N.+UROLOGY

= UROLOGY ﻿ =

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__OVERVIEW __

The Kidneys are an amazing and very important organ to our bodies. We go through much of our life not giving our kidneys enough credit in what they do until we have a problem, such as having to void (urinate) or an Urinary Tract Infection or maybe a kidney stone. The kidneys main function in our bodies is to maintain proper water and electrolyte balance in the body, as well as acid-base balance. The kidneys help to regulate the blood pH by getting rid of hydrogen via the urine and reabsorbing bicarbonate. The kidneys normally will reabsorb most of the bicarbonate and therefore, the urine your body makes will contain very little bicarbonate and will also be slightly acidic (pH of 5-7) due to the H+ majority in the urine. The bodies sodium (Na+) and potassium (K+) is also managed in the kidneys by the use of the corticosteroid hormone of Aldosterone, which is secreted from the posterior portion of the kidney called the adrenal cortex. The kidney also regulate the volume of blood plasma and indirectly contribute to the regulation of our blood pressure. For example, if you are retaining water (lets say you have CHF or hypertension), your blood pressure will be higher due to the increase of blood volume/interstitial fluid volume. If you are dehydrated (less water) the lower your blood pressure will be. What is also neat is that the blood in our body with is approximately 5.5 Liters is filtered through the kidneys urinary tubules about every 40 minutes. The average healthy adult will excrete 1.5 Liters every day. Another major contributor to the amt. of urine to be excreted or reabsorbed is a hormone called Anti-diuretic hormone, which is secreted from the posterior pituitary gland. This hormone works by a negative feedback mechanism, for example, dehydration (increase in plasma osmolality) stimulates osmoreceptors in the hypothalamus which sends hormones to the posterior pituitary to release an increase of ADH hormone to the kidneys, which will increase water reabsorption and your body will excrete less urine. If you drink a lot of water and are over-hydrated (decrease in plasma osmolality), stimulates osmoreceptors in the hypothalamus which sends hormones to the posterior pituitary to decrease the amount of ADH hormone to the kidneys, thus, decreasing water reabsorption and excreting more urine. Our bodies are amazing in the sense that all this is occurring 24/7 to maintain homeostasis and all we have to do is sit back and let it. Pamela Wandry

=

= Pamela Wandry

Fox, Stuart Ira. (2009). //Human Physiology//. New York, NY: McGraw-Hill.

The kidneys are a vital part of controlling many functions in the body and maintaining homeostasis. Kidneys are involved in blood plasma volume, blood pressure, the amount of wastes that are found in the blood plasma and urine, control of electrolyte amounts, and also the pH of the blood plasma. There are two kidneys, one on each side of the vetebral column and down below the liver and diaphram. The urine is formed in the kidneys. From there it drains into the renal pelvis and then drains down the ureters and hten finally into the urinary bladder. Did you know taht your kidneys filter through about 7.5L of blood per hour? This comes out to be about 45 gallons per day! The average blood volume is baout 5.5L, meaning that about every 40 min. the kidneys are filtering the bodies entire blood volume. The kidneys excrete about 1 to 2 L of urine in a day, about 1% of the 180L of ultrafiltrate that is produced in a day. This means about 99% of the ultrafiltrate is reabsorbed. The minimum amount of urine that can be excreted a day is 400 mL; also known as the obligatory water loss. This obligatory water loss is the minimum amount that can be excreted and still get rid of the waste products. This only happens when people are severely dehydrated. As you can see, your kidneys are fairly small organs but act as huge powerhouses. Pretty amazing.

