MCAT Biology : Kidney and Nephron Physiology

Study concepts, example questions & explanations for MCAT Biology

varsity tutors app store varsity tutors android store

Example Questions

1 2 4 Next →

Example Question #31 : Kidney And Nephron Physiology

Which of the following structures will be found in the renal medulla?

I. Glands that secrete aldosterone

II. Loop of Henle

III. Distal convoluted tubule

Possible Answers:

I and II

I only

I and III

II only

Correct answer:

II only

Explanation:

Recall that the renal medulla is the inner portion of the kidney. A nephron spans both the renal cortex and the renal medulla. Structures such as the glomerulus (capillary bed), Bowman's capsule, and the proximal and distal convoluted tubules are found in the renal cortex, whereas the loop of Henle is found in the renal medulla. The collecting duct (the structure that transports urine to the renal pelvis) spans both the renal cortex and the renal medulla.

As mentioned above, distal tubules are found in the renal medulla and function to reabsorb sodium ions. Reabsorption of sodium ions inside the nephron (for example in the distal tubules) is facilitated by the hormone aldosterone. Aldosterone is a steroid hormone that is produced in glands inside the adrenal cortex (in the adrenal gland, rather than the kidney).

Example Question #32 : Kidney And Nephron Physiology

Which of the following is true regarding a nephron?

Possible Answers:

Nephrons are only found in the adrenal medulla

A nephron is the functional unit of a neuron

Filtration begins in nephrons’ capillary beds, called the collecting duct

Nephrons create urine, but they cannot store urine

Correct answer:

Nephrons create urine, but they cannot store urine

Explanation:

A nephron is the functional unit of kidneys. It is the site of filtration, secretion, and reabsorption (processes essential for urine production).

Nephrons contain several structures that facilitate the proper excretion of waste through urine. A nephron contains structures that are found in both the adrenal medulla (inner region) and the adrenal cortex (outer region) of the kidneys; therefore, a single nephron spans both the adrenal medulla and the adrenal cortex. The first step in urine production occurs at the capillary beds of nephrons. Blood arrives at these capillary beds, known as the glomerulus, and initiates filtration. Filtration is the process by which potential waste products in the blood are filtered into the nephron, where they will ultimately become urine.

Remember that nephrons are the site of urine production; they do not store the urine. Once complete, urine exits the kidneys and is stored in the bladder. The bladder stores urine until it reaches the maximum capacity, causing smooth muscle around the organ to stretch. Once this maximum is reached the individual feels the urge to urinate, and the urine is excreted via the urethra.

Example Question #33 : Kidney And Nephron Physiology

In the urinary system, the ureter is most directly associated with the __________.

Possible Answers:

renal pelvis

liver

renal vein

adrenal gland

Correct answer:

renal pelvis

Explanation:

The renal pelvis (hollow structure within the kidney) narrows to become the ureter, which leads to the bladder.

Example Question #34 : Kidney And Nephron Physiology

Which components of the nephron can be found in the renal medulla?

Possible Answers:

The proximal and distal convoluted tubules

The loop of Henle and the collecting duct

The entire nephron can be found within the cortex of the kidney

The loop of Henle and the glomerulus

Correct answer:

The loop of Henle and the collecting duct

Explanation:

The loop of Henle descends into the medulla before ascending back into the cortex. The collecting duct, which ends the nephron, extends into the medulla.

Example Question #35 : Kidney And Nephron Physiology

Which of the following is true of a functioning kidney?  

Possible Answers:

Macromolecules, such as proteins, do not enter Bowman's capsule due to the impermeability of the podocyte membrane

Glucose, water, and ions permeate the visceral layer of Bowman's capsule to enter the blood vessels of the glomerulus

All blood solutes pass from the glomerulus into Bowman's capsule, adding to the volume of the filtrate

Only water can enter into Bowman's capsule by passive diffusion

Correct answer:

Macromolecules, such as proteins, do not enter Bowman's capsule due to the impermeability of the podocyte membrane

Explanation:

The visceral layer of Bowman's capsule is permeable to small blood solutes. Blood cells and most macromolecules remain in the blood stream.

One answer choice is nearly correct: "Glucose, water, and ions permeate the visceral layer of Bowman's capsule to enter the blood vessels of the glomerulus." While these solutes do in fact permeate the membrane, they exit the blood vessels of the glomerulus to enter Bowman's capsule.

Example Question #36 : Kidney And Nephron Physiology

Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:

A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.   

In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride  in the proximal tubule of the kidney. When sodium is reabsorbed back into the blood, the molecule creates an electrical force. This electrical force then pulls water along with it into the blood. As more water enters the blood, the blood volume increase. By preventing the reabsorption of sodium, water reabsorption is reduced and the blood pressure decreases. 

When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more  being expired. Based on Le Chatelier’s principle, the reaction will shift to the left. Since there is more bicarbonate than protons in the body, the blood will become more basic (respiratory alkalosis). To prevent such life threatening result, one would take a carbonic anhydrase inhibitor to prevent the reaction from shifting to the left.  

Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.

Which of the following statement(s) will contradict carbonic anhydrase inhibitors' usefulness in patients with hypertension? 

Possible Answers:

All of these

Water is only reabsorbed in the collecting tubule of the kidneys

The reabsorption of  will pull cations across the lumenal side of the proximal tubule

The reabsorption of  will create an electrochemical gradient 

None of these

Correct answer:

Water is only reabsorbed in the collecting tubule of the kidneys

Explanation:

In patients with hypertension, the blood volume is too high resulting in high blood pressure. carbonic anhydrase inhibitors will prevent water absorption by preventing sodium chloride reabsorption. As described from the passage, without sodium reabsorption at the proximal tubule, there will be no electrochemical drive for the reabsorption of water. carbonic anhydrase inhibitors mainly work on the proximal tubule where the majority of water reabsorption occurs.  

Example Question #37 : Kidney And Nephron Physiology

Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:

A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.   

In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride  in the proximal tubule of the kidney. When sodium is reabsorbed back into the blood, the molecule creates an electrical force. This electrical force then pulls water along with it into the blood. As more water enters the blood, the blood volume increase. By preventing the reabsorption of sodium, water reabsorption is reduced and the blood pressure decreases. 

When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more  being expired. Based on Le Chatelier’s principle, the reaction will shift to the left. Since there is more bicarbonate than protons in the body, the blood will become more basic (respiratory alkalosis). To prevent such life threatening result, one would take a carbonic anhydrase inhibitor to prevent the reaction from shifting to the left.  

Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.

Based on the passage, which of the following statements, if true, would contradict the effectiveness of carbonic anhydrase inhibitors as a treatment? 

Possible Answers:

When sodium chloride is absorbed, the electric force created will pull magnesium with greater force than water

None of these

Even in a basic environment, sometimes an acidic molecule is able to retain it's proton

The distal tubule of the kidney is impermeable to water

The proximal tubule of the kidney is impermeable to water

Correct answer:

The proximal tubule of the kidney is impermeable to water

Explanation:

The proximal tubule has a high permeability for water. In patients with hypertension and/or heart failure, blocking the reabsorption of water at the proximal tubule will lower the blood's volume and blood's pressure. Therefore, if the proximal tubule is impermeable to water, then regulating the site with a carbonic anhydrase inhibitor has no purpose.  

1 2 4 Next →
Learning Tools by Varsity Tutors