MCAT Biology : Kidney and Nephron Physiology

Study concepts, example questions & explanations for MCAT Biology

varsity tutors app store varsity tutors android store

Example Questions

Example Question #471 : Biology

A renal afferent arteriole has a larger radius than the efferent arteriole. What is the effect of this larger radius on the function of the kidney?

Possible Answers:

Reabsorption in the nephron tubules is increased

Afferent arteriole flow is decreased

Antidiuretic hormone (ADH) secretion is decreased

Blood flow to the kidney is decreased

Glomerular filtration rate is decreased

Correct answer:

Reabsorption in the nephron tubules is increased

Explanation:

A renal afferent arteriole is directed toward the glomerulus, while a renal efferent arteriole is directed away from the glomerlus. If the radius of the afferent arteriole is increased, there is more flow through it toward the glomerulus, and if there is a smaller radius in the efferent arteriole, there is a resultant back pressure in the glomerulus. This is can be imagined as trying to squeeze a high-pressure hose through a small pipe. This pressure increases the force within the glomerulus to increase filtration, and subsequently increase reabsorption.

Antidiuretic hormone (ADH) secretion has a neglible effect on the radius of renal arterioles. Blood flow to the kidney is increased when afferent arteriole radius is increased (this also increases the arteriole flow).

Example Question #474 : Biology

At which point in a nephron would the osmolarity of the filtrate be highest? Assume that antidiuretic hormone (ADH) is not present in the body.

Possible Answers:

The distal convoluted tubule

The bottom of the loop of Henle

The proximal convoluted tubule

The collecting duct

Correct answer:

The bottom of the loop of Henle

Explanation:

It is important to understand how urine is concentrated as it travels through the nephron. The proximal convoluted tubule does not alter the osmolarity of the filtrate, the loop of Henle increases the osmolarity of the filtrate, and the distal convoluted tubule lowers the osmolarity of the filtrate. In the absence of antidiuretic hormone, the collecting duct will be impermeable to water, preventing it from leaving the filtrate and resulting in more dilute urine. With the collecting duct impermeable to water, the filtrate will be most concentrated at the bottom of the loop of Henle.

Example Question #475 : Biology

The interaction between blood pressure and kidney function in humans requires coordination by the renin-angiotensin-aldosterone system (RAAS). This system involves the dynamic interplay of the kidneys, lungs, and blood vessels to carefully regulate sodium and water balance.

A normal human kidney has cells adjacent to the glomerulus called juxtaglomerular cells. These cells sense sodium content in urine of the distal convoluted tubule, releasing renin in response to a low level. Renin is an enzyme that converts angiotensinogen to angiotensin I (AI). AI is converted to angiotensin II (AII) by angiotensin converting enzyme (ACE) in the lung.

AII stimulates aldosterone secretion in the zona glomerulosa of the adrenal gland. Aldosterone then acts to upregulate the sodium-potassium pump on the basolateral side of distal tubule epithelial cells to increase sodium reabsorption from the urine, as well as increasing potassium excretion.

The passage notes that the RAAS functions at the distal tubule. What is the primary function of the proximal tubule?

Possible Answers:

Solute reabsorption and secretion

Transport of urine from the loop of Henle to the collecting duct

Filtration

Detoxification of filtrate

Concentration of filtrate

Correct answer:

Solute reabsorption and secretion

Explanation:

The proximal tubule is the primary site of solute reabsorption and secretion, modifying the urine after its initial filtration in the glomerulus.

Concentration of the filtrate primarily occurs in the collecting duct, and the distal convoluted tubule transports urine from the loop of Henle to the collecting duct. Filtration occurs in the glomerulus and Bowman's capsule, know together as the renal corpuscle.

Example Question #476 : Biology

The interaction between blood pressure and kidney function in humans requires coordination by the renin-angiotensin-aldosterone system (RAAS). This system involves the dynamic interplay of the kidneys, lungs, and blood vessels to carefully regulate sodium and water balance.

A normal human kidney has cells adjacent to the glomerulus called juxtaglomerular cells. These cells sense sodium content in urine of the distal convoluted tubule, releasing renin in response to a low level. Renin is an enzyme that converts angiotensinogen to angiotensin I (AI). AI is converted to angiotensin II (AII) by angiotensin converting enzyme (ACE) in the lung.

AII stimulates aldosterone secretion in the zona glomerulosa of the adrenal gland. Aldosterone then acts to upregulate the sodium-potassium pump on the basolateral side of distal tubule epithelial cells to increase sodium reabsorption from the urine, as well as increasing potassium excretion.

The first place that early urine is collected after filtration in the glomerulus is which of the following?