__ESSENTIAL QUESTIONS __

**Describe the renal processes of filtration, reabsorption, secretion, and excretion. Generally describe each process and give a specific example of each process occurring in the nephron and/or urinary system organs.**

__Filtration __
Filtration is a process where the kidneys filter waste products from the blood. Water and dissolved solutes pass from the blood plasma to the glomerular capsule then to the nephron tubules. Blood in the afferent arterioles of the kidney join the glomerulus. Here water and waste products are pulled into the glomerular capsule where it becomes filtrate. About 180 L of filtrate can be formed each day. The Blood plasma that enters the interior of the glomerular capsule is filtered through three potential barrier layers. The first is the capillary fenestrae. The glomerular basement membrane is the second potential barrier. The third layer and the hardest to pass through is the slit diaphragm. This layer is made of cells called podocytes. Each arm of the podocyte has many cytoplasmic extensions known as pedicels. The pedicels overlap each other as they surround the glomerular capillaries. The passages for the fluid are the slits between the adjacent pedicels. If molecules can pass through all these barriers to reach the glomerular capsule, they are then referred to as filtrate.



__Reabsorption __
Reabsorption is the return of filtrate to the vascular system. The kidneys secrete 1-2 L of urine in a day and since the kidneys produce 180 L of filtrate a day, almost all of the filtrate is returned to the vascular system to keep the blood volume at appropriate levels. Molecules that are reabsorbed pass through the proximal tubule cells by active and passive transport. Sodium has a coupled transport through the apical membrane of the tubule cells with glucose that move them into the cytoplasm. Then by active transport sodium passes through the basolateral membrane of the cell by sodium/potassium pumps. Then by facilitated diffusion the glucose is transported out of the cell through the basolateral membrane and reabsorbed into the blood.

__Secretion __
Reabsorption is the return of filtrate to the vascular system. The kidneys secrete 1-2 L of urine in a day and since the kidneys produce 180 L of filtrate a day, almost all of the filtrate is returned to the vascular system to keep the blood volume at appropriate levels. Molecules that are reabsorbed pass through the proximal tubule cells by active and passive transport. Sodium has a coupled transport through the apical membrane of the tubule cells with glucose that move them into the cytoplasm. Then by active transport sodium passes through the basolateral membrane of the cell by sodium/potassium pumps. Then by facilitated diffusion the glucose is transported out of the cell through the basolateral membrane and reabsorbed into the blood.



__Excretion __
Excretion is a process that takes all the waste molecules that have been filtered (filtrate) and secreted from the nephron to the collecting ducts. The collecting ducts pass through the renal pyramids. After this, the fluid is known as urine. The urine enters the minor calyxes, passes the major calyxes and moves on to the ureter. The ureter then transports the urine to the urinary bladder where it exits the body by micturation. Blood pH is regulated by the excretion of hydrogen in the urine. Hydrogen enters the filtrate by filtration and secretion. Hydrogen secretion occurs in exchange for reabsorption of sodium by antiport because sodium and hydrogen move in opposite directions. Bicarbonate is normally reabsorbed by the kidneys and hydrogen is excreted. Urine is slightly acidic with a pH between 5 and 7.

**Why is it so important to maintain a proper electrolyte balance? Give two examples**

It is important to maintain electrolyte balance in the body to maintain homeostasis. Concentrations of plasma electrolytes are regulated by the kidneys by matching the urinary excretion of sodium, potassium, chloride, bicarbonates and phosphates. Proper sodium concentration aids in the control of blood volume and pressure. Keeping the blood volume constant helps the body from becoming dehydrated. Dehydration occurs when the blood volume levels become more concentrated which causes the body to excrete less water in the urine. Proper concentrations of plasma potassium are needed to help prevent hypokalemia which is an excessive loss of potassium in the urine. This imbalance can lead to neuromuscular disorders or electrocardiographic abnormalities. These conditions can also be caused by the use of diuretics. Using potassium-sparing diuretics can decrease the risk of these conditions.



LJ Fox, Stuart Ira. (2009). //Human Physiology//. New York, NY: McGraw-Hill.

