Question

Integrative Urinary Case Study

While working as a general practitioner, your patient Lamar comes to your office for a standard checkup. Because Lamar is 60 years old and has type II diabetes, you frequently subject him to lab tests to evaluate kidney function, as you know that kidney function can be compromised in diabetics.

Urinary Case Study.01

One type of damage that you are worried about detecting is damage to the endothelial cells of the kidney glomeruli and the podocytes that make up the Bowman’s capsule epithelium. This damage can cause the openings in these tissue layers (e.g., intercellular clefts and other fenestrations) to widen in diabetic patients. Based on analysis of a urine sample from Lamar (urinalysis), which of the following would be the best evidence that such damage has occurred?

A Higher than normal protein levels in the urine.

B Higher than normal Na levels in the urine.

C Lower than normal protein levels in the urine.

D Lower than normal Na levels in the urine.

Urinary Case Study.02

Unfortunately, you detect the evidence of kidney damage that you identified in question #1 from Lamar’s urinalysis results. What effect, if any, do you predict this will have on the osmotic pressure (osmolarity) of his blood plasma?

A It should be higher than normal.

B It should be normal.

C It should be lower than normal.

Urinary Case Study.03

Given the answer to question #2, what should happen to Lamar’s interstitial fluid volume?

A It should be higher than normal.

B It should be normal.

C It should be lower than normal.

Urinary Case Study.04

Why does the answer to question #2 cause the answer to question #3?

A Because Lamar’s TPR is higher than that of a healthy individual.

B Since the osmotic pressure of Lamar’s blood plasma should be the same as that of a healthy individual, it makes sense that his interstitial fluid volume should be normal.

C Because Lamar’s GFR is higher than that of a healthy individual.

D Because the balance of Starling’s forces in Lamar’s systemic capillaries is altered relative to that of a healthy individual.

Urinary Case Study.05

You also detect significant amounts of glucose in Lamar’s urine sample, which is typical in diabetics. What does this tell you about his kidney function?

A His glucose reabsorption rate must exceed his glucose excretion rate.

B His glucose reabsorption rate must exceed his glucose secretion rate.

C His glucose filtration rate must exceed his glucose secretion rate.

D His glucose filtration rate must exceed his glucose reabsorption rate.

Urinary Case Study.06

Since Lamar’s diabetes is very poorly controlled, you decide that you want to prescribe him another anti-diabetic drug in addition to the ones he is already on: a glifozin, which is a class of drugs that inhibit SGLTs (sodium-dependent glucose transporters). These drugs reduce blood sugar through their actions on the urinary system. Why would inhibiting SGLTs reduce blood sugar?

A Inhibiting SGLTs will increase the rate that glucose is reabsorbed by secondary active transport.

B Inhibiting SGLTs will reduce the rate that glucose is reabsorbed by secondary active transport.

C Inhibiting SGLTs will increase the rate that glucose is reabsorbed by primary active transport.

D Inhibiting SGLTs will decrease the rate that glucose is reabsorbed by primary active transport.

Urinary Case Study.07

Before he leaves, you measure Lamar’s blood pressure and find that it is elevated, as it has been over the past few visits. To attempt to get his hypertension under control you decide to prescribe him an ACE inhibitor. How will this drug lower his blood pressure?

A It will cause vasoconstriction of the afferent arterioles feeding the kidney glomeruli.

B It will enhance the activity of Na-K-ATPases in the basolateral membranes of proximal convoluted tubule epithelial cells (causing reabsorption of more Na per unit time).

C It will cause vasodilation of the efferent arterioles exiting the kidney glomeruli.

D It will increase rates of Na and HO excretion via the urine.

Answer 1

Case study 1.
Podocytes are specialised cells that line the epithelium of bowman's capsule. During the process of blood filteration in kidney, the blood is filtered through the Bowman's capsule. The podocytes help to filter out large molecules such as proteins while allowing the passage of small molecules such as water. Damage to podocytes result in marked proteinuria.
So the answer is (A) Higher than normal protein levels in the urine.
Case study 2

We have seen that damage to glomeruli endothelium and podocytes results in increased loss of proteins in urine. This loss of protein from the blood into the urine results in decrease in osmotic pressure.
Correct answer is C It should be lower than normal.

case study 3.
Loss of plasma protein from blood causes osmotic pressure to drop. The low osmotic pressure results in movement of fluid from the capillary into the interstitium, thereby increasing the interstitial fluid volume.
So the correct answer is (A) It should be higher than normal.
Case study 4.
There are four starling forces : capillary hydrostatic pressure, interstitial hydrostatic pressure, capillary osmotic pressure, interstitial osmotic pressure.
The net movement of fluid between the capillary and interstitium depends upon thse four forces. In healthy individual, the hydrostatic pressure in capillary is higher than interstitial fluid. The osmotic pressure in capillaries is also higher than interstial fluid. Any disturbance in the pressure gradient developed by these forces results in interstitial fluid accumulation or vascular congestion.
As we know that Lamar's plasma osmotic pressure has decreased, it will cause fluid movement out of the capillary and into the interstitium increasing interstitial fluid volume.
So the answer is D Because the balance of Starling’s forces in Lamar’s systemic capillaries is altered relative to that of a healthy individual.

Case study 5.
In healthy individuals the glucose filtered by the glomeruli is reabsorbed the renal tubules. But in renal pathologies the reabsorption of glucose may become impaired. This results in excretion of glucose into the kidney known as glucosuria.
So for glucose to appear in urine the rate at which glucose is filtered must be higher at which the glucose is reabsorbed.
The correct answer is D His glucose filtration rate must exceed his glucose reabsorption rate.

case study 6

Sodium Glucose linked transporter (SGLT) are glucose transport proteins. These are found in proximal renal tubule. These are responsible for reabsorption of glucose into the blood and prevent glucose secretion in urine. By inhibiting SGLT through drugs such as  glifozin, SGLT will not be able to reabsorb glucose and glucose will be excreted in urine. This will help lower blood glucose.
Correct answer is B Inhibiting SGLTs will reduce the rate that glucose is reabsorbed by secondary active transport.

case study 7.
Angiotensin converting enzyme (ACE) inhibitor inhibits the activity of angiotensin converting enzyme which acts of angiotensin l to convert it to angiotensin ll during activation renin angiotensin system (RAS). This will result in deactivation of RAS which increases the blood pressure through activity of angiotensin ll. ACE inhibitors cause vasodilation amd decrease blood volume, thereby decreasing the blood pressure.
Correct answer is C It will cause vasodilation of the efferent arterioles exiting the kidney glomeruli.