Possible Answers:

Distal tubule

Collecting duct

Loop of Henle

Bowman's capsule

Proximal tubule

Correct answer:

Bowman's capsule

Explanation:

Bowman's capsule collects fluid filtered from the glomerulus and serves as a site of entry into the proximal tubule. The glomerulus is a convoluted capillary bed adjacent to Bowman's capsule. Osmotic and oncotic pressure gradients work to filter the blood from the glomerulus into Bowman's capsule. The nature of the epithelial cells that line the glomerulus determines the permeability of the filtration, and prevents unwanted content in the urine.

Filtrate moves from Bowman's capsule to the proximal tubule and into the loop of Henle, which dives into the renal medulla before returning to the renal cortex. From the loop of Henle, filtrate is transferred to the distal tubule and into the collecting duct, where it travels into the renal medulla for collection.

Example Question #477 : Biology

The interaction between blood pressure and kidney function in humans requires coordination by the renin-angiotensin-aldosterone system (RAAS). This system involves the dynamic interplay of the kidneys, lungs, and blood vessels to carefully regulate sodium and water balance.

A normal human kidney has cells adjacent to the glomerulus called juxtaglomerular cells. These cells sense sodium content in urine of the distal convoluted tubule, releasing renin in response to a low level. Renin is an enzyme that converts angiotensinogen to angiotensin I (AI). AI is converted to angiotensin II (AII) by angiotensin converting enzyme (ACE) in the lung.

AII stimulates aldosterone secretion in the zona glomerulosa of the adrenal gland. Aldosterone then acts to upregulate the sodium-potassium pump on the basolateral side of distal tubule epithelial cells to increase sodium reabsorption from the urine, as well as increasing potassium excretion.

A nephrologist is studying a normal glomerulus, and notes that it is actively filtering blood normally. What type of blood vessels comprise the bulk of the glomerulus?

Possible Answers:

Arterioles

Fenestrated capillaries

Arteries

Unfenestrated capillaries

Venules

Correct answer:

Fenestrated capillaries

Explanation:

The main purpose of the glomerulus is filtration; thus, it is mainly composed of the thinnest walled-blood vessels (capillaries), and specifically those with pores (fenestrations) to facilitate filtration.

Example Question #478 : Biology

The interaction between blood pressure and kidney function in humans requires coordination by the renin-angiotensin-aldosterone system (RAAS). This system involves the dynamic interplay of the kidneys, lungs, and blood vessels to carefully regulate sodium and water balance.

A normal human kidney has cells adjacent to the glomerulus called juxtaglomerular cells. These cells sense sodium content in urine of the distal convoluted tubule, releasing renin in response to a low level. Renin is an enzyme that converts angiotensinogen to angiotensin I (AI). AI is converted to angiotensin II (AII) by angiotensin converting enzyme (ACE) in the lung.

AII stimulates aldosterone secretion in the zona glomerulosa of the adrenal gland. Aldosterone then acts to upregulate the sodium-potassium pump on the basolateral side of distal tubule epithelial cells to increase sodium reabsorption from the urine, as well as increasing potassium excretion.

Aldosterone functions by increasing the rate at which the sodium-potassium pump functions in the basolateral surface of distal tubule epithelial cells of the nephron. Which of the following is true of the sodium-potassium pump?

Possible Answers:

It pumps two sodium ions out of the cytosol and three potassium ions into the cytosol

It pumps two sodium ions into the cytosol and three potassium ions out of the cytosol

It pumps three sodium ions into the cytosol and two potassium ions out of the cytosol

It pumps three sodium ions into the cytosol and three potassium ions out of the cytosol

It is electrogenic

Correct answer:

It is electrogenic

Explanation:

The sodium-potassium pump pumps three sodium ions out of the cytosol, and two potassium ions into the cytosol. It is electrogenic because each sodium and potassium ion have a charge of positive one, and the two ions are pumped in unequal quantities. The pump generates an electric gradient and current due to the directional flow of positive charge out of the cell.

When aldosterone is released, it increases the action of the sodium-potassium pump, causing excess sodium to be removed from the filtrate in the distal tubule, thus conserving sodium and drawing water out of the filtrate.

Example Question #479 : Biology

Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.

One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.

Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.

 

Untitled

In hypersensitivity reactions, antibodies can complex with antigens and fall out of solution from the blood. These immune complexes then deposit in body tissues inappropriately, and cause disease. This situation is especially noticeable in body tissues that have a direct filtering function. Which of the following structures would most likely be affected by a disease caused by immune complex deposition?