Blood plasma is filtered in the kidneys through a process called glomerular filtration. Fenestrae, which are large pores found in the endothelial cells, are located in the glomerular capillaries. These large pores are very permiabe to plama water and dissloved solutes but can still filter out white blood cells, platelets, and red blood cells. In the process of entering the glomerular capsules interior, blood plama must go through three filtration barriers. The fluid being filtered is called filtrate. The filtrate passes through the capillary fesetrae, the glomerular basement bembrane, and then the slit diaphram. The capillary fenestrae is the first tilftration barrier but is unable to remove any plama molecules due to having too large of pores. Next comes the glomerular basement membrane, which is found directly on the outside of the endothelium of the capillary. This membrane is make up of glycoprotiens. Finally, the filtrate heads for the slit diaphram. Podocytes, which contain foot processes that are cytoplamic extentions, compose this layer. The foot processes create very small spaces between them which are called slit diaphrams. Most plama solutes that are disolved have no problem passing thorugh all three of the filtration barrieres, but due to thier size and negative charge, most plama ptroteins are filtered out. Scientist have recently discovered that the slit diaphram is the most effective of all three barriers. They know this because if there is a genetic defect in the slit diaphrams, there is a lrage amount of tprotiens that will show up in the urine. There is always a little bit of albumin protein that is in the filtrate but only about 1% is visible in the urine and the rest is reabsorbed by receptor-mediated endocytosis. Filtrate can also be called ultrafiltrate because of the hydrostatic pressure from the blood it is made under. Filtration is conteracted by the hydrostatic pressure of hte glomerular capsule pressure. The protein concentration is greater in the plasmathan in the tubular fluid which causes return of water. Net filtraiton pressure, found be suptracting the opposing forces from the hydrostatic pressure, is usually about 10 mmHg. The amount of fluid the kidneys are bale to filter per minute is the glomerular filtration rate or GFR. As discussed in the introduction, on average the kidneys filter about 7.5L/hr, 180L/day, or about 5.5L every 40 minutes. Afferent arterioles affect the GFR by controlling blood flow to the glomerulus by vasodialation and vasoconstriction. The afferent areterioles are controlled by both extrinsic and intrinsic regulatroy mechanisms. If these mechanisms aren't function properly, the GFR may not remain high enough the get rid of waste and regulate blood pressure, or the GFR could become too high and cause too much water loss. Afferent areterioles are constricted when sympathetic nerves are hightly stimulated. This causes blood volume to be conserved and more blood to be sent the the heart and muscles. THe kidneys are able to regulate their won GFR regarless of blood pressure. This ability is called renal autoregulation. Because the afferent arterioles experience mygenic constriction and the chemicals released to the afferent arterioles during tubuloglomerular feedback, the kidneys are able to maintain autoregulation. The afferent and efferent arteriols come into contact with macula densa, which are cells responsible for the tubuloglomerular feedback, in the ascending linb. When there is too much NaCl and water in the distale tubule, affernt arterioles are constricted due to release of chemicals from the macula densa. Most of the reabsorption of the Na+, Cl-, and water occurs in the proximal tubule, about 65%. An additional 20% of the reabsorption occurs in the descending loop of henle. This reabsoprtion is not regulated and happens at a constant rate. The ultrafiltrate and the plama start out as isosmotic with eachother because the plama solutes are able to enter the ultrafiltrate. Therefore, the interstitial fluid has to be made to be hypertonic. This happens by the peritubular blood actively recieving Na+ from the filtrate. The interstitial fluid become more concentrated largely from the ascending limb of hte loop of henle. The ascending loop is thin a tht eh bottom the medulla and thicker toward the cortex. It is permeable to salt but not water. The thick part up towards the cortex is where the Na+ is actively transported out into the interstitial fluid. During transport of Na+, Cl- also passively leaves the filtrate. There is also some K+ that leaves the filtrate but just reenters. The Na+ is transported by Na+/K+ pumps across the basolateral membrane. The Cl- follows due to the electrical gradient. ADH is key in plama concentration. ADH is secreted during dehydration from the poterior pituitary gland. When ADH is secreted aquaporins are placed in the collecting ducts plasma membrane. Water is drawn out of the collecting duct when there is a large amount of ADH present. This is becasue the osmolality of the intersitial fluid is increased. A normally hydrated person puts out about 1.5L of urine in a day. This meas about 99.2% of the ultrafiltrate is reaborbed. When water intake is increased, the amount of ADH is decreased which causes the urine output volume to increase. Renal clearance is the kidney ability to clear supstances from teh blood and excrete them via the urine. Secretion and reabsorption are opposite eachother. Secretion happens when the peritubular capillaries activley move substances into the tubular fluid. Renal clearance is decreased with reabsorption and increased with secretion. Renal clearance is the filtration rate plus the secretion rate minus the reabsorpetion rate. There are transporters, located in teh basolateral membrane of the proximal tubule, that work to excrete xenobiotics, toxins, and drugs. These transporters are called organic anion transporters (OAT). The OAT in the kidneys are responsible for getting rid of small xenobiotics and OAT in the liver get rid of larger xenobiotics. Renal plasma clearance (RPC) is the amount of plamsa that is completely cleared of a substance within one minute. If a substance is fliter and not reabsorbed, the RPC will be the same as the GFR. If a substance is both reabsorbed and filtered, the RPC will be less than the GFR. IF a substance is filterd, secreted, and excreted, the RPC will be greater thatn the GFR. Electrolyte balance in the body is very important. Two examples of this would be blood volume and blood pressure are regulated by Na+ levels, and the skeletal muscles and cardiac muscles maintain control of function by K+ levels.JM

