneys help to regulate this effect.

Urinary output was expected to rise in the group that drank the 800ml of distilled water and to decrease in the group that consumed the 6mg NaCl dissolved in a shot of water. This was validated in the study. The specific gravity and the urine sodium content values essentially showed a decrease in the water drinking subjects and an increase in the salt consuming group. Since specific gravity represents the solute concentration in the urine, showing a decrease in value means that the urine is more diluted which is concurrent with drinking more water. The urine sodium content showed the same trend.

Flushing the body with water will trigger ADH secretion to decrease because osmolarity will be lowered because urine sodium content and solute concentration has dropped. If ADH secretion slows, urinary output will increase because the ADH receptors in the kidneys are not being activated. The kidneys will not retain water and it will be flushed out through the bladder. Examining the average values, the water averages begin to decrease again after the 60 minute test. ADH secretion would begin to prevent the body from losing too much water so as to keep the blood volume and pressure within normal limits.

The activation of aldosterone in response to a decreased sodium content in the blood would also occur and remembering that “water follows salt“ and that aldosterone functions optimally in the presence of ADH we should notice a difference in the sodium content around the same time. Notice the graphs of urine sodium content and specific gravity begin to increase at the same time showing that the later two tests are inversely related to the urinary output. The tests performed on the group that consumed the 6mg NaCl also reflect the science of ADH, aldosterone, and renal regulation of osmolarity.

Urinary output increased slightly in the first 30 minutes, then decreased showing that ADH secretion increased in response to an increase in osmolarity. Aldosterone would be inhibited at this point in order to release some of the sodium content in the urine. The urine sodium content and specific gravity inversely follow the same pattern, as compared to urinary output, here as well. Initially, the values decrease slightly and then increase. It seems in this group an extension of time would be a benefit to see just how long it took for the body to compensate completely from the experiment.

The values at the 60, 90, and 120 minute mark were constant so the body was not yet in homeostasis. Looking at the graphs, over time the urine sodium content and specific gravity values would eventually begin to decrease and urinary output would begin to increase as the plasma osmolarity achieved normal levels. Our bodies have many compensatory mechanisms and renal regulation of osmolarity is a very important one to consider. Normal osmolarity needs to lie between 275-295 mosmol/L of blood as discussed previously. When these values deviate from this range for too long of a time, cell damage and even death will occur.

Our systems were designed to operate in harmony and when the balance is disrupted our bodies will compensate. When we are placing too much stress and strain on these compensatory mechanisms, they may not function optimally and disease will occur. References: Kirkpatrick, W. Natriuretic Peptide Hormones. Anatomy & Physiology II, Spring 2010. Class Handout. Retrieved from: www. coursecompass. com/courses/1/kirkpatrick24127/content Martini, F. , Ober, W. , et al. Fundamentals of Anatomy & Physiology. Pearson Education Inc. 2006. 7th ed. www. microvet. arizona. edu/courses/vsc401/pdf_files/urinarysystem. PDF

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Renal Regulation of Blood Osmolarity. (2018, Jun 15). Retrieved from