Possible Answers:

Sinoatrial node

Neuromuscular junction

Haversian canal

Semicircular canals

Glomerulus

Correct answer:

Glomerulus

Explanation:

The glomerulus is the primary site of filtration in the kidney. Together, the glomerulus and Bowman's capsule for the renal corpuscle of the nephron and are responsible for collecting filtrate from the blood. Deposition and accumulation of immune complexes in the glomerulus would result in blockage of its filtering functions, impeding nephron function and preventing proper excretion of soluble wastes.

The sinoatrial node is the natural pacemaker region of the heart, located in the right atrium. Haversian canals are the central regions of osteons and often house nerves and blood vessels, facilitating cellular communication within bone. Neuromuscular junctions are the interface regions between a single neuron and the muscle fiber it innervates. The semicircular canals are located in the inner ear and function in the propagation an integration of sound vibrations. None of these structures are involved in filtration, and they would most likely be unaffected by the presence of immune complexes in the body.

Example Question #480 : Biology

Which of the following is true regarding the nephron?

Possible Answers:

Aldosterone acts at the collecting duct to increase membrane permeability to and

The collecting duct is permeable to water and responsive to aldosterone

Bowman's capsule is repsonsible for preventing all proteins from entering the filtrate

The renal corpuscle is made up of the glomerulus and Bowman's capsule

The distal tubule absorbs  and  while secreting , , and

Correct answer:

The renal corpuscle is made up of the glomerulus and Bowman's capsule

Explanation:

Together, Bowman's capsule and the glomerulus make up the renal corpuscle. Blood flows through the glomerulus, where high hydrostatic pressures force plasma through the fenestrations of the glomerular endothelium into Bowman's capsule. The substance that ends up in the capsule is called the filtrate, which then moves to the proximal tubule. Proteins, glucose, and ions are secreted from the proximal tubule back into the blood.

The collecting duct is impermeable to water and is not particularly sensitive to aldosterone. Instead, aldosterone, a steroid hormone produced by the adrenal cortex, acts primarily at the distal tubule to increase sodium reabsorption, potassium secretion, and ultimately water reabsorption to increase blood pressure. The distal tubule absorbs Na+ and Ca2+, not HCO3-

Example Question #21 : Kidney And Nephron Physiology

A researcher is analyzing two locations in the loop of Henle. His results indicate that a sample of filtrate from location A has a much higher solute concentration than a sample of filtrate from location B. Based on his results, what might the researcher conclude about the identity of the locations?

Possible Answers:

Location A is the ascending limb of the loop of Henle because both water and sodium are reabsorbed in the ascending limb

Location B is the ascending limb of the loop of Henle because both water and sodium are reabsorbed in the ascending limb

Location B is the descending limb of the loop of Henle because only water is reabsorbed in the descending limb

Location A is the descending limb of the loop of Henle because only water is reabsorbed in the descending limb

Correct answer:

Location A is the descending limb of the loop of Henle because only water is reabsorbed in the descending limb

Explanation:

The loop of Henle is a U-shaped structure found in the nephron. Its main function is to reabsorb water and essential solutes. Reabsorption is the process by which nutrients and water are transported from the filtrate back into the body.

The loop of Henle contains two parts: the descending limb and the ascending limb. The descending limb functions to reabsorb water, whereas the ascending limb functions to reabsorb sodium and chloride ions. The question states that filtrate in location A has a higher solute concentration. This means that filtrate in location A has more solutes (or less water) than filtrate in location B. Since the descending limb only reabsorbs water, the filtrate concentration is higher in the descending loop; water is removed without solute being able to follow. Location A would be the descending limp of the loop of Henle because it reabsorbs water and increases the solute concentration of the filtrate.

Concentration decreases in the ascending limb when ions are pumped out of the filtrate, removing solute.

Example Question #21 : Kidney And Nephron Physiology

Cortisol is a stress hormone that is produced in the __________, the__________ portion of adrenal gland.

Possible Answers:

adrenal cortex . . . inner

adrenal medulla . . . inner

adrenal cortex . . . outer

adrenal medulla . . . outer

Correct answer:

adrenal cortex . . . outer

Explanation:

The adrenal gland is situated superior to the kidney, and is responsible for the production of several key hormones.

One such hormone is cortisol. Cortisol is often released when an individual is highly stressed over an extended period. It is a steroid hormone that functions to increase blood glucose levels by inducing gluconeogenesis, the process that converts glycogen stores in the liver to glucose. Cortisol is released from cells in the adrenal cortex. Recall that the adrenal cortex is the outer portion of the gland, whereas the adrenal medulla is the inner portion of the gland.

Aldosterone is another hormone that is released by cells in the adrenal cortex, and is essential for sodium reabsorption in the kidney. Epinephrine is released from the adrenal medulla in response to stimulation by the sympathetic nervous system.

Learning Tools by Varsity Tutors