__<span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif;">SUMMARY __ Although interesting, I found this to be a complicated unit! Urology is extremely important to our existence as humans.



**Reabsorption of Glucose** Filtered glucose and amino acids are normally reabsorbed be the nephrons. When the plasma concentration is very high all of the carriers are full and reach the transport maximum. The excess glucose is therefore not all absorbed by the nephrons and continues through to the renal tubules and into the urine. This generally occurs when the plasma glucose concentration is more than triple the average glucose concentration of 125 mg per minute. When glucose passes through the tubules and is not reabsorbed and passes to the urine it is known as **glycosuria**. This occurs when the plasma glucose concentration is abnormally high and exceeds the renal plasma threshold. This is common in diabetes mellitus. People with diabetes mellitus excrete large amounts of urine due to the fact that excreted glucose carries water with it.

**Renal Acid-Base Regulation** The kidneys play an important part in the regulation of blood pH. H+ is excreted in the urine and the kidneys reabsorb bicarbonate. H+ is filtered through the glomeruli and is also secreted across the wall of the tubule in exchange for the reabsorption of Na+ by //antiport//. The kidneys normally reabsorb all of the bicarbonate and excrete H+ so normal urine is acidic with a pH of 5-7. When urine is acidic, HCO3- combines with H+ to form carbonic acid. Carbonic acid is converted to CO2 and H2O in a reaction catalyzed by carbonic anhydrase. The reaction that occurs in the filtrate is the same reaction that occurs in the red blood cells in the pulmonary capillaries. As CO2 concentration is increased in the filtrate it diffuses into the tubule cells. In the cytoplasm of the tubule cells carbonic anhydrase catalyzes the reaction where CO2 and H2O form carbonic acid. The carbonic acid is dissociated into HCO3- and H+. This makes it so the bicarbonate in the tubule cell can diffuse through the basolateral membrane and enter the blood. The proximal tubule generally reabsorbs 80-90% of the bicarbonate leaving very little H+ in the filtrate. When a person has **alkalosis** there is less H+ in the filtrate and less HCO3- is reabsorbed resulting in the excretion of HCO3- in the urine. When a person has **acidosis** the proximal tubule creates extra bicarbonate that can enter the blood. The extra HCO3- is created during the metabolism of glutamine. HCO3- is formed and released to the blood and NH3 and NH4+ are produced and enter the filtrate. The bicarbonate produced helps compensate for the acidosis and ammonia acts as a urinary buffer. When a person has acidosis the urine pH is usually below 5.5. The acid must be buffered for more H+ to be excreted. Phosphates and ammonia usually provide the buffering action for excreting most of the H+ in the urine. Phosphate enters urine by filtration whereas ammonia is produced in the tubule cells by deamination of amino acids. This is the equation that explains how the H+ is buffered. **NH3 + H+** **=****>** **NH4+ (ammonia ion)** **HPO42- + H+ => H2PO4-**



