Lab 4 Flashcards
People on a carbohydrate-free, weight-reducing diet are advised to check their urine for the presence of ketone bodies. Why?
When the body doesn’t have enough carbohydrates to use as its primary energy source, it begins to break down stored fat to use as fuel. This process is called ketosis, and it produces molecules called ketone bodies.
Ketone bodies can be detected in the urine of people who are on a carbohydrate-free diet because the body is producing more ketones than it can use for energy. By checking their urine for the presence of ketones, people can monitor their state of ketosis and ensure that they are following the diet correctly.
Consider the following: a dehydrated desert prospector and a person who has been drinking alcohol all night each drink a litre of water at time zero and then void at the end of 3 hours. What differences do you think there will be with respect to the volume and specific gravity of each sample? (hint: alcohol inhibits ADH secretion)
The dehydrated desert prospector has likely lost a significant amount of water through sweating and may have an elevated level of antidiuretic hormone (ADH) to conserve water. Therefore, when they drink a liter of water, their body will absorb and retain as much water as possible, resulting in a smaller volume of urine with a higher specific gravity.
On the other hand, the person who has been drinking alcohol all night may have inhibited ADH secretion, which can lead to a decrease in water reabsorption and an increase in urine volume. Therefore, when they drink a liter of water, their body may not absorb and retain as much water as possible, resulting in a larger volume of urine with a lower specific gravity.
Glomerular proteinuria is often accompanied by edema. Explain the relationship between these two conditions.
Glomerular proteinuria is a condition where there is an excessive amount of protein in the urine due to damage or dysfunction in the glomeruli
When there is proteinuria, the proteins that are supposed to be retained in the blood pass through the damaged glomeruli and are excreted in the urine.
Edema, on the other hand, is a condition where there is an abnormal accumulation of fluid in the tissues of the body, leading to swelling. This can occur due to a variety of reasons, including kidney dysfunction.
When there is glomerular proteinuria, the loss of protein in the urine can lead to a decrease in the amount of protein in the blood. This, in turn, can cause a decrease in the oncotic pressure, which is the pressure that draws fluid back into the blood vessels from the tissues. As a result, fluid can leak out of the blood vessels and accumulate in the tissues, leading to edema.
A patient with jaundice is admitted to the hospital. The doctor promptly asks the patient to provide a urine sample for urinalysis. Surprisingly, the patient’s urine tests negative for bilirubin. Which of the following disorders is this patient most likely to have? Explain.
(a) A stone in the bile duct
(b) An inherited defect in glucuronyl transferase (Gilbert’s syndrome)
(c) Early-stage hepatocellular carcinoma
If a patient with jaundice tests negative for bilirubin in the urine, the most likely cause is an inherited defect in glucuronyl transferase, also known as Gilbert’s syndrome. This is a relatively common genetic disorder that affects the metabolism of bilirubin in the liver.
Do you think it would be possible for someone to test positive for glucosuria under normoglycemic conditions? Explain. (hint: think about SGLT-2 function)
SGLT-2 is a protein located in the proximal tubules of the kidneys that is responsible for reabsorbing glucose from the filtered fluid back into the bloodstream. Normally, when blood glucose levels are elevated, SGLT-2 works to reabsorb as much glucose as possible to prevent it from being lost in the urine.
However, in some cases, SGLT-2 can be overactive and reabsorb more glucose than is necessary, even when blood glucose levels are within the normal range. This can lead to a condition called renal glucosuria, where glucose is excreted in the urine despite normal blood glucose levels.
Renal glucosuria can be a genetic disorder or can occur as a result of certain medications or conditions that affect the function of SGLT-2. In these cases, a person may test positive for glucosuria even when their blood glucose levels are within the normal range.
The amount of nitrogen present in the blood in the form of urea is termed blood urea nitrogen (BUN). BUN levels reflect both the rate of urea formation by the liver and the rate of urea excretion by the kidneys. With this in mind, think about and try to explain the mechanism by which each of the following conditions would lead to an increase in BUN.
(a) excessive protein intake(and/or excessive protein catabolism)
(b) inadequaterenalperfusion
(c)kidney disease
(a) Excessive protein intake or protein catabolism leads to an increase in the production of urea by the liver because the breakdown of proteins results in the formation of nitrogenous waste products such as ammonia, which is converted to urea in the liver. The increased urea formation leads to an increase in BUN levels. The excess urea is then excreted by the kidneys. If the kidneys are functioning normally, they will be able to excrete the excess urea, and BUN levels will return to normal. However, if the kidneys are unable to excrete the excess urea due to a decreased glomerular filtration rate (GFR) or other kidney dysfunction, BUN levels will remain elevated.
(b) Inadequate renal perfusion or decreased blood flow to the kidneys results in decreased GFR, and hence a decrease in the rate of urea excretion. This can occur due to conditions such as hypovolemia, heart failure, or renal artery stenosis. The decreased rate of urea excretion leads to an increase in BUN levels.
(c) Kidney disease, such as glomerulonephritis or acute tubular necrosis, can lead to a decrease in the rate of urea excretion by the kidneys, which leads to an increase in BUN levels. Additionally, kidney disease can also lead to a decrease in the GFR, which leads to a decrease in the rate of urea excretion and hence an increase in BUN levels.
Urea is filtered in the glomerulus and then partially reabsorbed, while glucose is normally reabsorbed completely. The molecule PAH is filtered and also secreted from the blood into the renal tubules, while inulin is filtered but neither reabsorbed nor secreted by the tubule cells. State whether the clearance rates of these four substances is less than, equal to, or greater than the GFR.
The clearance rates of the four substances can be classified as follows:
Urea: Urea is filtered in the glomerulus and partially reabsorbed in the renal tubules. Therefore, its clearance rate is less than the GFR.
Glucose: Glucose is normally completely reabsorbed in the proximal tubules. Therefore, its clearance rate is also less than the GFR.
PAH: PAH is both filtered and secreted by the renal tubules, which means that its clearance rate is greater than the GFR.
Inulin: Inulin is a substance that is freely filtered but not reabsorbed or secreted by the tubule cells. Therefore, its clearance rate is equal to the GFR.
In summary:
Clearance rate of urea < GFR
Clearance rate of glucose < GFR
Clearance rate of PAH > GFR
Clearance rate of inulin = GFR
These principles are fundamental to understanding renal physiology and are used to estimate GFR, which is a key clinical parameter for evaluating kidney function.