**Use of Diuretics** Diuretics are medications that increase the volume of the excreted urine. Diuretics are important for the lowering of blood volume in hypertension, congestive heart failure, and edema. They lower blood volume by increasing the proportion of the glomerular filtrate that is excreted as urine. They can also decrease interstitial fluid volume increase the concentration of plasma within capillaries promoting the osmosis of interstitial fluid into the capillary blood, reducing edema. The most powerful diuretics inhibit active salt transport out of the ascending limb of the loop of Henle. These are known as //loop diuretics//. //Thiazide diuretics// inhibit salt transport by the first segment of the distal convoluted tubule. //Carbonic anhydrase inhibitors// are much weaker than the first two. The prevent water reabsorption occurring when bicarbonate is reabsorbed in the proximal tubule. //Osmotic diuretics// are extra solutes in the filtrate that increase osmotic pressure of the filtrate and decrease reabsorption of water by osmosis. Potassium-sparing diuretics inhibit the action of aldosterone in the distal tubule and cortical collecting duct.



__<span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif;">APPLICATION __ As a nurse I would need to know that changes in urination can be indicators to serious ailments and disease. Polyuria and Polydipsia are two symptoms that are commonly linked to Diabetes mellitus, but commonly overlooked as indicators for Diabetes insipidus.

= Universal symptoms for DI =
 * increased thirst
 * increased drinking
 * increased urination

= Variable Symptoms for DI =
 * Bed- wetting
 * Frequent needs for nighttime urination
 * potential result of increased sodium levels (An unmanaged sodium level may result in dehydration. A sodium level greater than 140-150 mEq/1 indicates dehydration. If it gets no higher than 155 mEq/1, the dehydration is relatively mild and is unlikely to cause a severe problem but it could and probably would produce slight brain damage that could gradually increase over long periods of time. Therefore, an effort should be made to keep the sodium below 150 mEq/1.)

As a nurse I will be working with a lot of patients with DM either type 1 or type2 and also Diabetes Insipidus and am going to know the definitions of each, treatments, medications and how they are administered. I will have to be able to recognize symptoms to these and be able to react in a situation. Ex. hypoglycemia/hyperglycemia situations and what is to be done. AR

http://www.diabetesinsipidus.org

__<span style="color: #800080; font-family: 'Arial Black',Gadget,sans-serif;">CASE STUDY __**[|A Case of Diabetes Insipidus]**

__**Describe the mechanism by which normal fluid regulation in the body occurs.**__ The body has a complex system for balancing the volume and composition of body fluids. The kidneys remove extra body fluids from the bloodstream. These fluids are stored in the bladder as urine. If the fluid regulation system is working properly, the kidneys make less urine to conserve fluid when water intake is decreased or water is lost, for example, through sweating or diarrhea. The kidneys also make less urine at night when the body’s metabolic processes are slower. To keep the volume and composition of body fluids balanced, the rate of fluid intake is governed by thirst, and the rate of excretion is governed by the production of antidiuretic hormone (ADH), also called vasopressin. This hormone is made in the hypothalamus, a small gland located in the brain. ADH is stored in the nearby pituitary gland and released into the bloodstream when necessary. When ADH reaches the kidneys, it directs them to concentrate the urine by reabsorbing some of the filtered water to the bloodstream and therefore make less urine. DI occurs when this precise system for regulating the kidneys’ handling of fluids is disrupted.

An adult who urinates more than 50mL/kg body weight per 2 hours is generally considered to have a higher than normal output. Loosely translated, 50mL/kg is about 3.5 quarts per day for a 150-lb. adult. an adult who drinks more than 4 quarts (1 gallon) or approximately 12 glasses (144 oz) of beverages per day would have a higher than normal intake.
 * What is considered to be excessive thirst and urination in an adult?**

__**List and briefly describe the four types of diabetes insipidus.**__

Central DI
The most common form of serious DI, central DI, results from damage to the pituitary gland, which disrupts the normal storage and release of ADH. Damage to the pituitary gland can be caused by different diseases as well as by head injuries, neurosurgery, or genetic disorders. To treat the ADH deficiency that results from any kind of damage to the hypothalamus or pituitary, a synthetic hormone called desmopressin can be taken by an injection, a nasal spray, or a pill. While taking desmopressin, a person should drink fluids only when thirsty and not at other times. The drug prevents water excretion, and water can build up now that the kidneys are making less urine and are less responsive to changes in body fluids.

Nephrogenic DI
Nephrogenic DI results when the kidneys are unable to respond to ADH. The kidneys’ ability to respond to ADH can be impaired by drugs—like lithium, for example—and by chronic disorders including polycystic kidney disease, sickle cell disease, kidney failure, partial blockage of the ureters, and inherited genetic disorders. Sometimes the cause of nephrogenic DI is never discovered. Desmopressin will not work for this form of DI. Instead, a person with nephrogenic DI may be given hydrochlorothiazide (HCTZ) or indomethacin. HCTZ is sometimes combined with another drug called amiloride. The combination of HCTZ and amiloride is sold under the brand name Moduretic. Again, with this combination of drugs, one should drink fluids only when thirsty and not at other times.

Dipsogenic DI
Dipsogenic DI is caused by a defect in or damage to the thirst mechanism, which is located in the hypothalamus. This defect results in an abnormal increase in thirst and fluid intake that suppresses ADH secretion and increases urine output. Desmopressin or other drugs should not be used to treat dipsogenic DI because they may decrease urine output but not thirst and fluid intake. This fluid overload can lead to water intoxication, a condition that lowers the concentration of sodium in the blood and can seriously damage the brain. Scientists have not yet found an effective treatment for dipsogenic DI.

Gestational DI
Gestational DI occurs only during pregnancy and results when an enzyme made by the placenta destroys ADH in the mother. The placenta is the system of blood vessels and other tissue that develops with the fetus. The placenta allows exchange of nutrients and waste products between mother and fetus. Most cases of gestational DI can be treated with desmopressin. In rare cases, however, an abnormality in the thirst mechanism causes gestational DI, and desmopressin should not be used. __**How is pituitary diabetes insipidus diagnosed?**__ Urinalysis is the physical and chemical examination of urine. The urine of a person with DI will be less concentrated. Therefore, the salt and waste concentrations are low and the amount of water excreted is high. A physician evaluates the concentration of urine by measuring how many particles are in a kilogram of water or by comparing the weight of the urine with an equal volume of distilled water. A fluid deprivation test helps determine whether DI is caused by one of the following: This test measures changes in body weight, urine output, and urine composition when fluids are withheld. Sometimes measuring blood levels of ADH during this test is also necessary. In some patients, a magnetic resonance imaging (MRI) of the brain may be necessary as well. Although there share similar names (and both are indicated by thirst and [|frequent urination]), diabetes mellitus and diabetes insipidus are completely different conditions.<span style="position: static; text-decoration: underline !important;">Diabetes mellitus is caused by the lack of (or insufficient) insulin. This is when the body is unable to handle the standard amounts of sugar in a normal diet. [|Obesity], Heredity, stress and <span style="position: static; text-decoration: underline !important;">drugs are also common factors that can lead to diabetes mellitus. The required diagnostic tests are a Fast <span style="position: static; text-decoration: underline !important;">blood sugar -24hr test, a post-prandial test and a Glucose tolerance test. The treatment requires the correct sugar/[|insulin] <span style="position: static; text-decoration: underline !important;">intake and medication to prevent its progression. It also includes a change of diet.On the other hand, Diabetes insipidus is indicated by the lack of the <span style="position: static; text-decoration: underline !important;">hormone vasopressin or the inability of the kidneys to respond to it. It is not connected with either sugar or the lack of it. The diagnostic tests as well as their treatments too are entirely different. The tests needed to diagnose [|Diabetes] insipidus are a Water deprivation test and a vasopressin test. The most important part of the treatment is to replace vasopressin (usually with its synthetic counterpart desmopressin) also fluid <span style="position: static; text-decoration: underline !important;">intake and urine must be balanced.
 * excessive intake of fluid
 * a defect in ADH production
 * a defect in the kidneys’ response to ADH
 * In what ways is diabetes insipidus similar to diabetes mellitus? In what ways do they differ?**

Diabetes Insipidus; Central DI: Sudden or gradual urination of large amounts of clear, or almost colorless urine (polyuria), accompanied by excessive thirst (polydipsia). Dehydration can occur if fluid balance is not maintained. Diabetes Insipidus; Nephrogenic DI: Sudden or gradual urination of large amounts of clear, colorless urine (polyuria), accompanied by excessive thirst (polydipsia). Dehydration can occur if fluid balance is not maintained. Diabetes Mellitus: Excessive urination (polyuria), excessive thirst (polydipsia), excessive appetite (polyphagia). You may experience a sudden or gradual change with no symptoms. Other symptoms include tiredness, weight gain or loss, and skin infections that do not heal. The serum sodium concentration is regulated by the balance of water intake, renal filtration and reabsorption of sodium, and antidiuretic hormone (ADH) – mediated water conservation by the collecting duct. Water balance is normally mediated by thirst, the secretion of antidiuretic hormone (also known as vasopressin), the feedback mechanisms of the renin-angiotensin-aldosterone system, and renal handling of filtered sodium and water. Disorders in any one of these components of sodium balance can result in hyponatremia. ADH is secreted by supraoptic and paraventricular nuclei in the hypothalamus and transmitted via the neuronal axons to the posterior pituitary where it is secreted. It is released when a decrease in the effective circulatory volume is sensed by vascular baroreceptors primarily located in the large arterial vessels. The key action of ADH in the kidney is to trigger the insertion of aquaporin-2 into the principal cells of the collecting duct. Aquaporins' selective permeability allows water reabsorption and consequently urine concentration. The syndrome of inappropriate antidiuretic hormone secretion (SIADH) was initially described by Leaf and Mamby. They demonstrated a direct relationship between excessive vasopressin and fall in serum sodium concentration without any change in urine osmolality or flow rate.
 * How does the mechanism by which diuresis occurs with diabetes insipidus differ from that which occurs in diabetes mellitus?**
 * How does diabetes insipidus compare with a condition called syndrome of inappropriate anti-diuretic hormone ( SIADH )?**

Vitamin D toxicity, Postpartun necrosis, hypokalemia and decreased blood volume. DDVAP is desmopressin acetate, an antidiuretic. Can be adminstered nasally with a special nasal tube system or orally with tablets. Vasopressin: A relatively small (peptide) molecule that is released by the pituitary gland at the base of the brain after being made nearby (in the hypothalamus). Vasopressin has an antidiuretic action that prevents the production of dilute urine (and so is antidiuretic).
 * What other conditions result in polyuria and polydipsia ( PU / PD )?**
 * What is DDAVP and how is it administered?**
 * Why is ADH also known as //vasopressin//?**

Sources: http://www.ask.com/web?qsrc=2990&o=0&l=dir&q=compare+and+contrast+dm+and+diabetes+insipidus [] [] __ [|http://www.ask.com/web?qsrc=2990&o=0&l=dir&q=WHAT+is+ddvap+and+how+is+it+administered][|http://answers.yahoo.com/question/index?qid=20061130061456AAgKpN3] __